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BIOTROPICA 38(6): 743753 2006 10.1111/j.1744-7429.2006.00202.x A New Independently Derived Social Spider with Explosive Colony Proliferation

Summary: BIOTROPICA 38(6): 743­753 2006 10.1111/j.1744-7429.2006.00202.x
A New Independently Derived Social Spider with Explosive Colony Proliferation
and a Female Size Dimorphism1
Leticia AvilŽes2,5, Wayne P. Maddison2,3, and Ingi Agnarsson2,3,4
2Department of Zoology, and 3Department of Botany, The University of British Columbia, #3529-6270 University Blvd.,
Vancouver, B.C. V6T 1Z4, Canada
4Department of Entomology, Smithsonian Institution, NHB-105, P.O. Box 37012, Washington, D.C. 20013-7012, U.S.A.
Permanent cooperative sociality is rare in spiders. Here we describe sociality in a cobweb (Theridiidae) genus with no other known social species. In five areas of eastern
Ecuador, we found nests of Theridion nigroannulatum containing from a single to several thousand adults living together in a communal web. Spiders cooperated in
prey capture and shared their food. Subadult to young adult sex ratios were highly female biased, suggesting a strongly subdivided population structure as in other
permanent-social spiders. Unusual aspects of T. nigroannulatum's biology include the existence of adult females of two discrete sizes, an extreme boom and bust pattern
of colony growth, and the presence, within larger colonies, of populations of a predatory spider (Faiditus spp., Argyrodinae) that may play the role of a colony-level
parasite. The existence of females of two sizes may be the result of alternative female reproductive strategies, intracolony competition for resources, or an incipient
caste system in this species. A redescription and phylogenetic analysis corroborate the placement of this species in Theridion, indicating that sociality has evolved
independently in at least three theridiid genera.
El comportamiento social permanente es muy poco usual en ara~nas. AquŽi describimos comportamiento social en un gŽenero de la familia Theridiidae en el que no se
conocen otras especies sociales. En cinco areas del Oriente Ecuatoriano encontramos nidos de Theridion nigroannulatum que contuvieron en un nido comŽun desde
unas pocas hasta varios miles de ara~nas adultas. Las ara~nas cooperaron en la captura de la presa y compartieron su alimento. La proporciŽon de sexos entre individuos


Source: Agnarsson, Ingi - Department of Biology, Universidad de Puerto Rico


Collections: Biology and Medicine