Relationships among reproductive morphology, behavior, and testosterone in a natural population of green anole lizards.

Laboratory studies of reproductive systems have long supported the idea that neural and/or muscular structures used frequently are often enhanced in size. However, field studies integrating behavioral, morphological, and hormonal data are needed to better understand relationships in natural environments. We examined a natural population of green anole lizards (Anolis carolinensis) to determine whether variation in reproductive morphology both within and between the sexes paralleled differences in courtship and copulatory behaviors and circulating testosterone levels. Display rate in males was positively correlated with the sizes of the cartilage supporting the dewlap (a throat fan used in courtship and aggression) and renal sex segments (portions of the kidney that function similarly to the mammalian prostate), but correlated negatively with seminiferous tubule size. Plasma testosterone in males was negatively correlated with display behavior and was not correlated with any measures of morphology. Females, which display rarely, exhibited no relationships between morphology and frequency of behavior. Comparisons between the sexes show that males have consistently larger courtship and copulation morphologies than females, even when accounting for sex differences in body size. The results not only support the idea of relationships between increased function and enhanced structures, but also show the complexity of mechanistic interactions associated with reproductive behavior in wild animals.