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.

Journal cover in "Evolution" and the role of learned mate preferences in population divergence

Most of you have already seen this - but I post it again in case somebody missed it. We've got the journal cover in the November 2010 issue of Evolution, featuring our article about learned mate preferences in the banded demoiselle (Calopteryx splendens). This paper has also been highlighted by the popular science site Science Daily, and it will also be covered in a popular science radio programme in Germany, since I was recently interviewed about the study by a journalist from our southern neighboring country.

Apart from our own article, the same issue contains a number of interesting other articles about sexual selection, most notably Richard Prums paper about null models in sexual selection in which he argues that the Lande-Kirkpatrick (NK)-model as the most appropriate such null model, a paper we discussed at the lab-meeting last week. Here is the title and abstract of our own paper:


A ROLE FOR LEARNING IN POPULATION DIVERGENCE OF MATE PREFERENCES  


Erik I. Svensson, Fabrice Eroukhmanoff, Kristina Karlsson, Anna Runemark & Anders Brodin

Article first published online: 13 JUL 2010

DOI: 10.1111/j.1558-5646.2010.01085.x

Learning and other forms of phenotypic plasticity have been suggested to enhance population divergence. Mate preferences can develop by learning, and species recognition might not be entirely genetic. We present data on female mate preferences of the banded demoiselle (Calopteryx splendens) that suggest a role for learning in population divergence and species recognition. Populations of this species are either allopatric or sympatric with a phenotypically similar congener (C. virgo). These two species differ mainly in the amount of wing melanization in males, and wing patches thus mediate sexual isolation. In sympatry, sexually experienced females discriminate against large melanin wing patches in heterospecific males. In contrast, in allopatric populations within the same geographic region, females show positive (“open-ended”) preferences for such large wing patches. Virgin C. splendens females do not discriminate against heterospecific males. Moreover, physical exposure experiments of such virgin females to con- or hetero-specific males significantly influences their subsequent mate preferences. Species recognition is thus not entirely genetic and it is partly influenced by interactions with mates. Learning causes pronounced population divergence in mate preferences between these weakly genetically differentiated populations, and results in a highly divergent pattern of species recognition at a small geographic scale.

Lab-meeting on phenotypic plasticity, learning, sexual selection and mate preferences

This coming Wednesday (26 May), I wish to discuss a recent TREE-article by Charlie Cornwallis and Tobias Uller that recently came out. The title of this article is Towards an evolutionary ecology of sexual traits. I was one of the reviewers on this article, and I think they have some interesting things to say. Whether you agree or not with their general message, I think this paper should stimulate some discussion.

Also, postdoc Machteld Verzijden might send out one of her manuscripts about mate preference evolution in fish, that she want some input on. If she is able to finish this manuscript, she will send it out by e-mail to the group tomorrow (Tuesday).

Any fika-volunteer?

Lab meeting at the 8th of April

Dear all,
this is being posted late-as I had problems to upload something to the blog yesterday.
This is what I sent around yesterday (by email):

Erik is in South Africa now, but we will continue with the weekly meetings as much as we can.
The paper this week is by Anne Runemark et al. and investigates mate choice in Podarcis gaigae, the Skyros Wall Lizard.



Anna and her co-workers were interested to compare the strength of premating isolation between mainland and island populations of this species, and tested male and female preferences for chemical scents in several populations. Comparisons showed that the island populations preferred the smell of individuals from their own population, whereas no such preference was found in mainland populations. These results are discussed in light of the pheromone compositions and population genetic models. Anna's abstract is posted below.

Abstract
Reproductive isolation can arise when populations reside in different natural environments and experience either divergent natural or sexual selection, or both. When traits that are involved in mate choice diverge due to differences in local selective environments, parallel divergence in allopatric populations inhabiting similar environments strongly indicates that divergence is adaptive. The evolution of mate choice and degree of choosiness in isolated island populations has been topic to some debate. Here we show mate odour-based mate preferences for chemical cues and scent composition has diverged in island-mainland populations of Skyros wall lizard Podarcis gaigeae. We address the issue whether mate choice traits and mate preferences have diverged in parallel on geographically isolated islet populations, and if lizards on these islet populations are more or less choosy than neighbouring mainland populations. We found a heightened preference in islet lizards to prefer the scent from islet lizards, whereas the mainland populations were less discriminant and did not show a heightened preference for the scent of mainland lizards. However, the pheromone compositions of the islets were clearly more divergent from each other than between mainland populations and between mainland and islets. We found a parallel increase in one chemical substance (dl-a-tocopherol) in the islet populations, and a preference for that compound could potentially partly explain the islet populations’ preference for islet scent. Our result supports the recent population genetic models that suggest that islet populations are expected to be more choosy in their mate preferences than their founding populations. Local microenvironmental factors such as diets are likely to play a role in the more accelerated population divergence in chemical signals on the islets, possibly with some role for phenotypic plasticity in the development of these sexual signals.

Please send any suggestions for upcoming lab meetings to my email address
Maren.wellenreuther@zooekol.lu.se

Cheers, Maren