Madagascar: an unexpected hotspot of socialAnelosimusspider diversity (Araneae: Theridiidae)

Abstract

Abstract. The spider genusAnelosimusSimon, 1891 (Theridiidae) currently contains over forty described species, found worldwide in tropical to warm temperate areas. AmericanAnelosimusare all social, a rare trait among spiders, but social behaviour has not been reported forAnelosimusspecies elsewhere. Old WorldAnelosimusare poorly known, both behaviourally and taxonomically, and noAnelosimusspecies have yet been described from sub‐Saharan Africa or Madagascar. Based on a preliminary phylogenetic analysis we predicted sociality in an undescribed Madagascar species because it grouped among social New World species. An expedition to Madagascar then found no less than five undescribed periodic‐social (subsocial)Anelosimusspecies in Périnet reserve. A sixth species from the same locality is known from museum specimens and theAnelosimusdiversity of Périnet is comparable with the most diverse single locality in the Americas. Subsocial species play a key role in understanding the evolution of permanent sociality (quasisociality). This increased pool of available subsocial study species demonstrates the utility of phylogenies as predictors of traits in species thus far unstudied. Here,A. andasibesp.n.,A. mayAgnarssonsp.n.,A. nazarianisp.n.,A. salleesp.n.,A. salutsp.n.andA. vondronasp.n.are described.Anelosimus locketiRoberts, 1977 from Aldabra Atoll is a junior synonym ofA. decaryi(Fage, 1930) comb.n. from Madagascar. Preliminary data on the behaviour of the new species are given, indicating a level of sociality similar to the AmericanA.‘arizona’1. The phylogenetic analysis supports the monophyly of the Madagascar group and places it as sister to a clade containing theeximiuslineage from the Americas, and a pair of undescribed Tanzanian species.