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Open Access Research article

Sex-specific effects of a parasite evolving in a female-biased host population

David Duneau12*, Pepijn Luijckx13, Ludwig F Ruder1 and Dieter Ebert1

Author Affiliations

1 University of Basel, Zoological Institute, Vesalgasse 1, 4051, Basel, Switzerland

2 Department of Entomology, 3132 Comstock Hall, Cornell University, Ithaca, NY 14850, USA

3 University of Toronto, Department of Ecology and Evolutionary Biology, Toronto, ON M5S 3B2, Canada

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BMC Biology 2012, 10:104  doi:10.1186/1741-7007-10-104

Published: 18 December 2012



Males and females differ in many ways and might present different opportunities and challenges to their parasites. In the same way that parasites adapt to the most common host type, they may adapt to the characteristics of the host sex they encounter most often. To explore this hypothesis, we characterized host sex-specific effects of the parasite Pasteuria ramosa, a bacterium evolving in naturally, strongly, female-biased populations of its host Daphnia magna.


We show that the parasite proliferates more successfully in female hosts than in male hosts, even though males and females are genetically identical. In addition, when exposure occurred when hosts expressed a sexual dimorphism, females were more infected. In both host sexes, the parasite causes a similar reduction in longevity and leads to some level of castration. However, only in females does parasite-induced castration result in the gigantism that increases the carrying capacity for the proliferating parasite.


We show that mature male and female Daphnia represent different environments and reveal one parasite-induced symptom (host castration), which leads to increased carrying capacity for parasite proliferation in female but not male hosts. We propose that parasite induced host castration is a property of parasites that evolved as an adaptation to specifically exploit female hosts.

Sex-specific adaptation; Daphnia; Pasteuria; local adaptation; gigantism; castration; biased sex-ratio