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JPR Advance Access published online on September 8, 2006
Journal of Plankton Research, doi:10.1093/plankt/fbl043
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© The Author 2006. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org
Received June 10, 2006
Accepted September 4, 2006

Article

Direct and indirect effects of predation on the genetic structure of a Daphnia population

Leif K. Hembre 1 * and Robert O. Megard 2

1 Hamline University, 1536 Hewitt Ave, St. Paul, MN 55104 USA; Department of Ecology, Evolution, and Behavior, University of Minnesota, 1987 Upper Buford Circle, St. Paul, MN 55108 USA
2 Department of Ecology, Evolution, and Behavior, University of Minnesota, 1987 Upper Buford Circle, St. Paul, MN 55108 USA

* To whom correspondence should be addressed.
Leif K. Hembre, E-mail: lhembre{at}hamline.edu


  Abstract

The effects of fish predation on zooplankton communities are well documented, but relatively little is known about how predation structures the genetic composition of individual populations. This study illustrates how a perturbation in the timing and strength of predation by rainbow trout directly and indirectly altered the genetic composition of a Daphnia pulicaria population in a Minnesota (USA) lake. Trout were stocked in autumn in the first two years of the study and in spring in the second two years. In autumn stocking years, predation was highest over winter and in spring but relatively low during summer stratification. In contrast, in spring stocking years, predation was low over winter and high during summer stratification. In all years, the Daphnia population became genetically differentiated with respect to depth as summer stratification became more pronounced. In addition, allozyme analyses of trout stomach contents revealed selective predation on Daphnia in the metalimnion. In spring stocking years, when trout were abundant during the summer, this directly caused a shift in the dominant clone type from a metalimnetic to a hypolimnetic specialist. The fisheries manipulation indirectly affected the genetic composition of the Daphnia population by altering the importance of recruitment from diapausing embryos in the sediment (the egg bank). In autumn stocking years, when the overwintering population was small, genotype frequencies in early summer indicated the recent emergence of sexually-derived individuals from the egg bank. Conversely, in spring stocking years when over-wintering populations of Daphnia were large, no emergence events were detected.

Communicating Editor: KJ Flynn


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