- Email: [email protected]
Female comparative mate choice influences strategic male nesting strategy in the peacock blenny Salaria pavo
Behavioural Processes 170 (2020) 103988
Contents lists available at ScienceDirect
Behavioural Processes journal homepage: www.elsevier.com/locate/behavproc
Short report
Female comparative mate choice influences strategic male nesting strategy in the peacock blenny Salaria pavo
T
Lisa Locatello*, Elisa Bozzetta, Livia Pinzoni, Maria B. Rasotto Department of Biology, University of Padova, Via U. Bassi 58/b, 35121 Padova, Italy
A R T I C LE I N FO
A B S T R A C T
Keywords: Mate choice Mating context Male attractiveness Nesting strategies Fish
Emerging evidence endorses the idea that comparative instead of rational choice is widespread among species and mating contexts. In a comparative scenario the attractiveness of a male is not absolute but depends on the attractiveness of the other males to whom he is compared by females. Therefore, a male may benefit from the ability to choose the appropriate context that enhances his attractiveness. Here we test for the occurrence of strategic male nesting strategies in the peacock blenny, Salaria pavo, a fish species in which females evaluate potential mates by comparing males. Our results show that the large majority of males choose the context that maximize their attractiveness by nesting close to less attractive neighbours. Overall, we suggest that, in the peacock blenny, comparative, non-directional female choice is associated to strategic male nesting strategies and this scenario may contribute to the maintenance of genetic variability of male sexually-selected traits.
1. Introduction An emerging area of interest in mate choice is represented by the role of female perceptual and cognitive abilities and its consequences on the evolution of male signalling strategies (Ryan and Cummings, 2013; Rosenthal, 2017; Ryan et al., 2018). Traditional models assumed that individuals maximize their fitness by making absolute decisions in which the preferences between options remains stable over time even when additional options are presented (Jennions and Petrie, 1997). Nevertheless, comparative, rather than absolute, mate choice, might be favoured in socially complex situations, since it potentially mitigates the risk of costly choice errors in uncertain environments (Bateson and Healy, 2005; Ryan et al., 2018). Evidence supporting this hypothesis came recently from the green swordtail fish (Royle et al., 2008), the túngara frog (Lea and Ryan, 2015) and the peacock blenny (Locatello et al., 2015), in which the initial preference for two options is altered by the addition of inferior alternatives. Irrationality in favour of heuristic mate choice may result in predictable adjustments in male signalling strategies, such as males’ ability to increase their reproductive success by choosing the appropriate context that maximize their attractiveness (e.g. in proximity to less attractive rivals) (Bateson and Healy, 2005). Evidence that males actively choose the context in which their relative attractiveness to females is maximized is limited to two examples. In the house finch (Carpodacus mexicanus), attractive males are more likely to change social group and males that frequently moved had
⁎
greater pairing success than less social individuals with equivalent sexual ornamentation (Oh and Badyaev, 2010). In the guppy (Poecilia reticulata), males strategically prefer to mate with females surrounded by less attractive competitors (Gasparini et al., 2013). However, in both these species the choice for a context that maximizes male attractiveness cannot yet be directly associated with females’ ability to make a comparative choice of mates. The peacock blenny, Salaria pavo, is an ideal species to delve into this topic because male mating success is strongly influenced by female choice for multiple male traits, with females preferring larger males with larger and more coloured head crests (see Pizzolon et al., 2012; Locatello et al., 2012). Female choice is comparative and the attractiveness of a male depends on the attractiveness of the other males to whom he is compared, with the relative preference for a male increasing when a further inferior option for that trait is added to the choice context (Locatello et al., 2015; Locatello and Rasotto, 2017). Moreover, peacock blenny males nest in groups similar to leks, at a density of up to six individuals per square meter (Pizzolon, 2010), an ideal scenario not only for the evolution of female comparative choice, but also for male non-random nesting strategies. Here we test the hypothesis that, as a consequence of the occurrence of female comparative mate choice, peacock blenny males choose the nesting context that increase their attractiveness, thus closer to a less attractive neighbour. In this study a focal male was given the opportunity to chose his nest in proximity to a more or to a less ornamented stimulus, as well as in a neutral position.
Corresponding author. E-mail address: [email protected] (L. Locatello).
https://doi.org/10.1016/j.beproc.2019.103988 Received 30 July 2019; Received in revised form 15 October 2019; Accepted 15 October 2019 Available online 16 October 2019 0376-6357/ © 2019 Elsevier B.V. All rights reserved.
Behavioural Processes 170 (2020) 103988
L. Locatello, et al.
Fig. 1. Nest choice tank. Dashed lines: permanent transparent partitions that delimitate ì) the stimulus males’ compartments (S1 and S2) equipped with doors; ìì) the central compartment hosting 6 nest choices offered to the focal male; ììì) the front corridor hosting 4 females. Distance between nests 43 cm.
2. Methods
3. Results
Twenty triplets of 1 focal male and 2 stimulus males were tested in 20 trials in an outdoor experimental tank (60 males in total) (Fig. 1, Supplementary S1). With respect to the focal male the 2 stimuli were either smaller in total length (TL) and in the relative size of the yellow patch (patch size/crest size) (less attractive male), or larger in TL and yellow patch (more attractive male) (minimum difference focal-stimulus: 1.5 cm in TL; 12% in yellow patch) (details on the species and on traits measurements in S1). A preliminary observation was performed in each trial to check the high and low attractiveness of the stimulus males, by measuring the preference of a group of 4 ready to spawn females (TL: 6.7–12.5 cm) (80 females in total). At 9.00 a.m. of the 1st day of trial the stimulus males were randomly positioned on the left or right lateral compartment of the experimental tank, and furnished with their own nest (S1 and S2 in Fig. 1). Four randomly chosen females were positioned in the corridor in front of the stimuli compartments (Fig. 1). The mean TL of the female quartets did not differ among the 20 trials (Linear model: t78 = −0.781, P = 0.437). All the stimulus males regularly occupied their nest in few hours. At 3.00 p.m. of day 1, the doors of the two lateral compartments were opened, so that females could access stimulus males’ compartments, and an observation of 15 min per male (30 min total) allowed to register the total number of visits performed by the 4 females of the group to each stimulus male (with active interest in males showed by rapid respiratory movements, pectoral fin fanning and ventral region displays, Patzner, 1986). During observations we also registered the occurrence of any aggressive interaction between stimuli males that were free to move in the tank. At the end of the observation period the doors were again closed, after eventually encouraging the females to return in the front corridor by gently guiding them with a stick. Females were left in the central corridor during the following nest choice trial to keep the males interested in keeping their nests. At 5.00 p.m. of the 1st day, 6 other nests were added to the central compartments and the focal male was also introduced (Fig. 1). At 2.00 p.m. of the 2nd day the choice of the nest by focal male was registered. Occupation of nests n° 1 or n° 2 was considered as a nesting choice close to the left stimulus S1 (less attractive or more attractive), occupation of nests n° 5 or n° 6 was considered as a nesting choice close to the right stimulus S2 (less attractive or more attractive), the choice for nests n° 3 or n° 4 was considered as a choice for a central, neutral position neither close to S1 nor to S2 (Fig. 1). To analyse whether larger and more coloured males received more visits (i.e. was more attractive) than smaller and duller ones, we used a GLMM with a Poisson error distribution and a logarithm link function with trial number (i.e. the pair of males) included as random factor to account for the non-independence of data within each trial. The frequency of choice for nests close to a more attractive or a less attractive male or in a neutral position was analysed by chi-square tests.
Preliminary behavioural observations showed that the larger stimulus males with a relative larger yellow patch on the head crest received a significant higher amount of visits by females than the smaller and less coloured stimulus males (range: more attractive = 0–13 visits; less attractive: 0–1 visit. Mean ± SE: more attractive = 2.95 ± 0.90; less attractive = 0.20 ± 0.09. F1,19 = 26.29, p < 0.001), thus validating the assignment of more attractive and less attractive stimuli used for the following nest choice trials. We never observed aggressive interactions between the two stimulus males or any aggressive nest take over by larger males at the expense of small ones. On the 20 focal males tested only 2 males chose to nest in the central area, 3 males nested in the area close to the more attractive stimulus, 15 males nested in the area close to the less attractive stimulus (Fig. 2). These observed frequencies significantly differed from a random choice for the 3 tank’s areas (χ2 = 15.70, d.f. = 2, P < 0.001) (Fig.2). The preference for nests closer to less attractive males was significantly higher than the preference for nests closer to more attractive males (χ2 = 8, d.f. = 1, P < 0.01) or for central nests (χ2 = 9.94, d.f. = 1, P < 0.01) (Fig. 2). The nesting choice close to less attractive was not biased by its position in the tank since focal males did not show any particular preference for the left or the right tank’s side (χ2 = 2, d.f. = 1, P = 0.157).
Fig. 2. Number of focal males that chose to nest close to a more attractive male, less attractive male or in the neutral (‘central’) position. ** P < 0.01. 2
Behavioural Processes 170 (2020) 103988
L. Locatello, et al.
4. Discussion
regulations for the use of animals in scientific procedures (permission OPBA-University of Padova, Prot. n. 143601). At the end of the trial experimental animals were released at their capture sites.
Our results show that the focal males chose to nest in a dominant position, i.e. close to a less attractive neighbour, while avoiding those nests close to a more attractive neighbour as well as the solitary position in the central area. These results are in accordance with previous observations in the field, where the mean distance from nesting males is positively correlated to their attractiveness, meaning that more attractive males are more isolated than less attractive males, which have a larger number of closer neighbours (Pizzolon, 2010). Overall, these findings, combined with recent results on female comparative evaluation of potential mates (Locatello et al., 2015; Locatello and Rasotto, 2017), suggest that the nest choice by peacock blenny males may be strategically adjusted in order to maximize their attractiveness to females. Indeed, in this species the attractiveness of a male depends on the attractiveness of the other males to whom he is compared and, specifically, the relative preference for a male trait increases when a further inferior option for that trait is added (Locatello et al., 2015). In this scenario, a male is expected to gain a reproductive advantage by choosing to nest close to a less attractive neighbour. Other reasons might also contribute to explain the nesting choice we observed, such as the avoidance of sneaking, of competition for resources (nests or food) and of direct aggression by other males. However, alternative male mating tactics with sneaker males do not occur in our population and males from the entire size-range, even the smaller ones, regularly occupy nests (Pizzolon, 2010; Pizzolon et al., 2012). The reason plausibly relies on the fact that potential nests are very abundant in our study sites, and do not represent a limiting resource neither to compete for, nor to drive the occurrence of alternative sneaking tactics. The observed pattern of nest choice might have also been influenced by the competition for feeding resources, since a smaller neighbour is supposed to take away less food than a larger one. However, in the field males move to feed on a spatial range that exceeds the distance between two nests, thus feeding resources do not appear to be limited to the area shared with the next neighbours (LL personal observations). Moreover, we exclude that choice of nesting close to a larger male is driven by the avoidance of direct aggression, because during the preliminary phase of our experiment, when the doors were open, we never observed any aggressive interactions between large and small males or any aggressive nest take-over by large males over small ones. This is confirmed by observations in the field where aggressive interactions among males are rare, as happens in other populations where the nest availability is high and, as a consequence, the male-male competition is relaxed (LL personal observations; Saraiva et al., 2009). In conclusion, our findings suggest that, in the peacock blenny, comparative, non-directional female choice (Locatello et al., 2015; Locatello and Rasotto, 2017) may result in the adjustment of male signalling strategies that maximize male attractiveness to females. In this species male and female behavioural reproductive strategies may contribute in concert to the maintenance of genetic variability of sexually-selected traits.
Declaration of Competing Interest The authors declare that they have no conflict of interest. Acknowledgment The Authors thank Christian Drerup for his help in data collection. Financial support was provided by the University of Padova (‘Fondi di Ricerca DOR’ to MBR). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.beproc.2019.103988. References Bateson, M., Healy, S.D., 2005. Comparative evaluation and its implications for mate choice. Trends Ecol. Evol. 20, 659–664. Gasparini, C., Serena, G., Pilastro, A., 2013. Do unattractive friends make you look better? Context-dependent male mating preferences in the guppy. Proc. Royal. Soc. B 280, 20123072. Jennions, M.D., Petrie, M., 1997. Variation in mate choice and mating preferences: a review of causes and consequences. Biol. Rev. Camb. Philos. Soc. 72, 283–327. Lea, A.M., Ryan, M.J., 2015. Irrationality in mate choice revealed by tungara frogs. Science 349, 964. https://doi.org/10.1126/science.aab2012. Locatello, L., Pizzolon, M., Rasotto, M.B., 2012. One trait, many signals: different information on male quality is enclosed within the same trait in a blenny fish. Naturwissenschaften 99, 863–867. Locatello, L., Poli, F., Rasotto, M.B., 2015. Context-dependent evaluation of prospective mates in a fish. Behav. Ecol. Sociobiol. 69, 1119–1126. Locatello, L., Rasotto, M.B., 2017. Females sampling strategy to comparatively evaluate prospective mates in the peacock blenny Salaria pavo. Sci. Nat. 104, 57. Oh, K.P., Badyaev, A.V., 2010. Structure of social networks in a passerine bird: consequences for sexual selection and the evolution of mating strategies. Am. Nat. 176, 80–89. Patzner, R.A., Seiwald, M., Adlgasser, M., Kaurin, G., 1986. The reproduction of Blennius pavo. V: reproductive behavior in natural environment. Zool. Anz. 216, 338–350. Pizzolon, M., 2010. Multiple Male Traits and Female Choice in Salaria pavo. Ph.D. Thesis. University of Padova, Padova, Italy. Pizzolon, M., Locatello, L., Warner, R.R., Chimento, N., Finos, L., Rasotto, M.B., 2012. Linking male qualities to multiple display traits: an example in a fish with exclusive male care. Behav. Ecol. Sociobiol. 66, 497–504. Rosenthal, G.G., 2017. Mate Choice: the Evolution of Sexual Decision Making From Microbes to Humans. Princeton University Press, Princeton, NJ, USA. Royle, N.J., Lindstrom, J., Metcalfe, N.B., 2008. Context-dependent mate choice in relation to social composition in green swordtails Xiphophorus helleri. Behav. Ecol. 19, 998–1005. Ryan, M.J., Cummings, M.E., 2013. Perceptual biases and mate choice. Annu. Rev. Ecol. Evol. Sys. 44, 437 459. Ryan, M.J., Page, R.A., Hunter, K.L., Taylor, R.C., 2018. Crazy love’: nonlinearity and irrationality in mate choice. Anim. Behav. 147, 189–198. Saraiva, J.L., Gonçalves, D.M., Oliveira, R.F., 2009. Environmental modulation of androgen levels and secondary sex characters in two populations of the peacock blenny Salaria pavo. Horm. Behav. 57 (2), 192–197.
Compliance with ethical standards The study was carried out in accordance with current Italian
3
Contents lists available at ScienceDirect
Behavioural Processes journal homepage: www.elsevier.com/locate/behavproc
Short report
Female comparative mate choice influences strategic male nesting strategy in the peacock blenny Salaria pavo
T
Lisa Locatello*, Elisa Bozzetta, Livia Pinzoni, Maria B. Rasotto Department of Biology, University of Padova, Via U. Bassi 58/b, 35121 Padova, Italy
A R T I C LE I N FO
A B S T R A C T
Keywords: Mate choice Mating context Male attractiveness Nesting strategies Fish
Emerging evidence endorses the idea that comparative instead of rational choice is widespread among species and mating contexts. In a comparative scenario the attractiveness of a male is not absolute but depends on the attractiveness of the other males to whom he is compared by females. Therefore, a male may benefit from the ability to choose the appropriate context that enhances his attractiveness. Here we test for the occurrence of strategic male nesting strategies in the peacock blenny, Salaria pavo, a fish species in which females evaluate potential mates by comparing males. Our results show that the large majority of males choose the context that maximize their attractiveness by nesting close to less attractive neighbours. Overall, we suggest that, in the peacock blenny, comparative, non-directional female choice is associated to strategic male nesting strategies and this scenario may contribute to the maintenance of genetic variability of male sexually-selected traits.
1. Introduction An emerging area of interest in mate choice is represented by the role of female perceptual and cognitive abilities and its consequences on the evolution of male signalling strategies (Ryan and Cummings, 2013; Rosenthal, 2017; Ryan et al., 2018). Traditional models assumed that individuals maximize their fitness by making absolute decisions in which the preferences between options remains stable over time even when additional options are presented (Jennions and Petrie, 1997). Nevertheless, comparative, rather than absolute, mate choice, might be favoured in socially complex situations, since it potentially mitigates the risk of costly choice errors in uncertain environments (Bateson and Healy, 2005; Ryan et al., 2018). Evidence supporting this hypothesis came recently from the green swordtail fish (Royle et al., 2008), the túngara frog (Lea and Ryan, 2015) and the peacock blenny (Locatello et al., 2015), in which the initial preference for two options is altered by the addition of inferior alternatives. Irrationality in favour of heuristic mate choice may result in predictable adjustments in male signalling strategies, such as males’ ability to increase their reproductive success by choosing the appropriate context that maximize their attractiveness (e.g. in proximity to less attractive rivals) (Bateson and Healy, 2005). Evidence that males actively choose the context in which their relative attractiveness to females is maximized is limited to two examples. In the house finch (Carpodacus mexicanus), attractive males are more likely to change social group and males that frequently moved had
⁎
greater pairing success than less social individuals with equivalent sexual ornamentation (Oh and Badyaev, 2010). In the guppy (Poecilia reticulata), males strategically prefer to mate with females surrounded by less attractive competitors (Gasparini et al., 2013). However, in both these species the choice for a context that maximizes male attractiveness cannot yet be directly associated with females’ ability to make a comparative choice of mates. The peacock blenny, Salaria pavo, is an ideal species to delve into this topic because male mating success is strongly influenced by female choice for multiple male traits, with females preferring larger males with larger and more coloured head crests (see Pizzolon et al., 2012; Locatello et al., 2012). Female choice is comparative and the attractiveness of a male depends on the attractiveness of the other males to whom he is compared, with the relative preference for a male increasing when a further inferior option for that trait is added to the choice context (Locatello et al., 2015; Locatello and Rasotto, 2017). Moreover, peacock blenny males nest in groups similar to leks, at a density of up to six individuals per square meter (Pizzolon, 2010), an ideal scenario not only for the evolution of female comparative choice, but also for male non-random nesting strategies. Here we test the hypothesis that, as a consequence of the occurrence of female comparative mate choice, peacock blenny males choose the nesting context that increase their attractiveness, thus closer to a less attractive neighbour. In this study a focal male was given the opportunity to chose his nest in proximity to a more or to a less ornamented stimulus, as well as in a neutral position.
Corresponding author. E-mail address: [email protected] (L. Locatello).
https://doi.org/10.1016/j.beproc.2019.103988 Received 30 July 2019; Received in revised form 15 October 2019; Accepted 15 October 2019 Available online 16 October 2019 0376-6357/ © 2019 Elsevier B.V. All rights reserved.
Behavioural Processes 170 (2020) 103988
L. Locatello, et al.
Fig. 1. Nest choice tank. Dashed lines: permanent transparent partitions that delimitate ì) the stimulus males’ compartments (S1 and S2) equipped with doors; ìì) the central compartment hosting 6 nest choices offered to the focal male; ììì) the front corridor hosting 4 females. Distance between nests 43 cm.
2. Methods
3. Results
Twenty triplets of 1 focal male and 2 stimulus males were tested in 20 trials in an outdoor experimental tank (60 males in total) (Fig. 1, Supplementary S1). With respect to the focal male the 2 stimuli were either smaller in total length (TL) and in the relative size of the yellow patch (patch size/crest size) (less attractive male), or larger in TL and yellow patch (more attractive male) (minimum difference focal-stimulus: 1.5 cm in TL; 12% in yellow patch) (details on the species and on traits measurements in S1). A preliminary observation was performed in each trial to check the high and low attractiveness of the stimulus males, by measuring the preference of a group of 4 ready to spawn females (TL: 6.7–12.5 cm) (80 females in total). At 9.00 a.m. of the 1st day of trial the stimulus males were randomly positioned on the left or right lateral compartment of the experimental tank, and furnished with their own nest (S1 and S2 in Fig. 1). Four randomly chosen females were positioned in the corridor in front of the stimuli compartments (Fig. 1). The mean TL of the female quartets did not differ among the 20 trials (Linear model: t78 = −0.781, P = 0.437). All the stimulus males regularly occupied their nest in few hours. At 3.00 p.m. of day 1, the doors of the two lateral compartments were opened, so that females could access stimulus males’ compartments, and an observation of 15 min per male (30 min total) allowed to register the total number of visits performed by the 4 females of the group to each stimulus male (with active interest in males showed by rapid respiratory movements, pectoral fin fanning and ventral region displays, Patzner, 1986). During observations we also registered the occurrence of any aggressive interaction between stimuli males that were free to move in the tank. At the end of the observation period the doors were again closed, after eventually encouraging the females to return in the front corridor by gently guiding them with a stick. Females were left in the central corridor during the following nest choice trial to keep the males interested in keeping their nests. At 5.00 p.m. of the 1st day, 6 other nests were added to the central compartments and the focal male was also introduced (Fig. 1). At 2.00 p.m. of the 2nd day the choice of the nest by focal male was registered. Occupation of nests n° 1 or n° 2 was considered as a nesting choice close to the left stimulus S1 (less attractive or more attractive), occupation of nests n° 5 or n° 6 was considered as a nesting choice close to the right stimulus S2 (less attractive or more attractive), the choice for nests n° 3 or n° 4 was considered as a choice for a central, neutral position neither close to S1 nor to S2 (Fig. 1). To analyse whether larger and more coloured males received more visits (i.e. was more attractive) than smaller and duller ones, we used a GLMM with a Poisson error distribution and a logarithm link function with trial number (i.e. the pair of males) included as random factor to account for the non-independence of data within each trial. The frequency of choice for nests close to a more attractive or a less attractive male or in a neutral position was analysed by chi-square tests.
Preliminary behavioural observations showed that the larger stimulus males with a relative larger yellow patch on the head crest received a significant higher amount of visits by females than the smaller and less coloured stimulus males (range: more attractive = 0–13 visits; less attractive: 0–1 visit. Mean ± SE: more attractive = 2.95 ± 0.90; less attractive = 0.20 ± 0.09. F1,19 = 26.29, p < 0.001), thus validating the assignment of more attractive and less attractive stimuli used for the following nest choice trials. We never observed aggressive interactions between the two stimulus males or any aggressive nest take over by larger males at the expense of small ones. On the 20 focal males tested only 2 males chose to nest in the central area, 3 males nested in the area close to the more attractive stimulus, 15 males nested in the area close to the less attractive stimulus (Fig. 2). These observed frequencies significantly differed from a random choice for the 3 tank’s areas (χ2 = 15.70, d.f. = 2, P < 0.001) (Fig.2). The preference for nests closer to less attractive males was significantly higher than the preference for nests closer to more attractive males (χ2 = 8, d.f. = 1, P < 0.01) or for central nests (χ2 = 9.94, d.f. = 1, P < 0.01) (Fig. 2). The nesting choice close to less attractive was not biased by its position in the tank since focal males did not show any particular preference for the left or the right tank’s side (χ2 = 2, d.f. = 1, P = 0.157).
Fig. 2. Number of focal males that chose to nest close to a more attractive male, less attractive male or in the neutral (‘central’) position. ** P < 0.01. 2
Behavioural Processes 170 (2020) 103988
L. Locatello, et al.
4. Discussion
regulations for the use of animals in scientific procedures (permission OPBA-University of Padova, Prot. n. 143601). At the end of the trial experimental animals were released at their capture sites.
Our results show that the focal males chose to nest in a dominant position, i.e. close to a less attractive neighbour, while avoiding those nests close to a more attractive neighbour as well as the solitary position in the central area. These results are in accordance with previous observations in the field, where the mean distance from nesting males is positively correlated to their attractiveness, meaning that more attractive males are more isolated than less attractive males, which have a larger number of closer neighbours (Pizzolon, 2010). Overall, these findings, combined with recent results on female comparative evaluation of potential mates (Locatello et al., 2015; Locatello and Rasotto, 2017), suggest that the nest choice by peacock blenny males may be strategically adjusted in order to maximize their attractiveness to females. Indeed, in this species the attractiveness of a male depends on the attractiveness of the other males to whom he is compared and, specifically, the relative preference for a male trait increases when a further inferior option for that trait is added (Locatello et al., 2015). In this scenario, a male is expected to gain a reproductive advantage by choosing to nest close to a less attractive neighbour. Other reasons might also contribute to explain the nesting choice we observed, such as the avoidance of sneaking, of competition for resources (nests or food) and of direct aggression by other males. However, alternative male mating tactics with sneaker males do not occur in our population and males from the entire size-range, even the smaller ones, regularly occupy nests (Pizzolon, 2010; Pizzolon et al., 2012). The reason plausibly relies on the fact that potential nests are very abundant in our study sites, and do not represent a limiting resource neither to compete for, nor to drive the occurrence of alternative sneaking tactics. The observed pattern of nest choice might have also been influenced by the competition for feeding resources, since a smaller neighbour is supposed to take away less food than a larger one. However, in the field males move to feed on a spatial range that exceeds the distance between two nests, thus feeding resources do not appear to be limited to the area shared with the next neighbours (LL personal observations). Moreover, we exclude that choice of nesting close to a larger male is driven by the avoidance of direct aggression, because during the preliminary phase of our experiment, when the doors were open, we never observed any aggressive interactions between large and small males or any aggressive nest take-over by large males over small ones. This is confirmed by observations in the field where aggressive interactions among males are rare, as happens in other populations where the nest availability is high and, as a consequence, the male-male competition is relaxed (LL personal observations; Saraiva et al., 2009). In conclusion, our findings suggest that, in the peacock blenny, comparative, non-directional female choice (Locatello et al., 2015; Locatello and Rasotto, 2017) may result in the adjustment of male signalling strategies that maximize male attractiveness to females. In this species male and female behavioural reproductive strategies may contribute in concert to the maintenance of genetic variability of sexually-selected traits.
Declaration of Competing Interest The authors declare that they have no conflict of interest. Acknowledgment The Authors thank Christian Drerup for his help in data collection. Financial support was provided by the University of Padova (‘Fondi di Ricerca DOR’ to MBR). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.beproc.2019.103988. References Bateson, M., Healy, S.D., 2005. Comparative evaluation and its implications for mate choice. Trends Ecol. Evol. 20, 659–664. Gasparini, C., Serena, G., Pilastro, A., 2013. Do unattractive friends make you look better? Context-dependent male mating preferences in the guppy. Proc. Royal. Soc. B 280, 20123072. Jennions, M.D., Petrie, M., 1997. Variation in mate choice and mating preferences: a review of causes and consequences. Biol. Rev. Camb. Philos. Soc. 72, 283–327. Lea, A.M., Ryan, M.J., 2015. Irrationality in mate choice revealed by tungara frogs. Science 349, 964. https://doi.org/10.1126/science.aab2012. Locatello, L., Pizzolon, M., Rasotto, M.B., 2012. One trait, many signals: different information on male quality is enclosed within the same trait in a blenny fish. Naturwissenschaften 99, 863–867. Locatello, L., Poli, F., Rasotto, M.B., 2015. Context-dependent evaluation of prospective mates in a fish. Behav. Ecol. Sociobiol. 69, 1119–1126. Locatello, L., Rasotto, M.B., 2017. Females sampling strategy to comparatively evaluate prospective mates in the peacock blenny Salaria pavo. Sci. Nat. 104, 57. Oh, K.P., Badyaev, A.V., 2010. Structure of social networks in a passerine bird: consequences for sexual selection and the evolution of mating strategies. Am. Nat. 176, 80–89. Patzner, R.A., Seiwald, M., Adlgasser, M., Kaurin, G., 1986. The reproduction of Blennius pavo. V: reproductive behavior in natural environment. Zool. Anz. 216, 338–350. Pizzolon, M., 2010. Multiple Male Traits and Female Choice in Salaria pavo. Ph.D. Thesis. University of Padova, Padova, Italy. Pizzolon, M., Locatello, L., Warner, R.R., Chimento, N., Finos, L., Rasotto, M.B., 2012. Linking male qualities to multiple display traits: an example in a fish with exclusive male care. Behav. Ecol. Sociobiol. 66, 497–504. Rosenthal, G.G., 2017. Mate Choice: the Evolution of Sexual Decision Making From Microbes to Humans. Princeton University Press, Princeton, NJ, USA. Royle, N.J., Lindstrom, J., Metcalfe, N.B., 2008. Context-dependent mate choice in relation to social composition in green swordtails Xiphophorus helleri. Behav. Ecol. 19, 998–1005. Ryan, M.J., Cummings, M.E., 2013. Perceptual biases and mate choice. Annu. Rev. Ecol. Evol. Sys. 44, 437 459. Ryan, M.J., Page, R.A., Hunter, K.L., Taylor, R.C., 2018. Crazy love’: nonlinearity and irrationality in mate choice. Anim. Behav. 147, 189–198. Saraiva, J.L., Gonçalves, D.M., Oliveira, R.F., 2009. Environmental modulation of androgen levels and secondary sex characters in two populations of the peacock blenny Salaria pavo. Horm. Behav. 57 (2), 192–197.
Compliance with ethical standards The study was carried out in accordance with current Italian
3