ABSTRACT
I. Introduction................................................................................. 257 II. Effects of Early Factors on Neural Metabolism
and Behavior ............................................................................... 259 A. Leopard Geckos ..................................................................... 259 B. Mongolian Gerbils ................................................................. 261
III. Effects of Late Factors on Neural Metabolism and Behavior ............................................................................... 261 A. Rats ......................................................................................... 262 B. Leopard Geckos ..................................................................... 264
IV. Interactions between Early and Late Factors ........................... 266 V. Acknowledgments ...................................................................... 268
References ............................................................................................. 268
Sexual differentiation can be defined as the process by which the capacity to display homotypical or heterotypical phenotypes is altered. For example, the brain of a male rodent is both masculinized and defeminized during the process of sexual differentiation, and the end product is an individual who is predisposed to behave like a male. Pioneering studies have highlighted both hormonal and nonhormonal factors early in life that can affect the differentiation of the organism, and there has been a wealth of studies characterizing these neural effects. Intrasexual differences in behavior are also influenced by factors early in life, but the neural bases of these individual
differences are relatively poorly understood. Historically, the emphasis has been on critical periods during development; in other words, a restricted time period of biological plasticity that molds the differentiation of the organism. However, there has been an increasing awareness of the plasticity of the adult brain and a deeper understanding of immediate factors that can influence both the brain and behavior of adult individuals. For example, photoperiod and temperature are two abiotic factors that profoundly affect the capacity to display sexual behaviors, while the social environment and food abundance are two biotic factors that affect the display of sociosexual behaviors.
