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Effects of two courtship display components on female reproductive behaviour and physiology in the sagebrush lizard
ANIMAL BEHAVIOUR, 2008, 75, 639e646 doi:10.1016/j.anbehav.2007.07.017
Available online at www.sciencedirect.com
Effects of two courtship display components on female reproductive behaviour and physiology in the sagebrush lizard ERIN C. KEL SO & EMI´ LIA P. MARTINS
Department of Biology and Center for the Integrative Study of Animal Behavior, Indiana University, Bloomington (Received 13 March 2007; initial acceptance 22 May 2007; final acceptance 6 July 2007; published online 26 December 2007; MS. number: A10719)
Exposure to aggressive or courtship displays of conspecifics has been shown to alter the physiology and behaviour of observers. However, these effects are dependent on the information content of signals. Separate courtship signals that convey redundant information may be expected to have similar effects on female reproductive physiology or behaviour, while those that contain nonredundant information are expected to have differing effects. Using a mechanized model lizard painted to resemble a male sagebrush lizard, Sceloporus graciosus, we presented female sagebrush lizards with either a stationary model or one of two male display types: push-ups, a signal used in both aggressive and courtship displays, and shudders, a display used exclusively during courtship. Females exposed to push-ups showed more rejection behaviour when later paired with a live male lizard and produced less femoral pore secretions on the first day of stimulus presentation than females exposed to shudders. However, females exposed to either display were found in closer proximity to the live male than females exposed to the stationary model. These results suggest that both components of the courtship display (push-ups and shudders) cause lasting but distinctive changes in female behaviour, supporting a ‘multiple messages’ scenario for the evolution of the two signals. The Association for the Study of Animal Behaviour. Published by Elsevier Ltd.
Keywords: communication; courtship; physiology; sagebrush lizard; Sceloporus graciosus; signal evolution
Exposure to social displays has been shown to alter the physiology and behaviour of observers (Brockway 1965; Crews 1975; Runfeldt & Wingfield 1985; Lea et al. 2001). Individuals that experience defeat in agonistic encounters or are subjected to aggressive attacks often show elevated stress levels or alter their behaviour during subsequent interactions (Hsu & Wolf 2001). These physiological changes can further lead to disturbances in immune function and reproduction (Wingfield & Sapolsky 2003). Alternatively, exposure to certain displays can enhance or promote reproductive function. Female reproductive behaviour may be initiated by the presence of displaying males. Courtship displays, specifically, may
Correspondence: E. C. Kelso, Department of Biology, Indiana University, Bloomington, IN 47405, U.S.A. (email: [email protected]). 0003e 3472/08/$34.00/0
alter female mating behaviour and physiology (Crews 1975). Changes in female mating behaviour and physiology may be due to differences in the quality or content of male signals. Females may respond to differences in the quality or quantity of male signals (Tregenza et al. 2006; Byers 2007). Female fiddler crabs, Uca perplexa, for example, preferentially visit the burrows of males that are able to maintain higher claw heights during claw-waving displays (Murai & Backwell 2006). Potential mates may also adjust their own investment in reproductive activity so that it matches the investment signalled by their partners. For example, female spotless starlings, Sturnus unicolor, increase rates of nest-decorating behaviour when male nest decoration is experimentally supplemented (Polo & Veiga 2006). Exposure to courtship displays may have more direct effects on female physiology. Crews et al. (1986)
639 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd.
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have shown that, in female whiptail lizards (Cnemidophorus sp.), stimulation from intact males (C. inornatus) or intact females displaying male-like copulatory behaviour (unisexual species C. uniparens) promotes ovulation. Signals affecting female reproductive physiology can have fairly specific effects. For example, female canaries, Serinus canaria, perform more copulation solicitation displays in response to male songs containing ‘sexy’ phrases; however, ‘sexy’ and ‘nonsexy’ songs were equally effective in promoting nest building and egg laying (Leboucher et al. 1998). The same signal can also have multiple effects on female reproductive physiology: female canaries allocate more testosterone to eggs when exposed to attractive male songs or preferred song components (Gil et al. 2004; Tanvez et al. 2004). Crews (1975) found that male dewlap extension was the critical factor in determining female mate choice and promoting ovarian recrudescence in green anoles, Anolis carolinensis. The colour of the dewlap (red or blue) and head-bobbing displays that males produce during courtship does not appear to affect female behaviour or physiology (Crews 1975). Courtship interactions often involve the exchange of multiple displays, consisting of distinctive visual, tactile, chemical and auditory components (Iwasa & Pomiankowski 1994; Bradbury & Vehrencamp 1998). A number of ideas have been proposed to explain the prevalence of complex courtship displays. Research suggests that multiple signals or cues may evolve in the context of courtship when there is (1) selection for the communication of multiple messages (Borgia 1995; Badyaev & Hill 2000; Hankison & Morris 2003) or ‘backup signals’ that emphasize a single message (Johnstone 1996), (2) selection imposed by females for novel or complex signals (Forrest & Raspet 1994), or (3) selection by different classes of receivers (e.g. males and females responding to separate signals within a display; Andersson et al. 2002; Brooks 2002). Doucet & Montgomerie (2003) have shown that the ultraviolet plumage of male satin bowerbirds, Ptilonorhynchus violaceus, is related to the level of blood parasitism and feather growth rate, while bower quality is indicative of ectoparasitic infection. Both cues are assessed by females during courtship (Doucet & Montgomerie 2003). Few studies have examined the effect of individual courtship components on female reproductive physiology (but see Crews 1975; Cheng et al. 1998; Hebets & Uetz 1999; Ryback et al. 2002). However, it is reasonable to assume that social signals that convey different messages (nonredundant signals) will have differential effects on the reproductive physiology and behaviour of receivers because they impart different types of information to receivers. Signals that indicate species identity often override cues indicating male quality in mate choice decisions. For example, Hankison & Morris (2003) found that female swordtails, Xiphophorus pygmaeus, change their mating preferences based on the presence or absence of certain visual cues: when given the choice between larger males (which are generally preferred) and males with a species-typical colour pattern, females preferred to mate with conspecifics. As a result of this disparity, signals may act over different time courses and with different specificity depending on the messages they convey.
Moreover, courtship signals that act as ‘backup’ messages may be expected to have similar effects on female reproductive physiology or behaviour because the information they impart is identical. Partan & Marler (1999) proposed a framework for distinguishing between redundant and nonredundant signals based on responses to isolated and combined components. Briefly, isolated signal components that have similar effects on receiver behaviour or physiology are considered redundant, while those that have different effects are nonredundant (Partan & Marler 1999). Although this paradigm specifically addresses sequential or simultaneous signals occurring in multiple modalities, the same theory can be used to address the function of two signals in the same modality that, when combined, create a single courtship display. The courtship of the sagebrush lizard, Sceloporus graciosus, includes the combined performance of two very distinctive visual displays: the push-up, which is a multifunction signal that is used in aggressive interactions and as a nondirected display, and the shudder, which is exclusive to courtship. Although both displays are always given during courtship, the function of each display type in a courtship context is largely unknown. Here, we exposed females to either push-ups or shudders for 14 days to determine whether long-term exposure to either display type affected female reproductive physiology or behaviour. To determine differences in the specificity or effectiveness of the two display types in altering female behaviour, we examined their effects on two aspects of female physiology: (1) behavioural responses to courting males and (2) patterns of femoral pore secretions (FPS), a chemical scent mark. We also discuss the possible origins of push-ups and shudders as ‘multiple messages’ or ‘backup signals’, according to the criteria established by Partan & Marler (1999) for determining the information content of signals.
METHODS
Study Species Sceloporus graciosus is a small (approximately 55 mm in snout-to-vent length), diurnal lizard native to western North America (Stebbins 1985). They inhabit primarily dry shrub and sagebrush habitats at mid to high elevations (Stebbins 1985). Animals emerge from hibernation after snow melt and the breeding season extends from early June to August (Stebbins 1985). Both sexes are territorial, although a male’s home range may overlap the territories of a few females, which he may court repeatedly throughout the breeding season (Stebbins 1985; Deslippe & M’Closkey 1991). Adult S. graciosus show a species-typical push-up display, during which the head and anterior portion of the body is raised and lowered in sequence (Carpenter & Ferguson 1977). The degree to which the push-up is modified by certain body postures depends on the context in which it is given (aggressive versus courtship): displays during courtship generally lack the gular extension and lateral compression of those given during aggressive encounters (Martins 1993). Males also
KELSO & MARTINS: EFFECTS OF COURTSHIP ON BEHAVIOUR
produce a distinct shudder display during courtship interactions (Carpenter & Ferguson 1977), during which a short series of rapid, low-amplitude headbobs is given while the animal is in motion and/or in contact with a female (Carpenter & Ferguson 1977; Martins 1993). During a typical courtship, males will alternate the performance of both displays. Females that are sexually receptive will gradually decrease stereotypical courtship rejection behaviour (see below) and aggression, eventually allowing males to approach and mate (Carpenter & Ferguson 1977; E. C. Kelso, unpublished observation).
Animal Housing For this study, we collected adult S. graciosus from Table Mountain Campground in the San Gabriel Mountains of southern California during May 2001 and 2003 (California Department of Fish and Wildlife scientific collecting permit no. 2907). Animals were housed individually in the laboratory in 37.9-litre glass aquaria containing sand substrate and a single brick for perching. Full-spectrum lighting was provided as well as a single 40-W incandescent bulb per aquarium to provide heat for basking. We provided the animals with calcium-dusted crickets (Acheta domesticus) and mealworms (Tenebrio molitor) every 2 days and misted the enclosures each day to provide water and humidity. All animals were housed under a 12:12 h light:dark cycle at temperatures of 28 C (day) and 20 C (night). Animal care and testing was conducted in accordance with the Guidelines for the Treatment of Animals in Research (ASAB/ABS 2003) and approved by the Indiana University, Bloomington, Institutional Animal Care and Use Committee (protocol no. 01-008).
General Methods Display presentations To control the stimulus that a female received, we simulated two standardized displays, push-ups (P) and shudders (S), using a mechanized lizard model painted to resemble a male S. graciosus. The latex model was positioned on top of a box (12 7 5 cm) that concealed a small stepper motor (15-degree linear actuator, HIS 46000; Hayden Switch & Instrument, Inc., Waterbury, CT, U.S.A.). The movement of the model’s ‘head’, via the stepper motor, was controlled by a compact integrated driver (MicroLynx4, MX-CS100-400; Intelligent Motion Systems, Inc., Marlborough, CT, U.S.A.) that had been programmed to produce one of two displays (described below). This method elicits behaviour similar to that elicited during conspecific interactions staged in a laboratory setting (Martins et al. 2005). The latex model was posed in a nonaggressive manner (i.e. did not show any body postures, including leg extensions and lateral compression). The push-up displays produced by the model, therefore, resemble those given by males during courtship rather than those used by males and females during aggressive encounters. The entire apparatus was positioned on a platform so that the model lizard was presented laterally to test subjects during trials. Because the platform was
free-standing, any vibrations produced by the action of the motor were not transmitted to the females’ cages. We conducted two experiments (described in detail below). For each experiment, we positioned the model and robot assembly in front of a female’s cage for 2 min three times per day for 14 consecutive days. During these 2-min sessions, each female received one of three display treatments: push-ups, shudders, or the stationary model. The push-up display used during these presentations consisted of a sequence of one double headbob, followed by two single headbobs, followed by three double headbobs. A single push-up display sequence lasted 8 s and the entire display was repeated three times during the 2-min presentation period. The shudder display consisted of a sequence of five rapid headbobs, repeated three times, with 1-s intervals between headbob sequences. One shudder sequence lasted 5 s and was repeated four times during the 2-min display presentation. The timing and spatiotemporal structure of both stimulus displays were based on laboratory trials (E. C. Kelso & E. P. Martins, unpublished data) and field observations (Carpenter 1978; Martins 1991). Extended screens between the aquaria ensured that each female did not interact visually with neighbouring females and that each female experienced only her assigned display type. Care was taken to ensure that the model was within a female’s visual range before a display presentation began.
Behavioural observations Behavioural trials began 7 days after the last day of stimulus presentation. For both experiments, each female was paired once with a live male in a larger (approximately 0.6 0.6 m) enclosure containing sand substrate and a single brick, and their behaviour was recorded. Although males were used in multiple trials (see below for details), an individual male was used only once per day. The interactants were videotaped using a Panasonic camcorder (AG-188). Behavioural trials were conducted over a 7-day period, so that the final female was tested 14 days after she was last exposed to the display stimulus. We scored videotapes for the number and sequence of behaviour patterns given by both males and females. To reduce the number of variables, we grouped individual behaviour patterns into five functional categories: (1) male courtship behaviour, including shudders, nonaggressive push-ups and mounting attempts (given by males only); (2) courtship rejection behaviour (Greenberg 1977): ‘tail-up’ posture with lateral compression (given by females only) also called ‘sidlehopping’; (3) aggressive behaviour, such as push-ups performed in conjunction with aggressive body postures, lateral compression, gular extension and raised body; (4) scent-marking behaviour, including chin wiping, body wiping and femoral pore marking; and (5) chemosensory behaviour (i.e. tongueflicking of the substrate or conspecific). In all cases, data are presented as the number of behaviours given per 20 min. We also recorded distance (on a scale of 0e3) between individuals at 5-min intervals. To accomplish this, the experimental enclosure was divided into six areas of
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approximately 25 cm2. Distance was scored as 0 if the animals were in physical contact, as 1 if the animals were less than one body length (approximately 6 cm) apart, as 2 if the animals were in the same area, and as 3 if the animals were in different areas. Distance scores were averaged for each trial to give a single measurement. In addition, we measured the activity of female lizards by recording the number of times that a female crossed an area boundary during a trial.
treatment groups. Paper towel strips were taped to brick perches to absorb FPS. The towels were changed each day during general maintenance (feeding, watering). We recorded the number and size of spots deposited by females each day. We used 10 males during behavioural testing (described above in General Methods). Males were paired with two or three females from each treatment group (shudder or push-up) in random order for a total of five trials per male (48 trials total). The interactants were recorded for 20 min.
Experiment 1: Display versus Control In March 2002, we conducted an experiment comparing the behavioural responses of female S. graciosus to males after exposure to male displays (push-up or shudder) or to a control treatment (no display). Females were removed from hibernation (at 10 C) during January 2002 and maintained under the conditions described in animal housing (above). This procedure ensured that all females were in similar reproductive condition at the start of the study. Females (N ¼ 30) received one of three display treatments: shudder, push-up or no display (control) three times per day for 14 days as described above. We combined the shudder and push-up groups into one group (display group) to compare the effects of both displays to the control. Five males were used during the behavioural trials (described above in General Methods) for experiment 1: individual males encountered two females from each treatment (push-up, shudder, or control) in random order to give a total of six trials per male. The interactants were videotaped for 40 min. We recorded behavioural data as the number of behaviour patterns given per 20 min.
Statistical analyses Distance data were analysed with a two-way ANOVA with treatment (display or control group) and male identity as fixed factors (SAS, Proc Mixed, SAS Institute, Cary, NC, U.S.A.). We used a nonparametric test (Manne Whitney U ) to explore behavioural responses of males and females because these data did not meet the assumptions of parametric tests.
Experiment 2: Push-up versus Shudder During March 2004, we conducted a similar experiment, comparing the behavioural responses of females to males after long-term exposure to push-up or shudder displays. Females were removed from hibernation (at 10 C) during January 2003 and maintained under the conditions described in animal housing (above). This procedure ensured that all females were in similar reproductive condition at the beginning of the study. Females (N ¼ 58) received one of two display treatments: shudder or push-up three times per day for 14 days as described above. Females that had been used in experiment 1 (during March 2002) were not used in experiment 2. During the 2-week presentation period, we also collected femoral pore secretions (FPS) from females in all
Statistical analyses Distance data were analysed with a two-way ANOVA (Proc GLM, SAS) with treatment (push-up or shudder) and male identity as fixed factors. We used a nonparametric test (ManneWhitney U ) to explore behavioural responses of males and females because these data did not meet the assumptions of parametric tests. In addition to examining the amount of courtship behaviour shown by males, we also used a chi-square test to examine differences in the number of courting males. For the FPS data, we averaged the number of spots produced by females for days 1, 7 and 14 of stimulus presentation to give a single value for each female per day. In addition, we calculated the area of each spot produced on days 1, 7 and 14 and determined the average spot size for each female per day. We used ManneWhitney U tests to examine treatment differences in FPS spot number and size because these data did not meet parametric assumptions.
RESULTS
Experiment 1: Display versus Control Females showed no significant differences in behaviour when exposed to male displays or no displays (all P > 0.05; Table 1). In addition, males showed no significant differences in behaviour when paired with either of the two classes of females (ManneWhitney U test: scent-marking behaviour: U ¼ 97.5, N1 ¼ 20, N2 ¼ 10, P ¼ 0.911; chemosensory behaviour: U ¼ 88.5, N1 ¼ 20, N2 ¼ 10, P ¼ 0.613), and the number of males that courted females from each treatment group did not differ (chi-square test: c21 ¼ 0:085, P ¼ 0.770). Females were Table 1. Median and interquartile range (IQR) of behaviour recorded for female sagebrush lizards during experiment 1 (display versus control) and results of ManneWhitney U tests No display N¼10 Behaviour category Chemosensory Scent marking Aggressive Rejection
Median
IQR
10.56 0 0.51 0
10.34 0 1.25 0.44
Display N¼20 Median IQR 6.56 0 0 0
6.86 2.45 0.77 0.83
P (twotailed, U a¼0.05) 75 75 80 95
0.271 0.190 0.331 0.819
KELSO & MARTINS: EFFECTS OF COURTSHIP ON BEHAVIOUR
2.8
Distance score
2.6 *P < 0.03 2.4 2.2 2 1.8 1.6 No display (C)
Display (D)
Figure 1. Mean SD distance scores of female and male sagebrush lizards during behavioural trials for experiment 1 (display versus control). Distance scores: 0 ¼ animals were in physical contact; 1 ¼ animals were less than one body length (approximately 6 cm) apart; 2 ¼ animals were in the same area of the arena; 3 ¼ animals were observed in different areas of the arena.
consistently closer to the male during display (shudder þ push-up) trials than during control trials (ANOVA: F1,9 ¼ 5.24, P ¼ 0.033; Fig. 1), although there were no differences in distance scores between the two display types (data not shown). There was a marginally significant effect of male identity (F1,4 ¼ 3.08, P ¼ 0.040), but no male by treatment interaction effect (F1,4 ¼ 0.91, P ¼ 0.482). Date of behavioural testing (range 7e14 days poststimulus exposure) was also not significant.
Experiment 2: Push-up versus Shudder Females exposed to push-up displays performed more courtship rejection behaviour in response to male courtship than did females exposed to shudder displays (Manne Whitney U test: U ¼ 204, N1 ¼ 26, N2 ¼ 22, P ¼ 0.028). Females showed no significant differences in behaviour for the other three behaviour categories (all P > 0.05; Table 2). There was no treatment effect (push-up or shudder) on the activity (number of moves) of females (ANOVA: F1,47 ¼ 0.07, P ¼ 0.791) and no effect of male identity Table 2. Median and interquartile range (IQR) of behaviour recorded for female sagebrush lizards during experiment 2 (push-up versus shudder) and results of ManneWhitney U tests Push-up N¼22 Behaviour category Chemosensory Scent marking Aggressive Rejection *P < 0.05.
Shudder N¼26
Median IQR Median IQR 15 0 0 0.5
13 3 1 5
9 0 0.5 0
10 1 1 0
U
P (twotailed, a¼0.05)
221 235 270 193
0.197 0.245 0.753 0.028*
(F1,9 ¼ 0.89, P ¼ 0.545). In addition, males showed no significant differences in behaviour towards the two classes of females (ManneWhitney U test: scent-marking behaviour: U ¼ 275, N1 ¼ 26, N2 ¼ 22, P ¼ 0.814; chemosensory behaviour: U ¼ 246.5, N1 ¼ 26, N2 ¼ 22, P ¼ 0.413). The number of males showing courtship behaviour also did not differ between treatment groups (chi-square test: c21 ¼ 0:17, P ¼ 0.677). We observed no effect of display treatment (ANOVA: F1,47 ¼ 0.77, P ¼ 0.388) and no effect of male identity (F1,9 ¼ 0.87, P ¼ 0.562) on the proximity of males and females during behavioural trials (Fig. 2). Although individuals in both treatment groups (shudder and push-up) had slightly lower distance scores than those in the combined display group (shudder þ push-up) during experiment 1, the difference was not significant, suggesting that the results were consistent across the two experiments. Date of behavioural testing (range 7e14 days poststimulus exposure) was also not significant. Females in the two treatment groups differed in their FPS patterns on the first day of stimulus presentation. Females in the push-up group produced fewer spots than those in the shudder group (X SE ¼ 0:25 0:15 and 0:87 0:24, respectively; ManneWhitney U test: U ¼ 298.5, N1 ¼ 28, N2 ¼ 30, P ¼ 0.014). Females exposed to push-ups also produced spots that were smaller than those produced by females in the shudder group (X SE ¼ 0:19 0:11 and 0:37 0:12 cm2 , respectively; U ¼ 310, N1 ¼ 28, N2 ¼ 30, P ¼ 0.026). We found no differences in either the spot number or size of FPS on days 7 and 14 of stimulus presentation.
DISCUSSION In addition to responding to environmental conditions, such as changes in photoperiod or temperature, the reproductive physiology and behaviour of females may be influenced by the behaviour of conspecifics. The contribution of individual display elements to these effects and their specific action on different aspects of 1.9 1.8
Distance score
3
1.7 1.6 1.5 1.4 1.3 Shudder (S)
Push-up (P)
Figure 2. Mean SD distance scores of female and male sagebrush lizards during behavioural trials for experiment 2 (push-up versus shudder). Distance scores as described in Fig. 1.
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female behaviour is largely unknown for most species (but see Crews 1975; Cheng et al. 1998; Hebets & Uetz 1999). Our results indicate that brief exposure (6 min/day for 14 days) to either of two male courtship display components, push-up or shudder, affects the behaviour of female S. graciosus, although the specificity of these effects depends on the display type (push-up or shudder) and the particular female behaviour that is observed. Female S. graciosus that had been exposed to simulated shudders, the courtship-specific display, showed less stereotyped rejection behaviour in response to male courtship than did females exposed to push-up displays. In addition, FPS spots produced by females in the push-up treatment group were fewer and, on average, smaller than those produced by the shudder group on the first day of display presentation, indicating that females were more active during presentations of push-ups, but this difference was significant only on day 1. Animals that are actively moving about their enclosures tend to leave fewer, small secretions on their perches (Martins et al. 2006). These results suggest that push-ups and shudders have different influences on some aspects of female behaviour, including receptivity to courtship. However, females that had viewed either display type were consistently closer to the male during behavioural trials than females that had observed only the stationary model (experiment 1), although there were no differences in distance between the two display groups for either experiment. In this case, exposure to either display appears to result in similar behavioural changes that may be important for successful reproduction. Our findings differ from those of Crews (1975), who concluded that the push-up displays produced by male green anoles during courtship have no effect on female mating behaviour and that only the male dewlap display has a unique courtship function. In contrast, exposure to both types of courtship display seems to have relatively long-lasting effects on behaviour in female sagebrush lizards: females showed noticeable differences in behaviour up to 2 weeks poststimulus presentation. It is possible that some of the behavioural differences that we observed in our treatment groups could have been due to males adjusting their own courtship or responding to changes in female responsiveness or physiology (e.g. pheromone or colour cues). However, we found no differences in male behaviour towards any of the experimental groups of females, suggesting that males did not discriminate between classes of females. The behavioural differences that we observed during trials, therefore, were more likely the result of changes in female behaviour rather than responses on the part of males to differences in female physiology and/or behaviour. We found some evidence that push-ups and shudders have evolved via a ‘multiple messages’ scenario based on the framework proposed by Partan & Marler (1999) for determining the information content of signals. The separate displays had different effects on some aspects of female behaviour: shudders reduced the amount of female rejection behaviour, whereas push-ups did not, indicating that the information contained in the two displays is nonredundant (Partan & Marler 1999, 2005). Alternatively,
these results could be interpreted as one display being slightly more effective at provoking changes in female behaviour or physiology than the other, which would be more indicative of two redundant signals (Partan & Marler 1999, 2005). Another explanation for our results is that the two displays may convey different types of information about potential mates that ultimately lead to similar outcomes in female decision making or have similar physiological effects. The species-typical spatiotemporal structure of the push-up display could easily be used by females to identify conspecific males, while the ability to perform rapid shudders may indicate a male’s stamina. Females may respond to both types of information by allowing only high-quality conspecific males to approach more closely. However, female lizards appear to lack the strong preferences for attractive male displays that have been shown in other taxa, leading to some difficulty in establishing display parameters that are indicative of male quality (Tokarz 1995). Instead, mate choice decisions of female lizards are probably based on multiple male characters and may, therefore, be fairly complex (Hamilton & Sullivan 2005; Bissell & Martins 2006). Females that were exposed to either push-ups or shudders were closer to the male during behavioural trials than were females that observed only the stationary model. In the field, proximity between males and females is a reliable predictor of paternity in Sceloporus lizards (Abell 1997), and male S. virgatus tend to associate more closely with females in reproductive condition during the breeding season (Weiss 2002). Recently, Bissell & Martins (2006) found that a female’s choice of mate may be reflected in how often or how close she allows a male to approach. Both push-up and shudder displays, therefore, may be important aspects of courtship behaviour because they both increase maleefemale proximity. Push-ups are generally considered an aggressive display and are never performed in the context of courtship without also being accompanied by shudders. Push-ups have been studied most often in the context of malee male interactions, however, female lizards also use the display during territorial contests (Carpenter & Ferguson 1977; DeCourcy & Jenssen 1994). While exposure to courtship displays has been shown to enhance reproductive function, aggressive displays often have inhibitory effects on reproduction because they tend to elevate the stress response (Marchlewskakoj 1997; Wingfield & Sapolsky 2003). Because the push-up display is used extensively by both males and females during agonistic encounters, this could lead to a possible conflict in the potential effects on female physiology. However, the aggressive content of the push-up display may be conveyed in the body postures accompanying the display rather than in the spatiotemporal structure of the display itself (Martins 1993): push-up displays used during courtship are not usually accompanied by leg extension or lateral compression, although both body postures are used during agonistic displays. The simulated push-up displays used in this study were performed by a model posed in a ‘nonaggressive’ courtship-typical body posture. Evidence from other taxa suggests that some courtship signals have been co-opted
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from their origins in aggressive displays (Berglund et al. 1996; Borgia & Coleman 2000). Many other signals, such as bird song, often serve dual functions, attracting mates and deterring rival males simultaneously. The problem of inhibitory effects of aggressive displays on female reproductive behaviour may, therefore, be one that is easily overcome, evolutionarily. Little is known about the display behaviour of S. graciosus that occurs in other modalities. The natural courtship display of S. graciosus contains a number of nonvisual signals, including extensive scent-marking behaviour and tactile communication between the male and female. We were unable to include these additional components in our analyses because of the limitations of presenting artificial stimuli. However, it would be interesting to examine the contribution of nonvisual modalities to effects on female reproductive behaviour observed in this study. Acknowledgments We thank B. H. Bleakely for assistance with the animals. We also thank T. J. Ord, G. Ragland and B. Heidinger for helpful comments on earlier versions of the manuscript. E. C. Kelso was supported by a graduate research fellowship from the Center for Integrative Study of Animal Behavior (CISAB) at Indiana University. References Abell, A. J. 1997. Estimating paternity with spatial behaviour and DNA fingerprinting in the striped plateau lizard, Sceloporus virgatus (Phrynosomatidae). Behavioral Ecology and Sociobiology, 41, 217e226. Andersson, S., Pryke, S. R., Ornborg, J., Lawes, M. J. & Andersson, M. 2002. Multiple receivers, multiple ornaments, and a trade-off between agonistic and epigamic signaling in a widowbird. American Naturalist, 160, 683e691. ASAB/ABS. 2003. Guidelines for the treatment of animals in behavioural research and teaching. Animal Behaviour, 61, 271e275. Badyaev, A. V. & Hill, G. E. 2000. Evolution of sexual dichromatism: contribution of carotenoid- versus melanin-based coloration. Biological Journal of the Linnean Society, 69, 153e172. Berglund, A., Bisazza, A. & Pilastro, A. 1996. Armaments and ornaments: an evolutionary explanation of traits of dual utility. Biological Journal of the Linnean Society, 58, 385e399. Bissell, A. N. & Martins, E. P. 2006. Male approach and female avoidance as mechanisms of population discrimination in sagebrush lizards. Behavioral Ecology and Sociobiology, 60, 655e662. Borgia, G. 1995. Complex male display and female choice in the spotted bowerbird: specialized functions for different bower decorations. Animal Behaviour, 49, 1291e1301. Borgia, G. & Coleman, S. W. 2000. Co-option of male courtship signals from aggressive display in bowerbirds. Proceedings of the Royal Society of London, Series B, 267, 1735e1740. Bradbury, J. W. & Vehrencamp, S. L. 1998. Principles of Animal Communication. Sunderland, Massachusetts: Sinauer. Brockway, B. F. 1965. Stimulation of ovarian development and egg laying by male courtship vocalization in budgerigars (Melopsittacus undulatus). Animal Behaviour, 13, 575e578. Brooks, R. 2002. Variation in female mate choice within guppy populations: population divergence, multiple ornaments, and the maintenance of polymorphism. Genetica, 116, 343e358.
Byers, B. E. 2007. Extrapair paternity in chestnut-sided warblers is correlated with consistent vocal performance. Behavioral Ecology, 18, 130e136. Carpenter, C. C. 1978. Comparative display behaviour in the genus Sceloporus (Iguanidae). Contributions in Biology and Geology, Milwaukee Public Museum, 18, 1e71. Carpenter, C. C. & Ferguson, G. W. 1977. Variation and evolution of stereotyped behavior in reptiles. In: Biology of the Reptilia: Ecologia and Behavior A. Vol. 7 (Ed. by C. Gans & D. Tinkle), pp. 335e 554. New York: Academic Press. Cheng, M., Peng, J. P. & Johnson, P. 1998. Hypothalmic neurons preferentially respond to female nest coo stimulation: demonstration of direct acoustic stimulation of luteinizing hormone release. Journal of Neuroscience, 18, 5477e5489. Crews, D. 1975. Effects of different components of male courtship behavior on environmentally induced ovarian recrudescence and mating preferences in the lizard, Anolis carolinensis. Animal Behaviour, 23, 349e356. Crews, D., Grassman, M. & Lindzey, J. 1986. Behavioral facilitation of reproduction in sexual and unisexual whiptail lizards. Proceedings of the National Academy of Sciences, U.S.A., 83, 9547e9550. DeCourcy, K. R. & Jenssen, T. A. 1994. Structure and use of male territorial headbob signals by the lizard, Anolis carolinensis. Animal Behaviour, 47, 251e262. Deslippe, R. J. & M’Closkey, R. T. 1991. An experimental test of mate defense in an iguanid lizard (Sceloporus graciosus). Ecology, 72, 1218e1224. Doucet, S. M. & Montgomerie, R. 2003. Multiple sexual ornaments in satin bowerbirds: ultraviolet plumage and bowers signal different aspects of quality. Behavioral Ecology, 14, 503e509. Forrest, T. G. & Raspet, R. 1994. Models of female choice in acoustic communication. Behavioral Ecology, 5, 293e303. Gil, D., Leboucher, G., Lacroix, A., Cue, R. & Kreutzer, M. 2004. Female canaries produce eggs with greater amounts of testosterone when exposed to preferred male song. Hormones and Behavior, 45, 64e70. Greenberg, N. 1977. An ethogram of the blue spiny lizard, Sceloporus cyanogenys (Reptilia, Lacertilia, Iguanidae). Journal of Herpetology, 11, 177e195. Hamilton, P. S. & Sullivan, B. K. 2005. Female mate attraction in ornate tree lizards, Urosaurus ornatus: a multivariate analysis. Animal Behaviour, 69, 219e224. Hankison, S. J. & Morris, M. R. 2003. Avoiding a compromise between sexual selection and species recognition: female swordtail fish assess multiple species-specific cues. Behavioral Ecology, 14, 282e287. Hebets, E. A. & Uetz, G. W. 1999. Female responses to isolated signals from multimodal male courtship displays in the wolf spider genus Schizocosa (Araneae: Lycosidae). Animal Behaviour, 57, 856e872. Hsu, Y. & Wolf, L. L. 2001. The winner and loser effect: what fighting behaviours are influenced. Animal Behaviour, 61, 777e786. Iwasa, Y. & Pomiankowski, A. 1994. The evolution of mate preferences for multiple sexual ornaments. Evolution, 48, 853e867. Johnstone, R. A. 1996. Multiple displays in animal communication: ‘‘backup signals’’ and ‘‘multiple messages’’. Philosophical Transactions of the Royal Society of London, Series B, 351, 329e338. Lea, J., Dyson, M. & Halliday, T. 2001. Calling by male midwife toads stimulates females to maintain reproductive condition. Animal Behaviour, 61, 373e377. Leboucher, G., Depraz, V., Kreutzer, M. & Nagle, L. 1998. Male song stimulation of female reproduction in canaries: features relevant to sexual displays are not relevant to nest-building or egglaying. Ethology, 104, 613e624. Marchlewskakoj, A. 1997. Sociogenic stress and rodent reproduction. Neuroscience and Biobehavioral Reviews, 21, 699e703.
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Martins, E. P. 1991. Individual and sex differences in the use of the push-up display by the sagebrush lizard, Sceloporus graciosus. Animal Behaviour, 41, 403e416. Martins, E. P. 1993. Contextual use of the push-up display by the sagebrush lizard, Sceloporus graciosus. Animal Behaviour, 45, 25e36. Martins, E. P., Ord, T. J. & Davenport, S. W. 2005. Combining motions into complex displays: playbacks with a robotic lizard. Behavioral Ecology and Sociobiology, 58, 351e360. Martins, E. P., Ord, T. J., Slaven, J., Wright, J. L. & Housworth, E. A. 2006. Individual, sexual, seasonal, and temporal variation in the amount of sagebrush lizard scent marks. Journal of Chemical Ecology, 32, 881e893. Murai, M. & Backwell, P. R. Y. 2006. A conspicuous courtship signal in the fiddler crab Uca perplexa: female choice based on display structure. Behavioral Ecology and Sociobiology, 60, 736e741. Partan, S. R. & Marler, P. 1999. Communication goes multimodal. Science, 283, 1272e1273. Partan, S. R. & Marler, P. 2005. Issues in the classification of multimodal signals. American Naturalist, 166, 234e245. Polo, V. & Veiga, J. P. 2006. Nest ornamentation by female spotless starlings in response to a male display: an experimental study. Journal of Animal Ecology, 75, 942e947.
Runfeldt, S. & Wingfield, J. C. 1985. Experimentally prolonged sexual activity in female sparrows delays termination of reproductive activity in their untreated mates. Animal Behaviour, 33, 403e410. Ryback, F., Sureau, G. & Aubin, T. 2002. Functional coupling of acoustic and chemical signals in the courtship behaviour of the male Drosophila melanogaster. Proceedings of the Zoological Society of London, Series B, 269, 695e701. Stebbins, R. C. 1985. A Field Guide to Western Reptiles and Amphibians. Boston, Massachusetts: Houghton Mifflin. Tanvez, A., Be´guin, N., Chastel, O., Lacroix, A. & Leboucher, G. 2004. Sexually attractive phrases increase yolk androgens depositions in Canaries (Serinus canaria). General and Comparative Endocrinology, 138, 113e120. Tokarz, R. R. 1995. Mate choice in lizards: a review. Herpetological Monographs, 8, 17e40. Tregenza, T., Simmons, L. W., Wedell, N. & Zuk, M. 2006. Female preference for male courtship song and its role as a signal of immune function and condition. Animal Behaviour, 72, 809e818. Weiss, S. L. 2002. Reproductive signals of female lizards: pattern of trait expression and male response. Ethology, 108, 793e813. Wingfield, J. C. & Sapolsky, R. M. 2003. Reproduction and resistance to stress: when and how. Journal of Neuroendocrinology, 15, 711e724.
Available online at www.sciencedirect.com
Effects of two courtship display components on female reproductive behaviour and physiology in the sagebrush lizard ERIN C. KEL SO & EMI´ LIA P. MARTINS
Department of Biology and Center for the Integrative Study of Animal Behavior, Indiana University, Bloomington (Received 13 March 2007; initial acceptance 22 May 2007; final acceptance 6 July 2007; published online 26 December 2007; MS. number: A10719)
Exposure to aggressive or courtship displays of conspecifics has been shown to alter the physiology and behaviour of observers. However, these effects are dependent on the information content of signals. Separate courtship signals that convey redundant information may be expected to have similar effects on female reproductive physiology or behaviour, while those that contain nonredundant information are expected to have differing effects. Using a mechanized model lizard painted to resemble a male sagebrush lizard, Sceloporus graciosus, we presented female sagebrush lizards with either a stationary model or one of two male display types: push-ups, a signal used in both aggressive and courtship displays, and shudders, a display used exclusively during courtship. Females exposed to push-ups showed more rejection behaviour when later paired with a live male lizard and produced less femoral pore secretions on the first day of stimulus presentation than females exposed to shudders. However, females exposed to either display were found in closer proximity to the live male than females exposed to the stationary model. These results suggest that both components of the courtship display (push-ups and shudders) cause lasting but distinctive changes in female behaviour, supporting a ‘multiple messages’ scenario for the evolution of the two signals. The Association for the Study of Animal Behaviour. Published by Elsevier Ltd.
Keywords: communication; courtship; physiology; sagebrush lizard; Sceloporus graciosus; signal evolution
Exposure to social displays has been shown to alter the physiology and behaviour of observers (Brockway 1965; Crews 1975; Runfeldt & Wingfield 1985; Lea et al. 2001). Individuals that experience defeat in agonistic encounters or are subjected to aggressive attacks often show elevated stress levels or alter their behaviour during subsequent interactions (Hsu & Wolf 2001). These physiological changes can further lead to disturbances in immune function and reproduction (Wingfield & Sapolsky 2003). Alternatively, exposure to certain displays can enhance or promote reproductive function. Female reproductive behaviour may be initiated by the presence of displaying males. Courtship displays, specifically, may
Correspondence: E. C. Kelso, Department of Biology, Indiana University, Bloomington, IN 47405, U.S.A. (email: [email protected]). 0003e 3472/08/$34.00/0
alter female mating behaviour and physiology (Crews 1975). Changes in female mating behaviour and physiology may be due to differences in the quality or content of male signals. Females may respond to differences in the quality or quantity of male signals (Tregenza et al. 2006; Byers 2007). Female fiddler crabs, Uca perplexa, for example, preferentially visit the burrows of males that are able to maintain higher claw heights during claw-waving displays (Murai & Backwell 2006). Potential mates may also adjust their own investment in reproductive activity so that it matches the investment signalled by their partners. For example, female spotless starlings, Sturnus unicolor, increase rates of nest-decorating behaviour when male nest decoration is experimentally supplemented (Polo & Veiga 2006). Exposure to courtship displays may have more direct effects on female physiology. Crews et al. (1986)
639 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd.
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have shown that, in female whiptail lizards (Cnemidophorus sp.), stimulation from intact males (C. inornatus) or intact females displaying male-like copulatory behaviour (unisexual species C. uniparens) promotes ovulation. Signals affecting female reproductive physiology can have fairly specific effects. For example, female canaries, Serinus canaria, perform more copulation solicitation displays in response to male songs containing ‘sexy’ phrases; however, ‘sexy’ and ‘nonsexy’ songs were equally effective in promoting nest building and egg laying (Leboucher et al. 1998). The same signal can also have multiple effects on female reproductive physiology: female canaries allocate more testosterone to eggs when exposed to attractive male songs or preferred song components (Gil et al. 2004; Tanvez et al. 2004). Crews (1975) found that male dewlap extension was the critical factor in determining female mate choice and promoting ovarian recrudescence in green anoles, Anolis carolinensis. The colour of the dewlap (red or blue) and head-bobbing displays that males produce during courtship does not appear to affect female behaviour or physiology (Crews 1975). Courtship interactions often involve the exchange of multiple displays, consisting of distinctive visual, tactile, chemical and auditory components (Iwasa & Pomiankowski 1994; Bradbury & Vehrencamp 1998). A number of ideas have been proposed to explain the prevalence of complex courtship displays. Research suggests that multiple signals or cues may evolve in the context of courtship when there is (1) selection for the communication of multiple messages (Borgia 1995; Badyaev & Hill 2000; Hankison & Morris 2003) or ‘backup signals’ that emphasize a single message (Johnstone 1996), (2) selection imposed by females for novel or complex signals (Forrest & Raspet 1994), or (3) selection by different classes of receivers (e.g. males and females responding to separate signals within a display; Andersson et al. 2002; Brooks 2002). Doucet & Montgomerie (2003) have shown that the ultraviolet plumage of male satin bowerbirds, Ptilonorhynchus violaceus, is related to the level of blood parasitism and feather growth rate, while bower quality is indicative of ectoparasitic infection. Both cues are assessed by females during courtship (Doucet & Montgomerie 2003). Few studies have examined the effect of individual courtship components on female reproductive physiology (but see Crews 1975; Cheng et al. 1998; Hebets & Uetz 1999; Ryback et al. 2002). However, it is reasonable to assume that social signals that convey different messages (nonredundant signals) will have differential effects on the reproductive physiology and behaviour of receivers because they impart different types of information to receivers. Signals that indicate species identity often override cues indicating male quality in mate choice decisions. For example, Hankison & Morris (2003) found that female swordtails, Xiphophorus pygmaeus, change their mating preferences based on the presence or absence of certain visual cues: when given the choice between larger males (which are generally preferred) and males with a species-typical colour pattern, females preferred to mate with conspecifics. As a result of this disparity, signals may act over different time courses and with different specificity depending on the messages they convey.
Moreover, courtship signals that act as ‘backup’ messages may be expected to have similar effects on female reproductive physiology or behaviour because the information they impart is identical. Partan & Marler (1999) proposed a framework for distinguishing between redundant and nonredundant signals based on responses to isolated and combined components. Briefly, isolated signal components that have similar effects on receiver behaviour or physiology are considered redundant, while those that have different effects are nonredundant (Partan & Marler 1999). Although this paradigm specifically addresses sequential or simultaneous signals occurring in multiple modalities, the same theory can be used to address the function of two signals in the same modality that, when combined, create a single courtship display. The courtship of the sagebrush lizard, Sceloporus graciosus, includes the combined performance of two very distinctive visual displays: the push-up, which is a multifunction signal that is used in aggressive interactions and as a nondirected display, and the shudder, which is exclusive to courtship. Although both displays are always given during courtship, the function of each display type in a courtship context is largely unknown. Here, we exposed females to either push-ups or shudders for 14 days to determine whether long-term exposure to either display type affected female reproductive physiology or behaviour. To determine differences in the specificity or effectiveness of the two display types in altering female behaviour, we examined their effects on two aspects of female physiology: (1) behavioural responses to courting males and (2) patterns of femoral pore secretions (FPS), a chemical scent mark. We also discuss the possible origins of push-ups and shudders as ‘multiple messages’ or ‘backup signals’, according to the criteria established by Partan & Marler (1999) for determining the information content of signals.
METHODS
Study Species Sceloporus graciosus is a small (approximately 55 mm in snout-to-vent length), diurnal lizard native to western North America (Stebbins 1985). They inhabit primarily dry shrub and sagebrush habitats at mid to high elevations (Stebbins 1985). Animals emerge from hibernation after snow melt and the breeding season extends from early June to August (Stebbins 1985). Both sexes are territorial, although a male’s home range may overlap the territories of a few females, which he may court repeatedly throughout the breeding season (Stebbins 1985; Deslippe & M’Closkey 1991). Adult S. graciosus show a species-typical push-up display, during which the head and anterior portion of the body is raised and lowered in sequence (Carpenter & Ferguson 1977). The degree to which the push-up is modified by certain body postures depends on the context in which it is given (aggressive versus courtship): displays during courtship generally lack the gular extension and lateral compression of those given during aggressive encounters (Martins 1993). Males also
KELSO & MARTINS: EFFECTS OF COURTSHIP ON BEHAVIOUR
produce a distinct shudder display during courtship interactions (Carpenter & Ferguson 1977), during which a short series of rapid, low-amplitude headbobs is given while the animal is in motion and/or in contact with a female (Carpenter & Ferguson 1977; Martins 1993). During a typical courtship, males will alternate the performance of both displays. Females that are sexually receptive will gradually decrease stereotypical courtship rejection behaviour (see below) and aggression, eventually allowing males to approach and mate (Carpenter & Ferguson 1977; E. C. Kelso, unpublished observation).
Animal Housing For this study, we collected adult S. graciosus from Table Mountain Campground in the San Gabriel Mountains of southern California during May 2001 and 2003 (California Department of Fish and Wildlife scientific collecting permit no. 2907). Animals were housed individually in the laboratory in 37.9-litre glass aquaria containing sand substrate and a single brick for perching. Full-spectrum lighting was provided as well as a single 40-W incandescent bulb per aquarium to provide heat for basking. We provided the animals with calcium-dusted crickets (Acheta domesticus) and mealworms (Tenebrio molitor) every 2 days and misted the enclosures each day to provide water and humidity. All animals were housed under a 12:12 h light:dark cycle at temperatures of 28 C (day) and 20 C (night). Animal care and testing was conducted in accordance with the Guidelines for the Treatment of Animals in Research (ASAB/ABS 2003) and approved by the Indiana University, Bloomington, Institutional Animal Care and Use Committee (protocol no. 01-008).
General Methods Display presentations To control the stimulus that a female received, we simulated two standardized displays, push-ups (P) and shudders (S), using a mechanized lizard model painted to resemble a male S. graciosus. The latex model was positioned on top of a box (12 7 5 cm) that concealed a small stepper motor (15-degree linear actuator, HIS 46000; Hayden Switch & Instrument, Inc., Waterbury, CT, U.S.A.). The movement of the model’s ‘head’, via the stepper motor, was controlled by a compact integrated driver (MicroLynx4, MX-CS100-400; Intelligent Motion Systems, Inc., Marlborough, CT, U.S.A.) that had been programmed to produce one of two displays (described below). This method elicits behaviour similar to that elicited during conspecific interactions staged in a laboratory setting (Martins et al. 2005). The latex model was posed in a nonaggressive manner (i.e. did not show any body postures, including leg extensions and lateral compression). The push-up displays produced by the model, therefore, resemble those given by males during courtship rather than those used by males and females during aggressive encounters. The entire apparatus was positioned on a platform so that the model lizard was presented laterally to test subjects during trials. Because the platform was
free-standing, any vibrations produced by the action of the motor were not transmitted to the females’ cages. We conducted two experiments (described in detail below). For each experiment, we positioned the model and robot assembly in front of a female’s cage for 2 min three times per day for 14 consecutive days. During these 2-min sessions, each female received one of three display treatments: push-ups, shudders, or the stationary model. The push-up display used during these presentations consisted of a sequence of one double headbob, followed by two single headbobs, followed by three double headbobs. A single push-up display sequence lasted 8 s and the entire display was repeated three times during the 2-min presentation period. The shudder display consisted of a sequence of five rapid headbobs, repeated three times, with 1-s intervals between headbob sequences. One shudder sequence lasted 5 s and was repeated four times during the 2-min display presentation. The timing and spatiotemporal structure of both stimulus displays were based on laboratory trials (E. C. Kelso & E. P. Martins, unpublished data) and field observations (Carpenter 1978; Martins 1991). Extended screens between the aquaria ensured that each female did not interact visually with neighbouring females and that each female experienced only her assigned display type. Care was taken to ensure that the model was within a female’s visual range before a display presentation began.
Behavioural observations Behavioural trials began 7 days after the last day of stimulus presentation. For both experiments, each female was paired once with a live male in a larger (approximately 0.6 0.6 m) enclosure containing sand substrate and a single brick, and their behaviour was recorded. Although males were used in multiple trials (see below for details), an individual male was used only once per day. The interactants were videotaped using a Panasonic camcorder (AG-188). Behavioural trials were conducted over a 7-day period, so that the final female was tested 14 days after she was last exposed to the display stimulus. We scored videotapes for the number and sequence of behaviour patterns given by both males and females. To reduce the number of variables, we grouped individual behaviour patterns into five functional categories: (1) male courtship behaviour, including shudders, nonaggressive push-ups and mounting attempts (given by males only); (2) courtship rejection behaviour (Greenberg 1977): ‘tail-up’ posture with lateral compression (given by females only) also called ‘sidlehopping’; (3) aggressive behaviour, such as push-ups performed in conjunction with aggressive body postures, lateral compression, gular extension and raised body; (4) scent-marking behaviour, including chin wiping, body wiping and femoral pore marking; and (5) chemosensory behaviour (i.e. tongueflicking of the substrate or conspecific). In all cases, data are presented as the number of behaviours given per 20 min. We also recorded distance (on a scale of 0e3) between individuals at 5-min intervals. To accomplish this, the experimental enclosure was divided into six areas of
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approximately 25 cm2. Distance was scored as 0 if the animals were in physical contact, as 1 if the animals were less than one body length (approximately 6 cm) apart, as 2 if the animals were in the same area, and as 3 if the animals were in different areas. Distance scores were averaged for each trial to give a single measurement. In addition, we measured the activity of female lizards by recording the number of times that a female crossed an area boundary during a trial.
treatment groups. Paper towel strips were taped to brick perches to absorb FPS. The towels were changed each day during general maintenance (feeding, watering). We recorded the number and size of spots deposited by females each day. We used 10 males during behavioural testing (described above in General Methods). Males were paired with two or three females from each treatment group (shudder or push-up) in random order for a total of five trials per male (48 trials total). The interactants were recorded for 20 min.
Experiment 1: Display versus Control In March 2002, we conducted an experiment comparing the behavioural responses of female S. graciosus to males after exposure to male displays (push-up or shudder) or to a control treatment (no display). Females were removed from hibernation (at 10 C) during January 2002 and maintained under the conditions described in animal housing (above). This procedure ensured that all females were in similar reproductive condition at the start of the study. Females (N ¼ 30) received one of three display treatments: shudder, push-up or no display (control) three times per day for 14 days as described above. We combined the shudder and push-up groups into one group (display group) to compare the effects of both displays to the control. Five males were used during the behavioural trials (described above in General Methods) for experiment 1: individual males encountered two females from each treatment (push-up, shudder, or control) in random order to give a total of six trials per male. The interactants were videotaped for 40 min. We recorded behavioural data as the number of behaviour patterns given per 20 min.
Statistical analyses Distance data were analysed with a two-way ANOVA with treatment (display or control group) and male identity as fixed factors (SAS, Proc Mixed, SAS Institute, Cary, NC, U.S.A.). We used a nonparametric test (Manne Whitney U ) to explore behavioural responses of males and females because these data did not meet the assumptions of parametric tests.
Experiment 2: Push-up versus Shudder During March 2004, we conducted a similar experiment, comparing the behavioural responses of females to males after long-term exposure to push-up or shudder displays. Females were removed from hibernation (at 10 C) during January 2003 and maintained under the conditions described in animal housing (above). This procedure ensured that all females were in similar reproductive condition at the beginning of the study. Females (N ¼ 58) received one of two display treatments: shudder or push-up three times per day for 14 days as described above. Females that had been used in experiment 1 (during March 2002) were not used in experiment 2. During the 2-week presentation period, we also collected femoral pore secretions (FPS) from females in all
Statistical analyses Distance data were analysed with a two-way ANOVA (Proc GLM, SAS) with treatment (push-up or shudder) and male identity as fixed factors. We used a nonparametric test (ManneWhitney U ) to explore behavioural responses of males and females because these data did not meet the assumptions of parametric tests. In addition to examining the amount of courtship behaviour shown by males, we also used a chi-square test to examine differences in the number of courting males. For the FPS data, we averaged the number of spots produced by females for days 1, 7 and 14 of stimulus presentation to give a single value for each female per day. In addition, we calculated the area of each spot produced on days 1, 7 and 14 and determined the average spot size for each female per day. We used ManneWhitney U tests to examine treatment differences in FPS spot number and size because these data did not meet parametric assumptions.
RESULTS
Experiment 1: Display versus Control Females showed no significant differences in behaviour when exposed to male displays or no displays (all P > 0.05; Table 1). In addition, males showed no significant differences in behaviour when paired with either of the two classes of females (ManneWhitney U test: scent-marking behaviour: U ¼ 97.5, N1 ¼ 20, N2 ¼ 10, P ¼ 0.911; chemosensory behaviour: U ¼ 88.5, N1 ¼ 20, N2 ¼ 10, P ¼ 0.613), and the number of males that courted females from each treatment group did not differ (chi-square test: c21 ¼ 0:085, P ¼ 0.770). Females were Table 1. Median and interquartile range (IQR) of behaviour recorded for female sagebrush lizards during experiment 1 (display versus control) and results of ManneWhitney U tests No display N¼10 Behaviour category Chemosensory Scent marking Aggressive Rejection
Median
IQR
10.56 0 0.51 0
10.34 0 1.25 0.44
Display N¼20 Median IQR 6.56 0 0 0
6.86 2.45 0.77 0.83
P (twotailed, U a¼0.05) 75 75 80 95
0.271 0.190 0.331 0.819
KELSO & MARTINS: EFFECTS OF COURTSHIP ON BEHAVIOUR
2.8
Distance score
2.6 *P < 0.03 2.4 2.2 2 1.8 1.6 No display (C)
Display (D)
Figure 1. Mean SD distance scores of female and male sagebrush lizards during behavioural trials for experiment 1 (display versus control). Distance scores: 0 ¼ animals were in physical contact; 1 ¼ animals were less than one body length (approximately 6 cm) apart; 2 ¼ animals were in the same area of the arena; 3 ¼ animals were observed in different areas of the arena.
consistently closer to the male during display (shudder þ push-up) trials than during control trials (ANOVA: F1,9 ¼ 5.24, P ¼ 0.033; Fig. 1), although there were no differences in distance scores between the two display types (data not shown). There was a marginally significant effect of male identity (F1,4 ¼ 3.08, P ¼ 0.040), but no male by treatment interaction effect (F1,4 ¼ 0.91, P ¼ 0.482). Date of behavioural testing (range 7e14 days poststimulus exposure) was also not significant.
Experiment 2: Push-up versus Shudder Females exposed to push-up displays performed more courtship rejection behaviour in response to male courtship than did females exposed to shudder displays (Manne Whitney U test: U ¼ 204, N1 ¼ 26, N2 ¼ 22, P ¼ 0.028). Females showed no significant differences in behaviour for the other three behaviour categories (all P > 0.05; Table 2). There was no treatment effect (push-up or shudder) on the activity (number of moves) of females (ANOVA: F1,47 ¼ 0.07, P ¼ 0.791) and no effect of male identity Table 2. Median and interquartile range (IQR) of behaviour recorded for female sagebrush lizards during experiment 2 (push-up versus shudder) and results of ManneWhitney U tests Push-up N¼22 Behaviour category Chemosensory Scent marking Aggressive Rejection *P < 0.05.
Shudder N¼26
Median IQR Median IQR 15 0 0 0.5
13 3 1 5
9 0 0.5 0
10 1 1 0
U
P (twotailed, a¼0.05)
221 235 270 193
0.197 0.245 0.753 0.028*
(F1,9 ¼ 0.89, P ¼ 0.545). In addition, males showed no significant differences in behaviour towards the two classes of females (ManneWhitney U test: scent-marking behaviour: U ¼ 275, N1 ¼ 26, N2 ¼ 22, P ¼ 0.814; chemosensory behaviour: U ¼ 246.5, N1 ¼ 26, N2 ¼ 22, P ¼ 0.413). The number of males showing courtship behaviour also did not differ between treatment groups (chi-square test: c21 ¼ 0:17, P ¼ 0.677). We observed no effect of display treatment (ANOVA: F1,47 ¼ 0.77, P ¼ 0.388) and no effect of male identity (F1,9 ¼ 0.87, P ¼ 0.562) on the proximity of males and females during behavioural trials (Fig. 2). Although individuals in both treatment groups (shudder and push-up) had slightly lower distance scores than those in the combined display group (shudder þ push-up) during experiment 1, the difference was not significant, suggesting that the results were consistent across the two experiments. Date of behavioural testing (range 7e14 days poststimulus exposure) was also not significant. Females in the two treatment groups differed in their FPS patterns on the first day of stimulus presentation. Females in the push-up group produced fewer spots than those in the shudder group (X SE ¼ 0:25 0:15 and 0:87 0:24, respectively; ManneWhitney U test: U ¼ 298.5, N1 ¼ 28, N2 ¼ 30, P ¼ 0.014). Females exposed to push-ups also produced spots that were smaller than those produced by females in the shudder group (X SE ¼ 0:19 0:11 and 0:37 0:12 cm2 , respectively; U ¼ 310, N1 ¼ 28, N2 ¼ 30, P ¼ 0.026). We found no differences in either the spot number or size of FPS on days 7 and 14 of stimulus presentation.
DISCUSSION In addition to responding to environmental conditions, such as changes in photoperiod or temperature, the reproductive physiology and behaviour of females may be influenced by the behaviour of conspecifics. The contribution of individual display elements to these effects and their specific action on different aspects of 1.9 1.8
Distance score
3
1.7 1.6 1.5 1.4 1.3 Shudder (S)
Push-up (P)
Figure 2. Mean SD distance scores of female and male sagebrush lizards during behavioural trials for experiment 2 (push-up versus shudder). Distance scores as described in Fig. 1.
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female behaviour is largely unknown for most species (but see Crews 1975; Cheng et al. 1998; Hebets & Uetz 1999). Our results indicate that brief exposure (6 min/day for 14 days) to either of two male courtship display components, push-up or shudder, affects the behaviour of female S. graciosus, although the specificity of these effects depends on the display type (push-up or shudder) and the particular female behaviour that is observed. Female S. graciosus that had been exposed to simulated shudders, the courtship-specific display, showed less stereotyped rejection behaviour in response to male courtship than did females exposed to push-up displays. In addition, FPS spots produced by females in the push-up treatment group were fewer and, on average, smaller than those produced by the shudder group on the first day of display presentation, indicating that females were more active during presentations of push-ups, but this difference was significant only on day 1. Animals that are actively moving about their enclosures tend to leave fewer, small secretions on their perches (Martins et al. 2006). These results suggest that push-ups and shudders have different influences on some aspects of female behaviour, including receptivity to courtship. However, females that had viewed either display type were consistently closer to the male during behavioural trials than females that had observed only the stationary model (experiment 1), although there were no differences in distance between the two display groups for either experiment. In this case, exposure to either display appears to result in similar behavioural changes that may be important for successful reproduction. Our findings differ from those of Crews (1975), who concluded that the push-up displays produced by male green anoles during courtship have no effect on female mating behaviour and that only the male dewlap display has a unique courtship function. In contrast, exposure to both types of courtship display seems to have relatively long-lasting effects on behaviour in female sagebrush lizards: females showed noticeable differences in behaviour up to 2 weeks poststimulus presentation. It is possible that some of the behavioural differences that we observed in our treatment groups could have been due to males adjusting their own courtship or responding to changes in female responsiveness or physiology (e.g. pheromone or colour cues). However, we found no differences in male behaviour towards any of the experimental groups of females, suggesting that males did not discriminate between classes of females. The behavioural differences that we observed during trials, therefore, were more likely the result of changes in female behaviour rather than responses on the part of males to differences in female physiology and/or behaviour. We found some evidence that push-ups and shudders have evolved via a ‘multiple messages’ scenario based on the framework proposed by Partan & Marler (1999) for determining the information content of signals. The separate displays had different effects on some aspects of female behaviour: shudders reduced the amount of female rejection behaviour, whereas push-ups did not, indicating that the information contained in the two displays is nonredundant (Partan & Marler 1999, 2005). Alternatively,
these results could be interpreted as one display being slightly more effective at provoking changes in female behaviour or physiology than the other, which would be more indicative of two redundant signals (Partan & Marler 1999, 2005). Another explanation for our results is that the two displays may convey different types of information about potential mates that ultimately lead to similar outcomes in female decision making or have similar physiological effects. The species-typical spatiotemporal structure of the push-up display could easily be used by females to identify conspecific males, while the ability to perform rapid shudders may indicate a male’s stamina. Females may respond to both types of information by allowing only high-quality conspecific males to approach more closely. However, female lizards appear to lack the strong preferences for attractive male displays that have been shown in other taxa, leading to some difficulty in establishing display parameters that are indicative of male quality (Tokarz 1995). Instead, mate choice decisions of female lizards are probably based on multiple male characters and may, therefore, be fairly complex (Hamilton & Sullivan 2005; Bissell & Martins 2006). Females that were exposed to either push-ups or shudders were closer to the male during behavioural trials than were females that observed only the stationary model. In the field, proximity between males and females is a reliable predictor of paternity in Sceloporus lizards (Abell 1997), and male S. virgatus tend to associate more closely with females in reproductive condition during the breeding season (Weiss 2002). Recently, Bissell & Martins (2006) found that a female’s choice of mate may be reflected in how often or how close she allows a male to approach. Both push-up and shudder displays, therefore, may be important aspects of courtship behaviour because they both increase maleefemale proximity. Push-ups are generally considered an aggressive display and are never performed in the context of courtship without also being accompanied by shudders. Push-ups have been studied most often in the context of malee male interactions, however, female lizards also use the display during territorial contests (Carpenter & Ferguson 1977; DeCourcy & Jenssen 1994). While exposure to courtship displays has been shown to enhance reproductive function, aggressive displays often have inhibitory effects on reproduction because they tend to elevate the stress response (Marchlewskakoj 1997; Wingfield & Sapolsky 2003). Because the push-up display is used extensively by both males and females during agonistic encounters, this could lead to a possible conflict in the potential effects on female physiology. However, the aggressive content of the push-up display may be conveyed in the body postures accompanying the display rather than in the spatiotemporal structure of the display itself (Martins 1993): push-up displays used during courtship are not usually accompanied by leg extension or lateral compression, although both body postures are used during agonistic displays. The simulated push-up displays used in this study were performed by a model posed in a ‘nonaggressive’ courtship-typical body posture. Evidence from other taxa suggests that some courtship signals have been co-opted
KELSO & MARTINS: EFFECTS OF COURTSHIP ON BEHAVIOUR
from their origins in aggressive displays (Berglund et al. 1996; Borgia & Coleman 2000). Many other signals, such as bird song, often serve dual functions, attracting mates and deterring rival males simultaneously. The problem of inhibitory effects of aggressive displays on female reproductive behaviour may, therefore, be one that is easily overcome, evolutionarily. Little is known about the display behaviour of S. graciosus that occurs in other modalities. The natural courtship display of S. graciosus contains a number of nonvisual signals, including extensive scent-marking behaviour and tactile communication between the male and female. We were unable to include these additional components in our analyses because of the limitations of presenting artificial stimuli. However, it would be interesting to examine the contribution of nonvisual modalities to effects on female reproductive behaviour observed in this study. Acknowledgments We thank B. H. Bleakely for assistance with the animals. We also thank T. J. Ord, G. Ragland and B. Heidinger for helpful comments on earlier versions of the manuscript. E. C. Kelso was supported by a graduate research fellowship from the Center for Integrative Study of Animal Behavior (CISAB) at Indiana University. References Abell, A. J. 1997. Estimating paternity with spatial behaviour and DNA fingerprinting in the striped plateau lizard, Sceloporus virgatus (Phrynosomatidae). Behavioral Ecology and Sociobiology, 41, 217e226. Andersson, S., Pryke, S. R., Ornborg, J., Lawes, M. J. & Andersson, M. 2002. Multiple receivers, multiple ornaments, and a trade-off between agonistic and epigamic signaling in a widowbird. American Naturalist, 160, 683e691. ASAB/ABS. 2003. Guidelines for the treatment of animals in behavioural research and teaching. Animal Behaviour, 61, 271e275. Badyaev, A. V. & Hill, G. E. 2000. Evolution of sexual dichromatism: contribution of carotenoid- versus melanin-based coloration. Biological Journal of the Linnean Society, 69, 153e172. Berglund, A., Bisazza, A. & Pilastro, A. 1996. Armaments and ornaments: an evolutionary explanation of traits of dual utility. Biological Journal of the Linnean Society, 58, 385e399. Bissell, A. N. & Martins, E. P. 2006. Male approach and female avoidance as mechanisms of population discrimination in sagebrush lizards. Behavioral Ecology and Sociobiology, 60, 655e662. Borgia, G. 1995. Complex male display and female choice in the spotted bowerbird: specialized functions for different bower decorations. Animal Behaviour, 49, 1291e1301. Borgia, G. & Coleman, S. W. 2000. Co-option of male courtship signals from aggressive display in bowerbirds. Proceedings of the Royal Society of London, Series B, 267, 1735e1740. Bradbury, J. W. & Vehrencamp, S. L. 1998. Principles of Animal Communication. Sunderland, Massachusetts: Sinauer. Brockway, B. F. 1965. Stimulation of ovarian development and egg laying by male courtship vocalization in budgerigars (Melopsittacus undulatus). Animal Behaviour, 13, 575e578. Brooks, R. 2002. Variation in female mate choice within guppy populations: population divergence, multiple ornaments, and the maintenance of polymorphism. Genetica, 116, 343e358.
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