Asymmetry in a visual signaling character and sexual selection in a wolf spider

Fluctuating asymmetry (FA) can indicate developmental instability in bilate rally symmetric organisms, and studies have shown that the degree of asymme try in male secondary sexual characters influences female mate choice in a number of taxa. In male Schizocosa ocreata wolf spiders, conspicuous tufts of bristles on the forelegs are a critical component of visual courtship si gnals, which appear to play a role in female mate choice. Previous studies have shown that females exhibit reduced receptivity to males with regenerat ive asymmetry, a consequence of leg loss and regeneration that causes males to be grossly asymmetric with respect to this important signaling characte r. We provide data on the occurrence of FA in the tufts of S. ocreata, and examine further the influence of asymmetry on female mate choice. The distr ibution of tuft area asymmetry values from a sample of field-collected male s was normal, with a mean value of zero, indicating true FA. For a subset o f males measured directly after field collection and prior to feeding, tuft asymmetry was significantly negatively correlated with measures of body si ze (body length) and condition (abdomen volume/cephalothorax width). Recept ivity responses of females to visual signals from live males of similar siz e varied with the degree of asymmetry in male tufts. Since FA covaries with male body size and condition, which may also influence behavioral vigor, w e used video image manipulation to alter the degree of asymmetry in tufts o f a courting male while holding size and condition constant. Asymmetry trea tments represented values within the range of natural FA variation as well as more extreme values characteristic of regenerative asymmetry. With the c onfounding effects of male size, condition, and behavior held constant, fem ale spiders exhibited reduced receptivity responses to all experimental asy mmetric video images relative to a control video stimulus. There were no di fferences in the frequency of female receptivity among the various asymmetr y treatments, suggesting that discrimination against asymmetry in conspecif ic male signal characters is not simply a rejection of extreme phenotypes. Results suggest that asymmetry in a key male secondary character used in vi sual signaling, independent of any concomitant behavioral or size factor, i s an important criterion in mate choice.