Female secondary sexual coloration and sex recognition in the keeled earless lizard, Holbrookia propinqua

Abstract

Relationships between male social behaviour and female reproductive coloration in the iguanid lizard Holbrookia propinqua were examined by introduction of tethered non-resident lizards into the territories of adult males. Introduced lizards were plainly coloured females, females having bright reproductive coloration, adult males, plain females painted to resemble brightly coloured females, bright females painted to mimic plain females, and males painted with the bright yellow and orange secondary sexual coloration of females. Resident males courted all unpainted females, despite being aggressively rejected by the brightly coloured ones. They also courted all but two females in each of the painted groups. All unaltered non-resident males were challenged, attacked or subjected to other aggressive behaviour by residents, but all non-resident males painted to resemble bright females were courted. This differential treatment is highly significant. It clearly demonstrates that the bright female pigmentation functions in sex recognition, identifying a female to males. Other stimuli, especially pheromonal and behavioural cues, may contribute to sex recognition. Because sex recognition alone seems insufficient to account for the evolution of bright female coloration in H. propinqua and several other iguanids, several proposed additional functions are discussed.