Male mate choice and size-assortative pairing in a jumping spider, Phidippus clarus

Male choice is receiving greater attention from biologists, but remains understudied compared to investigations of female choice. I studied male choice and its potential role in size-assortative pairing in the jumping spider Phidippus clarus. Adult males cohabit with and guard immature females shortly before they mature. During this period, I monitored the sex ratio and maturation rate of females in the field, because these parameters can influence conditions favouring male choice. The adult sex ratio was initially male biased and became female biased following a relatively synchronous female maturation period. I collected male–female pairs from the field and found that they were size-assortatively paired for tibia length. I then tested whether males could discriminate between females by size, using tibia length as a measure of size. Both small and large males preferred to pair with large females that matured sooner compared with small females that matured later. Males also discriminated between females when exposed only to female silken nests, suggesting that cues associated with silk convey information about maturation and tibia length, two characters that were highly inversely correlated. Finally, large males were more likely to defeat small males in male–male contests, and as the size disparity between contestants increased, the likelihood that the larger individual would win also increased. A male preference for larger females combined with a large male advantage in male–male contests is likely to strongly influence size-assortative pairing. Species that are known to mate or pair assortatively may be valuable for studies of male choice.