On the antagonistic relationship between sexual selection and assortative mating

Posted by Erik Svensson


It is time for lab-meeting again, and this week we are happy to welcome Machteld Verzijden back from Rutgers University, where she has been working with Jessica Ware. Let's start the lab-meeting with her telling us about her work and the progress made during the visit.

Note the new time: Wednesday March 28 at 13.30 (not 13.00!).


After this, I was thinking we should discuss the relationship between sexual selection and assortative mating, two processes that are often confused and mixed up, particularly in the field of sympatric speciation. Although these processes are by no means totally independent, they are not identical and their population genetic consequences are very different. Moreover, they can counteract each other and hence could be antagonistic.

To understand the finer details of the complex relationship between assortative mating and sexual selection, we'll have to leave the murky shallow waters of "Adaptive Dynamics" and instead to turn to a clear thinker and a population genetic theoretician who knows what he is talking about: Mark Kirkpatrick från Austin (Texas). I was thinking we should read a much-cited papers from Proceedings of the Royal Society, entitled "Sexual selection can constrain sympatric speciation". Below, you will find the Abstract and here is a downloadable link to the PDF:


Sexual selection can constrain sympatric speciation

1. Mark Kirkpatrick^* and 
2. Scott L. Nuismer†

Source: PROCEEDINGS OF THE ROYAL SOCIETY OF LONDON SERIES B-BIOLOGICAL SCIENCES  Volume: 271   Issue: 1540   Pages: 687-693   DOI:10.1098/rspb.2003.2645   Published: APR 7 2004

Abstract

Recent theory has suggested that sympatric speciation can occur quite easily when individuals that are ecologically similar mate assortatively. Although many of these models have assumed that individuals have equal mating success, in nature rare phenotypes may often suffer decreased mating success. Consequently, assortative mating may often generate stabilizing sexual selection. We show that this effect can substantially impede sympatric speciation. Our results emphasize the need for data on the strength of the stabilizing component of selection generated by mating in natural populations.

Greetings from "Speciation-meeting" in Vienna!

Together with several other colleagues from Lund, Sweden and other countries, our lab was well-represented at the first European Speciation Conference, organized by the Institute for Advanced System Analysis (IIASA) in Vienna (Austria). This three-day conference has gathered a number of researchers working on the problems of speciation, both theoretically and empirically. A list of talks from the conference can be found here.  

The first evening of the conference, we enjoyed nice Austrian food (LOTS of meat!) and good wine, and of course the company of many of our colleagues. On the picture above you can see how happy we are after tasting some great wine. From left to right you see Anna Runemark (Lund University), Fredrik Haas (currently at Oslo University), Erik Svensson (Lund University), Andrew Hendry (McGill University, Canada), Anna Qvarnström (Uppsala University) and Jörgen Ripa (Lund University).Although this time there was a Scandinavian bias at the table, we have also of course interacted and entertained ourselves with some other great colleagues, such as Maria Servedio as well as former McArthur student and legendary ecologist Mike Rosenzweig.

 Personally, I mostly enjoyed the talk by Daniel Bolnick (University of Texas at Austin), about the rarity of sympatric speciation in sticklebacks, which was somewhat heretical in a conference that has been so dominated by the "Adaptive Dynamics"-school, led by Ulf Dieckmann at IIASA, where the importance of sympatric speciation has been vastly exaggerated, in relation to its real importance in natural populations (in my personal opinion). If sympatric speciation was as common as these models of "evolutionary branching" indicate, there would essentially be a new species on every twig of a bush, which there clearly isn't. This very fact in itself suggests (at least to me) that constraints on sympatric speciation are likely to operate and be important, and that the asexual modelling approach in the adaptive dynamics school has underestimated the severity of recombination.

As a primarily empirically oriented evolutionary biologist, I see a major weakness of the Adaptive Dynamics-school in that their models are only weakly connected to empirical work and the parameters they include in their models are not as natural to estimate as the classical and well-established estimates typically  used by field evolutionary biologists that are derived from quantitative genetics (i. e. selection coefficients). In the absence of such transparent models with parameters defined in an empirically meaningful way, the jury is still out whether adaptive and sympatric speciation is really important in nature, or whether it is mainly a phenomena that gains more attention from theoreticians than it deserves from an empirical point of view of practicing naturalists and field biologists.