¹NERC Centre for Population Biology, Imperial College London, Silwood Park Campus, Ascot, Berks, UK

Correspondence: Dr AR Kraaijeveld, School of Biological Sciences, University of Southampton, Bassett Crescent East, Southampton, Hants SO16 7PX, UK. E-mail: arkraa@soton.ac.uk

²Current address: School of Biological Sciences, University of Southampton, Southampton, Hants, UK.

³Current address: Department of Zoology, University of Oxford, Oxford, UK.

Received 3 September 2007; Revised 9 November 2007; Accepted 11 December 2007; Published online 27 February 2008.

Abstract

An artificial selection experiment designed to explore the evolution of resistance to a fungal pathogen, Beauveria bassiana, in Drosophila melanogaster is reported here. The experiment was designed to test whether there is sufficient additive genetic variation in this trait for increased resistance to evolve, and, if so, whether there are correlated responses that might represent a cost to defence. After 15 generations of selection, flies from selected lines did not have higher overall fitness after infection compared with control lines. The response to selection for resistance against this pathogen is thus much weaker than against other species, in particular, parasitoids. There was, however, evidence for increased late-life fecundity in selected lines, which may indicate evolved tolerance of fungal infection. This increase was accompanied by reduced early-life fitness, which may reflect the well-known trade-off between early and late reproduction. In the absence of fungal infection, selected flies had lower fitness than control flies, and the possibility that this is also a trade-off with increased tolerance is explored.