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Robinson CD, Hale MD, Wittman TN, Cox CL, John-Alder HB, Cox RM. Species differences in hormonally mediated gene expression underlie the evolutionary loss of sexually dimorphic coloration in Sceloporus lizards. J Hered 2023; 114:637-653. [PMID: 37498153 DOI: 10.1093/jhered/esad046] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2023] [Accepted: 07/24/2023] [Indexed: 07/28/2023] Open
Abstract
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.
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Affiliation(s)
| | - Matthew D Hale
- University of Virginia, Department of Biology, Charlottesville, VA, United States
- U.S. Military HIV Research Program, Walter Reed Army Institute of Research, Silver Spring, MD, United States
- Henry M. Jackson Foundation for the Advancement of Military Medicine Inc., Bethesda, MD, United States
| | - Tyler N Wittman
- University of Virginia, Department of Biology, Charlottesville, VA, United States
| | - Christian L Cox
- Florida International University, Department of Biological Sciences and Institute of Environment, Miami, FL, United States
| | - Henry B John-Alder
- Rutgers University, Department of Ecology, Evolution, and Natural Resources, New Brunswick, NJ, United States
| | - Robert M Cox
- University of Virginia, Department of Biology, Charlottesville, VA, United States
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Wittman TN, Carlson TA, Robinson CD, Bhave RS, Cox RM. Experimental removal of nematode parasites increases growth, sprint speed, and mating success in brown anole lizards. J Exp Zool A Ecol Integr Physiol 2022; 337:852-866. [PMID: 35871281 PMCID: PMC9796785 DOI: 10.1002/jez.2644] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/22/2022] [Revised: 06/29/2022] [Accepted: 07/01/2022] [Indexed: 01/07/2023]
Abstract
Parasites interact with nearly all free-living organisms and can impose substantial fitness costs by reducing host survival, mating success, and fecundity. Parasites may also indirectly affect host fitness by reducing growth and performance. However, experimentally characterizing these costs of parasitism is challenging in the wild because common antiparasite drug formulations require repeated dosing that is difficult to implement in free-living populations, and because the extended-release formulations that are commercially available for livestock and pets are not suitable for smaller animals. To address these challenges, we developed a method for the long-term removal of nematode parasites from brown anole lizards (Anolis sagrei) using an extended-release formulation of the antiparasite drug ivermectin. This treatment eliminated two common nematode parasites in captive adult males and dramatically reduced the prevalence and intensity of infection by these parasites in wild adult males and females. Experimental parasite removal significantly increased the sprint speed of captive adult males, the mating success of wild adult males, and the growth of wild juveniles of both sexes. Although parasite removal did not have any effect on survival in wild anoles, parasites may influence fitness directly through reduced mating success and indirectly through reduced growth and performance. Our method of long-term parasite manipulation via an extended-release formulation of ivermectin should be readily adaptable to many other small vertebrates, facilitating experimental tests of the extent to which parasites affect host phenotypes, fitness, and eco-evolutionary dynamics in the wild.
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Affiliation(s)
- Tyler N. Wittman
- Department of BiologyUniversity of VirginiaCharlottesvilleVirginiaUSA
| | - Torun A. Carlson
- Department of BiologyUniversity of VirginiaCharlottesvilleVirginiaUSA
| | | | - Rachana S. Bhave
- Department of BiologyUniversity of VirginiaCharlottesvilleVirginiaUSA
| | - Robert M. Cox
- Department of BiologyUniversity of VirginiaCharlottesvilleVirginiaUSA
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Cox RM, Hale MD, Wittman TN, Robinson CD, Cox CL. Evolution of hormone-phenotype couplings and hormone-genome interactions. Horm Behav 2022; 144:105216. [PMID: 35777215 DOI: 10.1016/j.yhbeh.2022.105216] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Revised: 06/05/2022] [Accepted: 06/20/2022] [Indexed: 12/22/2022]
Abstract
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.
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Affiliation(s)
- Robert M Cox
- Department of Biology, University of Virginia, Charlottesville, VA, USA.
| | - Matthew D Hale
- Department of Biology, University of Virginia, Charlottesville, VA, USA
| | - Tyler N Wittman
- Department of Biology, University of Virginia, Charlottesville, VA, USA
| | | | - Christian L Cox
- Department of Biology, University of Virginia, Charlottesville, VA, USA; Biological Sciences, Florida International University, Miami, FL, USA
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Cox RM, Wittman TN, Calsbeek R. Reproductive trade-offs and phenotypic selection change with body condition, but not with predation regime, across island lizard populations. J Evol Biol 2021; 35:365-378. [PMID: 34492140 DOI: 10.1111/jeb.13926] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Revised: 08/27/2021] [Accepted: 08/31/2021] [Indexed: 11/27/2022]
Abstract
Trade-offs between reproduction and survival are central to life-history theory and are expected to shape patterns of phenotypic selection, but the ecological factors structuring these trade-offs and resultant patterns of selection are generally unknown. We manipulated reproductive investment and predation regime in island populations of brown anole lizards (Anolis sagrei) to test (1) whether previously documented increases in the survival of experimentally non-reproductive females (OVX = ovariectomy) reflect the greater susceptibility of reproductive females (SHAM = control) to predation and (2) whether phenotypic selection differs as a function of reproductive investment and predation regime. OVX females exceeded SHAM controls in growth, mass gain and body condition, indicating pronounced energetic costs of reproduction. Although mortality was greatest in the presence of bird and snake predators, differences in survival between OVX and SHAM were unrelated to predation regime, as were patterns of natural selection on body size. Instead, we found that body condition at the conclusion of the experiment differed significantly across populations, suggesting that local environments varied in their ability to support mass gain and positive energy balance. As mean body condition improved across populations, the magnitude of the survival cost of reproduction increased, linear selection on body size shifted from positive to negative, and quadratic selection shifted from stabilizing to weakly disruptive. Our results suggest that reproductive trade-offs and patterns of phenotypic selection in female brown anoles are more sensitive to inferred variation in environmental quality than to experimentally induced variation in predation.
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Affiliation(s)
- Robert M Cox
- Department of Biological Sciences, Dartmouth College, Hanover, NH, USA.,Department of Biology, University of Virginia, Charlottesville, VA, USA
| | - Tyler N Wittman
- Department of Biology, University of Virginia, Charlottesville, VA, USA
| | - Ryan Calsbeek
- Department of Biological Sciences, Dartmouth College, Hanover, NH, USA
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Wittman TN, Robinson CD, McGlothlin JW, Cox RM. Hormonal pleiotropy structures genetic covariance. Evol Lett 2021; 5:397-407. [PMID: 34367664 PMCID: PMC8327939 DOI: 10.1002/evl3.240] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2020] [Revised: 05/03/2021] [Accepted: 05/17/2021] [Indexed: 11/08/2022] Open
Abstract
Quantitative genetic theory proposes that phenotypic evolution is shaped by G, the matrix of genetic variances and covariances among traits. In species with separate sexes, the evolution of sexual dimorphism is also shaped by B, the matrix of between‐sex genetic variances and covariances. Despite considerable focus on estimating these matrices, their underlying biological mechanisms are largely speculative. We experimentally tested the hypothesis that G and B are structured by hormonal pleiotropy, which occurs when one hormone influences multiple phenotypes. Using juvenile brown anole lizards (Anolis sagrei) bred in a paternal half‐sibling design, we elevated the steroid hormone testosterone with slow‐release implants while administering empty implants to siblings as a control. We quantified the effects of this manipulation on the genetic architecture of a suite of sexually dimorphic traits, including body size (males are larger than females) and the area, hue, saturation, and brightness of the dewlap (a colorful ornament that is larger in males than in females). Testosterone masculinized females by increasing body size and dewlap area, hue, and saturation, while reducing dewlap brightness. Control females and males differed significantly in G, but treatment of females with testosterone rendered G statistically indistinguishable from males. Whereas B was characterized by low between‐sex genetic correlations when estimated between control females and males, these same correlations increased significantly when estimated between testosterone females and either control or testosterone males. The full G matrix (including B) for testosterone females and either control or testosterone males was significantly less permissive of sexually dimorphic evolution than was G estimated between control females and males, suggesting that natural sex differences in testosterone help decouple genetic variance between the sexes. Our results confirm that hormonal pleiotropy structures genetic covariance, implying that hormones play an important yet overlooked role in mediating evolutionary responses to selection.
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Affiliation(s)
- Tyler N Wittman
- Department of Biology University of Virginia Charlottesville Virginia 22904
| | | | - Joel W McGlothlin
- Department of Biological Sciences Virginia Tech Blacksburg Virginia 24061
| | - Robert M Cox
- Department of Biology University of Virginia Charlottesville Virginia 22904
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Wittman TN, Cox RM. The evolution of monogamy is associated with reversals from male to female bias in the survival cost of parasitism. Proc Biol Sci 2021; 288:20210421. [PMID: 33977790 DOI: 10.1098/rspb.2021.0421] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The extent to which parasites reduce host survival should depend upon how hosts balance trade-offs between reproduction and survival. For example, parasites are predicted to impose greater survival costs under polygynous or promiscuous mating systems in which competition for mates favours increased reproductive investment, particularly in males. We provide, to our knowledge, the first comparative test of the hypothesis that the mating system of the host is an important determinant of (i) the extent to which parasites reduce survival, and (ii) the extent to which males and females differ in the survival cost of parasitism. Using meta-analysis of 85 published estimates of the survival cost of parasitism from 72 studies of 64 species representing diverse animal lineages, we show that parasites impose a mean 3.5-fold increase in the odds of mortality on their hosts. Although this survival cost does not differ significantly across monogamous, polygynous and promiscuous mating systems, females incur a greater survival cost than males in monogamous species, whereas males incur a greater survival cost than females in polygynous and promiscuous species. Our results support the idea that mating systems shape the relative extent to which males and females invest in reproduction at the expense of defence against parasites.
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Affiliation(s)
- Tyler N Wittman
- Department of Biology, University of Virginia, Charlottesville, VA, USA
| | - Robert M Cox
- Department of Biology, University of Virginia, Charlottesville, VA, USA
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Wittman TN, Miller KA, King BH. Finding Prospective Mates by the Parasitoid Wasp Urolepis rufipes (Hymenoptera: Pteromalidae). Environ Entomol 2016; 45:1489-1495. [PMID: 28028096 DOI: 10.1093/ee/nvw136] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/23/2016] [Accepted: 09/10/2016] [Indexed: 06/06/2023]
Abstract
Cues from emergence sites may be predictive of mating opportunities if potential mates are slow to disperse after emergence, and particularly if emergence sites are clumped, as in the solitary parasitoid wasp Urolepis rufipes Ashmead. Males emerge before females, and the present study suggests that males may use emergence sites of conspecific males to locate mates. In choice experiments, virgin males spent more time on a male-emerged host (a host from which a male had recently emerged) than on a female-emerged host. Relative to when no host was present, virgin males also marked more in the presence of a male-emerged host, but did not mark more in the presence of a female-emerged host. Females, but not other males, are known to be attracted to male marks. Unlike for males, there was no evidence that females distinguished between male-emerged and female-emerged hosts. Virgin females preferred areas where multiple males had marked over areas where a single male had marked. Such areas had more total marks, yet marks per male did not differ between aggregated and solitary males. Thus, through his own attraction to male-emerged hosts and by marking near other males a male may find and attract females, and with no apparent increase in the cost of attraction.
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Affiliation(s)
- T N Wittman
- Department of Biological Sciences, Northern Illinois University, DeKalb, IL 60115 (; ; )
- Current address: Department of Biology, University of Virginia, Charlottesville, VA 22904
| | - K A Miller
- Department of Biological Sciences, Northern Illinois University, DeKalb, IL 60115 (; ; )
- Current address: Entomology Department, Monsanto, 8350 Minnegans Rd., Waterman, IL 60556
| | - B H King
- Department of Biological Sciences, Northern Illinois University, DeKalb, IL 60115 (; ; )
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