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Mayer C, Russell L, McKinney M, Litton M, Mendyk RW, Cutler D, Liu C, Nevarez JG. Sexual dimorphism in Louisiana pine snakes (Pituophis ruthveni). Zoo Biol 2023; 42:529-536. [PMID: 36905189 DOI: 10.1002/zoo.21762] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2022] [Revised: 12/15/2022] [Accepted: 02/14/2023] [Indexed: 03/12/2023]
Abstract
The Louisiana pine snake, Pituophis ruthveni, is a cryptic, federally threatened snake species with several fragmented populations in Louisiana and Texas, USA. There are currently four captive breeding populations in zoos in the USA; however, little scientific data exists on their life history and anatomy. Accurate sex determination and identification of normal reproductive anatomy are an essential part of a veterinary exam and conservation programs. The authors had encountered various cases of sex misidentification in this species that were attributed to lack of lubrication of the sexing probes and enlarged musk glands. Anecdotal observation led to a hypothesis of sexual dimorphism based on body and tail shape. To test this hypothesis, we measured body length, tail length and width, and body to tail taper angle in 15 P. ruthveni (9 males and 6 females). We also obtained tail radiographs of all animals to document the presence of mineralized hemipenes. Significant dimorphism was identified in relative tail length, width, and taper angle; females consistently exhibited a more acute taper angle. Contrary to previous studies in other Pituophis species, a male-biased sexual size dimorphism was not identified. Mineralized hemipenes were confirmed in all males (a newly described trait in this species), and we found that the lateral view was consistently more reliable for identification of hemipenes compared to the ventrodorsal view. This information contributes to the scientific community's understanding of this species and is of use to biologists and veterinarians working toward conservation of this threatened species.
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Affiliation(s)
- C Mayer
- School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana, USA
| | - L Russell
- School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana, USA
| | - M McKinney
- Audubon Zoo, New Orleans, Louisiana, USA
| | - M Litton
- Audubon Zoo, New Orleans, Louisiana, USA
| | - R W Mendyk
- Audubon Zoo, New Orleans, Louisiana, USA
| | - D Cutler
- Audubon Zoo, New Orleans, Louisiana, USA
| | - C Liu
- School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana, USA
| | - J G Nevarez
- School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana, USA
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2
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Anderson NK, Goodwin SE, Schuppe ER, Dawn A, Preininger D, Mangiamele LA, Fuxjager MJ. Activational vs. organizational effects of sex steroids and their role in the evolution of reproductive behavior: Looking to foot-flagging frogs and beyond. Horm Behav 2022; 146:105248. [PMID: 36054981 DOI: 10.1016/j.yhbeh.2022.105248] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/25/2022] [Revised: 07/14/2022] [Accepted: 08/18/2022] [Indexed: 11/21/2022]
Abstract
Sex steroids play an important role in regulation of the vertebrate reproductive phenotype. This is because sex steroids not only activate sexual behaviors that mediate copulation, courtship, and aggression, but they also help guide the development of neural and muscular systems that underlie these traits. Many biologists have therefore described the effects of sex steroid action on reproductive behavior as both "activational" and "organizational," respectively. Here, we focus on these phenomena from an evolutionary standpoint, highlighting that we know relatively little about the way that organizational effects evolve in the natural world to support the adaptation and diversification of reproductive behavior. We first review the evidence that such effects do in fact evolve to mediate the evolution of sexual behavior. We then introduce an emerging animal model - the foot-flagging frog, Staurois parvus - that will be useful to study how sex hormones shape neuromotor development necessary for sexual displays. The foot flag is nothing more than a waving display that males use to compete for access to female mates, and thus the neural circuits that control its production are likely laid down when limb control systems arise during the developmental transition from tadpole to frog. We provide data that highlights how sex steroids might organize foot-flagging behavior through its putative underlying mechanisms. Overall, we anticipate that future studies of foot-flagging frogs will open a powerful window from which to see how sex steroids influence the neuromotor systems to help germinate circuits that drive signaling behavior. In this way, our aim is to bring attention to the important frontier of endocrinological regulation of evolutionary developmental biology (endo-evo-devo) and its relationship to behavior.
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Affiliation(s)
- Nigel K Anderson
- Department of Ecology, Evolution, and Organismal Biology, Brown University, Providence, RI, United States of America
| | - Sarah E Goodwin
- Department of Biological Sciences, Smith College, Northampton, MA, United States of America
| | - Eric R Schuppe
- Center for Integrative Neuroscience, University of California, San Francisco, San Francisco, CA, United States of America
| | - AllexAndrya Dawn
- Department of Biological Sciences, Smith College, Northampton, MA, United States of America
| | - Doris Preininger
- Department of Evolutionary Biology, University of Vienna, Vienna, Austria; Vienna Zoo, Vienna, Austria
| | - Lisa A Mangiamele
- Department of Biological Sciences, Smith College, Northampton, MA, United States of America.
| | - Matthew J Fuxjager
- Department of Ecology, Evolution, and Organismal Biology, Brown University, Providence, RI, United States of America.
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Duncan CA, Cohick WS, John-Alder HB. Testosterone Reduces Growth and Hepatic IGF-1 mRNA in a Female-Larger Lizard, Sceloporus undulatus: Evidence of an Evolutionary Reversal in Growth Regulation. Integr Org Biol 2021; 2:obaa036. [PMID: 33791574 PMCID: PMC7715992 DOI: 10.1093/iob/obaa036] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
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.
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Affiliation(s)
| | - Wendie S Cohick
- Graduate Program in Endocrinology and Animal Biosciences, Rutgers University, 84 Lipman Drive, New Brunswick, NJ 08901, USA
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4
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Rollings N, Waye HL, Krohmer RW, Uhrig EJ, Mason RT, Olsson M, Whittington CM, Friesen CR. Sperm telomere length correlates with blood telomeres and body size in red‐sided garter snakes,
Thamnophis sirtalis parietalis. J Zool (1987) 2020. [DOI: 10.1111/jzo.12789] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- N. Rollings
- School of Life and Environmental Sciences University of Sydney Sydney NSW Australia
| | - H. L. Waye
- Division of Science and Mathematics University of Minnesota Morris Morris MN USA
| | - R. W Krohmer
- Department of Biological Sciences Saint Xavier University Chicago IL USA
| | - E. J. Uhrig
- Department of Integrative Biology Oregon State University Corvallis OR USA
| | - R. T. Mason
- Department of Integrative Biology Oregon State University Corvallis OR USA
| | - M. Olsson
- Department of Biological & Environmental Sciences University of Gothenburg Gothenburg Sweden
- School of Earth, Atmospheric and Life Sciences University of Wollongong Wollongong NSW Australia
| | - C. M. Whittington
- School of Life and Environmental Sciences University of Sydney Sydney NSW Australia
| | - C. R. Friesen
- School of Earth, Atmospheric and Life Sciences University of Wollongong Wollongong NSW Australia
- Illawarra Health and Medical Research Institute (IHMRI)University of Wollongong Wollongong NSW Australia
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5
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Cox RM. Sex steroids as mediators of phenotypic integration, genetic correlations, and evolutionary transitions. Mol Cell Endocrinol 2020; 502:110668. [PMID: 31821857 DOI: 10.1016/j.mce.2019.110668] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/17/2019] [Revised: 11/19/2019] [Accepted: 11/26/2019] [Indexed: 02/06/2023]
Abstract
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.
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Affiliation(s)
- Robert M Cox
- Department of Biology, University of Virginia, Charlottesville, VA, 22904, USA.
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6
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Loebens L, Hendges CD, Almeida-Santos SM, Cechin SZ. Morphological variation and sexual dimorphism in two sympatric dipsadine snakes from Southern Brazil. ZOOL ANZ 2019. [DOI: 10.1016/j.jcz.2019.03.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Rollings N, Uhrig EJ, Krohmer RW, Waye HL, Mason RT, Olsson M, Whittington CM, Friesen CR. Age-related sex differences in body condition and telomere dynamics of red-sided garter snakes. Proc Biol Sci 2018; 284:rspb.2016.2146. [PMID: 28381620 DOI: 10.1098/rspb.2016.2146] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2016] [Accepted: 03/06/2017] [Indexed: 12/15/2022] Open
Abstract
Life-history strategies vary dramatically between the sexes, which may drive divergence in sex-specific senescence and mortality rates. Telomeres are tandem nucleotide repeats that protect the ends of chromosomes from erosion during cell division. Telomeres have been implicated in senescence and mortality because they tend to shorten with stress, growth and age. We investigated age-specific telomere length in female and male red-sided garter snakes, Thamnophis sirtalis parietalis We hypothesized that age-specific telomere length would differ between males and females given their divergent reproductive strategies. Male garter snakes emerge from hibernation with high levels of corticosterone, which facilitates energy mobilization to fuel mate-searching, courtship and mating behaviours during a two to four week aphagous breeding period at the den site. Conversely, females remain at the dens for only about 4 days and seem to invest more energy in growth and cellular maintenance, as they usually reproduce biennially. As male investment in reproduction involves a yearly bout of physiologically stressful activities, while females prioritize self-maintenance, we predicted male snakes would experience more age-specific telomere loss than females. We investigated this prediction using skeletochronology to determine the ages of individuals and qPCR to determine telomere length in a cross-sectional study. For both sexes, telomere length was positively related to body condition. Telomere length decreased with age in male garter snakes, but remained stable in female snakes. There was no correlation between telomere length and growth in either sex, suggesting that our results are a consequence of divergent selection on life histories of males and females. Different selection on the sexes may be the physiological consequence of the sexual dimorphism and mating system dynamics displayed by this species.
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Affiliation(s)
- Nicky Rollings
- School of Life and Environmental Sciences, University of Sydney, Heydon-Laurence Building (A08), New South Wales 2006, Australia
| | - Emily J Uhrig
- Department of Physics, Chemistry and Biology, Linköping University, Linköping, Sweden.,Department of Integrative Biology, Oregon State University, Corvallis, OR, USA
| | - Randolph W Krohmer
- Department of Biological Sciences, Saint Xavier University, Chicago, IL, USA
| | - Heather L Waye
- Division of Science and Mathematics, University of Minnesota, Morris, MN, USA
| | - Robert T Mason
- Department of Integrative Biology, Oregon State University, Corvallis, OR, USA
| | - Mats Olsson
- Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden
| | - Camilla M Whittington
- School of Life and Environmental Sciences, University of Sydney, Heydon-Laurence Building (A08), New South Wales 2006, Australia.,Sydney School of Veterinary Science, Faculty of Science, University of Sydney, Sydney, Australia
| | - Christopher R Friesen
- School of Life and Environmental Sciences, University of Sydney, Heydon-Laurence Building (A08), New South Wales 2006, Australia
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8
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Stuginski DR, Mendes GF, Sant'Anna SS, Rubio DT, Vieira SEM, Oitaven LPC, Grego KF. Sexual Differences in Growth Rates of Juveniles from a Litter ofBothrops fonsecai: The Role of Feeding Conversion in a Female-Biased SSD Species. SOUTH AMERICAN JOURNAL OF HERPETOLOGY 2017. [DOI: 10.2994/sajh-d-17-00001.1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
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9
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Pollock NB, Feigin S, Drazenovic M, John-Alder HB. Sex hormones and the development of sexual size dimorphism: 5α-dihydrotestosterone inhibits growth in a female-larger lizard ( Sceloporus undulatus). ACTA ACUST UNITED AC 2017; 220:4068-4077. [PMID: 28912255 DOI: 10.1242/jeb.166553] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2017] [Accepted: 09/11/2017] [Indexed: 12/18/2022]
Abstract
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.
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Affiliation(s)
- Nicholas B Pollock
- Graduate Program in Ecology and Evolution, Rutgers University, New Brunswick, NJ 08901, USA
| | - Stephanie Feigin
- Department of Ecology, Evolution, and Natural Resources, Rutgers University, New Brunswick, NJ 08901, USA
| | - Marko Drazenovic
- Department of Ecology, Evolution, and Natural Resources, Rutgers University, New Brunswick, NJ 08901, USA
| | - Henry B John-Alder
- Graduate Program in Ecology and Evolution, Rutgers University, New Brunswick, NJ 08901, USA.,Department of Ecology, Evolution, and Natural Resources, Rutgers University, New Brunswick, NJ 08901, USA
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10
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Kashian DR, Dodson SI. Effects of common-use pesticides on developmental and reproductive processes in Daphnia. Toxicol Ind Health 2016; 18:225-35. [PMID: 14653311 DOI: 10.1191/0748233702th146oa] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Daphnia magna were evaluated for use as a screen for pesticides that have been demonstrated to have estrogenic (o?p?-DDT, di-n-butyl phthalate, toxaphene), anti-androgenic (p?p-DDE, linuron), thyroid (acetochlor, alachlor, metribuzin), insulin (amitraz) or lutenizing hormone (2,4-D) activity in vertebrates, and to establish daphnid sensitivity to these compounds. Pesticides with unknown effects on vertebrate endocrine systems (chlorosulfuran, cyanazine, diflubenzuron, metolachlor, and diquat) were also evaluated. Compounds were assayed for six days at environmentally relevant concentrations ranging from 0.001 to 100 mg/L, using female Daphnia and their offspring. Sublethal endpoints included offspring sex (sex determination), clutch size (fecundity), and adult size (growth rate). Toxaphene was the only compound that affected sexual differentiation, increasing male production. Daphnia fecundity declined with exposure to toxaphene, and daphnid growth rates were reduced by acetochlor exposure. Diflubenzuron, o?p?-DDT, and p?p-DDE significantly reduced Daphnia survival. No correlation existed between affected reproductive or developmental processes and specific endocrine systems or subsystems. Results from this study indicate that Daphnia make a good screen for assessing potential environmental impacts but are not a useful indicator of pesticide hormonal activity in vertebrates. This assay consistently detected sublethal but ecologically relevant effects of these pesticides on Daphnia at environmentally relevant concentrations typically below their listed EC50 value.
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Affiliation(s)
- Donna R Kashian
- Department of Fisheries and Wildlife Biology, Colorado State University, Fort Collins, CO 80523-1474, USA.
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11
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Cox CL, Hanninen AF, Reedy AM, Cox RM. Female anoles retain responsiveness to testosterone despite the evolution of androgen‐mediated sexual dimorphism. Funct Ecol 2014. [DOI: 10.1111/1365-2435.12383] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
- Christian L. Cox
- Department of Biology University of Virginia Charlottesville VirginiaUSA
| | - Amanda F. Hanninen
- Department of Biology University of Virginia Charlottesville VirginiaUSA
| | - Aaron M. Reedy
- Department of Biology University of Virginia Charlottesville VirginiaUSA
| | - Robert M. Cox
- Department of Biology University of Virginia Charlottesville VirginiaUSA
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12
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Kubička L, Golinski A, John-Alder H, Kratochvíl L. 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. Gen Comp Endocrinol 2013; 188:183-8. [PMID: 23545460 DOI: 10.1016/j.ygcen.2013.03.016] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Revised: 03/11/2013] [Accepted: 03/12/2013] [Indexed: 12/15/2022]
Abstract
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.
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Affiliation(s)
- Lukáš Kubička
- Faculty of Science, Charles University in Prague, Department of Ecology, Viničná 7, 128 44 Praha 2, Czech Republic.
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13
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Starostová Z, Kubička L, Golinski A, Kratochvil L. Neither male gonadal androgens nor female reproductive costs drive development of sexual size dimorphism in lizards. J Exp Biol 2013; 216:1872-80. [DOI: 10.1242/jeb.079442] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Summary
Sexual size dimorphism (SSD) is an extensively studied phenomenon in animals, including reptiles, but the proximate mechanism of its development is poorly understood. The most pervasive candidates are (1) androgen-mediated control of growth, i.e. positive effect of gonadal androgens (testosterone) on male growth in male-larger species, while negative in female-larger species; and (2) sex-specific differences in energy allocation to growth, e.g. sex with larger reproductive costs should reach smaller body size. We tested these hypotheses in adults of the male-larger lizard Paroedura picta by conducting castrations with and without testosterone implants in males and manipulating reproductive status in females. Castration or testosterone replacement had no significant effect on final body length in males. High investment to reproduction had no significant effect on final body length in intact females. Interestingly, ovariectomized females and females with testosterone implants grew to larger body size than intact females. We found support for neither of the above hypotheses and suggest that previously reported effects of gonadal androgens on growth in male lizards could be a consequence of altered behaviour or social status in manipulated individuals. Exogenous testosterone in females led to decreased size of ovaries, its effect on body size may be caused by interference with normal ovarian function. We suggest that ovarian factors, perhaps estrogens, not reproductive costs, can modify growth in female lizards and may thus contribute to the development of SSD. This hypothesis is largely supported by published results on effect of testosterone treatment or ovariectomy on body size in female squamates.
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14
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Helle S, Laaksonen T, Huitu O. Sex-specific offspring growth according to maternal testosterone, corticosterone, and glucose levels. Behav Ecol 2012. [DOI: 10.1093/beheco/ars155] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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15
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BONNET XAVIER, LORIOUX SOPHIE, PEARSON DAVID, AUBRET FABIEN, BRADSHAW DON, DELMAS VIRGINIE, FAUVEL THOMAS. Which proximate factor determines sexual size dimorphism in tiger snakes? Biol J Linn Soc Lond 2011. [DOI: 10.1111/j.1095-8312.2011.01633.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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16
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Cox RM, Calsbeek R. Severe costs of reproduction persist in Anolis lizards despite the evolution of a single-egg clutch. Evolution 2009; 64:1321-30. [PMID: 19930451 DOI: 10.1111/j.1558-5646.2009.00906.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A central tenet of life-history theory is that investment in reproduction compromises survival. We tested for costs of reproduction in wild brown anoles (Anolis sagrei) by eliminating reproductive investment via surgical ovariectomy and/or removal of oviductal eggs. Anoles are unusual among lizards in that females lay single-egg clutches at frequent intervals throughout a lengthy reproductive season. This evolutionary reduction in clutch size is thought to decrease the physical burden of reproduction, but our results show that even a single egg significantly impairs stamina and sprint speed. Reproductive females also suffered a reduction in growth, suggesting that the cumulative energetic cost of successive clutches constrains the allocation of energy to other important functions. Finally, in each of two separate years, elimination of reproductive investment increased breeding-season survival by 56%, overwinter survival by 96%, and interannual survival by 200% relative to reproductive controls. This extreme fitness cost of reproduction may reflect a combination of intrinsic (i.e., reduced allocation of energy to maintenance) and extrinsic (i.e., increased susceptibility to predators) sources of mortality. Our results provide clear experimental support for a central tenet of life-history theory and show that costs of reproduction persist in anoles despite the evolution of a single-egg clutch.
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Affiliation(s)
- Robert M Cox
- Department of Biological Sciences, Dartmouth College, 401 Gilman Hall, Hanover, New Hampshire 03755, USA.
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17
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COX RM, STENQUIST DS, CALSBEEK R. Testosterone, growth and the evolution of sexual size dimorphism. J Evol Biol 2009; 22:1586-98. [PMID: 19549143 DOI: 10.1111/j.1420-9101.2009.01772.x] [Citation(s) in RCA: 109] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- R. M. COX
- Department of Biological Sciences, Dartmouth College, Hanover, NH, USA
| | - D. S. STENQUIST
- Department of Biological Sciences, Dartmouth College, Hanover, NH, USA
| | - R. CALSBEEK
- Department of Biological Sciences, Dartmouth College, Hanover, NH, USA
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18
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Krause MA, Burghardt GM. Sexual dimorphism of body and relative head sizes in neonatal common garter snakes. J Zool (1987) 2007. [DOI: 10.1111/j.1469-7998.2006.00251.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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19
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COX ROBERTM, JOHN-ALDER HENRYB. Increased mite parasitism as a cost of testosterone in male striped plateau lizards Sceloporus virgatus. Funct Ecol 2007. [DOI: 10.1111/j.1365-2435.2007.01251.x] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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COX RM, ZILBERMAN V, JOHN-ALDER HB. Environmental sensitivity of sexual size dimorphism: laboratory common garden removes effects of sex and castration on lizard growth. Funct Ecol 2006. [DOI: 10.1111/j.1365-2435.2006.01177.x] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Cox RM, John-Alder HB. Testosterone has opposite effects on male growth in lizards(Sceloporus spp.) with opposite patterns of sexual size dimorphism. J Exp Biol 2005; 208:4679-87. [PMID: 16326949 DOI: 10.1242/jeb.01948] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARY
Sexual 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. In the present study,we examined the effects of T on male growth in two sympatric congeners with opposite patterns of SSD (S. virgatus: female-larger; S. jarrovii: male-larger). During the mating season, yearling males of both species have higher plasma T levels than females, but whereas yearling males of S. virgatus grow only half as fast as females, yearling males of S. jarrovii grow more quickly than females. Thus, we hypothesized that T inhibits growth in yearling S. virgatus males, but promotes growth in yearling S. jarrovii males. In support of this hypothesis,we found that castrated (CAST) males of S. virgatus grew faster than castrated males given T implants (TEST). In contrast, TEST males of S. jarrovii grew faster than CAST males. Our results provide the first direct evidence for opposite effects of T on male growth in closely related species with opposite patterns of SSD. We speculate that growth inhibition by T reflects an energetic trade-off between growth and reproductive investment,and propose that such `costs' of male reproduction may help explain the evolution of female-larger SSD in Sceloporus.
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Affiliation(s)
- Robert M Cox
- Graduate Program in Ecology and Evolution, Department of Animal Sciences, Rutgers University, New Brunswick, NJ 08901, USA.
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Does prey size induce head skeleton phenotypic plasticity during early ontogeny in the snake Boa constrictor ? J Zool (1987) 2005. [DOI: 10.1017/s0952836905007624] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Taylor EN, Denardo DF. Sexual size dimorphism and growth plasticity in snakes: an experiment on the Western Diamond-backed Rattlesnake (Crotalus atrox). ACTA ACUST UNITED AC 2005; 303:598-607. [PMID: 15945080 DOI: 10.1002/jez.a.189] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We conducted an experiment to examine the effects of sex and food intake on growth, mass gain, and attainment of sexual maturity in Western Diamond-backed Rattlesnakes (Crotalus atrox). We also measured testosterone levels to determine whether testosterone might be involved in the male-biased sexual size dimorphism observed in this species. We collected neonate rattlesnakes and raised them in the laboratory for 2 years on either a high-intake diet (fed one mouse per week) or a low-intake diet (fed one mouse every 3 weeks). High-intake snakes grew and gained mass more rapidly than low-intake snakes, but males did not grow or gain mass more rapidly than females in either treatment group. High-intake snakes attained reproductive maturity earlier than low-intake snakes, indicating that size, not age, is the critical determinant of reproductive maturity. Males had higher levels of testosterone than females but did not grow more quickly, suggesting that testosterone may not affect growth in this species and may therefore not be the proximate determinant of sexual size dimorphism.
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Affiliation(s)
- Emily N Taylor
- School of Life Sciences, Arizona State University, Tempe, Arizona 85287, USA.
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Cox RM, Skelly SL, John-Alder HB. Testosterone Inhibits Growth in Juvenile Male Eastern Fence Lizards (Sceloporus undulatus): Implications for Energy Allocation and Sexual Size Dimorphism. Physiol Biochem Zool 2005; 78:531-45. [PMID: 15957108 DOI: 10.1086/430226] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/18/2004] [Indexed: 11/04/2022]
Abstract
In 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. To test this hypothesis, we used surgical castration and subsequent administration of exogenous T to alter the physiological and behavioral phenotypes of field-active males during the period of sexual growth divergence. As predicted, T inhibited male growth, while castration promoted long-term growth. Males treated with T also exhibited increased daily activity period, movement, and home range area. Food consumption did not differ among male treatments or sexes, suggesting that the inhibitory effects of T on growth are mediated by patterns of energy allocation rather than acquisition. On the basis of estimates derived from published data, we conclude that the energetic cost of increased daily activity period following T manipulation is sufficient to explain most (79%) of the associated reduction in growth. Further, growth may have been constrained by additional energetic costs of increased ectoparasite load following T manipulation. Similar studies of the proximate behavioral, ecological, and physiological mechanisms involved in growth regulation should greatly improve our understanding of sexual size dimorphism.
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Affiliation(s)
- Robert M Cox
- Graduate Program in Ecology and Evolution, Rutgers University, New Brunswick, NJ 08901, USA
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