AbstractHormones can induce trait development in one species yet have no effect on the same trait in a closely related species, but the mechanisms underlying these differences are unclear. Here, we compare two closely related lizard species to explore the cellular mechanisms associated with the evolutionary loss of hormonally mediated ventral coloration. The eastern fence lizard () has sexually dimorphic blue and black ventral coloration that develops when maturational increases in androgens induce melanin synthesis in males.
View Article and Find Full Text PDFAbstractHormones 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 lizard species before sexual divergence in circulating testosterone and then characterizing transcriptomic responses in the liver.
View Article and Find Full Text PDFIn 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.
View Article and Find Full Text PDFPhenotypic 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.
View Article and Find Full Text PDFComp Biochem Physiol A Mol Integr Physiol
July 2023
Herein we review our work involving dispersed adrenocortical cells from several lizard species: the Eastern Fence Lizard (Sceloporus undulatus), Yarrow's Spiny Lizard (Sceloporus jarrovii), Striped Plateau Lizard (Sceloporus virgatus) and the Yucatán Banded Gecko (Coleonyx elegans). Early work demonstrated changes in steroidogenic function of adrenocortical cells derived from adult S. undulatus associated with seasonal interactions with sex.
View Article and Find Full Text PDFComp Biochem Physiol A Mol Integr Physiol
December 2021
The present study examined how food availability interacts with age to modulate lizard adrenal steroidogenic function at the cellular level. Adult male and juvenile male and female Eastern Fence Lizards (Sceloporus undulatus) underwent a period of food deprivation with or without a shorter re-feeding period. Lizards maintained on a full feeding regimen served as the controls.
View Article and Find Full Text PDFPrevious 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 () mRNA and circulating IGF-1 hormone in , 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.
View Article and Find Full Text PDFGen Comp Endocrinol
August 2020
Ecological factors, such as habitat quality, influence the survival and reproductive success of free-living organisms. Urbanization, including roads, alters native habitat and likely influences physiology, behavior, and ultimately Darwinian fitness. Some effects of roads are clearly negative, such as increased habitat fragmentation and mortality from vehicle collision.
View Article and Find Full Text PDFOur previous work with adrenocortical cells from several Sceloporus lizard species suggests that gonadal hormones influence the steroidogenic capacity and the sensitivity to ACTH. However, there are discrepancies in these cellular response parameters suggesting that the effects of gonadal hormones on adrenocortical function vary with species, sex, age, season, and environmental/experimental conditions. To gain further insight into these complex interactions, here we report studies on Coleonyx elegans, Eublepharidae (Yucatán Banded Gecko), which is only distantly related to Sceloporus lizards via a basal common ancestor and in captivity, reproduces throughout the year.
View Article and Find Full Text PDFSexual 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 (E) or 5α-dihydrotestosterone (DHT).
View Article and Find Full Text PDFNutrition and energy balance are important regulators of growth and the growth hormone/insulin-like growth factor (GH/IGF) axis. However, our understanding of these functions does not extend uniformly to all classes of vertebrates and is mainly limited to controlled laboratory conditions. Lizards can be useful models to improve our understanding of the nutritional regulation of the GH/IGF-1 axis because many species are relatively easy to observe and manipulate both in the laboratory and in the field.
View Article and Find Full Text PDFChanges in energy balance can lead to functional alterations at all levels of the hypothalamic-pituitary-adrenal (HPA) axis. However, relatively little is known about how energy balance affects functional properties of adrenocortical cells themselves. We investigated effects of restricted food intake on sensitivity to ACTH and rates of steroidogenesis in adrenocortical cells isolated from growing female and male Yarrow's Spiny Lizards (Sceloporus jarrovii).
View Article and Find Full Text PDFWe used the "morphology-performance-fitness" paradigm (Arnold, 1983) as our framework to investigate endocrine control of performance and fitness in Sceloporus undulatus (Eastern Fence Lizard). Focusing on males, we used the "natural experiments" of seasonal, sexual, and developmental variation in growth and in exercise endurance to identify testosterone and corticosterone as potential modulators of performance and related traits of interest. We followed with experimental manipulations of testosterone to investigate functional relationships, both in the laboratory and in the field.
View Article and Find Full Text PDFEffects of adrenal corticosteroids on reproductive and endocrine functions of the gonads are well known, but reciprocal effects of gonadal hormones on the hypothalamo-pituitary-adrenal (HPA) axis and on adrenocortical steroidogenesis in particular have received much less attention. We investigated effects of gonadectomy and testosterone (T) replacement on adrenocortical cell function in a year-long field study of male Sceloporus undulatus (Eastern Fence Lizard) and in a shorter term laboratory study with male Sceloporus jarrovii (Yarrow's Spiny Lizard). We also compared females to males in Sceloporus virgatus (Striped Plateau Lizard) and investigated effects of gonadectomy in short-term laboratory experiment on females of this species.
View Article and Find Full Text PDFJ Exp Zool A Ecol Genet Physiol
November 2008
The sex steroid testosterone has been shown to regulate the development of male-specific coloration in many organisms that exhibit sexual dichromatism, but the role of testosterone is less certain for species in which both sexes express bright coloration. Lizards in the genus Sceloporus possess bright blue patches on their throats and abdomens. These patches, which are used in social signaling, are often regulated by testosterone and are consequently expressed only in males of most species.
View Article and Find Full Text PDFSexual dimorphism in size (sexual size dimorphism; SSD) is nearly ubiquitous, but the relative importance of genetic versus environmental control of SSD is not known for most species. We investigated proximate determinants of SSD in several species of squamate reptiles, including three species of Sceloporus lizards and the diamond-backed rattlesnake (Crotalus atrox). In natural populations of these species, SSD is caused by sexual differences in age-specific growth.
View Article and Find Full Text PDFSexual size dimorphism (SSD) has received considerable attention from evolutionary biologists, but relatively little is known about the physiological mechanisms underlying sex differences in growth that lead to SSD. Testosterone (T) stimulates growth in many male-larger vertebrates, but inhibits growth in the female-larger lizard Sceloporus undulatus. Thus, opposite patterns of SSD may develop in part because of underlying differences in the hormonal regulation of male growth.
View Article and Find Full Text PDFElucidation of the role of natriuretic peptides (NPs) in vertebrate adrenal steroidogenesis has been facilitated by the use of freshly dispersed adrenocortical cells. Our recent characterization of lizard adrenocortical cells [Carsia, R.V.
View Article and Find Full Text PDFIn the eastern fence lizard, Sceloporus undulatus, female-larger sexual size dimorphism develops because yearling females grow faster than males before first reproduction. This sexual growth divergence coincides with maturational increases in male aggression, movement, and ventral coloration, all of which are influenced by the sex steroid testosterone (T). These observations suggest that male growth may be constrained by energetic costs of activity and implicate T as a physiological regulator of this potential trade-off.
View Article and Find Full Text PDFIt is commonly argued that sexual size dimorphism (SSD) in lizards has evolved in response to two primary, nonexclusive processes: (1) sexual selection for large male size, which confers an advantage in intrasexual mate competition (intrasexual selection hypothesis), and (2) natural selection for large female size, which confers a fecundity advantage (fecundity advantage hypothesis). However, outside of several well-studied lizard genera, the empirical support for these hypotheses has not been examined with appropriate phylogenetic control. We conducted a comparative phylogenetic analysis to test these hypotheses using literature data from 497 lizard populations representing 302 species and 18 families.
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