Predation by three species of spiders on a cave fish in a Mexican sulphur cave

摘要

Previously, giant water bugs (Belostoma sp., Belostoma-tidae) were thought to be the only predators of the cave-dwelling fish Poecilia mexicana (Poeciliidae) in a southern Mexican sulphur cave (Cueva del Azufre). Here, we report on three species of Araneae [Ctenidae gen. sp., Tinus sp. (Pisauridae), and Hemirrhagus pernix (Theraphosidae)] from that cave, which also prey on P. mexicana. To our knowledge, this is the first report of spider predation on a cave fish. Caves have often been assumed to be predator-free environments for fish living in them (Romero & Green, 2005; Tobler, Schlupp et al, 2006). Only recently we have demonstrated a previously unreported case of a predator-prey interaction between an aquatic insect of the genus Belostoma Latreille, 1807 (Heteroptera: Belos-tomatidae) and a cave fish (i.e. the cave molly), a cave-adapted form of the Mexican livebearer Poecilia mexicana Steindachner, 1863 (Teleostei: Poeciliidae; Tobler, Schlupp et al., 2007; Tobler, Franssen et ah, 2008; Tobler,2009). In the southern Mexican Cueva del Azufre (also known as Cueva de las Sardinas or Cueva de Villa Luz), cave mollies not only live in permanent darkness, but also have to cope with high concentrations of hydrogen sulphide (H2S; Gordon & Rosen, 1962; Tobler, Schlupp et al., 2006), which are acutely toxic to metazoans (Grieshaber & Volkel, 1998). Hydrogen sulphide leads to extreme hypoxia in the water (Tobler, Schlupp et al, 2006); hence cave mollies perform so-called Aquatic Surface Respiration (ASR) to exploit the more oxygenated (and thus less sulphidic) top-most layer of the water column (Plath, Tobler et al, 2007; Tobler, Riesch et al, 2009). This behaviour exposes the mollies to predation by the sit-and-wait predator Belostoma sp., which waits for passing, surfacing fish at the edge of the water (Tobler, Schlupp et al, 2007; see also Kramer, Manley et al., 1983 for increased predation risk for fish exhibiting ASR).