Lab-meeting on intraspecific assortative mating, disruptive selection and sympatric speciation

Posted by Erik Svensson on behalf of John Waller

This week's lab-meeting will continue on the theme of assorative mating and how it can possibly work together with disruptive selection to cause sympatric speciation. We will discuss two papers by Daniel Bolnick at University of Texas (Austin): one review paper in American Naturalist and one modelling paper in American Zoologist. Abstracts are found below.

Date: Tuesday March 25, 10.30
Place: "Argumentet", 2nd floor, Ecology Building

Assortative Mating in Animals

Yuexin Jiang, Daniel I. Bolnick and Mark Kirkpatrick

Abstract

Assortative mating occurs when there is a correlation (positive or negative) between male and female phenotypes or genotypes across mated pairs. To determine the typical strength and direction of assortative mating in animals, we carried out a meta-analysis of published measures of assortative mating for a variety of phenotypic and genotypic traits in a diverse set of animal taxa. We focused on the strength of assortment within populations, excluding reproductively isolated populations and species. We collected 1,116 published correlations between mated pairs from 254 species (360 unique species-trait combinations) in five phyla. The mean correlation between mates was 0.28, showing an overall tendency toward positive assortative mating within populations. Although 19% of the correlations were negative, simulations suggest that these could represent type I error and that negative assortative mating may be rare. We also find significant differences in the strength of assortment among major taxonomic groups and among trait categories. We discuss various possible reasons for the evolution of assortative mating and its implications for speciation.

Current Zoology    2012, 58(3): 484 - 492

Daniel I. BOLNICK, Mark KIRKPATRICK

The term 'assortative mating' has been applied to describe two very different phenomena: (1) the tendency for individuals to choose phenotypically similar mates from among conspecifics; or (2) the tendency to prefer conspecific over hete- rospecific mates (behavioral reproductive isolation). Both forms of assortative mating are widespread in nature, but the relationship between these behaviors remains unclear. Namely, it is plausible that a preference for phenotypically similar conspecifics incidentally reduces the probability of mating with phenotypically divergent heterospecifics. We present a model to calculate how the level of reproductive isolation depends on intraspecific assortative mating and the phenotypic divergence between species. For empirically reasonable levels of intraspecific assortment on a single trait axis, we show that strong reproductive isolation requires very substantial phenotypic divergence. We illustrate this point by applying our model to empirical data from threespine stickleback Gasterosteus aculeatus and Darwin’s Finches (Geospiza spp). We conclude that typical levels of intraspecific assortment cannot generally be extrapolated to explain levels of interspecific reproductive isolation. Instead, reproductive isolation between species likely arises from different mate choice behaviors, or multivariate assortative mating

Greetings from Austin (Texas)

Posted by Erik Svensson

After about two weeks in Texas, around its capital Austin, I am heading home to Sweden again, after a very nice visit to my colleagues at Section for Integrative Biology at University of Texas. This department is certainly one of the strongest in ecology, evolution and behaviour in the US, and I can strongly recommend a visit here. Interestingly, they do not have any bird research at all, but most empirical work is on fish on insects, and the department is particularly strong in animal behaviour, sexual selection, neurobiology and evolutionary population genetics. This is the second time I visit, and I gave a talk already in spring 2003, nine years ago. Remarkably, almost all who attended my talk then were here this time as well, including Mark Kirkpatrick, Mike Ryan and legendary lizard evolutionary ecologist Eric Pianka.

I also met with some new folks, which have arrived since 2003, including PhD student Eben Gehring who works in the lab of Molly Cummings, and who does research on Ischnura-damselflies and evolutionary ecology professor Dan Bolnick, with whom I share many research interests, including the evolution of assortative mating and its consequences. Tonight, I am going to dinner with Scott Edwards, who is also visiting from Harvard this same week as I am here, and who will be the opponent of PhD-student Anna Runemark in our lab on May 25 next month.

Apart from Monday, this week, when I gave my talk, I have spent most time in the field, looking for and researching on Texas odonates. You can see one particularly stunning species that I saw here. Texas is especially species-rich, as half of North America's species occur here, more than 250 species, and several tropical elements from Mexico and Central America. As a comparision, Sweden has about 55 species, less than a fifth of Texas (although it should be said that Texas is slightly bigger than Sweden - everything is bigger in Texas, actually!). It is good to keep in mind that biodiversity is quite low in Europe, mainly due to the effects of past ice ages, and perhaps our faunas have not yet even been saturated, as re-colonziation from the last Ice Age might still be ongoing?

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.