Current research on the behavioral neuroendocrinology of reptiles Juli Wade T Departments of Psychology and Zoology and Neuroscience Program, Michigan State University, Neuroscience Program, 108 Giltner Hall, East Lansing, MI 48824-1101, USA Received 31 January 2005; revised 21 February 2005; accepted 24 February 2005 Available online 7 April 2005 Abstract Selected reptilian species have been the targets of investigations in behavioral neuroendocrinology for many years. Reptiles offer a particularly powerful set of traits that facilitate comparisons at multiple levels, including those within and between individuals of a particular species, between different environmental and social contexts, as well as across species. These types of studies, particularly as they are considered within the framework of results from other vertebrates, will enhance our understanding of the genetic and hormonal influences regulating changes in the structure and function of the nervous system. Work on the hormonal and environmental factors influencing courtship and copulatory behaviors in green anoles, including the development and maintenance of the neuromuscular structures critical for their display, is highlighted. Some very recent work on other model systems is also discussed to provide a context for suggested future research directions. D 2005 Elsevier Inc. All rights reserved. Keywords: Sexual differentiation; Green anole; Leopard gecko; Neural plasticity; Reproductive behavior; Sexual dimorphism Background The neural and hormonal regulation of social inter- actions were investigated in reptiles long before the emergence of ‘‘social neuroscience’’ (Insel and Fernald, 2004). The rich history of this research is described elsewhere in this volume (Crews and Moore, 2005), and it has spanned major fields within behavioral neuro- endocrinology, including stress, aggression, and repro- duction. Godwin and Crews (2002) provide an excellent, recent overview of this type of work across reptilian species, so after a brief general introduction, this report takes a more narrow approach. It focuses on current research on the neural and muscular systems controlling courtship and copulation, which have been investigated in only two reptilian species, and only in the green anole lizard (Anolis carolinensis ) in detail. At the end of the review of this line of research, I broaden the discussion to include some particularly recent work on the neuro- endocrinology of other reptilian species and another social behavior in this lizard, to provide some context for potential directions for future comparative research. Courtship and copulatory systems have been used to elucidate mechanisms involved in sexual differentiation and adult plasticity of the structure and function of the nervous system (e.g., see Cooke et al., 1998). In many cases, gonadal hormones play prominent roles in both the early, permanent organization of and more transient adult changes in morphology and sexual behavior. However, increasing evidence suggests that direct genetic mecha- nisms, likely stemming from the sex chromosomes, may have important influences as well (Arnold, 2002). Crews and Moore (2005) emphasize the benefit of comparing neural and endocrine mechanisms across naturally occur- ring variability in life histories; reptiles offer a particularly rich set of opportunities, both across species and between different types of individuals within species. Value also exists in taking these sorts of comparisons one step further, by investigating multiple levels of the nervous system in the same types of individuals. Elegant studies have 0018-506X/$ - see front matter D 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.yhbeh.2005.02.006 T Fax: +1 517 432 2744. E-mail address: wadej@msu.edu. Hormones and Behavior 48 (2005) 451 – 460 www.elsevier.com/locate/yhbeh