Evol Ecol Res 1: 581-589 (1999)     Full PDF if your library subscribes.

Rapid accumulation of a vertically transmitted parasite triggered by relaxation of natural selection among hosts

Lev Yu. Yampolsky, Colleen T. Webb, Svetlana A. Shabalina and Alexey S. Kondrashov

Section of Ecology and Systematics, Cornell University, Ithaca, NY 14853, USA

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e-mail: ask3@cornell.edu


The fate of a parasite with exclusively vertical transmission depends critically on its virulence, the magnitude of its negative impact on fitness of the infected host. Relaxation of natural selection within the host population should favour the parasite by reducing this impact. We studied the dynamics of the sigma virus, a vertically transmitted parasite of Drosophila melanogaster, within a captive host population kept under relaxed natural selection. The frequency of infected flies in the population grew from 5% to 70% in just 15 generations. In contrast, strong natural selection among the host curbed the propagation of the virus. Two of 15 populations originating from a pair of infected parents and kept under intense competition for 10 generations have lost the virus completely. The implications of these findings for host–parasite co-evolution are discussed.

Keywords: Drosophila, host–parasite co-evolution, sigma virus, vertical transmission.

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        © 1999 Alexey S. Kondrashov. All EER articles are copyrighted by their authors. All authors endorse, permit and license Evolutionary Ecology Ltd. to grant its subscribing institutions/libraries the copying privileges specified below without additional consideration or payment to them or to Evolutionary Ecology, Ltd. These endorsements, in writing, are on file in the office of Evolutionary Ecology, Ltd. Consult authors for permission to use any portion of their work in derivative works, compilations or to distribute their work in any commercial manner.

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