Fox Lab Behavioral and Evolutionary Ecology / Herpetology

Differences promoted by sexual selection, e.g., sexual dimorphism and sex differences in behavior, arise usually at the time individuals become sexually mature. However, there is no logical reason to suspect that sex differences in morphology, color, or behavior cannot develop before puberty, influence social interactions before puberty, and then have adaptive significance later in life, realized as increased reproductive success, i.e., precocial sexual selection. One such apparent case is seen in the collared lizard (Crotaphytus collaris), in which hatchling males develop individually variable conspicuous lateral orange bars (hatchling orange bars, HOB) in the fall months before sexual maturation and gradually lose them as they gain reproductive maturity the next spring. Adults are sexually dimorphic and dichromatic, but in other traits. Hatchling males establishing territories use the HOB to distinguish the sexes and then treat males more aggressively than females. The aggression toward other hatchling males serves to repel them spatially such that competition with them as sexual rivals for females the next spring is reduced; and the non-aggressive treatment of females initiates social bonding that extends to the next spring and beyond and gives that male a subsequent mating advantage. We are studying this apparent precocial sexual selection in C. collaris over multiple breeding seasons. We determine if early pair bonding with hatchling females and aggression toward hatchling male rivals occur in sexually immature male hatchlings. We compare HOB, androgens, aggression, space use, and consorting behavior of male subjects in the field when they are hatchlings and subsequently appraise their space use, consorting behavior, and genetic fitness when they are yearlings and adults. We employ DNA analysis to quantify fitness and determine if hatchling males with more developed HOB ultimately sire more offspring than those with less developed HOB, and do so with the females with whom they interacted as hatchlings. Finally, we assess the cost of HOB through comparison of survivorship, growth, feeding rates, and immune response of males with varying development of HOB, attack frequencies of clay lizard models with and without HOB, and perceived conspicuousness to predators of hatchlings with and without HOB in their natural spectral background.