Female choice and pre-existing bias: visual cues during courtship in two Schizocosa wolf spiders (Araneae: Lycosidae)

摘要

Male wolf spiders, Schizocosa ocreata, possess tufts of bristles on the forelegs, which are used in visual courtship displays, but males of a closely related species, S. rovneri, lack tufted forelegs. In studies with live males, female S. ocreata showed receptivity more often to males with larger tufts than to males with smaller or shaved tufts. Male body size and/or shaving of tufts may affect male courtship behaviour, however, which could influence female receptivity. Manipulated video images of the same courting male were used to control for male behaviour and to test the hypothesis that these tufts influence female choice. Video images of S. ocreata, and images of S. rovneri males (control: without tufts; experimental: with tufts added) were shown to females of both species. Female S. ocreata showed lowered receptivity to a video of a male with tufts removed and equal receptivity to a video of a male with enhanced tufts compared to a control video of a conspecific male with typical tufts. Responses of female S. ocreata to heterospecific video male S. rovneri were significantly lower than to conspecifics. In contrast, female S. rovneri are more receptive to video images of conspecific males with tufts added and heterospecific male S. ocreata than to control images. Phylogenetic analyses suggest that tufts are apomorphic, and that S. rovneri is more basal within the clade than S. ocreata. Since female S. rovneri respond receptively to both conspecific and heterospecific males with tufts and/or active leg waving displays, these results may provide evidence of pre-existing bias and/or sexual selection for a novel trait.