Male-biased predation of a cave fish by a giant water bug

Abstract

Male-biased predation has been described from several epigean species, and in many cases, intrinsic differences between the sexes (such as male ornaments) have been suggested as an explanation. Here we report on male-biased predation of a cave fish (Poecilia mexicana) by an aquatic insect (Belostoma sp.) in a Mexican sulfur cave. P. mexicana use aquatic surface respiration (ASR) to survive in their sulfidic, hypoxic habitat. We found that males typically exhibit more ASR activity than females, which leads to increased exposure to the sit-and-wait predator that catches fish near the water surface. Our finding is novel, because male vulnerability to predation is not directly related to male traits involved in courtship, but rather due to other sexual differences in behavior and ultimately, oxygen demands.

Characterizing a novel predator–prey relationship between native Diplonychus esakii (Heteroptera: Belostomatidae) and invasive Gambusia affinis (Teleostei: Poeciliidae) in central China

“…Using prey choice experiments under semi-natural conditions, we first experimentally confirmed the assumption that D. esakii prey on G. affinis, as previous studies found other belostomatines (including members of the genus Diplonychus) to include fish prey (Plath et al 2003(Plath et al , 2011Tobler et al 2007Tobler et al , 2008Tobler et al , 2013Hazarika and Goswami 2012). Having confirmed this assumption, (1) we then asked if a pattern of size-specific predation exists.…”

“…By contrast, a strong signal of male-biased predation was uncovered in a study on predation by B. cf. bakeri on P. mexicana in a hydrogen sulfide-rich cave (Tobler et al 2008). The authors reported on higher oxygen demands of male fish leading to more aquatic surface respiration under hypoxic conditions, thus exposing males to elevated levels of predation risk.…”

“…(2) As previous studies found male-biased predation by B. cf. bakeri on another poeciliid (Tobler et al 2008), we predicted a similar pattern in the predatory interaction between D. esakii and G. affinis, as poeciliid males expose themselves more to predators during their continuous mate searching and mating behavior (Godin 1995). (3) Furthermore, we asked if the predators' body size would affect their prey selection (e.g., in the form of large-bodied predators preferring large prey items and small-bodied predators preferring smaller prey).…”

“…Due to the toxic effects of hydrogen sulfide (H 2 S) and the associated extreme hypoxia in the water, cave mollies must spent considerable time performing aquatic surface respiration , rendering them vulnerable to attacks by giant water bugs (Tobler et al 2009). Prey choice experiments found the heteropterans to preferentially prey upon large-bodied fish (Plath et al 2003;Tobler et al 2007), and to prefer gestating over non-gestating females (Plath et al 2011), and males over females (Tobler et al 2008). While higher predation risk of largebodied fish could be explained by better (non-visual) detectability of surfacing large-bodied individuals, higher predation on males and gestating females is likely a function of increased energy demands of males and gestating females, leading to increased aquatic surface respiration and, thus, increase likelihood of falling victim to heteropteran predators (Tobler et al 2008;Plath et al 2011).…”

Does a predatory insect contribute to the divergence between cave- and surface-adapted fish populations?

“…Belostoma have been shown to preferentially attack certain sizes and sexes of prey, and thus may exert strong selective pressures on prey species (Tobler et al , 2008b. Similarly, immigrants to cave and surface habitats could be attacked selectively, as cave and surface fish have diverged in sensory structures (Parzefall 2001).…”