Sexual dimorphism in the spinning apparatus of Allocosa senex (Araneae: Lycosidae), a wolf spider with a reversal in typical sex roles.

Allocosa senex (Mello-Leitão, 1945) is a sex role-reversed wolf spider that inhabits sandy water-margin environments of southern South America. Males are larger than females and dig deeper burrows. Females are the courting sex and they prefer to mate with males that build deep burrows, suggesting high selective pressures on male digging behavior. Our aim was to investigate the external morphology and histological constitution of the spinning apparatus of males, females and juveniles of A. senex. Our results showed that A. senex adult males possess more piriform glands and spigots than adult females and juveniles. These glands produce silk for attachment discs that are crucial for the stability of the burrows. The differences according to the sex could be related to females’ and males’ digging strategies and strong selection on male burrow length in this species.