Does Testosterone Facilitate Dynamic Relationships in Lizard Behavior, Morphology, and Physiology?

Testosterone regulates a wide variety of sexual and social behaviors, but the extent to which variation in muscle physiology facilitates these behaviors is not clear. We investigated the effects of testosterone on the morphology, physiology, and behavioral use of two muscles in green anole (Anolis carolinensis) and brown anole (A. sagrei) lizards. We examined the ceratohyoid (CH), the muscle that moves the throat fan called the dewlap in social display, and the retractor penis magnus (RPM), a muscle that moves the hemipenes during copulation. We assigned males of each species to one of three treatment groups: high T males were gonadectomied and received a testosterone implant; low T males were gonadectomied and received a blank implant; and control males underwent sham surgery, where their testes were left intact, and they received a blank implant. We found that testosterone regulates behaviors and the muscles underlying them in a complex manner. Before surgery, males assigned to these groups did not differ in morphology or behavior. Six weeks after hormone manipulation, high T males displayed their dewlaps more frequently than low T males, but testosterone did not affect dewlap or CH morphology. However, testosterone did increase the size of both the copulatory hemipenes and RPM. We also found that testosterone regulates dewlap and push-bob behaviors in a context-specific fashion (aggressive male-male contexts vs. sexual male-female contexts), and this pattern was similar across the green and brown anole. Overall, the role of testosterone in mechanisms underlying social behaviors appears to vary among muscles, yet remains consistent between species