An experimental test of frequency-dependent selection on male mating strategy in the field

Abstract

We provide field-based experimental evidence for the frequency-dependent nature of the fitness of alternative mating strategies. We manipulated the frequency of genetically determined phenotypic strategies in six wild populations of the side-blotched lizard,Uta stansburiana. The within-population pattern of mating was assessed using nine microsatellite loci to assign paternity. Within populations of the side-blotched lizard exist three colour morphs (orange, blue and yellow) associated with male mating strategy. The frequency of these morphs has previously been found to oscillate over a 4- to 5-year period. We found, as predicted, that the common phenotype lost fitness to its antagonist. The mating patterns of all six populations adhered toa prioripredictions that were derived from previous empirical and theoretical observations on this system. We found that the frequency-dependent nature of male fitness could be accounted for by the composition of their competitors at a small local population level, driven by associations within a focal female's social neighbourhood.