Evol Ecol Res 11: 965-973 (2009)     Full PDF if your library subscribes.

Parasitism and environmental sex determination in Daphnia

Alison B. Duncan, Sarah A. Hall and Tom J. Little

Institute of Evolutionary Biology, School of Biology, University of Edinburgh, Edinburgh, UK

Correspondence: A.B. Duncan, Institut des Sciences de l’Evolution (ISEM), UMR 5554 (CC065), Université Montpellier 2, Place Eugène Bataillon, 34095 Montpellier Cedex 05, France.
e-mail: alison.duncan@univ-montp2.fr


Hypothesis: Daphnia exposed to cues associated with the onset of a parasite epidemic will have more males and resting eggs.

Organisms: Seven clones of Daphnia magna (chosen for high levels of sexual reproduction) and the bacterial parasite Pasteuria ramosa.

Methods: We explored how parasite infection (simulated by creating crowding conditions using infected hosts) might influence male and resting egg production compared with crowding conditions created using healthy hosts. We also explored the effects of putting bacterial spores in water.

Conclusions: Both crowding and crowding with infected hosts led to higher numbers of males and resting eggs. Direct exposure to parasite transmission spores had no effect. Male production in response to treatment was host-clone specific, with some clones responding strongly to the presence of infected hosts, but others not responding or only responding to water crowded with healthy Daphnia. Resting-egg production in response to treatment was also host-clone specific, but differences were not affected by crowding conditions.

Keywords: crowding, evolution, males, Pasteuria ramose, resistance, resting egg, sexual reproduction.

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