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Evolutionary ecology of vertically transmitted parasites: transovarial transmission of a microsporidian sex ratio distorter in Gammarus duebeni

Published online by Cambridge University Press:  06 April 2009

A. M. Dunn ,
M. J. Hatcher ,
R. S. Terry  and
C. Tofts
A. M. Dunn
Affiliation:
Department of Pure and Applied Biology, University of Leeds, Leeds, LS2 9JT, UK
M. J. Hatcher
Affiliation:
Department of Pure and Applied Biology, University of Leeds, Leeds, LS2 9JT, UK
R. S. Terry
Affiliation:
Department of Pure and Applied Biology, University of Leeds, Leeds, LS2 9JT, UK
C. Tofts
Affiliation:
Department of Computer Science, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
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Summary

Vertically transmitted parasites are transmitted from generation to generation of hosts usually via the host's gametes. Owing to gamete size dimorphism, the major transmission route is transovarial and selection (on the parasite) favours strategies which increase the relative frequency of the transmitting (female) host sex. These strategies impose unusual selection pressures on the host, and coevolution between hosts and vertically transmitted parasites has been implicated in speciation, in the evolution of symbiosis, and in the evolution of novel systems of host reproduction and sex determination. We review the evolutionary implications of vertically transmitted parasites in arthropods before focusing on strategies of transmission of a parasitic sex ratio distorter in Gammarus duebeni. The efficiency of parasite transmission to new hosts is a key factor underlying the relationship between vertically transmitted parasites and their hosts. Vertically transmitted parasites must overcome 2 bottlenecks in order to ensure successful infection of future host generations: first, transmission from adult to gamete; and secondly, transmission to the germ-line of the infected host. We investigate these 2 processes with regard to transovarial transmission by a microsporidian parasite in Gammarus duebeni. Parasite transmission from adult to eggs is highly efficient, with 96% of eggs of infected mothers inheriting the infection, whereas transmission to germ-line within infected embryos is relatively inefficient (72%). We measure parasite distribution between cells of developing embryos, and use these distributions to infer possible mechanisms of parasite transmission to germ-line. Parasite distribution within the embryo is dependent on host cell lineage, and is not consistent with unbiased segregation between daughter cells. These results indicate that parasites segregate together at host cell division, and may reflect a strategy of differential segregation to the host germ-line. We consider alternative parasite strategies at the cell-level in terms of their evolutionary implications.

Keywords

transovarial transmissionsex ratio distorterGammarus duebeni
Type
Research Article
Information
Parasitology , Volume 111 , Supplement S1: Ecology of wildlife host-parasite interactions , January 1995 , pp. S91 - S109
Copyright
Copyright © Cambridge University Press 1995

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