Summary: Natal dispersal and demography of a subsocial
Anelosimus species and its implications for the
evolution of sociality in spiders
L. Avilés and G. Gelsey
Abstract: The transition to permanent-sociality in spiders is thought to have involved the suppression of the dispersal
phase characteristic of hypothetical subsocial or periodic-social ancestral species. Extant periodic-social species may
provide insights into this transition. The periodic-social Anelosimus jucundus in southern Arizona was found to form
motheroffspring and sibling associations that disintegrate prior to the mating season. Following the breakdown of the
social phase, more than twice as many females as males became established within a few metres of the natal nest.
Given that the predispersal sex ratio was 1:1, a fraction of the males may have dispersed beyond the local area. The
short dispersal distances of at least a fraction of individuals of both sexes, the clustering of nests in local areas, and at
least two possible cases of sibling mating suggest, however, that dispersal may not eliminate the possibility of close
inbreeding in this species. Estimated transition probabilities between life-history stages show that the heaviest loss of
individuals occurs during dispersal. Once established, 41% of the females that reached maturity succeeded in producing
grown progeny. We discuss the implications of these findings in terms of the transition from periodic to permanent
sociality in spiders and of current models that consider the interplay between competition and inbreeding avoidance in
the evolution of dispersal.
Résumé : On croit généralement que la transition vers une vie sociale permanente chez les araignées est née de la
suppression de la phase de dispersion caractéristique d'espèces ancestrales hypothétiques subsociales ou périodiquement
sociales. L'examen d'espèces actuelles périodiquement sociales peut jeter de la lumière sur ce phénomène de transition.