What makes the cnemidophorus lizards so unique

Journal of Thermal Biology Body temperature of field active Amazonian Savana lizards. Journal of Herpetology 27 1 : The correlates of forraging mode in a community of Brazilian lizards.

Herpetologica 41 3 : Relative effects of size, season and species on the diets of some Amazonian savanna lizards. Journal of Herpetology 27 4 : Revista de Etologia 2: Reproductive ecology of the parthenogenetic whiptail lizard Cnemidophorus nativo in a Brazilian restinga habitat. Journal of Herpetology 38 2 : Brazilian Journal of Biology 66 3 : Feeding habits of the endemic tropical parthenogenetic lizard Cnemidophorus nativo Teiidae in a restinga area of the northeastren Brazil.

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Biology of the Reptilia. New York, Academic Press, vol. Ecology and Natural History of Desert Lizards. New Jersey, Princeton University Press, p. Phylogenetic relationships of whiptail lizards of the genus Cnemidophorus Squamata: Teiidae : a test of monophyly, reevaluation of karyotypic evolution, and review of hybrid origins.

American Museum Novitates Seasonal shift in the diet: the seasonality in food resouces affecting the diet of Liolaemus lutzae Tropiduridae. Sexual dimorphism in the lizard Liolaemus lutzae of southeastern Brazil, p. In: J. Ecologia de Restingas e Lagoas Costeiras. Oecologia Brasiliensis 13 1 : Thermal ecology of five sympatric species of Cnemidophorus Sauria: Teiidae.

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Pseudosexual behavior in parthenogenetic whiptails is related to the ovarian cycle. Female-like receptive behavior is limited to the preovulatory stage of the follicular cycle, when estradiol levels are high; but the expression of male-like mounting behavior occurs most frequently during the postovulatory stages of the cycle, when progesterone levels are highest Moore et al.

The transition from female- to male-like pseudosexual behavior occurs at ovulation, when there is a parallel transition from estradiol dominance to progesterone dominance. The time of this occurrence suggests that changes in hormone levels could underlie the changes in behavior. Exogenous administration of progesterone to ovariectomized animals elicits pseudosexual behavior, whereas estradiol elicits female-typical receptive behavior Grassman and Crews Thus it appears that the postovulatory surge in progesterone has been exploited as the hormonal cue, which triggers male-like pseudosexual behaviors in the parthenogen.

The display of pseudosexual behavior in the parthenogen appears to be functionally significant. Whereas individuals housed in isolation ovulate eventually, those housed with other reproductively active individuals ovulate sooner.

Likewise, intact parthenogens housed with a hormonally stimulated individual displaying only male-like behaviors ovulate more frequently and produce an average of 2. This disparity is analogous to the fact that females of the sexual species housed in isolation ovulate considerably less frequently than those housed with sexually active males Crews et al. Thus the display of male-like pseudosexual behavior in the parthenogen is evolutionarily relevant.

Whereas progesterone levels are uniformly low in C. For example, sexual behavior in castrated males can be reinstated with androgen and, in a subset of males, with progesterone; such individuals are referred to as progesterone-sensitive males Lindzey and Crews , , These individual differences in progesterone sensitivity appear to be consistent across repeated administrations of progesterone Lindzey and Crews ; J. Sakata and D. Crews, unpublished data and are correlated with individual differences in androgen sensitivity Lindzey and Crews The decline of sexual behavior late in the reproductive season can also be delayed with progesterone administration Lindzey and Crews With regard to the evolution of pseudosexual behavior in the parthenogen, it is possible that a progesterone-sensitive male was involved in the hybridization events leading to the formation of C.

Thus the sensitivity of male sexual behavior to progesterone may have been co-opted in the parthenogen, enabling progesterone to become the primary hormonal trigger inducing male-like pseudosexual behavior Crews In light of these findings, we tested the generality of the facilitatory role of progesterone across other species such as rats and mice. Whereas previous studies highlighted the inhibitory role of a supraphysiological dose of progesterone e. Moreover, work on progesterone receptor knockout mice indicates that progesterone stimulation is important not only in the display of mounting behavior while intact but also in experience-dependent plasticity Phelps et al.

The latter finding is interesting because preliminary studies have found differences in experience-dependent plasticity between progesterone-sensitive and -insensitive male C. Crews, unpublished data. Thus studies originally performed on a parthenogenetic species eventually led to a re-evaluation and new understanding of the role of progesterone in the display of copulatory behavior in male vertebrates. Although both testosterone and progesterone can facilitate the display of male sexual behavior in a number of species, their relative potencies have not been compared.

Whiptail lizards are a useful model in which to study the effects of testosterone and progesterone because both hormones elicit the full repertoire of courtship behavior in both C. We recently assessed differences in the capacity of exogenous testosterone and progesterone to induce male-typical courtship behavior in gonadectomized whiptail lizards Sakata et al. In both species, individuals implanted with testosterone showed more frequent courtship behavior than those implanted with progesterone or cholesterol.

We also examined whether testosterone and progesterone differentially affected the retention of courtship behavior after implant removal. We administered behavior tests to the animals after they had received hormone implants and until all individuals were displaying similar levels of behavior. We then removed the implants and administered additional behavior tests: 10 to C. In both species, individuals previously implanted with testosterone retained the expression of courtship behavior longer after implant removal than those previously given progesterone.

Therefore the hormone that was more effective at activating courtship behavior was also more effective at maintaining courtship behavior after implant removal. Although both hormones have the capacity to elicit identical sexual behaviors in both species, testosterone has a greater and more lasting effect on courtship behavior and possibly on the neural circuits underlying courtship behavior. Studies of sexual behavior in mammals have traditionally focused on nuclei within the preoptic area and hypothalamus.

We know that across species, the medial preoptic area is critical to the regulation of male sexual behavior, and the ventromedial hypothalamus VMH 1 is involved in the display of female receptive behaviors. Studies on whiptail lizards have indicated that these brain areas are also involved in the regulation of sexual behavior in C. Similarly, implantation of estradiol into the VMH increases the display of receptive behaviors in C. There is considerable evolutionary conservation in the distribution of steroid hormone receptors across species.

Using polymerase chain reaction, we cloned fragments of the progesterone receptor PR 1 , androgen receptor AR 1 , and estrogen receptor ER 1 genes of whiptail lizards; we used these clones to synthesize probes for use in in situ hybridization assays Young et al.

The neuroanatomical distribution of these receptors in the brains of parthenogenetic and sexual whiptail lizards are similar to each other and, moreover, to the distribution in other species, with receptor-containing cells concentrated in septal, amygdaloid, cortical, preoptic, and hypothalamic nuclei Young et al.

Yet both species and sex differences exist in the regulation and amount of receptor expression. Open circles indicate low levels of expression; closed circles indicate high levels of expression.

Cloning and in situ hybridization analysis of estrogen receptor, progesterone receptor, and androgen receptor expression in the brain of whiptail lizards Cnemidophorus uniparens and C. J Comp Neurol As in females of other species, circulating concentrations of gonadal steroid hormones and reproductive behavior vary as a function of ovarian state in whiptail lizards. Although the pattern of circulation of steroid hormones is similar between C.

Yet the display of receptive behaviors does not differ between the species Young et al. Consistent with the difference in circulating concentrations of estradiol is the finding that receptive behavior is elicited at lower estradiol concentrations in ovariectomized parthenogens than in ovariectomized female C.

Because steroid hormone concentration in the periphery are governed by negative feedback, we postulate that the lower estradiol concentrations in the parthenogen could be due to heightened sensitivity to estradiol and increased negative feedback. In many brain areas, the parthenogen expresses higher levels of hormone receptor mRNA, an effect that is consistent with species differences in ploidy Neaves and Gerald ; but the magnitude of the difference fluctuates with reproductive state, indicating that there might be additional differences between the species governing the expression of steroid hormone receptors.

In the VMH, the level of ER mRNA in the parthenogen is lower in postovulatory individuals than in vitellogenic individuals, but this difference does not exist in females of the sexual species Young et al.

Species differences in neural response to exogenous estradiol administration 0. For example, estradiol increases the abundance of ER mRNA in the VMH in females of the sexual species and the parthenogen, but the magnitude of the increase is greater in the parthenogen Godwin and Crews ; Young et al.

Because of the evolutionarily conserved role of the VMH in the expression of female-like receptive behaviors, this species difference in ER mRNA expression may account for the increased sensitivity to estradiol in the parthenogen.

This finding suggests a possible proximate mechanism underlying species differences in behavior. In other words, estradiol during vitellogenesis increases PR expression in the PvPOA of the parthenogen, thereby sensitizing them to the postovulatory progesterone surge and potentially priming the display of male-like pseudosexual behavior.

Species differences in the induction of progesterone receptor mRNA in the periventricular preoptic area. Adapted from Godwin J, Crews D. Hormonal regulation of progesterone receptor mRNA expression in the hypothalamus of whiptail lizards: Regional and species differences. J Neurobiol Yet testosterone-treated adult parthenogens that display male-like mounting behavior do not show masculinization of the volumes of hypothalamic or preoptic nuclei Wade et al.

One possibility is that sex-determining genes differentially modulate sensitivity to androgens. Adapted with data from Crews et al. A complication in testing whether differences in sex-determining genes or differences in the secretion of gonadal steroids are paramount in the generation of sexual dimorphisms is that in most species, the sexes differ both genetically and hormonally.

For example, male mammals have both X and Y chromosomes, and female mammals have only X chromosomes. As a consequence of the expression of genes on the Y chromosome, males develop male-like gonadal morphology as well as masculine patterns of hormone secretion.

Thus the effects of sex-linked genes are intertwined with the effects of sex-linked patterns of hormone secretion. An ideal system for the study of sexual dimorphisms would enable the dissociation of genetic and hormonal factors. Parthenogenetic lizards offer a tremendous opportunity to study this question. Estrogen is necessary during development in C. Treatment of C. Thus because created males have a female genotype, it is possible that the capacity for androgens to alter neuromorphology and engender sex differences is linked to male-determining genes.

This difference in receptor regulation is paralleled by behavioral differences in response to estradiol because only females show receptive behavior after estradiol administration. Estradiol treatment also increases ER mRNA expression in the dorsal hypothalamus in females but not in males. Whether similar differences in regulation exist between created males and normal parthenogens has yet to be investigated.

Studies have revealed that catecholamines modulate the display of social and sexual behaviors in mammals and birds Absil et al. In addition, there is considerable homology in the expression of catecholamine synthesizing enzymes across taxa, including mammals, birds, reptiles, amphibians, and fish Smeets ; Smeets and Gonzalez Nevertheless, whether the similar catecholamine populations found in reptiles underlie functions that are similar in birds and mammals is relatively unknown.

To determine whether dopamine modulates the display of courtship behavior in lizards, we tested a range of doses of a specific dopamine D1 receptor agonist on the display of mounting behavior in gonadectomized C.

In both species, the D1 agonist increased the proportion of individuals displaying mounting behavior, and it decreased the latency for individuals to display mounting behavior. Interestingly, the dose that was most effective differed between the species. For example, it is plausible that the parthenogen has elevated levels of D1 receptor expression because it is triploid.

The Cnemidophorus system makes it possible to study the evolution of behavioral and neural phenotypes. Our studies have revealed that a postovulatory surge in progesterone may have been co-opted as a hormonal trigger for the display of male-like pseudosexual behavior in the parthenogen. These studies have led to a reassessment of the role of progesterone in male sexual behavior in mammals. We have also uncovered species differences in the regulation of steroid hormone receptors, which may provide a molecular mechanism for the behavioral differences between the species.

Finally, the finding that dopamine increases the display of mounting behavior in both species indicates that similar distributions of dopamine in reptiles, birds, and mammals may underlie similar behavioral functions.

It will be interesting to determine the neural mechanisms underlying the behavioral differences between the species in sensitivity to dopamine and, in particular, whether the behavioral differences are correlated with species differences in the regulation of dopamine receptor expression.

Effects of apomorphine on sexual behavior in male quail. Pharmacol Biochem Behav 47 : 77 — Google Scholar. Differential effects of D1 and D2 receptor agonists and antagonists on appetitive and consummatory aspects of male sexual behavior in Japanese quail. Physiol Behav 62 : — Crews D. Google Preview. When desert grassland whiptail lizards' eggs are laid, they weigh about 0. Desert grassland whiptails are triploid, meaning that they have three sets of homologous chromosomes.

These lizards are parthenogenic, meaning that they develop from an unfertilized egg. They are genetic clones of the female that laid the egg.

Once hatched, the hatchling lizards grow at a rate of 0. Like all other lizards, they have indeterminate growth, meaning that they grow for the rest of their lives. These lizards are fully developed sexually after an average of seven months. Allen, ; Bateman, et al. Desert grassland whiptail lizards are parthenogenic, meaning that they are all females and they do not mate to reproduce.

Even though they do not mate sexually, they often display pseudocopulatory behavior. The female-like pseudocopulatory behavior consists of allowing dominance by another desert grassland whiptail, that is displaying male-like behavior. The male-like pseudocopulatory behavior consists of general aggression, biting, and mounting. Sometimes there is even an alignment of the cloacae as though mating will occur but it does not. They most often display female-like behavior while they are producing their clutches of eggs.

They most often display male-like behaviors before and after laying their eggs and before their next production of eggs. Crews and Fitzgerald, ; Crews and Moore, ; Crews, et al. The reproductive season of desert grassland whiptail lizards extends from the beginning of May through July. These lizards reach sexual maturity at the minimum size of 60 mm SVL during the first reproductive season after they hatch, which is on average seven months old.

These lizards are parthenogenic, meaning they develop in unfertilized eggs. They are also clones of their single parent, and so are siblings genetically.

Each sexually mature individual produces 2 to 3 clutches per year with 21 to 28 days between each clutch. Clutches range from 1 to 4 eggs with an average of 2. The amount of eggs per clutch correlates strongly with the size of the lizard. Females of SVL length smaller than 65 mm are reported to have an average of 2 eggs per clutch. Females with SVLs ranging 65 to 70 mm averaged 3 eggs per clutch. Females larger than 70 mm averaged 4 eggs per clutch.

Desert grassland whiptail eggs, freshly laid, are cream-colored, oval shaped, and on average 0. Eggs hatch after approximately months. When desert grassland whiptails hatch they weigh, on average, 0. Lizard hatchlings are immediately independent from their parent. These lizards are precocial, meaning they are well developed when hatched. There is no parental investment beyond the act of egg-laying. Allen, ; Congdon, et al. There is very limited information detailing lifespans of desert grassland whiptail lizards.

There is no information concerning the longevity of captive desert grassland whiptail lizards because they are not kept in captivity. These data are based on western whiptails Cnemidophorus tigris , and suggests a similar lifespan but does not confirm one. According to Carey and Judge , the longest known lifespan of a western whiptail in captivity is 7.

Carey and Judge, ; Turner, et al. Desert grassland whiptail lizards are not a very social species. Most of their time during the day is spent foraging for food and basking in sunlight. Most interactions between desert grassland whiptails are not aggressive. This lack of aggressive behavior compared to other lizard species is likely because they are all female and have no need to compete for mates or establish dominance in most settings.

Most interactions between lizards occur during their reproductive season. At nighttime, desert grassland whiptail lizards retreat into their burrows within their home ranges, until dawn when they come out and resume foraging. These lizards are active during overcast days, but activity ceases during rainfall.

According to Eifler and Eifler , desert grassland whiptails' median home ranges are square meters. These lizards are not territorial. Desert grassland whiptail lizards use their visual, tactile, and olfactory senses to perceive their environment. They have eyes to see their surroundings and they can use their limbs and bodies to feel their surroundings. Lizards hear their surroundings using an organ called the cochlea. Lizards have a Jacobson's organ, a specialized olfactory organ that allows them to use their tongues to smell their surroundings.

Using this organ, they perceive chemical signals that tell them when prey is near. Desert grassland whiptail lizards use several means of communication, even though they are not very social lizards. They sometimes use touch to communicate through mounting and biting. They also use pheromones to communicate their intentions to other lizards about mating and homestead range. Cooper, ; Crews and Fitzgerald, ; Ferguson, Desert grassland whiptail lizards are insectivores.

Eifler and Eifler found that their diets consisted of both fossorial and surface insects, A second study reported that these termites were arid land subterranean termites, Reticulitermes tibialis. About 6. When foraging for prey, desert grassland whiptails will use a series of movements and intermittent sessions of digging and searching. They also use their tongues to smell the surrounding area and locate prey. When predators are nearby, desert grassland whiptails search for prey far less often.

This is likely because digging attracts the attention of said predators. The known predators of desert grassland whiptail lizards are long-nosed leopard lizards Gambelia wislizenii , greater roadrunners Geococcyx californianus , burrowing owls Speotyto cunicularia , and loggerhead shrikes Lanius ludovicianus.

There is no difference in predators between juveniles and adults. These lizards have been observed to behave differently in the presence of a predator. When a predator is near, foraging lizards keep movement short and infrequent. This is likely in an effort not to attract the attention of predators.