Evol Ecol Res 4: 147-153 (2002)     Full PDF if your library subscribes.

An experimental manipulation of the growth and dispersal strategy of a parasitic infection using monoclonal aphid colonies

David J. Hodgson*

Imperial College of Science, Technology and Medicine, Silwood Park, Ascot, Berks SL5 7PY, UK

Address all correspondence to David J. Hodgson, CEH Oxford, Mansfield Road, Oxford OX1 3SR, UK.
e-mail: djhod@ceh.ac.uk


Parasite life-history theory predicts the potential for prudent host resource use by monoclonal infections. Deterministic models show that prudence will be favoured if an infection suffers density-dependent limits to population growth on or in a host individual. This implies that the release of transmission stages throughout the infection cycle should maximize the reproductive output (and hence fitness) of a monoclonal parasite infection. This hypothesis was tested by experimentally imposing a maximum sustainable yield harvesting strategy on monoclonal aphid colonies grown in the laboratory. Harvesting increased colony longevity, but its effect on total dispersal and colony fitness (a measure that accounted for the timing of dispersal) was subtle. Harvesting increased dispersal and fitness due to adult unwinged dispersers, at the expense of nymphal dispersers. This effect is predicted to increase clonal fitness, since adult unwinged dispersers will have more chance of surviving dispersal costs and represent a unit of colony investment similar to the more specialized winged disperser morph. Despite this, unmanipulated aphid colonies showed a bang–bang dispersal strategy, suggesting that factors promoting late dispersal outweigh the influence of density-dependent colony growth on dispersal strategies in natural aphid populations. Candidate selection pressures include genotypic diversity within aphid colonies and interactions with natural enemies.

Keywords: aphid, Aphis fabae, clonal parasite, density dependence, dispersal, life history.

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