Cnemidophorus Inornatus Research Articles

Corrigenda: Davis DR, LaDuc TJ (2018) Amphibians and reptiles of C. E. Miller Ranch and the Sierra Vieja, Chihuahuan Desert, Texas, USA. ZooKeys 735:97-130. https://doi.org/10.3897/zookeys.735.22200.

[This corrects the article DOI: 10.3897/zookeys.735.22200.].

The population genomics of rapid adaptation: disentangling signatures of selection and demography in white sands lizards.

Understanding the process of adaptation during rapid environmental change remains one of the central focal points of evolutionary biology. The recently formed White Sands system of southern New Mexico offers an outstanding example of rapid adaptation, with a variety of species having rapidly evolved blanched forms on the dunes that contrast with their close relatives in the surrounding dark soil habitat. In this study, we focus on two of the White Sands lizard species, Sceloporus cowlesi and Aspidoscelis inornata, for which previous research has linked mutations in the melanocortin-1 receptor gene (Mc1r) to blanched coloration. We sampled populations both on and off the dunes and used a custom sequence capture assay based on probed fosmid libraries to obtain >50 kb of sequence around Mc1r and hundreds of other random genomic locations. We then used model-based statistical inference methods to describe the demographic and adaptive history characterizing the colonization of White Sands. We identified a number of similarities between the two focal species, including strong evidence of selection in the blanched populations in the Mc1r region. We also found important differences between the species, suggesting different colonization times, different genetic architecture underlying the blanched phenotype and different ages of the beneficial alleles. Finally, the beneficial allele is dominant in S. cowlesi and recessive in A. inornata, allowing for a rare empirical test of theoretically expected patterns of selective sweeps under these differing models.

Neaves' Whiptail Lizard: The First Known Tetraploid Parthenogenetic Tetrapod (Reptilia: Squamata: Teiidae)

Abstract The first known tetraploid amniote that reproduces through parthenogenetic cloning by individual females is named and described. The species originated through hybridization between Aspidoscelis exsanguis (triploid parthenogen) × Aspidoscelis inornata (diploid bisexual or gonochoristic species) in the laboratory. We compared multivariate morphological variation between two lineages that arose from separate F1 hybrid zygotes in one clutch and among several generations in those lineages. The tetraploid species is also compared with its ancestral taxa, with two hybrids of A. exsanguis × A. inornata that were found in nature at two localities that are 100 km apart in southern New Mexico, and with three laboratory hybrid males. This will facilitate identification of field-caught tetraploids in the future.

Conservation and Management of Polytypic Species: The Little Striped Whiptail Complex (Aspidoscelis inornata) as a Case Study

Subspecies have most often been described qualitatively with small sample sizes as excerpted from geographic continua. They present a long-standing conflict with evolutionary and statistical principles as well as conservation planning that often relies upon a phylogenetic perspective. Herpetological subspecies have been recognized in the literature as exceeding numerical expectations and subsequent reevaluations during the last decade have decreased their numbers ∼50%, the exception being whiptail lizards (Aspidoscelis, family Teiidae). Here we used 842 base pairs of mitochondrial (mt) DNA to examine potential taxonomic and conservation boundaries among two putative species and four subspecies of the abundantly polytypic Aspidoscelis inornata (Little Striped Whiptail Complex, LSWC) of southwestern North America. Body coloration, but not mtDNA, distinguished two putative species inhabiting alkali deposits, whereas neither dataset could diagnose three paraphyletic subspecies. A trend to elevate putative subspecies following a more contemporary evaluation is premature for the LSWC: we suggest that two species (arizonae, pai) and three subspecies (gypsi, junipera, llanuras) lack molecular and morphological differentiation and thus should be rescinded in taxonomic rank. These uncertainties concerning the LSWC with regard to its distributions and relationships impinge upon conservation proposals that, for example, seek to list A. arizonae as ‘threatened’ under the Endangered Species Act.Frecuentemente las subespecies han sido descritas cualitativamente y con tamaños de muestra pequeños extraídos de un continum geográfico. Ellas representan un viejo conflicto con los principios evolutivos y estadísticos así como para desarrollar planes de conservación que frecuentemente dependen de una perspectiva filogenética. Las subespecies herpetológicas han sido reconocidas en la literatura como excediendo las expectativas numéricas y una reevaluación subsecuente durante la década pasada ha disminuido sus números en ∼50%, siendo la excepción los Huicos (Aspidoscelis, familia Teiidae). Aquí utilizamos 842 pares de ADN mitocondrial (mt) para examinar el potencial taxonómico y límites de conservación entre dos supuestas especies y cuatro subespecies de la abundante y politípica Aspidoscelis inornata (complejo del Huico Liso, CDHL) del suroeste de Norteamérica. El patrón de coloración, pero no el ADN mitocondrial, distingue a dos supuestas especies que habitan en los depósitos de álcali mientras que ningún conjunto de datos pudo diferenciar las tres subespecies parafiléticas. Elevar a estas supuestas subespecies siguiendo una evaluación más contemporánea es prematuro para CDHL: sugerimos que las dos especies (arizonae y pai) y las tres subespecies (gypsi, junipera, llanuras) carecen de diferenciación morfológica y molecular por lo que deben ser consideradas sin rango taxonómico. Esta incertidumbre con respecto a las CDHL en cuanto a sus relaciones y distribuciones impacta propuestas de conservación que, por ejemplo, buscan enlistar a A. arizonae como “amenazada” bajo la ley de especies en peligro de extinción.

Ecological release and directional change in White Sands lizard trophic ecomorphology

A species’ trophic ecomorphology can change drastically following the colonization of a new environment. Resource shifts may result in dietary change of colonists and therefore, the evolution of ecomorphological adaptations such as changes in bite force, head, and body size. To understand the drivers and dynamics of ecomorphological change after colonization we studied prey availability, diet, performance, and morphology in three lizard species (Aspidoscelis inornata, Holbrookia maculata, and Sceloporus cowlesi) in the ecologically distinct environment of White Sands, New Mexico. White Sands, which formed within the last 6,000 years, was most likely colonized by nearby “dark soils” populations. Therefore, for each species we compared White Sands individuals to conspecific inhabiting the surrounding Chihuahuan Desert habitat. The White Sands habitat had higher prey morphospecies richness, increased breadth of prey orders, and a higher percentage of hard-bodied prey than the dark soils habitat. Differences in prey availability in White Sands and dark soils habitats were reflected in lizard diets. Specifically, morphospecies richness and percentage of hard bodied prey were higher in the diet of White Sands lizards compared to dark soils lizards. These similarities in resource use across the three species in two habitats indicated parallel responses to a shared environment. Although some dietary shifts in the three species were predictable and reflected prey availability, differences in performance and morphology traits indicated different ecological responses in each species. In general, average prey hardness was higher in the two White Sands species that had stronger absolute bite force and larger absolute head size. While White Sands lizards generally also included a larger proportion of hard prey in their diets, had higher absolute bite-force, head size, and body size than dark soils lizards, the magnitude of these differences varied across species.

Extreme variant of the triploid parthenogenetic lizardAspidoscelis exsanguis(Squamata: Teiidae) from New Mexico

Abstract Parthenogenetic reproduction in several all-female species of whiptail lizards (genus Aspidoscelis) does not preclude the occasional production of extreme variants. An adult lizard with a unique combination of dorsal color pattern, scutellation, and meristic characters captured 20 August 2013 approximately 200 m east of the Rio Grande in Bosque Farms, Valencia County, New Mexico, was inferred to be an extreme variant of triploid, hybrid-derived Aspidoscelis exsanguis which was also observed near the point of capture. There was no basis for identifying the specimen as a tetraploid hybrid because morphology did not reflect that origin and no gonochoristic species (e.g., Aspidoscelis marmorata or Aspidoscelis inornata) was known to occur at the site. Morphological analyses also ruled out the possibility that it could be an extreme variant of diploid parthenogenetic Aspidoscelis neomexicana, which is syntopic with A. exsanguis in Bosque Farms.

Beyond black and white: divergent behaviour and performance in three rapidly evolving lizard species at White Sands

Determining which traits enable organisms to colonize and persist in new environments is key to understanding adaptation and ecological speciation. New environments can present novel selective pressures on colonists' morphology, behaviour, and performance, collectively referred to as ecomorphology. To investigate ecomorphological change during adaptation and incipient ecological speciation, we measured differences in morphology (body shape and size), behaviour (startle response), and performance (sprint speed) in three New Mexican lizard species: Holbrookia maculata, Sceloporus undulatus, and Aspidoscelis inornata. Each species is represented by dark morphs, cryptic on the brown adobe soils of the Chihuahuan Desert, and white morphs, cryptic on the gypsum substrate of White Sands. For each species, we then determined the effects of morphology and startle response on sprint speed on matched and mismatched substrate. For two of the three species, white morphs had larger body size and longer limbs. However, we found no statistical evidence that these morphological differences affected sprint speed. Colour morphs also exhibited different escape responses on the two substrates: in all species, dark morphs were less likely to immediately sprint from a simulated predator on white sand. As a result, escape response had a significant effect on sprint speed for two of the three species. Not surprisingly, all lizards sprinted faster on dark soil, which was probably due to the lizards' more immediate escape response and the higher compaction of dark soil. The relationship between escape response and sprint performance across the dark soil and white sand habitats suggests that behavioural differences may be an important component of adaptation and speciation in new environments. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111, 169–182.

Morphological Diagnosability ofAspidoscelis arizonae(Squamata: Teiidae) as an Indication of Evolutionary Divergence in theAspidoscelis inornataComplex

Lizards of the gonochoristic Aspidoscelis inornata (Little Striped Whiptail) complex are ubiquitous components of vertebrate faunas in diverse habitats in the southwestern United States and northern Mexico. One of these, Aspidoscelis arizonae ( = A. inornata arizonae, Arizona Striped Whiptail), is extant at only a few grassland areas in southeastern Arizona, but nonetheless played an important evolutionary role in the hybrid origins of seven obligatory parthenogenetic species. Although recognized as a distinct species by many, A. arizonae lacks a valid species description and only anecdotal data argue for its recognition. We were unable to separate it from geographically proximate A. inornata in southwestern New Mexico, using diagnostic morphological features (i.e., number of stripes, dark field coloration, sky blue ventral suffusion) previously used to delineate aspidoscelids. Furthermore, we evaluated additional diagnostic characters (i.e., body size plus ten meristic characters) in samples of A. arizon...

Androgens coordinate neurotransmitter‐related gene expression in male whiptail lizards

Sex steroid hormones coordinate neurotransmitter systems in the male brain to facilitate sexual behavior. Although neurotransmitter release in the male brain has been well documented, little is known about how androgens orchestrate changes in gene expression of neurotransmitter receptors. We used male whiptail lizards (Cnemidophorus inornatus) to investigate how androgens alter neurotransmitter-related gene expression in brain regions involved in social decision making. We focused on three neurotransmitter systems involved in male-typical sexual behavior, including the N-methyl-d-aspartate (NMDA) glutamate receptor, nitric oxide and dopamine receptors. Here, we show that in androgen-treated males, there are coordinated changes in neurotransmitter-related gene expression. In androgen-implanted castrates compared with blank-implanted castrates (control group), we found associated increases in neuronal nitric oxide synthase gene expression in the nucleus accumbens (NAcc), preoptic area and ventromedial hypothalamus, a decrease of NR1 gene expression (obligate subunit of NMDA receptors) in the medial amygdaloid area and NAcc and a decrease in D1 and D2 dopamine receptor gene expression in the NAcc. Our results support and expand the current model of androgen-mediated gene expression changes of neurotransmitter-related systems that facilitate sexual behavior in males. This also suggests that the proposed evolutionarily ancient reward system that reinforces sexual behavior in amniote vertebrates extends to reptiles.

Ecological release in White Sands lizards.

Ecological opportunity is any change that allows populations to escape selection from competition and predation. After encountering ecological opportunity, populations may experience ecological release: enlarged population size, broadened resource use, and/or increased morphological variation. We identified ecological opportunity and tested for ecological release in three lizard colonists of White Sands, New Mexico (Sceloporus undulatus, Holbrookia maculata, and Aspidoscelis inornata). First, we provide evidence for ecological opportunity by demonstrating reduced species richness and abundance of potential competitors and predators at White Sands relative to nearby dark soils habitats. Second, we characterize ecological release at White Sands by demonstrating density compensation in the three White Sands lizard species and expanded resource use in White Sands S. undulatus. Contrary to predictions from ecological release models, we observed directional trait change but not increased trait variation in S. undulatus. Our results suggest that ecological opportunity and ecological release can be identified in natural populations, especially those that have recently colonized isolated ecosystems.

Neuronal Nitric Oxide Synthase as a Substrate for the Evolution of Pseudosexual Behaviour in a Parthenogenetic Whiptail Lizard

The evolution of neuroendocrine mechanisms governing sex-typical behaviour is poorly understood. An outstanding animal model is the whiptail lizard (Cnemidophorus) because both the ancestral and descendent species still exist. The ancestral little striped whiptail, Cnemidophorus inornatus, consists of males and females, which exhibit sex-specific mating behaviours. The descendent desert grassland whiptail, Cnemidophorus uniparens, consists only of females that alternately exhibit both female-like and male-like pseudosexual behaviour. Castrated male C. inornatus will mount a conspecific in response to exogenous androgen, although some are also sensitive to progesterone. This polymorphism in progesterone sensitivity in the ancestral species may have been involved in evolution of progesterone-mediated male-typical behaviour in the descendant unisexual lizards. We tested whether progesterone activates a typically androgenic signalling pathway by investigating hormonal regulation of neuronal nitric oxide synthase (nNOS) using in situ hybridisation and NADPH diaphorase histochemistry, a stain for nNOS protein. NADPH diaphorase is widely distributed throughout the brain of both species, although only in the periventricular nucleus of the preoptic area (pvPOA) are there differences between mounting and non-mounting individuals. The number of cells expressing nNOS mRNA and NADPH diaphorase is higher in the pvPOA of individuals that mount in response to progesterone or androgen. Furthermore, the nNOS promoter has both androgen and progesterone response elements, and NADPH diaphorase colocalises with the progesterone receptor in the pvPOA. These data suggest that a polymorphism in progesterone sensitivity in the sexual ancestor reflects a differential regulation of nNOS and may account for the male-typical behaviour in unisexual whiptail lizards.

Molecular characterization and brain distribution of the progesterone receptor in whiptail lizards

Progesterone and its nuclear receptor are critical in modulating reproductive physiology and behavior in female and male vertebrates. Whiptail lizards (genus Cnemidophorus) are an excellent model system in which to study the evolution of sexual behavior, as both the ancestral and descendent species exist. Male-typical sexual behavior is mediated by progesterone in both the ancestral species and the descendant all-female species, although the molecular characterization and distribution of the progesterone receptor protein throughout the reptilian brain is not well understood. To better understand the gene targets and ligand binding properties of the progesterone receptor in whiptails, we cloned the promoter and coding sequence of the progesterone receptor and analyzed the predicted protein structure. We next determined the distribution of the progesterone receptor protein and mRNA throughout the brain of Cnemidophorus inornatus and Cnemidophorus uniparens by immunohistochemistry and in situ hybridization. We found the progesterone receptor to be present in many brain regions known to regulate social behavior and processing of stimulus salience across many vertebrates, including the ventral tegmental area, amygdala, nucleus accumbens and several hypothalamic nuclei. Additionally, we quantified immunoreactive cells in the preoptic area and ventromedial hypothalamus in females of both species and males of the ancestral species. We found differences between both species and across ovarian states. Our results significantly extend our understanding of progesterone modulation in the reptilian brain and support the important role of the nuclear progesterone receptor in modulating sexual behavior in reptiles and across vertebrates.

Laboratory Hybridization Among North American Whiptail Lizards, IncludingAspidoscelis Inornata Arizonae × A. tigris marmorata(Squamata: Teiidae), Ancestors of Unisexual Clones in Nature

The natural origin of diploid parthenogenesis in whiptail lizards has been through interspecific hybridization. Genomes of the parthenogens indicate that they originated in one generation, as the lizards clone the F1 hybrid state. In addition, hybridization between diploid parthenogens and males of bisexual species has resulted in triploid parthenogenetic clones in nature. Consequently, the genus Aspidoscelis contains numerous gonochoristic (= bisexual) species and numerous unisexual species whose closest relatives are bisexual, and from whom they originated through instantaneous sympatric speciation and an abrupt and dramatic switch in reproductive biology.

Rapid divergence of social signal coloration across the White Sands ecotone for three lizard species under strong natural selection

Animal social signals are important for population recognition, communication, and mate choice. Although natural selection often favours cryptic coloration, sexual selection can underlie patterns of coloration that function in interor intrasexual communication. We compared social signal coloration of three lizard species across a substrate colour ecotone in New Mexico. These species exhibit cryptic blanched dorsal coloration on the gypsum dunes of White Sands and dark coloration on the surrounding desert soils. We detected corresponding population divergence in colour used for intra- (Aspidoscelis inornata, Sceloporus undulatus) or inter- (Holbrookia maculata) sexual signalling. Although the magnitude and direction of change in coloration varied among taxa, differences in hue and chroma accounted for more variation in social coloration than for dorsal coloration. The relative conspicuousness of social signals also varied across the ecotone. We discuss the possibilities that divergent signalling colours in this system are the result of: (1) stochastic processes, (2) direct selection, and/or (3) a correlated response to natural selection on dorsal coloration. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 243–255.

Preoptic neuronal nitric oxide synthase induction by testosterone is consistent with a role in gating male copulatory behavior

Copulatory behaviors are generally dependent on testicular androgens in male vertebrates, being eliminated by castration and reinstated by testosterone administration. It is postulated that a critical factor in this hormonal gating is up-regulation of neuronal nitric oxide synthase (nNOS) in the preoptic area, and consequent enhanced nitric oxide synthesis in response to stimuli associated with a receptive female. Previous studies have suggested that nNOS protein is more abundant in behaviorally relevant preoptic regions of testosterone-exposed animals than in hormone-deprived controls. This study sought to elucidate the molecular events underlying this apparent up-regulation by examining preoptic nNOS mRNA abundance at several time points following testosterone administration in a castration and replacement paradigm. Castrated male whiptails (Cnemidophorus inornatus) were implanted with testosterone, and at four time points over the subsequent 18 days their sexual behavior was tested. A rostral periventricular area previously implicated in hormonal gating of male-typical copulatory behavior was then excised by laser microdissection, and nNOS transcript abundance was assessed by quantitative PCR. As neither this technique nor nNOS mRNA measurements have previously been performed in this area of the brain, expression was concomitantly assayed on adjacent sections by in situ hybridization or NADPH diaphorase histochemistry. Results are consistent with transcriptional up-regulation of nNOS by testosterone and a central role for the enzyme in mediating hormonal gating of copulatory behavior.

Thirteen polymorphic microsatellite DNA loci from whiptails of the genus Aspidoscelis (Teiidae: Squamata) and related cnemidophorine lizards

We describe polymerase chain reaction primers and amplification conditions for 13 microsatellite DNA loci isolated from two bisexual species of whiptail lizards Aspidoscelis costata huico and Aspidoscelis inornata. Primers were tested on either 16 or 48 individuals of A.c. huico and/or 26 individuals of A. inornata. Ten of the 13 primers were also tested against a panel of 31 additional whiptail taxa. We detected three to nine alleles per locus in A.c. huico and four to 19 alleles per locus in A. inornata, with observed heterozygosity ranging from 0.60 to 0.87 and from 0.15 to 1.00, respectively. These primers will be an important resource for surveys of genetic variation in these lizards.

The Role of Phenotypic Plasticity in Color Variation of Tularosa Basin Lizards

An experimental approach was taken to evaluate the role of phenotypic plasticity in reptile coloration for three lizard species which exhibit dramatic variation in dorsal body darkness associated with different substrate environments. In southern New Mexico, blanched color morphs of Aspidoscelis inornata, Holbrookia maculata, and Sceloporus undulatus inhabit the gypsum dunes of White Sands, and a melanic color morph of S. undulatus is found on the Carrizozo lava flow. Temperature was manipulated to determine the extent of physiological (rapid) plasticity in coloration for all three species. Color change in response to short-term stimuli did not explain the variation among lizards from different habitats. Although lizards of all color morphs were slightly darker when colder, more melanic lizards displayed a diminished capacity for rapid color change. Common garden experiments were conducted to evaluate the potential for ontogenetic plasticity in coloration for H. maculata and S. undulatus. Offspring from mothers of different substrate environments were distinguishable by color despite identical developmental conditions. Hatchlings and adults exhibited similar coloration for H. maculata, but a developmental trajectory in coloration was observed in S. undulatus. Overall, environmental variation alone did not explain differences in dorsal coloration among lizards from distinctive habitats. Results from these experiments support the hypotheses that color morphology in Tularosa Basin lizards has a strong heritable component and that observed variation is likely adaptive.

Tyrosine hydroxylase expression is affected by sexual vigor and social environment in male Cnemidophorus inornatus.

Although the distribution of catecholamine-synthesizing cells has been described for a variety of taxa, less is known about the functional significance of particular populations in nonmammalian species, especially reptiles. To understand the role of these populations in the display of social behaviors in lizards, we studied the interactive effects of sexual vigor (sexually vigorous vs. sluggish) and social condition (housing in isolation vs. with females) on the number and somal areas of cells expressing tyrosine hydroxylase (TH), a rate-limiting enzyme in catecholamine synthesis, in male whiptail lizards, Cnemidophorus inornatus. We found that, regardless of social condition, sexually vigorous males had more TH-immunoreactive (TH-ir) cells in the dorsal hypothalamus (DH) relative to sluggish males. Sexually vigorous males also had more TH-ir cells in the substantia nigra pars compacta (SNpc), but this difference was significant only among males housed with females. Sexually vigorous males that had been housed with females had smaller TH-ir cells in the preoptic area (POA) than vigorous males housed in isolation. On the other hand, no significant differences were found in the anterior hypothalamus. These results highlight the regional heterogeneity in the plasticity of TH expression and suggest that, just as in other species, the DH, SNpc, and POA might be involved in the expression of social behaviors and in behavioral plasticity following social experiences in lizards.

ADAPTIVE REPTILE COLOR VARIATION AND THE EVOLUTION OF THE MC1R GENE

The wealth of information on the genetics of pigmentation and the clear fitness consequences of many pigmentation phenotypes provide an opportunity to study the molecular basis of an ecologically important trait. The melanocortin-1 receptor (Mc1r) is responsible for intraspecific color variation in mammals and birds. Here, we study the molecular evolution of Mc1r and investigate its role in adaptive intraspecific color differences in reptiles. We sequenced the complete Mc1r locus in seven phylogenetically diverse squamate species with melanic or blanched forms associated with different colored substrates or thermal environments. We found that patterns of amino acid substitution across different regions of the receptor are similar to the patterns seen in mammals, suggesting comparable levels of constraint and probably a conserved function for Mc1r in mammals and reptiles. We also found high levels of silent-site heterozygosity in all species, consistent with a high mutation rate or large long-term effective population size. Mc1r polymorphisms were strongly associated with color differences in Holbrookia maculata and Aspidoscelis inornata. In A. inornata, several observations suggest that Mc1r mutations may contribute to differences in color: (1) a strong association is observed between one Mc1r amino acid substitution and dorsal color; (2) no significant population structure was detected among individuals from these populations at the mitochondrial ND4 gene; (3) the distribution of allele frequencies at Mc1r deviates from neutral expectations; and (4) patterns of linkage disequilibrium at Mc1r are consistent with recent selection. This study provides comparative data on a nuclear gene in reptiles and highlights the utility of a candidate-gene approach for understanding the evolution of genes involved in vertebrate adaptation.

Differential effects of testosterone and progesterone on the activation and retention of courtship behavior in sexual and parthenogenetic whiptail lizards

Both testosterone (T) and progesterone (P) facilitate the expression of male-typical sexual behavior in a variety of animals, including rodents and lizards. In two species of whiptail lizards, Cnemidophorus inornatus and C. uniparens, both hormones elicit the full repertoire of courtship behavior. However, the relative efficacy of the two hormones is unknown. In Experiments 1 and 2 we assessed differences in capacity of exogenous T and P to induce male-typical courtship behavior in gonadectomized whiptail lizards. In both species, individuals implanted with T showed more frequent courtship behavior relative to those implanted with P or cholesterol. In Experiments 3 and 4 we examined whether T and P differentially affected the retention of courtship behavior following implant removal. In both species, individuals implanted with T showed more courtship behavior following implant removal than those previously given P. In these experiments, implants were removed at a time when individuals in both groups were behaviorally similar; therefore, the differences in behavior following implant removal were not due to differences in the amount of courtship experience. Taken together, the hormone that was more effective at activating courtship behavior was also more effective at maintaining courtship behavior following implant removal. In summary, though both T and P can elicit identical sexual behaviors in both whiptail species, T has a greater and more lasting effect on courtship behavior and possibly on the neural circuits underlying courtship behavior.