Do parasitoids explain differential abundance of two syntopic orb-weaver spiders (araneae: araneidae)?

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)In this study, we examined the relative abundance of two congeneric species of orb-weaver spiders, Cyclosa fililineata and Cyclosa morretes, in an area of Atlantic forest in southeastern Brazil, and the relationship of this variable with fecundity and attacks by parasitoids. We also investigated responses to vibrational stimuli that simulated the approach of a wasp and described architectural changes in webs of parasitized individuals of C. fililineata. C fililineata was more abundant throughout the year, although this species produced a lower number of egg sacs and a lower number of eggs per egg sac when compared with C. morretes. Both species showed similar types of behavioral responses to vibrational stimuli, but C. fililineata remained motionless more often. The frequency of parasitism by the wasp Polysphincta janzeni on adults and juveniles was low and similar for C. fililineata and C. morretes in both dry and wet seasons. The parasitoid caused alterations in the web design of C. fililineata similar of those observed in other orb-weavers attacked by ichneumonid wasps. Webs constructed by spiders parasitized by larvae in their last instar had a lower number of radii and sticky spirals were completely absent. An egg parasitoid, Baeus cyclosae, attacked C. morretes more often than C. fililineata, possibly as a consequence of its greater clutch size and/or larger eggs. These results indicate that egg mortality caused by B. cyclosae, but not subadult and adult mortality promoted by P. janzeni, may be an important factor determining the relative abundance of these two Cyclosa species. (C) 2015 Elsevier Masson SAS. All rights reserved.In this study, we examined the relative abundance of two congeneric species of orb-weaver spiders, Cyclosa fililineata and Cyclosa morretes, in an area of Atlantic forest in southeastern Brazil, and the relationship of this variable with fecundity and att69113120FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAIS - FAPEMIGFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)FAPESP [99/06089-4]99/06089-4300539/94-0306157/2014-4403733/2012-0445832/2014-2CRA-30058/12APQ-02104-14The authors thank Ian Gauld for identifying Polysphincta janzeni, and Nicholas Stevens and Marta Loi acono for information on the genus Baeus. We also thank Glauco Machado, Paulo S. Oliveira, Hilton F. Japyassú and Andrea L. T. Souza for comments on a fi