THE MATING SYSTEM OF A LIZARD

In polymorphic male painted dragon lizards (Ctenophorus pictus), red males win staged contests for females over yellow males, and yellow males have greater success in staged sperm competition trials than red males. This predicts different reproductive strategies in the wild with red males being more coercive or better mate guarders than yellow males. Yellow males would be expected to sire more offspring per copulation and have a greater proportion of offspring from clutches with mixed paternity. However, here we show using microsatellites that the frequency of mixed paternity in the wild is low (< 20% on average across years), that all morphs on average have the same number of offspring sired per year, and that mating system variation (polyandry vs. monandry) is strongly correlated with perch density on male territories. Furthermore, a logistic regression on male successful vs. unsuccessful mate acquisition showed that red males were under negative selection when they dominated the population, which suggests ongoing frequency dependent selection on male colouration.

Variation in mating system structure is common in lizards, especially the herbivorous iguanids (Stamps, 1977, 1983). Many male iguanids defend non-overlapping territories to control access to mates during a well defined mating season (reviewed by Dugan and Wiewandt, 1982; Stamps, 1977, 1983). Some anecdotal evidence suggests that males may also defend resources important to females rather than females per se. For example, male Galapagos land iguanas, Conolophus subcristatus, defend territories based partly on food resources, which they guard before the arrival of females (Werner, 1982). Territoriality in iguanids often breaks down when population densities become high, causing males of numerous species to exhibit dominance polygyny (Berry, 1974; Brattstrom, 1974; Dugan and Wiewandt, 1982; Evans, 1951; Prieto and Ryan, 1978; Ryan, 1982). One often-cited example of the association between density and mating system structure is ...