Does sexual and natural selection operate against each other or in the same direction?

Posted by Erik Svensson

During last week's lab-meeting we talked a little about the relationship between natural and sexual selection, and to what extent these processes are opposed to each other vs. operate in the same direction and favours the same phenotypic trait values. Next week we will continue discussing this theme based on a recent article about sexual and natural selection in fruitflies (Drosophila melanogaster) in Current Biology. This article by Long, Agrawal and Rowe does also have some important implications for what kind of inferences that can be made to natural populations based on studies in laboratory settings, with a cautionary tale.

Time and place as usual: "Argumentet "(2nd floor, Ecology Building) at 10.30, Tuesday, February 5.

Below, you will find Abstract and link to the article.

The Effect of Sexual Selection on Offspring Fitness Depends on the Nature of Genetic Variation

• Tristan A.F. Long^1, 2, , , 
• Aneil F. Agrawal¹, 
• Locke Rowe¹

• ¹ Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON M5S 3B2, Canada
• ² Department of Biology, Wilfrid Laurier University, Waterloo, ON N2L 3C5, Canada

• http://dx.doi.org.ludwig.lub.lu.se/10.1016/j.cub.2011.12.020, How to Cite or Link Using DOI

• Permissions & Reprints

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Summary

Whether the changes brought about by sexual selection are, on the whole, congruent or incongruent with the changes favored by natural selection is a fundamentally important question in evolutionary biology. Although a number of theoretical models have assumed that sexual selection reinforces natural selection [1 and 2], others assume these forces are in opposition [3, 4 and 5]. Empirical results have been mixed (see reviews in [1, 6, 7 and 8]) and the reasons for the differences among studies are unclear. Variable outcomes are expected if populations differ in their evolutionary histories and therefore harbor different amounts and types of segregating genetic variation. Here, we constructed populations of Drosophila melanogaster that differed in this regard to directly test this hypothesis. In well-adapted populations, sexually successful males sired unfit daughters, indicating sexual and natural selection are in conflict. However, in populations containing an influx of maladaptive alleles, attractive males sired offspring of high fitness, suggesting that sexual selection reinforces natural selection. Taken together, these results emphasize the importance of evolutionary history on the outcome of sexual selection. Consequently, studies based on laboratory populations, cultured for prolonged periods under homogeneous conditions, may provide a skewed perspective on the relationship between sexual and natural selection.

Lab-meeting about gene expression, sexual dimorphism, sexual selection and condition dependence

This week, I was thinking that we should discuss sexual dimorphism from two different perspectives: a "G-matrix" perspective and a gene expression perspective. The two different papers I have chosen hopefully shed different light on sexual selection and the process of sexual selection. The two papers show how sexual selection might leave a signature, either on the molecular level (the first paper) or on the trait-level (the second paper).

The first paper I would like to discuss is from Locke Rowe's group at University of Ontario (Canada), and you can download it here. I heard Locke give a talk about this at the European Evolutionary Biology Meeting ("ESEB") in Italy in August last year, and I already then thought that this was a very interesting subject.

In particular since most of us (at least me!) are not particularly interested in these novel molecular tools per se, but rather wish to understand how they can be used to illuminate problems and processes in phenotypic evolution, at the whole-organism level, I was thinking that we could get some idéa of how transcriptomics might be used to achieve this goal. Hopefully, we will have a good discussion about this on this coming lab-meeting.

The second paper is a more tradition quantitative-genetic study of intersexual genetic correlations by Steve Arnold's group, and this other paper can be downloaded here.

We meet at the usual time and place, i. e.:

Where: "Darwin" room, 2nd floor (Ecology Building)
When: Wednesday, May 5, at 10.15.