The effect of mermithid parasitism on predation of nymphal Baetis bicaudatus (Ephemeroptera) by invertebrates |
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Authors: | Sarah A Vance Barbara L Peckarsky |
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Institution: | (1) Department of Entomology, Cornell University, Comstock Hall, Ithaca, NY 14853, USA, US |
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Abstract: | We investigated how infection by the mermithid nematode Gasteromermis sp. affected predation on its nymphal mayfly host, Baetisbicaudatus, by two invertebrate predators – the stonefly nymphs of Kogotusmodestus and the caddisfly larvae of Rhyacophilahyalinata. Predation trials and behavioral observations were conducted in stream-side, flow-through experimental chambers. When parasitized
and unparasitized prey were offered in equal numbers, K. modestus consumed significantly more parasitized than unparasitized nymphs. R. hyalinata consumed equal numbers of both prey types. Behavioral observations of foraging K.␣modestus on parasitized and unparasitized prey suggested that the increased consumption of parasitized nymphs was due to differences
in the behavior of infected mayflies in response to the predator. Specifically, parasitized nymphs drifted less often to escape
an approaching predator (non-contact encounters) compared to unparasitized nymphs, which increased the number of contact encounters
and attacks that occurred between K.␣modestus and parasitized prey. Because all hosts are castrated, these behavioral alterations affect only the fitness of the parasite,
which is killed along with its host by invertebrate predation. We present a number of hypotheses to explain why the parasite
causes increased predation on its host. These include the large size of the parasite affecting the sensory abilities of the
host, the larger energetic costs of escape behavior for parasitized individuals, and natural selection from fish predation
against drifting behavior by parasitized individuals.
Received: 27 May 1996 / Accepted: 30 September 1996 |
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Keywords: | Predation Parasitism Mayfly Behavioral alterations Mermithid |
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