Revision and phylogenetic analysis of American ethicus and rupununi groups of Anelosimus (Araneae, Theridiidae)

Two species groups of the social spider genus Anelosimus are revised. The ethicus group contains six species found in South America, in an area ranging from the Guianas to southern Brazil and Argentina. Of these, A. rabus Levi, 1963, A. ethicus (Keyserling, 1884), and A. nigrescens (Keyserling, 1884) are redescribed, while A. nigrescens is removed from synonymy with A. ethicus. Three new species are described: A. misiones sp. nov., A. sumisolena sp. nov. and A. inhandava sp. nov. Anelosimus ethicus is reportedly either subsocial or solitary, while the behaviour of the other species in the group is unknown. The rupununi group contains two quasisocial species, A. rupununi Levi, 1956 and A. lorenzo Fowler & Levi, 1979, from the Caribbean and tropical South America. Both are redescribed here. A parsimony analysis of morphological characters provides support for the monophyly of both groups. In the phylogeny, subsociality optimizes to the base of Anelosimus, indicating that the common ancestor of the ethicus group was subsocial. Its members can thus be predicted to be subsocial, or secondarily solitary. Quasisociality arose de novo in the rupununi group, representing one of 6-7 independent origins in theridiids. Study of the biology of Anelosimus is important to advance our understanding of the evolution of sociality in spiders.