Retreat selection is critical for animals that spend much of their diel cycle in retreats. At issue is how retreat availability and social dynamics interact to influence whether retreats are defended from or shared with conspecifics. The prolonged subsocial huntsman spider, Delena lapidicola (Hirst 1991, Sparassidae), lives in family groups under rock retreats which are relatively abundant on granite headlands in Western Australia. Their more social congener, D. cancerides (Walckenaer, 1837), lives in rare retreats under the bark of trees in southern Australia. We tested retreat sharing patterns with kin and non-kin in D. lapidicola, and of unrelated adult female D. cancerides using laboratory assays. For each trial, two spiders were introduced 12-hr apart in a large arena with two retreats and given 24-hr to share a retreat or occupy their own retreat. Aggression and mortality were recorded. In this study, 42% of D. lapidicola shared retreats regardless of kinship, age, sex, mass or natal colony. Even adult females shared retreats peacefully. Aggression only occurred once. In stark contrast, no D. cancerides adult females shared retreats and 36% of the trials resulted in mortality or serious injury. Our results support the hypothesis that an abundance of retreats in D. lapidicola habitats reduces pressure to defend and allows sharing with little discrimination of kinship, while the rarity of retreats in D. cancerides habitats results in aggressive defense.
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Vol. 45 • No. 3