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Monday, June 4, 2007 - 1:15 PM
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Fish predation risk and sediment subsurface use by shellmorphs of the snail Potamopyrgus antipodarum
Joseph R. Holomuzki, Evolution, Ecology, and Organismal Biology, The Ohio State University, 1680 University Drive, Mansfield, OH 44906 and Barry J.F. Biggs, National Institute of Water and Atmospheric Research, P.O. Box 8602, Christchurch, New Zealand.
We examined how spiny and smooth shellmorphs of the hydrobiid snail Potamopyrgus antipodarum use sediment subsurfaces in response to predation risk by native common bullies (Gobiomorphus cotidianus) and by non-native brown trout (Salmo trutta). In New Zealand, spiny-shelled morphs are predominant in lakes, whereas smooth-shelled morphs are dominant in streams, but both phenotypes are eaten by these fishes. A survey of South Island lakes and streams with these fishes revealed that sediment surface use varied widely, but usually both shellmorphs were mainly atop sediments during daylight. In slow-flow conditions in a laboratory flume, significantly more spiny morphs burrowed into sand subsurfaces than smooth morphs, but subsurface use by either morph was not affected by bully chemical cues. However, in no-flow conditions, both shellmorphs increased subsurface use in the presence of bully chemical cues, but spiny-morphs responded more strongly and quickly than smooth-shelled forms. Similarly, both shellmorphs increased their subsurface use in the chemical and physical presence of brown trout, but the response did not differ between shell types. Predation risk appears to affect subsurface use by both shellmorphs, but risks associated with drag forces or sediment abrasion may override predation in triggering burrowing behavior by spiny morphs in flowing waters.