CONICET | Buscador de Institutos y Recursos Humanos

Courting males of 18 species of fiddler crabs (Uca Leach, 1814) are known to build mud or sand structures at the entrances of theirburrows. Females orient to these structures when seeking mates and, in some species, males sometimes orient to their own structuresas well to relocate their burrows. We studied hood building in the temperate species Uca uruguayensis Nobili, 1901, the southernmostfiddler crab species, which mates both underground in males? burrows, especially at high densities, and on the surface at the entrance tofemales? burrows, a more common mode at low densities. Uca uruguayensis is relatively inactive during the winter and it was expectedthat the intensity of hood building would vary seasonally, with more hoods built when underground mating was more common. Courtingmale U. uruguayensis built nearly symmetrical cupped hoods of muddy sand, approximately half as high and two-thirds as deep as wide.Male courtship and mating occurred in summer from November 2001 to January 2002, but hood building was largely restricted to the lastsemi-monthly cycle, when the maximum number of matings were coincident with the maximum occurrence of hoods. The predominanceof hood building at the end of the season may reflect the amount of time following winter inactivity that males need to feed before theyexceed a threshold in the trade-off between allocation of resources to growth or reproduction. Contrary to expectations, males built morehoods at low densities where inter-burrow distances were greater. Males more often build hoods at lower densities because hoods enablethem to venture further from their burrows to court both passing and burrow resident females. The temporal pattern of hood building bymale U. uruguayensis may therefore reflect the mechanisms courting males use to relocate their burrows as well as variation in the socialand spatial context of courtship and mate choice.