Evol Ecol Res 13: 133-144 (2011)     Full PDF if your library subscribes.

Giant water bug (Belostoma sp.) predation on a cave fish (Poecilia mexicana): effects of female body size and gestational state

Martin Plath1, Rüdiger Riesch2, Zach Culumber3, Bruno Streit1 and Michael Tobler4

1Department of Ecology and Evolution, University of Frankfurt, Frankfurt am Main, Germany, 2Department of Biology and W.M. Keck Center for Behavioral Biology, North Carolina State University, Raleigh, North Carolina, USA,  3Department of Biology, Texas A&M University, College Station, Texas, USA and  4Department of Zoology, Oklahoma State University, Stillwater, Oklahoma, USA

Correspondence: M. Plath, Department of Ecology and Evolution, University of Frankfurt, Siesmayerstrasse 70a, 60054 Frankfurt am Main, Germany.
e-mail: mplath@bio.uni-frankfurt.de


Background: Predation is an important driver of life-history trait evolution. Fish predators may prey selectively on certain prey size classes, or pregnant females, particularly those of livebearing prey species. This selectivity ought to affect the evolutionary trajectory of the prey population. In sulphidic and hypoxic habitats, Atlantic mollies (Poecilia mexicana) have to spend considerable time engaging in aquatic surface respiration, exposing themselves to predation by giant water bugs (Belostoma sp.). Compared with other females, pregnant P. mexicana experience greater oxygen demands leading to more aquatic surface respiration.

Questions: Are pregnant P. mexicana females more likely to be captured by Belostoma as a result of more aquatic surface respiration and decreased flight abilities (i.e. slower fast–start responses)?

Organisms and location: (1) Atlantic mollies (P. mexicana: Poeciliidae, Teleostei) inhabiting a sulphidic cave (Cueva del Azufre) in Tabasco, México. (2) A co-existing sit-and-wait predator, the giant water bug Belostoma sp. (Belostomatidae, Hemiptera), which catches surfacing fish at the water’s edge.

Methods: Predation experiments inside the Cueva del Azufre. In Experiment 1, one randomly selected cave molly female was placed into a perforated bottle with one individual water bug. In Experiment 2, two size-matched females (one pregnant and one non-pregnant) were placed into a perforated bottle with one individual water bug.

Results: Capture rates after 24 h in Experiment 1 were correlated mainly with female body size. But larger females were also more likely to be pregnant, making it difficult to disentangle the effects of size and pregnancy. Experiment 2 isolated the effect of pregnancy, and water bugs clearly preferred pregnant over non-pregnant prey.

Keywords: aquatic surface respiration, cave fish, life-history evolution, Poeciliidae, size-selective predation.

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