Juvenile-juvenile social signalling: A case for precocial sexual selection in the collared lizard, Crotaphytus collaris (Squamata: Crotaphytidae)?

Abstract

Sexual selection is widespread in animals, but quite naturally studied in adults. Juvenile males in most animals are not differentiated from females and coloration is usually drab. However, there is no reason to suspect that sexual differences cannot develop before puberty, influence social interactions, and then have fitness pay-offs later in life. Juvenile collared lizards (Crotaphytus collaris (Say, 1822)) show marked dichromatism: males develop bright dorsolateral orange bars whereas females do not. These juvenile orange bars (JOB) disappear at sexual maturity, when males develop different colour traits maintained by sexual selection. We conducted field experiments with juvenile males on their developing territories in which we utilized staged intruders of juvenile males (with JOB) and juvenile females (lacking JOB) and also juvenile male intruders whose JOB were manipulated. Residents reacted significantly more aggressively toward males vs. females, and also toward males whose JOB were emphasized with paint than those whose JOB were masked by paint. These JOB are used in signalling among juveniles and we suggest the social relations established then are retained until sexual maturation the next spring (after the JOB are lost) to benefit males that previously displayed strong JOB by increased matings in the spring as sexually mature yearlings as per a phenomenon we call precocial sexual selection.