A dual status-signalling system: a matter of redundancy or differing roles?

Abstract

Abstract. Some populations of tree lizards, Urosaurus ornatus, are polymorphic for throat (gular) coloration. In these populations, males with blue or green throats tend to dominate males with less blue/green (more orange) throats during short-term encounters. In other populations, where males are monomorphic with respect to throat coloration, males may signal 'high' (dominant) status by turning very dark dorsally. Month-long experiments conducted in semi-natural outdoor pens determined that males from a polymorphic population, which are rarely seen to darken in the wild, are capable of dorsal darkening. Also, these males signalled dominant status by dorsal darkening when throat coloration of all males in the group was the same. Consequently, a second set of month-long experiments tested the hypothesis that dorsal darkening is rarely seen in the field because the throat signal takes precedence over the dorsal signal when throat coloration differs among males. The results do not support this hypothesis. Furthermore, there was no correlation between male throat coloration and dominance status in these experiments. Thus, dorsal darkening is not merely a back-up signal when the throat colour of the contestant males is the same. It may serve, instead, as a long-distance dominance signal when population density is high.