Testing sexual size dimorphism and nocturnal surface activity in the coastal wolf spider Allocosa alticeps

Abstract

Allocosa alticeps (Mello-Leitão, 1944) inhabits coastal sandy areas in the south of Buenos Aires, Argentina. Information about the natural history and reproductive strategies of this species is extremely scarce. Allocosa senex (Mello-Leitão, 1945) and Allocosa marindia Simó, Lise, Pompozzi & Laborda 2017 are two burrowing wolf spiders from the subfamily Allocosinae which inhabit similar environments to A. alticeps. Both species show reversal in traditional sexual size dimorphism and sex roles expected in spiders. Males are larger than females and females are the wandering sex. These non-traditional patterns have been associated with the harsh coastal habitat where these two Allocosa live. Our objectives were to study nocturnal surface activity in A. alticeps, and analyse sexual dimorphism in this species. We performed nocturnal samplings to estimate surface activity and measured traits related to size, mobility, and burrowing in adults of both sexes (carapace, forelegs, and chelicerae). Females and males showed similar nocturnal surface activity. We did not find differences between the sexes in body size orother body traits, except that chelicerae were larger in males. Contrary to our expectations and, in spite of being an allocosine that inhabits coastal habitats, A. alticeps did not show reversal in mobility patterns and sexual dimorphism as described for A. senex and A. marindia. These results highlight the importance of studying A. alticeps, since they could reflect the transition to reverse SSD, for understanding the evolution of sex role reversal in the subfamily Allocosinae.