Tracing the Evolution of Brain and Behavior Using Two Related Species of Whiptail Lizards: Cnemidophorus uniparens and Cnemidophorus inornatus

Coevolution of Genome Architecture and Social Behavior

Although social behavior can have a strong genetic component, it can also result in selection on genome structure and function, thereby influencing the evolution of the genome itself. Here we explore the bidirectional links between social behavior and genome architecture by considering variation in social and/or mating behavior among populations (social polymorphisms) and across closely related species. We propose that social behavior can influence genome architecture via associated demographic changes due to social living. We establish guidelines to exploit emerging whole-genome sequences using analytical approaches that examine genome structure and function at different levels (regulatory vs structural variation) from the perspective of both molecular biology and population genetics in an ecological context.

Species Diversity Matters in Biological Research

Species diversity in experimental neuroscience research provides a vital resource. Addressing contemporary questions using nontraditional model systems (i.e., studies of species other than rats or mice) have regularly led to serendipitous breakthroughs in this discipline. The “comparative” approach to neuroscience and neuroendocrinology harnesses the diversity of organisms—and their nervous systems—that have been refined and differentiated over evolutionary timescales. Here, we review some recent examples of unexpected and impactful outcomes resulting from research on nontraditional study species. This work shows that maintaining broad diversity in study species will continue to provide the best path forward for extraordinary advances and insights into the neural mechanisms of behavior.

Neuroendocrine disruption of organizational and activational hormone programming in poikilothermic vertebrates

In vertebrates, sexual differentiation of the reproductive system and brain is tightly orchestrated by organizational and activational effects of endogenous hormones. In mammals and birds, the organizational period is typified by a surge of sex hormones during differentiation of specific neural circuits; whereas activational effects are dependent upon later increases in these same hormones at sexual maturation. Depending on the reproductive organ or brain region, initial programming events may be modulated by androgens or require conversion of androgens to estrogens. The prevailing notion based upon findings in mammalian models is that male brain is sculpted to undergo masculinization and defeminization. In absence of these responses, the female brain develops. While timing of organizational and activational events vary across taxa, there are shared features. Further, exposure of different animal models to environmental chemicals such as xenoestrogens such as bisphenol A-BPA and ethinylestradiol-EE2, gestagens, and thyroid hormone disruptors, broadly classified as neuroendocrine disrupting chemicals (NED), during these critical periods may result in similar alterations in brain structure, function, and consequently, behaviors. Organizational effects of neuroendocrine systems in mammals and birds appear to be permanent, whereas teleost fish neuroendocrine systems exhibit plasticity. While there are fewer NED studies in amphibians and reptiles, data suggest that NED disrupt normal organizational-activational effects of endogenous hormones, although it remains to be determined if these disturbances are reversible. The aim of this review is to examine how various environmental chemicals may interrupt normal organizational and activational events in poikilothermic vertebrates. By altering such processes, these chemicals may affect reproductive health of an animal and result in compromised populations and ecosystem-level effects.

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.

Gene expression polymorphism inDrosophilapopulations

Although changes in gene expression have long been recognized as critical to evolutionary processes, the extent of natural polymorphism in gene expression has yet to be assessed, thus opening a new area of active research. We present microarray and quantitative real-time polymerase chain reaction (RT-PCR) data from Cosmopolitan and Zimbabwe morphs of Drosophila melanogaster. These morphs provide a useful model for investigations into the incipient stages of speciation because Zimbabwe females tend to preferentially mate with their own males and discriminate against Cosmopolitan males, while Cosmopolitan females mate indiscriminately. We analysed expression profiles from heads of mated and nonmated females and identified 45 candidate genes whose expression levels were associated with the behavioural morphs and were modified by mating. Genes with altered transcription levels were randomly distributed across the genome and fell into diverse categories of biological activities. Several candidate genes, such as desaturase2 and Odorant receptor 63a, were additionally subjected to quantitative RT-PCR analysis. Notably, desaturase2, which has been invoked to play a role in sexual isolation between Cosmopolitan and Zimbabwe D. melanogaster/races/strains and predicted to be translational-inactive in Cosmopolitan due to a major deletion, was found to be up-regulated in Zimbabwe and down-regulated, but still expressed, in Cosmopolitan.

Evolutionary insights into the regulation of courtship behavior in male amphibians and reptiles

Comparative studies of species differences and similarities in the regulation of courtship behavior afford an understanding of evolutionary pressures and constraints shaping reproductive processes and the relative contributions of hormonal, genetic, and ecological factors. Here, we review species differences and similarities in the control of courtship and copulatory behaviors in male amphibians and reptiles, focusing on the role of sex steroid hormones, the neurohormone arginine vasotocin (AVT), and catecholamines. We discuss species differences in the sensory modalities used during courtship and in the neural correlates of these differences, as well as the value of particular model systems for neural evolution studies with regard to reproductive processes. For example, in some genera of amphibians (e.g., Ambystoma) and reptiles (e.g., Cnemidophorus), interspecific hybridizations occur, making it possible to compare the ancestral with the descendant species, and these systems provide a window into the process of behavioral and neural evolution as well as the effect of genome size. Though our understanding of the hormonal and neural correlates of mating behavior in a variety of amphibian and reptilian species has advanced substantially, more studies that manipulate hormone or neurotransmitter systems are required to assess the functions of these systems.

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.

From wild wolf to domestic dog: gene expression changes in the brain

Despite the relatively recent divergence time between domestic dogs (Canis familiaris) and gray wolves (Canis lupus), the two species show remarkable behavioral differences. Since dogs and wolves are nearly identical at the level of DNA sequence, we hypothesize that the two species may differ in patterns of gene expression. We compare gene expression patterns in dogs, wolves and a close relative, the coyote (Canis latrans), in three parts of the brain: hypothalamus, amygdala and frontal cortex, with microarray technology. Additionally, we identify genes with region-specific expression patterns in all three species. Among the wild canids, the hypothalamus has a highly conserved expression profile. This contrasts with a marked divergence in domestic dogs. Real-time PCR experiments confirm the altered expression of two neuropeptides, CALCB and NPY. Our results suggest that strong selection on dogs for behavior during domestication may have resulted in modifications of mRNA expression patterns in a few hypothalamic genes with multiple functions. This study indicates that rapid changes in brain gene expression may not be exclusive to the development of human brains. Instead, they may provide a common mechanism for rapid adaptive changes during speciation, particularly in cases that present strong selective pressures on behavioral characters.