Madagascar: an unexpected hotspot of social Anelosimus spider diversity (Araneae: Theridiidae)

Abstract. The spider genus Anelosimus Simon, 1891 (Theridiidae) currently contains over forty described species, found worldwide in tropical to warm temperate areas. American Anelosimus are all social, a rare trait among spiders, but social behaviour has not been reported for Anelosimus species elsewhere. Old World Anelosimus are poorly known, both behaviourally and taxonomically, and no Anelosimus species 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) Anelosimus species in Périnet reserve. A sixth species from the same locality is known from museum specimens and the Anelosimus diversity 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. andasibe sp.n. , A. may Agnarsson sp.n. , A. nazariani sp.n. , A. sallee sp.n. , A. salut sp.n. and A. vondrona sp.n. are described. Anelosimus locketi Roberts, 1977 from Aldabra Atoll is a junior synonym of A. 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 American A.‘arizona’¹. The phylogenetic analysis supports the monophyly of the Madagascar group and places it as sister to a clade containing the eximius lineage from the Americas, and a pair of undescribed Tanzanian species.