EFFECTS OF AGE AND SOCIOSEXUAL EXPERIENCE ON THE MORPHOLOGY AND METABOLIC CAPACITY OF BRAIN NUCLEI IN THE LEOPARD GECKO (EUBLEPHARIS-MACULARIUS), A LIZARD WITH TEMPERATURE-DEPENDENT SEX DETERMINATION

In vertebrates having sex chromosomes, sexual behavior is influenced b y steroid hormones throughout life as well as by the cumulative experi ences of the individual. Because males and females differ genetically as well as hormonally, it would be valuable to distinguish the contrib ution of sex-specific genes from hormones. In addition, since animals age as they gain sociosexual experience, but do not necessarily gain s ociosexual experience as they age, it is important to separate the eff ects of age from those attributable to experience. The leopard gecko i s a lizard lacking sex chromosomes, depending instead upon the tempera ture during incubation to establish gonadal sex, This effectively remo ves sex-specific genetic influences from any study of sexual different iation. Eggs were incubated at either 26 degrees C or 32.5 degrees C, temperatures that produce only female hatchlings or a male-biased sex ratio, respectively. By raising geckoes in isolation and then housing some animals together in breeding groups at different ages after they attained sexual maturity, it was possible to assess the relative effec ts of age and sociosexual experience on the volume and metabolic capac ity of limbic and non-limbic brain areas. In general, males showed mor e changes compared to females. For example, there was a decrease with age in the volume of the preoptic area and the ventromedial hypothalam us in males, but not in females. Both age and sociosexual experience i nfluenced cytochrome oxidase activity in these and other brain areas. Experienced animals had greater metabolic capacity in nuclei functiona lly associated with sociosexual behavior in Lizards and other vertebra tes. For example, cytochrome oxidase activity was higher in the anteri or hypothalamus of males, in the ventromedial hypothalamus of both mal es and females from the male-biased incubation temperature, and in the preoptic area of females from both incubation temperatures. These dif ferences were not paralleled by differences in circulating levels of s ex hormones; only plasma androgen levels differed as a function of exp erience in males. These data suggest that the volume and metabolic cap acity of specific brain regions change as animals age and gain sociose xual experience, but the nature and degree of change depend upon prena tal events.