Characterisation of burrow architecture under natural conditions in the sand-dwelling wolf spider Allocosa brasiliensis

Abstract

Allocosa brasiliensis (Petrunkevitch, 1910) is a wolf spider that constructs silk-lined burrows along the coastal sand dunes of Argentina, Brazil and Uruguay. This species shows a reversal in typical sex roles and sexual size dimorphism expected for spiders. Females are the smaller and mobile sex, which initiates courtship at the male burrow entrance. Mating occurs in the male burrow, and when it ends, the male leaves and the female stays inside. Females prefer to mate with those males showing longest burrows, so burrow dimensions would be under strong sexual selection pressures. Previous studies in the laboratory indicated that male burrows are longer than those of virgin females, which were described as simple silk capsules. Preliminary observations suggested that juvenile burrows presented differences from those of adults; however, detailed observations of A. brasilienisis burrow characteristics at the field were lacking. The aim of this study was to characterise the burrows of adults and juveniles of A. brasiliensis under natural conditions. We recorded the dimensions of burrows inhabited by males, females and juveniles (n = 30 for each category) and created beeswax moulds that reflected burrow shape. Juveniles inhabited tubular burrows with two branches and two openings; on the contrary, adults were found in tubular burrows with a single entry. Males and females inhabited burrows of similar length and width, but those of juveniles were shorter and narrower. We discuss the results and their possible functional explanations according to the selective pressures expected for each developmental stage and sex.

Keywords:

• Sand dunes
• refuge
• burrow dimensions
• digging
• wax mould

Acknowledgements

We thank Ana Celia Albín and Adriana Albín for their help during fieldwork. We are also grateful to Fabiana Baldenegro, Matilde Carballo and Estefanía Stanley for helping us breed the spiders, and to Rodrigo Postiglioni for his help with the figure. The Editor and three anonymous reviewers improved the final version of this manuscript.

Additional information

Funding

This research was supported by a grant from Agencia Nacional de Investigación e Innovación (ANII) awarded to A. Albín. A. Aisenberg and M. Simó acknowledge financial support by Programa de Desarrollo de Ciencias Básicas (PEDECIBA) and SNI (ANII).