Observations on a Commensal Relationship of the Microhylid Frog Chiasmocleis ventrimaculata and the Burrowing Theraphosid Spider Xenesthis immanis in Southeastern Peru

Abstract

A commensal relationship of Chiasmocleis ventrimaculata and Xenesthis immanis was studied over a 3-mo period at Tambopata Reserved Zone, Peru. Observations indicate that both species simultaneously utilize the same diurnal retreats and forage in overlapping areas. Feeding trials suggest that Xenesthis readily feed on some species of anurans, and observations implicate the role of chemical defenses in preventing Xenesthis predation on Chiasmocleis. The commensalism is similar to that of ecologically similar terrestrial frogs and burrowing spiders in North America. REPORTS OF ECOLOGICAL INTERACTIONS between spiders and frogs have documented predator-prey relationships and suggested that some spiders may be important predators of frogs, especially of juveniles (Neill 1948, Sharma & Sharma 1977, Groves & Groves 1978, Littlejohn & Wainer 1978, Formanowicz et al. 1981, Hayes 1983). However, some authors have shown that certain frogs are capable of avoiding spider predation. Szelistowski (1985) found that the Costa Rican poison-dart frog Dendrobates pumilio was unpalatable to the ctenid spider Cupiennius coccineus, which was shown to eat other frogs. Blair (1936) and Hunt (1980) describe an association in the southern United States in which the microhylid frog Gastrophryne olivacea inhabits active burrows of the theraphosid spider Dugesiella hentzi. Powell et al. (1984) found the frog Physalaemus pustulosus in occupied burrows of the theraphosid spider Aphonopelma sp. in Mexico. We report here an association in southeastern Peru between the microhylid frog Chiasmocleis ventrimaculata (Andersson) and the burrow-dwelling theraphosid spider Xenesthis immanis (Aus-