Abstract
BackgroundThe theory of trade-off suggests that limited resources should lead to trade-off in resource intensive traits such as, immunity related and sexually selected traits in males. Alternatively, sexual exaggerations can also act as an honest indicator of underlying immunocompetence, leading to positive correlations between these traits. Evidences in support of either hypothesis in invertebrates are equivocal. Whereas several studies have addressed this question, few have used naturally occurring pathogens and realized post infection realized immunity (e.g., survivorship) to assay the fitness correlations between these two sets of traits.ResultsAdopting an experimental evolution approach, we evolved replicate populations of Drosophila melanogaster under high and low sexual selection regimes for over a hundred generations and found the following in virgin and mated males in three separate assays:Post infection survivorship against two natural pathogens - Pseudomonas entomophila (Pe) and Staphylococcus succinus (Ss): Mated males survived better against Pe, but were no different than virgins against Ss.Bacterial clearance ability against a third natural pathogen Providencia rettgeri (Pr): Mated males had significantly lower CFUs than virgins.However, sexual selection history had no effect on realized immunity of either virgin or mated males.ConclusionWe show that while mating can affect realized immunity in a pathogen specific way, sexual selection did not affect the same. The results highlight that complex polygenic traits such as immunity and reproductive traits not necessarily evolve following a binary trade-off model. We also stress the importance natural pathogens while studying sexual selection-immunity correlations.
Highlights
The theory of trade-off suggests that limited resources should lead to trade-off in resource intensive traits such as, immunity related and sexually selected traits in males
We attempt to contribute to this body of studies using experimentally evolved replicate populations of Drosophila melanogaster and measuring their postinfection realized immunity against three different natural pathogens – Pseudomonas entomophila (Pe), Providentia rettgeri (Pr) and Staphylococcus succinus (Ss)
Using three different pathogens of Drosophila melanogaster, we found no evolutionary effect of the intensity of sexual selection on the immunocompetence of males
Summary
The theory of trade-off suggests that limited resources should lead to trade-off in resource intensive traits such as, immunity related and sexually selected traits in males. Post infection survivorship against two natural pathogens - Pseudomonas entomophila (Pe) and Staphylococcus succinus (Ss): Mated males survived better against Pe, but were no different than virgins against Ss. Two of the most important sets of traits that determine a male’s fitness are sexually selected traits and immunity related traits. Sexually selected and immunity related traits are expected to trade-off with each other In males, such trade-offs can be apparent only with reproductive effort, because. Populations evolving under differential levels of sexual selection can evolve differential levels of reproductive investment during mating [6, 10,11,12,13] This difference might result in differential effect of mating in their response to pathogenic infections. Studies addressing genetic correlation between mating and immunity in vertebrates have been the focus of much research following this pioneering work [15, 16]
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