Social spiders of the Ecuadorian Amazonia, with notes on six previously undescribed social species

The Ecuadorian Amazon region is exceptionally rich in terms of the number a nd variety of social spiders it contains. In this area there are representa tives of three of the four forms of social behavior described for spiders, comprising species in 10 genera and seven families. Here we review the natu ral history of the fourteen species from this area that we have identified as having some form of social behavior, including six species -Cyclosa sp., Plesiometa sp., Tapinillus sp. 2, Achaearanea cf. mundula, a pholcid, and a sparassid- whose sociality has not been previously described. In the intr oduction we review the characteristics of spider sociality, noting several significant differences with insect social systems. In particular, we note that social spiders have not developed reproductive castes and that in the species with the most complex social behaviors the social groups are also r elatively isolated population lineages. We discuss how the Ecuadorian socia l spiders, in particular those recently discovered, may help test existing hypotheses for the evolution of sociality in spiders. We also outline some of the evolutionary and ecological problems that social spiders may help cl arify, such as the evolution of female-biased sex ratios in subdivided popu lations, the levels of selection, and the patterns of extinction and disper sal of local populations in a metapopulation. An electronic Appendix with E nglish descriptions of the six previously undescribed social species can be found at http://www.scielo.cl/.