Testosterone has opposite effects on male growth in lizards(Sceloporus spp.) with opposite patterns of sexual size dimorphism

Effects of Testosterone on Gene Expression Are Concordant between Sexes but Divergent across Species of Sceloporus Lizards

AbstractHormones mediate sexual dimorphism by regulating sex-specific patterns of gene expression, but it is unclear how much of this regulation involves sex-specific hormone levels versus sex-specific transcriptomic responses to the same hormonal signal. Moreover, transcriptomic responses to hormones can evolve, but the extent to which hormonal pleiotropy in gene regulation is conserved across closely related species is not well understood. We addressed these issues by elevating testosterone levels in juvenile females and males of three Sceloporus lizard species before sexual divergence in circulating testosterone and then characterizing transcriptomic responses in the liver. In each species, more genes were responsive to testosterone in males than in females, suggesting that early developmental processes prime sex-specific transcriptomic responses to testosterone later in life. However, overall transcriptomic responses to testosterone were concordant between sexes, with no genes exhibiting sex-by-treatment interactions. By contrast, hundreds of genes exhibited species-by-treatment interactions, particularly when comparing distantly related species with different patterns of sexual dimorphism, suggesting evolutionary lability in gene regulation by testosterone. Collectively, our results indicate that early organizational effects may lead to sex-specific differences in the magnitude, but not the direction, of transcriptomic responses to testosterone and that the hormone-genome interface accrues regulatory changes over evolutionary time.

Variable juvenile growth rates and offspring size: a response to anthropogenic shifts in prey size among populations

Environmental variables, such as resource quality, shape growth in organisms, dictating body size, an important correlate of fitness. Variation in prey characteristics among populations is frequently associated with similar variation in predator body sizes. Anthropogenic alterations to prey landscapes impose novel ecological pressures on predators that may shift predator phenotypes. Research has focused on determining the adaptability of the phenotypic response by testing its genetic heritability. Here, we asked if anthropogenic shifts in prey size across the landscape correlate with juvenile growth rates among populations of watersnakes with divergent life-history phenotypes. We sought to determine if growth rate variation is the product of genetic adaptation or a non-heritable phenotypic response. Using a common-garden design, we measured growth of neonate snakes from fish farms varying in prey size. We found juvenile growth rates are faster for snakes with larger initial body sizes and from populations with larger average prey sizes. Our data suggest variability in juvenile grow rates within and among populations are not the product of genetic adaptation, but the indirect consequence of initial offspring size variation and prey consumption. We propose larger offspring sizes may favor increased juvenile growth rates, mediated through a larger morphological capacity to consume and process energy resources relative to smaller individuals. This experiment provides evidence supporting the growing body of literature that non-heritable responses may be significant drivers of rapid phenotypic divergence among populations across a landscape. This mechanism may explain the stability and colonization of populations in response to rapid, human-mediated, landscape changes.

Effects of testosterone on urogenital tract morphology and androgen receptor expression in immature Eastern Fence lizards (Sceloporus undulatus)

In non-avian reptiles, the onset of sexual dimorphism of the major structures of the urogenital tract varies temporally relative to gonadal differentiation, more so than in other amniote lineages. In the current study, we used tonic-release implants to investigate the effects of exogenous testosterone (T) on postnatal development of the urogenital tract in juvenile Eastern Fence Lizards (Sceloporus undulatus) to better understand the mechanisms underlying the ontogeny of sexual differentiation in reptiles. We examined gonads, mesonephric kidneys and ducts (male reproductive tract primordia), paramesonephric ducts (oviduct primordia), sexual segments of the kidneys (SSKs), and hemiphalluses to determine which structures were sexually dimorphic independent of T treatment and which structures exhibited sexually dimorphic responses to T. To better understand tissue-level responsiveness to T treatment, we also characterized androgen receptor (AR) expression by immunohistochemistry. At approximately 4 months after hatching in control animals, gonads were well differentiated but quiescent; paramesonephric ducts had fully degenerated in males; mesonephric kidneys, mesonephric ducts, and SSKs remained sexually undifferentiated; and hemiphalluses could not be everted in either sex. Exogenous T caused enlargement, regionalization, and secretory activity of the mesonephric ducts and SSKs in both sexes; enlargement and regionalization of the oviducts in females; and enlargement of male hemipenes. The most responsive tissues exhibited moderate but diffuse staining for AR in control lizards and intense nuclear staining in T-treated lizards, suggestive of autoregulation of AR. The similarity between sexes in the responsiveness of the mesonephric ducts and SSK to T indicates an absence of sexually dimorphic organizational effects in these structures prior to treatment, which was initiated approximately 2 months after hatching. In contrast, the sex-specific responses in oviducts and hemipenes indicate that significant organization and/or differentiation had taken place prior to treatment.

Species differences in hormonally mediated gene expression underlie the evolutionary loss of sexually dimorphic coloration in Sceloporus lizards

Phenotypic sexual dimorphism often involves the hormonal regulation of sex-biased expression for underlying genes. However, it is generally unknown whether the evolution of hormonally mediated sexual dimorphism occurs through upstream changes in tissue sensitivity to hormone signals, downstream changes in responsiveness of target genes, or both. Here, we use comparative transcriptomics to explore these possibilities in 2 species of Sceloporus lizards exhibiting different patterns of sexual dichromatism. Sexually dimorphic S. undulatus develops blue and black ventral coloration in response to testosterone, while sexually monomorphic S. virgatus does not, despite exhibiting similar sex differences in circulating testosterone levels. We administered testosterone implants to juveniles of each species and used RNAseq to quantify gene expression in ventral skin. Transcriptome-wide responses to testosterone were stronger in S. undulatus than in S. virgatus, suggesting species differences in tissue sensitivity to this hormone signal. Species differences in the expression of genes for androgen metabolism and sex hormone-binding globulin were consistent with this idea, but expression of the androgen receptor gene was higher in S. virgatus, complicating this interpretation. Downstream of androgen signaling, we found clear species differences in hormonal responsiveness of genes related to melanin synthesis, which were upregulated by testosterone in S. undulatus, but not in S. virgatus. Collectively, our results indicate that hormonal regulation of melanin synthesis pathways contributes to the development of sexual dimorphism in S. undulatus, and that changes in the hormonal responsiveness of these genes in S. virgatus contribute to the evolutionary loss of ventral coloration.

Effects of long-term sex steroid hormones (estradiol and testosterone)-supplemented feeds on the growth performance of Chinese tongue sole (Cynoglossus semilaevis)

The phenomenon of sexual size dimorphism (SSD), existing in mammals, birds, reptiles, spiders, amphibians, insects, and fishes, is generally related to feeding efficiency, energy allocation, sex steroids, and somatotropic and reproductive endocrine axes. Recently, positive and negative regulations of sex steroids have been reported on SSD in various species. Chinese tongue soles (Cynoglossus semilaevis) at 4 months were fed with 17β-estradiol (E2) and testosterone (T) supplemented feeds for 8 months to assess the effect of sex steroids on growth traits in different sexes. The potential genetic regulation was examined using several growth-related genes. The results showed that two sex steroid hormones had inhibitory effects on the growth performance of different sexes of C. semilaevis. At the age of 8 months, the expression of insulin-like growth factor 2 gene (igf2), 24-dehydrocholesterol reductase (dhcr24), leptin, and estrogen receptor 2 (esr2) in the liver showed an overall downward trend. The expression of insulin-like growth factor 1 (igf1) was reduced, while thyroid hormone receptor-associated protein 3 (thrap3) expression tended to increase in the gonad after T and E2 treatments. In the brain, somatostatin 1, tandem duplicate 2 (sst1.2) expression increased with the treatment of T and E2 (P < 0.05), while growth hormone-releasing hormone (ghrh) expression decreased. E2 and T had different effects on growth differentiation factor 8 (gdf8) and insulin-like growth factor-binding protein 7 (igfbp7) expression in the muscle. Expression of gdf8 increased in the treated fishes in contrast to the reduction expression of igfbp7. This study provided important clues for understanding the role of sex steroids in flatfish SSD.

Species-Specific Expression of Growth-Regulatory Genes in 2 Anoles with Divergent Patterns of Sexual Size Dimorphism

Sexual size dimorphism is widespread in nature and often develops through sexual divergence in growth trajectories. In vertebrates, the growth hormone/insulin-like growth factor (GH/IGF) network is an important regulator of growth, and components of this network are often regulated in sex-specific fashion during the development of sexual size dimorphism. However, expression of the GH/IGF network is not well characterized outside of mammalian model systems, and the extent to which species differences in sexual size dimorphism are related to differences in GH/IGF network expression is unclear. To begin bridging this gap, we compared GH/IGF network expression in liver and muscle from 2 lizard congeners, one with extreme male-biased sexual size dimorphism (brown anole, Anolis sagrei), and one that is sexually monomorphic in size (slender anole, A. apletophallus). Specifically, we tested whether GH/IGF network expression in adult slender anoles resembles the highly sex-biased expression observed in adult brown anoles or the relatively unbiased expression observed in juvenile brown anoles. We found that adults of the 2 species differed significantly in the strength of sex-biased expression for several key upstream genes in the GH/IGF network, including insulin-like growth factors 1 and 2. However, species differences in sex-biased expression were minor when comparing adult slender anoles to juvenile brown anoles. Moreover, the multivariate expression of the entire GH/IGF network (as represented by the first two principal components describing network expression) was sex-biased for the liver and muscle of adult brown anoles, but not for either tissue in juvenile brown anoles or adult slender anoles. Our work suggests that species differences in sex-biased expression of genes in the GH/IGF network (particularly in the liver) may contribute to the evolution of species differences in sexual size dimorphism.

Evolution of hormone-phenotype couplings and hormone-genome interactions

When selection favors a new relationship between a cue and a hormonally mediated response, adaptation can proceed by altering the hormonal signal that is produced or by altering the phenotypic response to the hormonal signal. The field of evolutionary endocrinology has made considerable progress toward understanding the evolution of hormonal signals, but we know much less about the evolution of hormone-phenotype couplings, particularly at the hormone-genome interface. We briefly review and classify the mechanisms through which these hormone-phenotype couplings likely evolve, using androgens and their receptors and genomic response elements to illustrate our view. We then present two empirical studies of hormone-phenotype couplings, one rooted in evolutionary quantitative genetics and another in comparative transcriptomics, each focused on the regulation of sexually dimorphic phenotypes by testosterone (T) in the brown anole lizard (Anolis sagrei). First, we illustrate the potential for hormone-phenotype couplings to evolve by showing that coloration of the dewlap (an ornament used in behavioral displays) exhibits significant heritability in its responsiveness to T, implying that anoles harbor genetic variance in the architecture of hormonal pleiotropy. Second, we combine T manipulations with analyses of the liver transcriptome to ask whether and how statistical methods for characterizing modules of co-expressed genes and in silico techniques for identifying androgen response elements (AREs) can improve our understanding of hormone-genome interactions. We conclude by emphasizing important avenues for future work at the hormone-genome interface, particularly those conducted in a comparative evolutionary framework.

Sex-specific growth arrest in a lizard

(1) In contrast to mammals and birds, reptiles have been considered as indeterminate growers, whose growth reflects differential allocation of resources to growth versus other energetically demanding processes such as reproduction. (2) We monitored the growth and activity of bone growth plates, hormonal profiles, and reproductive activity in males and females of the male-larger gecko Paroedura picta. We show that growth plates fuse in this species in a sex-specific manner. The more abrupt epiphyseal closure and more pronounced growth deceleration in females coincide with the increased activity of their reproductive organs. (3) We conclude that at least some lizards are determinate growers whose sexual size dimorphism is potentially driven by ovarian hormones. The major difference in growth between endothermic and ectothermic amniotes appears to be in the magnitude of growth before and after the first reproduction, not in the mechanistic processes such as senescence of growth plate cells

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We monitored activity of bone growth plates in a male-larger gecko

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Growth plates fused in a sex-specific manner

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At least some lizards are determinate growers

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Their sexual size dimorphism seems to be driven by ovarian hormones

A chromosome-level genome assembly for the eastern fence lizard (Sceloporus undulatus), a reptile model for physiological and evolutionary ecology

BACKGROUND

High-quality genomic resources facilitate investigations into behavioral ecology, morphological and physiological adaptations, and the evolution of genomic architecture. Lizards in the genus Sceloporus have a long history as important ecological, evolutionary, and physiological models, making them a valuable target for the development of genomic resources.

FINDINGS

We present a high-quality chromosome-level reference genome assembly, SceUnd1.0 (using 10X Genomics Chromium, HiC, and Pacific Biosciences data), and tissue/developmental stage transcriptomes for the eastern fence lizard, Sceloporus undulatus. We performed synteny analysis with other snake and lizard assemblies to identify broad patterns of chromosome evolution including the fusion of micro- and macrochromosomes. We also used this new assembly to provide improved reference-based genome assemblies for 34 additional Sceloporus species. Finally, we used RNAseq and whole-genome resequencing data to compare 3 assemblies, each representing an increased level of cost and effort: Supernova Assembly with data from 10X Genomics Chromium, HiRise Assembly that added data from HiC, and PBJelly Assembly that added data from Pacific Biosciences sequencing. We found that the Supernova Assembly contained the full genome and was a suitable reference for RNAseq and single-nucleotide polymorphism calling, but the chromosome-level scaffolds provided by the addition of HiC data allowed synteny and whole-genome association mapping analyses. The subsequent addition of PacBio data doubled the contig N50 but provided negligible gains in scaffold length.

CONCLUSIONS

These new genomic resources provide valuable tools for advanced molecular analysis of an organism that has become a model in physiology and evolutionary ecology.

Testosterone Reduces Growth and Hepatic IGF-1 mRNA in a Female-Larger Lizard, Sceloporus undulatus: Evidence of an Evolutionary Reversal in Growth Regulation

Previous research has demonstrated that testosterone (T) can inhibit growth in female-larger species and stimulate growth in male-larger species, but the underlying mechanisms of this regulatory bipotentiality have not been investigated. In this study, we investigated the effects of T on the expression of hepatic insulin-like growth factor-1 (IGF-1) mRNA and circulating IGF-1 hormone in Sceloporus undulatus, a species of lizard in which females grow faster to become larger than males and in which T inhibits growth. Experiments were performed in captivity on mature female and male adults in the asymptotic phase of their growth curve and on actively growing, pre-reproductive juveniles. In adult males, the expression of hepatic IGF-1 mRNA increased following surgical castration and returned to control levels with T replacement; in intact adult females, exogenous T had no effect on IGF-1 mRNA expression. In juveniles, T significantly reduced both growth and the expression of hepatic IGF-1 mRNA to similar extents in intact females and in castrated males. The relative inhibitory effects of T on mRNA expression were greater in juveniles than in adults. Plasma IGF-1 hormone was about four times higher in juveniles than in adults, but T had no significant effect on IGF-1 hormone in either sex or in either age group. Our finding of inhibition of the expression of hepatic IGF-1 mRNA stands in contrast to the stimulatory effects of T in the published body of literature. We attribute our novel finding to our use of a species in which T inhibits rather than stimulates growth. Our findings begin to explain how T has the regulatory bipotentiality to be stimulatory in some species and inhibitory in others, requiring only an evolutionary reversal in the molecular regulation of growth-regulatory genes including IGF-1. Further comparative transcriptomic studies will be required to fully resolve the molecular mechanism of growth inhibition.

Steroid hormones, ectoparasites, and color: Sex, species, and seasonal differences in Sceloporus lizards

Testosterone, in addition to promoting the expression of sexual ornaments can negatively affect immune function, leaving individuals more susceptible to parasites (immunocompetence handicap hypothesis). Immunosuppressive effects of testosterone also can occur indirectly, through increased glucocorticoid hormones (corticosterone, cortisol). Therefore, the expression of sexual ornaments and the ability to respond to parasites and diseases may be influenced by the interaction between testosterone and corticosterone. In this study we examined correlations of both testosterone and corticosterone with ectoparasite load and with expression of colorful sexual ornaments (patches on belly and throat) in three species of Sceloporus lizards (S. grammicus, S. megalepidurus, S. torquatus). In addition, we evaluated contributions of sex, body condition, and reproductive season. We expected that individuals with higher testosterone and lower corticosterone levels would have more colorful ornaments than individuals with higher corticosterone levels. In addition, if testosterone has negative effects on immune function but only at higher corticosterone levels, individuals with higher levels of testosterone and corticosterone should have higher ectoparasite loads. Contrary to these expectations, we did not detect an interaction between testosterone and corticosterone statistically affecting either ectoparasite load or the expression of colorful ornaments. Further, we did not find a positive association of either testosterone or corticosterone on ectoparasite loads in any of the three study species. Only in S. grammicus males was a hormone statistically associated with ectoparasite load, but it was a negative association with testosterone. The relationships between both hormones and different aspects of the colorful patches (brightness and chroma) varied drastically among the three species as well as between sexes. Hence, even among congeneric species, we did not observe consistent patterns among color, steroid hormones and ectoparasites. Different associations between these variables may reflect different physiological strategies for the production of colorful signals and immune defense.

Sex-biased parasitism and expression of a sexual signal

Given that sexual signals are often expressed more highly in one sex than the other, they can impose a sex-specific cost of reproduction through parasitism. The two primary paradigms regarding the relationship of parasites to sexual signals are the good genes hypothesis and the immunocompetence handicap hypothesis; however, there are other ecological, morphological and energetic factors that might influence parasite infections in a sex-specific fashion. We tested the relationship between expression of a sexual signal (the dewlap) and ecological, morphological and energetic factors mediating ectoparasite (mite) load between male and female Panamanian slender anoles (Anolis apletophallus). We found that males were more highly parasitized than females because of the preponderance of ectoparasites on the larger dewlap of males. Indeed, ectoparasite infection increased with both body size and dewlap size in males but not in females, and parasite infection was related to energy storage in a sex-specific fashion for the fat bodies, liver and gonads. Our work and previous work on testosterone in anoles suggests that this pattern did not arise solely from immunosuppression by testosterone, but that mites prefer the dewlap as an attachment site. Thus, the expression of this sexual signal could incur a fitness cost that might structure life-history trade-offs.

Sex steroids as mediators of phenotypic integration, genetic correlations, and evolutionary transitions

In recent decades, endocrinologists have increasingly adopted evolutionary methods and perspectives to characterize the evolution of the vertebrate endocrine system and leverage it as a model for developing and testing evolutionary theories. This review summarizes recent research on sex steroids (androgens and estrogens) to illustrate three ways in which a detailed understanding of the molecular and cellular architecture of hormonally mediated gene expression can enhance our understanding of general evolutionary principles. By virtue of their massively pleiotropic effects on the expression of genes and phenotypes, sex steroids and their receptors can (1) structure the patterns of phenotypic variance and covariance that are available to natural selection, (2) alter the underlying genetic correlations that determine a population's evolutionary response to selection, and (3) facilitate evolutionary transitions in fitness-related phenotypes via subtle regulatory shifts in underlying tissues and genes. These principles are illustrated by the author's research on testosterone and sexual dimorphism in lizards, and by recent examples drawn from other vertebrate systems. Mechanistically, these examples call attention to the importance of evolutionary changes in (1) androgen- and estrogen-mediated gene expression, (2) androgen and estrogen receptor expression, and (3) the distribution of androgen and estrogen response elements in target genes throughout the genome. A central theme to emerge from this review is that the rapidly increasing availability of genomic and transcriptomic data from non-model organisms places evolutionary endocrinologist in an excellent position to address the hormonal regulation of the key evolutionary interface between genes and phenotypes.

Little if any role of male gonadal androgens in ontogeny of sexual dimorphism in body size and cranial casque in chameleons

Proximate control of the development of sexual dimorphism is still hotly debated in reptiles. In some squamates, many male-typical exaggerated traits including body size were assumed to be controlled by masculinization by male gonadal androgens. We performed a manipulative experiment to test the importance of this mechanism in the development of pronounced sexual differences in body size and size of head casque in the chameleon Chamaeleo calyptratus. Castrated males attained male-typical body size highly deviating from the body size of control females. Ontogenetic allometries of casque size on head length revealed that sexes depart considerably in casque growth later in the ontogeny; however, castrated males still follow male-typical casque growth. Paradoxically, exogenous testosterone led in females to slight increase of casque size, which might reflect interference with the feminizing effects of female gonadal hormones. The results in males strongly suggest that masculinization by male gonadal androgens during growth is not required for the development of sexual dimorphism in body size and casque size in the chameleon. The ontogeny of sexually dimorphic body size and exaggerated traits in at least some squamates is likely controlled by other proximate mechanism, possibly by feminization by ovarian hormones.

Sexual dimorphism in Belostoma angustum Lauck (Insecta: Heteroptera: Belostomatidae) may be related to paternal care

The structures involved in parental care are often dimorphic. Female Belostoma angustum water bugs lay eggs on the hemelytra of their mates, where the eggs are brooded until hatching. Males use their hind legs to carry, aerate and protect the eggs. After controlling for covariance between variables, we fitted a series of structural equation models (SEMs) and evaluated the existence of sexual dimorphism in the size of the body and hind legs, in the shape and centroid size of the hemelytrum, and among the static allometry slopes of the size-related differences. Landmarks were used to capture phenotypic variation, by eliminating all non-shape variations with a Procrustes superimposition. Neither the shape of the hemelytrum nor its centroid size was related significantly to the aforementioned linear body measurements. Instead, the differences in the size of the hind legs were mediated by body dimensions only in males. We also found that males were wider and had longer heads than females, according to the SEM intercept values. Our findings suggest that sexual dimorphism in B. angustum may be related to a balance between sexual role reversal and viability costs.

The association of latent toxoplasmosis and level of serum testosterone in humans

Objectives

Latent toxoplasmosis modifies various hormones and behaviors in infected hosts and possibly involves in etiology of different neurologic and psychiatric disorders. The aim of the current study was to assess possible associations between latent toxoplasmosis and testosterone concentration in Toxoplasma infected and free subjects. Briefly, 18–49 year-old participated in the study. After collected blood samples, sera were analyzed for the detection of anti-Toxoplasma IgG antibody. Totally, 76 positive sera were selected as study group (38 from men and 38 from women) and a same number of negative sera as control group.

Results

Comparison of testosterone concentrations and control groups showed that testosterone concentration in study group was higher than that in control group with statistically significant difference (P = 0.024 and P = 0.043 for men and women, respectively). Significant differences were found in testosterone concentrations and anti-Toxoplasma IgG antibody levels in study and control groups (P < 0.05). Toxoplasmosis can affect the mean concentration of serum testosterone in human. Alteration of testosterone during latent toxoplasmosis can result in alterations in behavioral, physiologic and immunological parameters in long time.

A comparative study of growth: different body weight trajectories in three species of the genus Eublepharis and their hybrids

An extensive research effort is devoted to the evolution of life-histories and processes underlying the variation in adult body weight; however, in this regard, some animal taxa remain neglected. Here we report rates and timing of growth recorded in two wild-derived populations of a model lizard species, Eublepharis macularius (M, W), other two related species, i.e., E. angramainyu (A) and E. sp. (D), and their between-species hybrids. We detected clear differences among the examined species/populations, which can be interpreted in the terms of "fast - slow" continuum of life-history strategies. The mean asymptotic body size was the highest in A and further decreased in the following order: M, W, and D. In contrast, the growth rate showed an opposite pattern. Counter-intuitively, the largest species exhibited the slowest growth rates. The final body size was determined mainly by the inflexion point. This parameter reflecting the duration of exponential growth increased with mean asymptotic body size and easily overcompensated the effect of decreasing growth rates in larger species. Compared to the parental species, the F1 and backcross hybrids exhibited intermediate values of growth parameters. Thus, except for the case of the F2 hybrid of MxA, we failed to detect deleterious effects of hybridization in these animals with temperature sex determination.

Characterization of seasonal reproductive and stress steroid hormones in wild Radiated Tortoises, Astrochelys radiata

The critically endangered Radiated Tortoise (Astrochelys radiata) is endemic to the southern coastlines of Madagascar. Once common, wild populations of this tortoise have undergone dramatic declines in recent years. Although there have been studies documenting reproductive activities, reproductive physiological parameters are unknown yet may be crucial in the recovery of the species. Over four research seasons in remote field locations native to A. radiata, we surveyed for, radio-tracked, and sampled wild, free ranging tortoises. We sampled and measured stress and reproductive parameters (corticosterone [CORT], testosterone [T], estradiol-17β [E2], and progesterone [P]) in 311 plasma samples from 203 wild A. radiata, capturing their active period. Generally, hormone concentrations were associated with body condition, temperature, and humidity. There was wide variation in CORT that varied monthly and by group. Juvenile tortoises maintained more than twice the mean basal CORT concentrations than either adult sex, with the most dramatic distinctions in the middle of the wet season. For adult sex hormones, the last months of the dry season and into the wet season when ground humidities are low and just begin to rise prior to temperature declines, male T concentrations gradually increased to a peak before returning to near undetectable values into the dry season. We had limited data for T concentrations in females, but found average T concentrations were much lower than in males and positively correlated with larger female home range sizes. For female hormone cycles, E2 also peaked in the early 1/3 of the wet season along with male T, and was followed by an uptick in P which correlates to the putative ovulatory cycle. Females tracked over four years showed variation in patterns of P, indicating that number and frequency of clutches vary. Our results suggest that 1) there is high species plasticity in response to stress; 2) A. radiata reproductive cycling is somewhat dissociated with courtship timing and is instead triggered by environmental cues; and 3) individual female reproductive output is irregular. This study is oone of the first to document and describe multi-year seasonal stress and reproductive hormones in a free-ranging Malagasy chelonian. These data may be used to identify key high-production habitats for conservation, and aide in captive management and reproduction in assurance colonies for species health and survival.

Sex hormones and the development of sexual size dimorphism: 5α-dihydrotestosterone inhibits growth in a female-larger lizard (Sceloporus undulatus)

Sexual differences in adult body size [sexual size dimorphism (SSD)] and color (sexual dichromatism) are widespread, and both male- and female-biased dimorphisms are observed even among closely related species. A growing body of evidence indicates testosterone can regulate growth, thus the development of SSD, and sexual dichromatism. However, the mechanism(s) underlying these effects are conjectural, including possible conversions of testosterone to estradiol (E₂) or 5α-dihydrotestosterone (DHT). In the present study, we hypothesized that the effects of testosterone are physiological responses mediated by androgen receptors, and we tested two specific predictions: (1) that DHT would mimic the effects of testosterone by inhibiting growth and enhancing coloration, and (2) that removal of endogenous testosterone via surgical castration would stimulate growth. We also hypothesized that females share downstream regulatory networks with males and predicted that females and males would respond similarly to DHT. We conducted experiments on eastern fence lizards (Sceloporus undulatus), a female-larger species with striking sexual dichromatism. We implanted Silastic^® tubules containing 150 µg DHT into intact females and intact and castrated males. We measured linear growth rates and quantified color for ventral and dorsal surfaces. We found that DHT decreased growth rate and enhanced male-typical coloration in both males and females. We also found that, given adequate time, castration alone is sufficient to stimulate growth rate in males. The results presented here suggest that: (1) the effects of testosterone on growth and coloration are mediated by androgen receptors without requiring aromatization of testosterone into E₂, and (2) females possess the androgen-receptor-mediated regulatory networks required for initiating male-typical inhibition of growth and enhanced coloration in response to androgens.

Testosterone production in response to exogenous gonadotropin releasing hormone (GnRH challenge) depends on social environment and color polymorphism

Testosterone is an important mediator of behavior, morphology and physiology. A cascade of signals regulates the amount of testosterone (T) circulating in the plasma; in response to stimulus the hypothalamus releases gonadotropin-releasing hormone (GnRH), which triggers secretion of gonadotropins from the pituitary, stimulating the synthesis and release of T from the gonads. Previous work has shown that changes to the social environment can alter circulating T-levels, which may have important fitness consequences, but it is currently unclear whether these changes are due to alterations in the signal from the brain, or changes in the ability of the pituitary and gonads to respond to this signal. Further, the strength and direction of response to a changing environment may differ according to life-history strategy. Species with genetically determined alternative strategies offer a pathway for examining these differences. Here we use a finch with a genetically determined polymorphism, the Gouldian finch (Erythrura gouldiae), to determine whether T-levels change in response to social environment. We also use injections of GnRH to determine whether these changes are due to alterations in the ability of the pituitary and gonads to respond to this signal. We found that social environment (presence of females) had a rapid effect on male circulating T-levels, and that this difference was reflected in responsiveness to GnRH. We observed no overall morph differences in T-levels, but we did observe morph differences in the pattern of T secretion across environments, and morph differences in the repeatability of T-levels across time and environment.

Ovarian control of growth and sexual size dimorphism in a male-larger gecko

Sexual size dimorphism (SSD) reflects sex-specific solutions to the allocation of energy among growth, reproduction and survival; however, the proximate mechanisms behind these solutions are still poorly known even in vertebrates. In squamates, sexual differences in body size used to be attributed to direct energy allocation to energetically demanding processes, largely to reproduction. In addition, SSD is assumed to be controlled by specific endogenous mechanisms regulating growth in a sex-specific manner, namely masculinization by male gonadal androgens or feminization by ovarian hormones. We performed a manipulative growth experiment in females of the male-larger gecko Paroedura picta in order to test the reproductive cost hypothesis, the male androgen hypothesis and the ovarian hormone hypothesis. Specifically, we investigated the effect of total ovariectomy, prepubertal ovariectomy, unilateral ovariectomy, and total ovariectomy followed by exogenous estradiol, dihydrotestosterone or testosterone treatment, on female growth in comparison to males and reproductively active females. The present results and the results of our previous experiments do not support the hypotheses that SSD reflects direct energy allocation to reproduction and that male gonadal androgens are involved. However, all lines of evidence, particularly the comparable growth of reproducing intact and unilaterally ovariectomized females, were concordant with the control of SSD by ovarian hormones. We suggest that feminization of growth by female gonadal hormones should be taken into consideration as an endogenous pathway responsible for the ontogeny of SSD in squamates.

Identification of differentially expressed genes associated with differential body size in mandarin fish (Siniperca chuatsi)

Body size is an obvious and important characteristic of fish. Mandarin fish Siniperca chuatsi (Basilewsky) is one of the most valuable perciform species widely cultured in China. Individual differences in body size are common in mandarin fish and significantly influence the aquaculture production. However, little is currently known about its genetic control. In this study, digital gene expression profiling and transcriptome sequencing were performed in mandarin fish with differential body size at 30 and 180 days post-hatch (dph), respectively. Body weight, total length and body length of fish with big-size were significantly higher than those with small-size at both 30 and 180 dph (P < 0.05). 2171 and 2014 differentially expressed genes were identified between small-size and big-size fish at 30 and 180 dph, respectively. RT quantitative PCR (qPCR) analysis showed that the differential expression of 10 selected genes in mandarin fish that went through the same training procedure. The genes were involved in the growth hormone-insulin-like growth factor axis, cell proliferation and differentiation, appetite control, glucose metabolism, reproduction and sexual size dimorphism pathways. This study will help toward a comprehensive understanding of the complexity of regulation of body size in mandarin fish individuals and provide valuable information for future research.

Melanism and ontogeny: a case study in lizards of the Liolaemus fitzingerii group (Squamata: Liolaemini)

Color polymorphisms in general and melanism in particular have been the focus of many evolutionary adaptation studies. In lizards of the genus Liolaemus Wiegmann, 1834, patterns of melanism have been poorly studied, although they have been used as diagnostic characters for identifying and describing new species. We investigated the relationships between melanism, body size, sex, and time in a population of Rawson Lizard (Liolaemus xanthoviridis Cei and Scolaro, 1980) with extensive ventral melanism. The study took place in Bahía Isla Escondida, Chubut (Argentina), during three summer seasons (2012 to 2014). We tagged each individual, recorded body measurements and sex, and took ventral photographs to estimate the proportion of melanism. Our results showed that ventral melanism increased over time as each individual increased its snout–vent length (SVL). Body size explained 44% of the variation in melanism and males were more melanistic than females. Previous comparative studies of lizards in this species group showed no relationship between melanism and different taxonomic units or with thermal functionality. Here, we present evidence suggesting that melanism might be a character with an ontogenetic origin that is strongly associated with sex and body size. This pattern could be shared among species of this group of lizards, and even more importantly, it may be related to variable selection forces occurring throughout ontogeny.

Endogenous control of sexual size dimorphism: Gonadal androgens have neither direct nor indirect effect on male growth in a Madagascar ground gecko (Paroedura picta)

Changes in the effect of gonadal androgens on male growth are considered as a possible mechanism allowing shifts in magnitude and even direction of sexual size dimorphism in vertebrates, particularly squamate reptiles. Positive effects of gonadal androgens on male growth were found in several male-larger species of lizards. Contrastingly, we document that in the male-larger Madagascar ground gecko (Paroedura picta) gonadal androgens do not affect male growth under constant thermal conditions. However, the absence of a thermal gradient might prevent the potential indirect effect of gonadal androgens on growth via the influence of circulating hormones on an individual's thermoregulation and hence metabolic rate. In order to study this, we monitored the growth and body temperature of socially isolated sham-operated and castrated males of the same species in a thermal gradient. We also compared the oxygen consumption and activity between the treatment groups in the open field to test the effect of gonadal hormones on these traits potentially affecting growth. Even under a thermal gradient we found no effect of gonadal androgens on growth rate or final body dimensions. Castration also did not significantly affect oxygen consumption or activity in the open field test. Together with our previous findings, we can exclude both the direct effect of male gonadal androgens on the ontogeny of sexual size dimorphism via the influence on the growth axis, and the indirect influence of gonadal androgens acting on the ontogeny of SSD through the effect on thermoregulation, metabolic rate and activity.

Voltammetric Behavior of Testosterone on Bismuth Film Electrode: Highly Sensitive Determination in Pharmaceuticals and Human Urine by Square‐Wave Adsorptive Stripping Voltammetry

In this paper, an electrochemical application of bismuth‐film electrode (BiFE) fabricated via ex‐situ electrodeposition onto a glassy carbon electrode for testosterone determination was investigated in aqueous and aqueous/surfactant solutions. In cyclic voltammetry, the compound showed one irreversible and adsorption‐controlled reduction peak. The BiFE revealed good linear response in the examined concentration range of 1 to 45 nmol L−1 testosterone in BrittonRobinson buffer, pH 5.0 containing 3 mmol L−1 cetyltrimethylammonium bromide. The limit of detection was 0.3 nmol L−1 (0.09 ng mL−1). Finally, the BiFE was satisfactorily applied for quantitation of testosterone in both pharmaceutical (oil‐based ampoule) and biological (human urine) samples.

Rare earths exposure and male infertility: the injury mechanism study of rare earths on male mice and human sperm

The weight; testis/body coefficient; levels of LDH, SDH, SODH, G-6PD, and testosterone; cell cycle; and cell apoptosis of the male mice were influenced after being treated with 200 mg/[kg/day] of rare earths suspension for 3 weeks. The "Raman fingerprints" of the human sperm DNA exposed to 0.040 mg/ml CeCl3 were very different from those of the untreated; the Raman bands at 789 cm(-1) (backbone phosphodiester), PO4 backbone at 1,094 cm(-1), methylene deformation mode at 1,221 cm(-1), methylene deformation mode at 1,485 cm(-1), and amide II at 1,612 cm(-1), of which intensities and shifts were changed, might be the diagnostic biomarkers or potential therapeutic targets. The injury mechanism might be that the rare earths influence the oxidative stress and blood testosterone barrier, tangle the big biomolecule concurrently, which might cause the testicular cells and vascular system disorder and/or dysfunction, and at the same time change the physical and chemical properties of the sperm directly.

Elevated testosterone is required for male copulatory behavior and aggression in Madagascar ground gecko (Paroedura picta)

Elevated levels of gonadal androgens are often required for the expression of male-specific behavioral and morphological traits in all classes of vertebrates, including reptiles. Here, we tested the role of male gonadal androgens in the control of male sexual behavior, aggressive behavior, and size of the hemipenes in the gecko Paroedura picta. We performed hormonal manipulations involving castration with and without testosterone (T) replacement in males and application of exogenous T and ovariectomy in females. Castration suppressed sexual behavior and hemipenes size in males, and these effects were fully rescued by exogenous T. Sexual behavior and growth of the hemipenes were masculinized by male-typical levels of T in females, while ovariectomized females retained female-typical expression of these traits. These results indicate that the development of male sexual behavior in adult females does not require early or pubertal organization. Elevated T increased the likelihood of aggressive behavior directed toward a male intruder, but aggression occurred only rarely. Elevated T is necessary and sufficient for enlargement of the hemipenes and the expression of male sexual behavior in both males and females of Paroedura picta. In contrast to sexual behavior, the expression of aggressive behavior is apparently more dependent on other factors in addition to T itself.

The oestrogen pathway underlies the evolution of exaggerated male cranial shapes in Anolis lizards

Sexual dimorphisms vary widely among species. This variation must arise through sex-specific evolutionary modifications to developmental processes. Anolis lizards vary extensively in their expression of cranial dimorphism. Compared with other Anolis species, members of the carolinensis clade have evolved relatively high levels of cranial dimorphism; males of this clade have exceptionally long faces relative to conspecific females. Developmentally, this facial length dimorphism arises through an evolutionarily novel, clade-specific strategy. Our analyses herein reveal that sex-specific regulation of the oestrogen pathway underlies evolution of this exaggerated male phenotype, rather than the androgen or insulin growth factor pathways that have long been considered the primary regulators of male-biased dimorphism among vertebrates. Our results suggest greater intricacy in the genetic mechanisms that underlie sexual dimorphisms than previously appreciated.

The proximate causes of sexual size dimorphism in Phrynocephalus przewalskii

Sexual size dimorphism (SSD) is a common phenomenon and is a central topic in evolutionary biology. Recently, the importance of pursuing an ontogenetic perspective of SSD has been emphasized, to elucidate the proximate physiological mechanisms leading to its evolution. However, such research has seldom focused on the critical periods when males and females diverge. Using mark-recapture data, we investigated the development of SSD, sex-specific survivorship, and growth rates in Phrynocephalus przewalskii (Agamidae). We demonstrated that both male and female lizards are reproductively mature at age 10-11 months (including 5 months hibernation). Male-biased SSD in snout-vent length (SVL) was only found in adults and was fully expressed at age 11 months (June of the first full season of activity), just after sexual maturation. However, male-biased SSD in tail length (TL), hind-limb length (LL), and head width (HW) were fully expressed at age 9-10 months, just before sexual maturation. Analysis of age-specific linear growth rates identified sexually dimorphic growth during the fifth growth month (age 10-11 months) as the proximate cause of SSD in SVL. The males experienced higher mortality than females in the first 2 years and only survived better than females after SSD was well developed. This suggests that the critical period of divergence in the sizes of male and female P. przewalskii occurs between 10 and 11 months of age (May to June during the first full season of activity), and that the sexual difference in growth during this period is the proximate cause. However, the sexual difference in survivorship cannot explain the male-biased SSD in SVL. Our results indicate that performance-related characteristics, such as TL, HW, and LL diverged earlier than SVL. The physiological mechanisms underlying the different growth patterns of males and females may reflect different energy allocations associated with their different reproductive statuses.

Individual variation in testosterone and parental care in a female songbird; the dark-eyed junco (Junco hyemalis)

When competition for sex-specific resources overlaps in time with offspring production and care, trade-offs can occur. Steroid hormones, particularly testosterone (T), play a crucial role in mediating such trade-offs in males, often increasing competitive behaviors while decreasing paternal behavior. Recent research has shown that females also face such trade-offs; however, we know little about the role of T in mediating female phenotypes in general, and the role of T in mediating trade-offs in females in particular. Here we examine the relationship between individual variation in maternal effort and endogenous T in the dark-eyed junco, a common songbird. Specifically, we measure circulating T before and after a physiological challenge (injection of gonadotropin releasing hormone, GnRH), and determine whether either measure is related to provisioning, brooding, or the amount of T sequestered in egg yolk. We found that females producing more T in response to a challenge spent less time brooding nestlings, but provisioned nestlings more frequently, and deposited more T in their eggs. These findings suggest that, while T is likely important in mediating maternal phenotypes and female life history tradeoffs, the direction of the relationships between T and phenotype may differ from what is generally observed in males, and that high levels of endogenous T are not necessarily as costly as previous work might suggest.

Ontogeny of pronounced female-biased sexual size dimorphism in the Malaysian cat gecko (Aeluroscalabotes felinus: Squamata: Eublepharidae): a test of the role of testosterone in growth regulation

Species differences in the effect of male gonadal androgens on male growth are considered a possible mechanism allowing shifts in magnitude and even direction of sexual size dimorphism (SSD) in squamate reptiles. According to the bipotential growth regulation hypothesis, the androgen testosterone (T) enhances male growth in species with male-biased SSD and conversely inhibits male growth in males of female-larger species. In the present study, we describe the ontogeny of the pronounced female-biased SSD and report the effect of T on growth via hormonal manipulations in males and females of the Malaysian cat gecko (Aeluroscalabotes felinus). In accord with the predictions of the bipotential growth regulation hypothesis, growth was inhibited by replacement of T in castrated males. Additionally, exogenous T inhibited growth of females to male-typical levels. Nevertheless, male castration alone did not significantly affect growth, contrary to the prediction of the bipotential growth regulation hypothesis, which contradicts the generality of this hypothesis. Application of exogenous T to females can interfere with normal ovarian function. Therefore, although not directly tested in this study, we suggest that ovarian effects on the ontogeny of SSD in A. felinus are consistent with our results. The development of SSD is a function of differential growth between the sexes, and potential sex-specific growth regulation in both males and females should be taken into account as possible proximate mechanisms responsible for SSD.

Seasonal variations in plasma vitellogenin and sex steroids in male and female Eastern Box Turtles, Terrapene carolina carolina

The Eastern Box Turtle (Terrapene carolina carolina) is a widespread species that has recently experienced precipitous declines throughout its range. Although many studies have documented aspects of reproduction in box turtles, reproductive physiology of free-ranging animals is unknown and can be crucial in this species' recovery. Over a two-year period, we measured reproductive parameters, (vitellogenin [Vtg], estradiol-17β [E2], and total testosterone [TT]), in plasma of 116 free-ranging Eastern Box Turtles across their active season. We found similar seasonal variations of Vtg and E2 within females. Mid-season, females showed a sharp peak in E2 that correlates with the putative beginning of the ovarian cycle. Individual females lacking these expected peaks of both Vtg and E2 suggest that some female T. c. carolina may not reproduce annually. Females typically expressed undetectable levels of TT, yet there was a small peak in TT early in the active season. Male Eastern Box Turtles exhibited a dual peak in TT. Elevated TT in males was significantly associated with observed sexual behaviors and smaller home ranges. Body condition had no effect on the concentration of TT or E2 in either sex. This is the first study to (1) document Vtg and sex steroid hormones in free-ranging animals of this genus, and (2) relate those metrics to individuals, the population, the purported annual cycle, and to other chelonian species.