Is corticosterone-mediated phenotype development adaptive? Maternal corticosterone treatment enhances survival in male lizards

Hormones and Behavior 48 (2005) 44 – 52 www.elsevier.com/locate/yhbeh

Is corticosterone-mediated phenotype development adaptive? Maternal corticosterone treatment enhances survival in male lizards Sandrine MeylanT, Jean Clobert Laboratoire d’Ecologie, Universite´ Pierre et Marie Curie, UMR 7625, 7, quai Saint Bernard, Case 237, F-75252 Paris cedex 05, France Received 18 March 2004; revised 31 August 2004; accepted 5 November 2004 Available online 11 March 2005

Abstract Hormones are an important interface between genome and environment, because of their ability to modify the phenotype. More particularly, glucocorticoids are known to affect both morphological, physiological and behavioral traits. Many studies suggest that prenatal stress (associated with an elevation of corticosterone) has deleterious effects on offspring, an altered physiology resulting in retardation of fetal growth and higher percentage of dead neonates. In this study, we investigate the consequences of an artificial increase of corticosterone in pregnant female Lacerta vivipara on two important fitness components: growth and survival. Do stressed females decrease or enhance offspring survival? In 2000 and 2001, we collected pregnant females from four populations of the C2vennes and kept them in the laboratory until parturition. We applied a corticosterone solution daily onto the backs of some females. A similar solution, but without corticosterone, was applied to the remaining females as a control. Immediately after birth, we measured juveniles’ morphological characteristics and released them on the field. In September of the year of release and in May of the following year, we recaptured offspring to estimate growth and survival. The elevation of the corticosterone level in pregnant females L. vivipara had a profound impact on juvenile traits. The size, the body condition and the growth of juveniles were decreased by the corticosterone treatment. In contrast, in male juveniles, survival was higher for juveniles from corticosterone-treated females than from placebo females. Thus, corticosterone does not seem to have detrimental effects on offspring survival, suggesting that it may have an adaptive function. D 2005 Elsevier Inc. All rights reserved. Keywords: Corticosterone; Gestation; Phenotype; Maternal effects; Survival; Growth; Lacerta vivipara; Adaptation

Introduction Activational effects of hormones have been repeatedly described as affecting of animal behavior (Ketterson and King, 1977; Ketterson and Nolan, 1999; Nelson, 1994). Although these effects have been explained in the context of the species life history, there are few demonstrations of their adaptive nature (Ketterson and Nolan, 1999). For example, Sinervo and DeNardo (1996) observed that corticosterone, a glucocorticosteroid hormone, had a positive effect on both total clutch mass and survival in some years and negative effect in other years. To understand these condition-depend-

T Corresponding author. Fax: +33 1 44 27 35 16. E-mail address: [email protected] (S. Meylan).

ent effects of hormones (see Dufty and Belthoff, 2001 for a review), one has to consider the history of the individual (Dufty et al., 2002). For example, the stress reaction of juvenile rats is strongly influenced by the level of corticosterone that its mother experienced during pregnancy (Barbazanges et al., 1996; Pollard, 1986; Takahashi et al., 1988). Moreover, theses variations in steroid hormones, that can produce changes in gene transcription, may also have organizational effects (Astheimer et al., 1992; Dufty et al., 2002; Holmes and Phillips, 1976; Wingfield and Ramenofsky, 1999). These signals modify organizational pathways of developing brain nuclei (Catalani et al., 2000; de Kloet and Reul, 1987; Feldman and Dafny, 1970), affecting physiological and behavioral responses in offspring (Pollard, 1986; Takahashi et al., 1988) in ways that are thought to influence their survival and reproductive success in a

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S. Meylan, J. Clobert / Hormones and Behavior 48 (2005) 44 – 52

given environment (Clark and Galef, 1998; Sinervo and DeNardo, 1996). In other words, hormones play a major role in orchestrating alternative physiological and behavioral reaction patterns (Nijhout, 1994; Rankin, 1978; Siegel, 1980; Silverin, 1998). Hormones might mediate important trade-offs either between physiological functions, for example between the immune and the reproductive system, (Axelrod and Reisine, 1984; Holmes and Phillips, 1976; Munck et al., 1984) or between physiological and behavioral profiles (Ketterson and Nolan, 1999). Corticosterone has also been demonstrated to mediate long-term maternal effects between rodent mothers living under stressful conditions and their independent offspring. Pollard (1986) demonstrated that stress effects were persistent in second generation rats bred from females whose own mothers had been stressed during pregnancy. Moreover, these effects are still persistent in adulthood. Daughters of physically stressed mothers are less fertile and less fecund than daughters of unstressed mothers (Clark and Galef, 1998; Herrenkohl, 1979; Zielinski et al., 1991). Thus, hormones play a major role in shaping the phenotype development and the organization of the maternal effects (Barbazanges et al., 1996). As for the activational effects, organizational effects of hormones have never properly been shown to be adaptive. In the medical and psychological literature, most of the effects of maternal stress on progeny behavior and physiology have been described as pathologies or life impairments (Lou et al., 1994; Wadhwa et al., 1993). However, if these modifications are seen in the context of maternal effect and alternative phenotype development, they might be viewed as adaptations rather than constraints. To verify this scenario, one needs to examine the fitness consequences of prenatal hormonal-induced phenotypes. In the common lizard Lacerta vivipara, sustained elevation of maternal corticosterone blood levels during pregnancy affects many behavioral components of offspring at birth (activity, exploration, reaction towards mother odor, dispersal de Fraipont et al., 2000; Meylan et al., 2002) and later in life (Meylan et al., in prep). In this species, there is an important competition between the mother and her offspring (L2na et al., 1998; Ronce et al., 1998). A chronic elevation of corticosterone (that may be associated of a health problem) during pregnancy suggests poor survival prospects for the mother, and therefore may indicate decreased potential competition between the mother and her offspring. Thus, an increase in offspring philopatry is expected under such a situation and indeed has been found (de Fraipont et al., 2000; Meylan et al., 2002). However, the adaptive nature of this modification in the phenotype, although likely, was not demonstrated. Indeed, the increase in philopatry might be the result of a constraint of corticosterone on metabolism efficiency. If the later scenario is correct, we should observe a detrimental effect of corticosterone administration on offspring fitness.

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In the present paper, we measured fitness components by releasing offspring in the field and following them by capture and recapture to estimate their growth rate and survival. Moreover, because of the condition-dependent effects of corticosterone (Wingfield and Ramenofsky, 1999), we decided to cross the hormonal treatment with a density manipulation. Indeed, density, which could induce a social stress, plays an important role in the life history traits in this species (Massot et al., 1992). Therefore, it is important to verify the validity of our results in different density conditions.

Materials and methods Species The common lizard is a small lacertid that is widely distributed across Europe and Asia. We studied populations on Mont-Loz6re (Massif Central, South-eastern France, 44- 30V N 3- 45V E), where males emerge from hibernation in mid-April followed by yearlings and females in mid-May. Mating takes place as soon as females emerge from hibernation. Embryos are only surrounded by a thin membrane that is 9 Am thick (Heulin et al., 1991). A primitive chorioallantoic placenta allows respiratory and hydric exchanges between mother and embryos during pregnancy (Panigel, 1956). Parturition occurs after 2 months of gestation, when young are fully formed. Females lay a clutch, on average, of 5 soft-shelled eggs. Offspring hatch within 1 h of oviposition. Young (18 mm snout-vent length) are independent of their mother immediately after birth. Individuals enter hibernation in mid – late September in the same sequence; males first, followed by females and young. Exchanges between the mother and the eggs during gestation have been documented in this species (DauphinVillemant and Xavier, 1986). In particular, an important influx of water into uterine eggs occurs at precise stages of embryonic development. This process is thought to be essential for the completion of development and the survival of newborns (Massot et al., 1992). In contrast, no important incorporation of nutrients is seen in L. vivipara. Maternal adrenal activity also increases during gestation and an elevation of plasma corticosterone takes place at the precise embryonic stages during which egg water intake is maximal (Dauphin-Villemant and Xavier, 1986). Thus, corticosterone might be involved in the regulation of water and, consequently, in embryonic development. Capture and rearing conditions We selected four populations located in the same geographical area that displayed comparable population structure and density (Table 1). The most distant sites were separated by 4.5 km, and all sites were at an average

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S. Meylan, J. Clobert / Hormones and Behavior 48 (2005) 44 – 52

Table 1 Estimation of the social repartition and density in the four studied populations Surface (m2)

Pop A 3589

Pop B 6600

Pop C 4916

Pop D 5422

Structure % of adult males % of adult females % of subadults

20.9 27.3 51.8

14.4 20.6 65

14.7 23.8 61.5

18.8 26.6 54.6

Density (ind./hect.) Year 2000 Year 2001

1047 [937 – 1369] 1100 [831 – 1520]

1293 [1056 – 1640] 1230 [1030 – 1730]

1169 [894 – 1573] 1219 [917 – 1469]

1412 [1184 – 1676] 1292 [1038 – 1599]

Densities are estimated by the number of individuals per hectare before the density manipulation (in brackets the 95% confidence intervals).

elevation of 1450 m. Capture and recapture sessions, conducted during early spring 2000, provided data for density estimation. Density estimates were obtained using capture– mark – recapture model with the computer program Mark (White, 1998). To manipulate population density, we removed a quarter of the individuals in two of the four chosen populations in spring 2000 and 2001. In populations C and D, a total of 811 individuals were removed and released in a site with similar characteristics (Table 2, see Meylan and Clobert, 2004 for more details). In a previous density manipulation experiment (Lecomte et al., 1994; Massot et al., 1992), it was shown that many variables (female home range, movement and fecundity) were strongly affected by reducing population density, witnessing an important effect of density on social interactions. We, indeed, found again that density manipulation significantly affected fecundity (v 21 = 27.58 P < 0.0001). Thus, in mid-June 2000 and 2001, we captured 249 and 172 gravid females in these populations and kept them in the laboratory until parturition (usually at the beginning of August). Females were maintained in individual terraria (18  12  12 cm) with opportunities for thermoregulation provided through incandescent illumination for 6 h a day. They were also offered water ad libitum and Pyralis larvae once a day. Immediately after parturition, mothers and juveniles were separated. Siblings were housed in the same terrarium with the same opportunity for thermoregulation and water than females. We marked juveniles by toe clipping, sexed by ventral scale count (Lecomte et al., 1992) and measured snout-vent length (mm) and weighed (mg). Body condition of hatchlings was calculated as the residual from a

Table 2 Removal density manipulation: number of individuals removed in each class in 2000 and 2001 Sites

Female adults removed

Male adults removed

Yearlings removed

C in 2000 C in 2001 D in 2000 D in 2001

48 40 74 40

36 30 26 30

75 150 112 150

regression of body mass against snout-vent length. Within 3 days after birth, juveniles (n = 941 in 2000 and n = 771 in 2001) were released in the field. In order to manipulate the density of the juvenile release site, siblings were divided into two groups. One half was released in a control habitat (A or B) and the other half in a decreased density habitat (C or D). Juveniles were never released in the population of mother’s origin in order to avoid confusion between HABITAT effect and mother presence effect, but also to avoid dispersal motivated by mother’s presence. Mothers were released at their site of capture. Hormonal treatment Stress was mimicked by increasing corticosterone levels in pregnant females. Our study required a method that would elevate plasma corticosterone levels, without surgery, to avoid surgery-associated increases in corticosterone levels. Circulating levels of corticosterone were manipulated using a non-invasive method for sustained elevation of steroid hormone levels in reptiles, similar to that described by Knapp and Moore (1997a,b). Corticosterone was delivered transdermally to the lizards by using a mixture of the steroid hormone and sesame oil. We diluted corticosterone (Sigma C2505) in commercial sesame oil (3 Ag corticosterone/1 Al sesame oil). The high concentration of lipids in lizard skin (Mason, 1992) enables lipophilic molecules, such as steroid hormones, to readily cross the skin (Meylan et al., 2002, 2003). By day 5 of the treatment corticosterone concentrations rose to 281.9 T 46 ng/ml in corticosterone-treated females, where they remained for the duration of the experiment (versus 18.18 T 10 ng/ml in placebo-treated females, F 1,55 = 25.8 P < 0.0001; 21.64 T 4.52 ng/ml as the average of corticosterone values in free ranging females, for more details see Meylan et al., 2003). Similar increases in baseline plasma corticosterone levels (a 12-fold increase) have been found in other reptile species (Knapp and Moore, 1997a,b; Tyrrell and Cree, 1998). Randomly chosen pregnant females (n = 129 in 2000 and n = 85 in 2001) were given 4.5 Al of the hormone solution dorsally, every day until parturition (15 days on average), whereas control females (n = 120 in 2000 and n = 87 in

S. Meylan, J. Clobert / Hormones and Behavior 48 (2005) 44 – 52 Table 3 Size and weight of females in the two hormonal treatments at the beginning of the experiment

47

2001) received the same amount of sesame oil. Females in the two treatments presented similarities in term of size and weight at the start of the study (Table 3).

et al., 1992). We tested the effects of TREATMENT, DENSITY OF ORIGIN, RELEASE SITE DENSITY, HABITAT and YEAR (and their interactions) independently on survival (U) and capture probability ( p) before hibernation. No goodness of fit test (Lebreton et al., 1992) was possible since only two sessions of recapture were available. At each recapture, the weight and the snout-vent length of juveniles were recorded. The juvenile growth rate before hibernation (n = 145 in 2000, n = 181 in 2001) was measured as the mean body length gain per days (SVL1 SVL0) / (t1 t0), where t0 = date of birth, t1 = date of the first recapture, SVL0 = snout-vent length at birth and SVL1 = snout-vent length at the recapture.

Survival and growth before hibernation

Data analyses

To estimate probability of survival between release and hibernation independently from capture probability, we needed 2 recapture sessions. After being released in the field, offspring belonging to the 2000 and 2001 cohorts were recaptured in September of the year of release (first session of recapture) and in May of the following year (second recapture). This was necessary because, in order to estimate survival probabilities independently from the capture probability (an individual not recaptured in September can either have died before or be alive but not captured), we needed a second recapture session (in May) to estimate the proportion missed in September (Clobert, 1995). Each recapture session lasted at least 10 days. Each day, two sites (order selected at random) were visited. As each site was divided in 5 m  5 m squares with small numbered marks, we picked one location (one mark) at random at each visit and, from this location, we started capturing individuals along a path defined in such a way that we visited all the site without revisiting one given location. This ensured to have the same capture effort for all the parts of each site. Moreover, we looked for juveniles out of the sites to search for long distance dispersal (none were found). The juveniles’ apparent survival rate was estimated using the Cormack – Jolly –Seber model (Cormack, 1964; Jolly, 1965; Seber, 1965) extended to groups effects (Lebreton et al., 1992; Pradel et al., 1990). In particular, these methods measure differences in capture probabilities according to habitat, treatment and year. The computer program MARK (White, 1998) was used to fit models. Models were compared by Akaike Information Criterion (AIC calculated as 2  model log likelihood + 2  number of parameters) and we retained the most parsimonious of them. The best model is the most consistent with the data, while using the fewest numbers of parameters (lowest AIC, Anderson and Burnham, 1999; Anderson et al., 1994). As likelihood ratiotest are selecting models with a too high number of parameter, AIC corrects for this bias by weighting a model by its degree of freedom (its number of parameter, Lebreton

CORTICOSTERONE, DENSITY OF ORIGIN, RELEASE SITE DENSITY and YEAR were class factors. We tested these effects and their interactions on females’ and juveniles’ traits. After verifying the normality (Shapiro –Wilk test, proc univariate, SAS, 1992) of the continuous dependent variables (size, body condition. . .) and the homosedasticity (Barlett test), we used the procedure GLM (ANOVA) of SAS Institute (SAS, 1992). Because siblings cannot be assumed to be independent statistical units (Massot et al., 1994), we computed a mean per family and per year, which was then used as the statistical unit. For categorical dependent variables, we used the procedure GENMOD (Anova) of SAS Institute. We used a new extension (DSCALE option) of the GENMOD procedure (SAS 1996) developed for the application of generalized linear models (McCullagh and Nelder, 1989). The DSCALE option allows the calculation of an overdispersion factor of data, c (caused, for example, by nonindependence between individuals), and corrects the model selection by this factor (deviance of the model divided by its degrees of freedom, see McCullagh and Nelder, 1989 for more details). This procedure efficiently corrects for overdispersion due to non-independence between individuals (Massot and Clobert, 2000; Massot et al., 1994). We then performed a covariance analysis with the different factors (and their interactions) and we simplified the models by a backward selection (McCullagh and Nelder, 1989). We present the probabilities associated with each factor and their interactions together with the final model in the Results section. Survival was estimated using the software MARK as explained in Survival and growth before hibernation section.

Female size (mm) Year 2000 Year 2001 Female weight (g) Year 2000 Year 2001

Placebo group

Corticosterone group

58.3 T 0.5 (n = 120) 57.3 T 0.4 (n = 87)

58.7 T 0.4 (n = 129) 57.3 T 0.5 (n = 85)

4.39 T 0.07 (n = 120) 4.13 T 0.09 (n = 87)

4.38 T 0.08 (n = 129) 4.06 T 0.09 (n = 85)

Results No interactions among corticosterone treatment, density of origin, density of release site and habitat (replicates) were

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S. Meylan, J. Clobert / Hormones and Behavior 48 (2005) 44 – 52

significant (all P > 0.05). Here, we only present the results concerning the effects of corticosterone. The density effects will be presented elsewhere (Meylan et al., submitted). Clutch size and hatchling morphological traits The 421 captive females gave birth to 395 clutches for which we measured juvenile body length and body condition. Fecundity was affected neither by the hormonal treatment nor by the year. Only female size correlates significantly with fecundity ( F 1,394 = 23.68 P < 0.0001). Hatchling body length was dependant on both hormonal treatment ( F 1,393 = 73.0, P < 0.0001) and maternal size ( F 1,393 = 9.34, P = 0.0024). Corticosterone-treated females gave birth to smaller juveniles than placebo-treated females (Table 4). Hatchling body condition was negatively affected by the corticosterone treatment of their mothers ( F 1,393 = 27.56, P < 0.0001, Fig. 1). Body condition was also higher in 2001 than in 2000 ( F 1,393 = 15.43, P < 0.0001), but the year effect did not interact with the corticosterone treatment ( F 1,393 = 0.92, P > 0.1). Growth prior to hibernation Juvenile growth rate was higher for juveniles born from placebo-treated females than those of corticosterone-treated females ( F 1,135 = 7.03, P = 0.0087, Fig. 1). The growth was independent of both juvenile’s size at birth and sex, with no difference between years. Survival rate before hibernation We conducted separate analyses for the two sexes. The male juvenile survival probability was determined by both years and hormonal treatment (AIC of the model U treatment + year P constant = 927.45 Table 5). In 2000, the offspring survival rate was lower than in 2001. However, the male juveniles born from corticosterone-treated females had higher survival rate than those of placebo females (Fig. 2). Including individual size at birth had no effect on the model. For juvenile females, the most parsimonious model does not include year or treatment (AIC of the model U treatment + P constant = 1097.11 versus AIC of the model U density of the release site + year P constant = 1090.06, see Table 5 and

Table 4 Snout-vent length (mm) at birth per hormonal and density treatments Hormonal treatment

Placebo Corticosterone

Density manipulation Reduced density

Control density

20.9 T 0.1 (n = 100) 20.0 T 0.1 (n = 108)

20.9 T 0.1 (n = 99) 20.0 T 0.1 (n = 88)

Fig. 1. Juvenile body condition (n = 179 for placebo and n = 160 for corticosterone) and growth rate (n = 75 for placebo and n = 63 for corticosterone). Data are expressed as mean T SEM.

Fig. 2) but does include other habitat characteristics such as the density (Meylan et al., submitted). Moreover, there was no difference in capture probability according to the hormonal treatment, the year and the density for both males and females (P constant = 0.62 for males and 0.58 for females). Thus, the treatment did not affect the detectability of individuals.

Discussion Elevation of the corticosterone level in pregnant female L. vivipara had a large impact on juvenile traits. Juvenile size, body condition and growth were decreased by the corticosterone treatment. In contrast, male juvenile survival was higher for juveniles born from corticosterone-treated females than for those issued from placebo females. Moreover, the effect of the corticosterone was not dependent on the social (density of origin and of release) or the non social environment (habitat).

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Table 5 Survival analysis and model selection in male and in female juveniles Males U

Year

Treatment

Year + treatment

Density of origin

P Year Treatment Constant

932.26 931.27 930.16

933.71 940.93 938.10

931.58 931.72 927.45

938.19 944.42 936.72

Constant 936.14 942.30 941.96

Females U

Year

Treatment

Release

Release + year

Density of origin

Constant

P Year Release Constant

1097.78 1094.17 1092.31

1099.11 1099.05 1097.11

1094.65 1093.37 1092.70

1090.82 1091.07 1090.06

1098.95 1098.89 1098.89

1097.14 1097.07 1095.14

Akaike Information Criterion (AIC) are reported for different models. We show how we reduced the models by selecting effects on survival (U) and capture probability (P). Constant: no effect. Lowest AIC (best model) are reported in bold.

Corticosterone and development In humans, prenatal stress is correlated with premature birth, decreases in weight and size of offspring (Lou et al., 1994; Wadhwa et al., 1993), with similar deleterious effects in other animals (Takahashi et al., 1988). In rodents, numerous studies have shown that the weight and size of offspring are markedly altered by the physiological changes induced by maternal stress, for example by decreasing fetal growth and increasing mortality at birth in both sexes (Kinsley and Svare, 1988; Meek et al., 2000, 2001; Pollard, 1984). As in those studies, we also found a negative effect of maternal corticosterone manipulation on offspring body size, body condition and growth. Results are ambivalent in the literature about the link between size, corpulence and fitness in reptiles (Ferguson and Fox, 1984; Forsman, 1993; Jayne and Bennett, 1990; Sinervo et al., 1992; Sorci and Clobert, 1999). Evidence is accumulating that being bigger, being fatter or growing faster is not necessarily adaptive in all environments. For example, Brooks et al. (1991) demonstrated that variation in size at hatching, which arose from differences in moisture conditions during gestation, had no effect on growth or survival of offspring. In our species, juvenile size at birth is smaller in humid than in dry habitats. With a reciprocal transplant experiment, we experimentally demonstrated that small juvenile size at birth in humid habitats is associated with better survival, while it is the opposite in dry habitats (Lorenzon et al., 2001). It therefore appears that offspring size and quality are somehow decoupled (Brooks et al., 1991; Sinervo et al., 1992; Sorci and Clobert, 1999). Indeed, we have found that not only size is modified by a maternal corticosterone manipulation, but also the corpulence and growth (this study), behavior (de Fraipont et al., 2000; Meylan et al., 2002), locomotor performance (Meylan and Clobert, 2004) and thermoregulation (Belliure et al., 2004), with some of these differences persisting throughout life. Thus, the overall offspring phenotype is modified by

increasing the corticosterone level of the mother. If such changes are the result of adaptive phenotypic plasticity, then one may expect that it will pre-adapt offspring to live in their future environment. Adaptive value of corticosterone-produced phenotypes Juvenile males born from corticosterone-treated females had significantly higher survival than juvenile males from placebo females, while juvenile female survival was not dependent on treatment. Thus, the modifications of the juvenile phenotype induced by increased maternal corticosterone during pregnancy do not seem to reflect a constraint, that is, they do not impair offspring fitness. Although we did not measure all the fitness components (age at maturity, fecundity), we know that juvenile survival is the component having the highest impact on fitness in this species (Lorenzon et al., 2001). Therefore, it is most likely that the treatment did not produce low quality offspring. It appears even to be the contrary for juvenile males, whose survival was higher for corticosterone versus placebotreated mother. This latter result was unexpected, although several explanations can be provided to understand it. First, elevated maternal corticosterone promotes offspring philopatry, especially when the mother is aged or in poor condition (de Fraipont et al., 2000; Meylan et al., 2002). The age of the female can reflect its future survival prospects, independently of the quality of the environment, and therefore might indicate a low probability of mother – offspring competition (therefore increasing offspring philopatry). In the common lizard (L. vivipara), support for this hypothesis has been found. Ronce et al. (1998) studied the effect of mother’s age on juvenile dispersal in L. vivipara and found a decrease in dispersal propensity when mothers reached 4 years of age (senescence), as predicted by kin competition theory (Hamilton and May, 1977; Ronce et al., 1998). However, the presence of the mother just after birth seems to be necessary for the juvenile dispersal decision. In

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S. Meylan, J. Clobert / Hormones and Behavior 48 (2005) 44 – 52

and DeNardo, 1996). Stronger selection in-utero will then be reflected by the production of better quality offspring with higher survival prospects. Finally, a third possibility is that the number of juveniles with a long-distant dispersal propensity was reduced in corticosterone-treated females compared to placebo ones. We focus on long-distant dispersers because we did not find any modification in the dispersal patterns within our study sites. As our populations are not close to each other, long-distant dispersers will escape capture, and therefore survival rate estimates will be negatively biased in the direction of the treatment if a large number of long-distant dispersers is produced. Whatever the explanation for this result, the likelihood that corticosterone acts as a constraint on offspring development is weak, and our results add more support to the production of adaptive phenotypes. Finally, the absence of a corticosterone effect on females’ survival could be due to sex-dependant mechanisms, like differences in hormonal levels between males and females, in particular differences in testosterone levels. It has been shown that female testosterone levels were generally lower than male testosterone levels (Nelson, 1994). Thus, corticosterone could have positive effects only on male survival by inhibiting testosterone (Knapp and Moore, 1997a,b) which has negative effects on physiological parameters like immune system (Hasselquist et al., 1999) and/or promotes aggressive interactions (e.g. territoriality, DeNardo and Sinervo, 1994). The condition-dependent nature of corticosterone effects is indeed well known (Wingfield and Ramenofsky, 1999).

Acknowledgments Fig. 2. Survival probabilities of juvenile males and females depending on the years and on the maternal hormonal treatment. Data are expressed as mean T SEM. The survival estimations have been base on 75 juveniles recaptured for placebo and 63 for corticosterone on respectively 179 and 160 release juveniles.

our design, the offspring were not released in the same site as their mother, so they did not experience any competition with her or any sign of her presence. This might have changed the conditions (pressure of the kin competition) under which the philopatric phenotype normally develops after birth, leading, by an unknown mechanism (such as, for example, by manipulating the trade-off between growth and survival), to better survival for males issued from corticosterone-treated females. A second possibility is that embryos within corticosterone-treated females undergo a higher intrautero selection as found several times in previous experiments (de Fraipont et al., 2000; Meylan et al., 2002). Although we did not find a corticosterone-induced decrease in the number of live births in this experiment, this might have affected one sex more than the other, or clutches with specific sex-ratios, as was found in another lizard (Sinervo

We thank Tobias Uller for discussion. We are grateful to the FParc National des C2vennes_ and the FOffice National des For4ts_ for providing facilities during our field seasons. We acknowledge a PhD grant from the French Ministry of Research and Education and the CNRS (grant Fenvironnement, vie et soci2t2_ 98, N62/0120). Thanks to graduate students for their help on the field.

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