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.

"The Origin of Species - 150 years later"

I am currently at the Marin Biology Research Station in Kristineberg (Fiskebäckskil) in Bohuslän att symposium in celebration of Charles Darwin. This year (2009), it is 150 years since "The Origin of Species" was published, and 200 years since Darwin was born. To celebrate the memory of Darwin, Hans Ellegren (professor of evolutionary genetics in Uppsala) and Staffan Ulfstrand (professor emeritus of animal ecology, also from Uppsala) has arranged a symposium in the beatiful archipelago on the swedish west coast. Funding for this meeting comes from The Wennergren Foundation. Unfortunately, this meeting was only open for a small group of invited people, apart from the speakers, so here is a little report from the first day.

The theme of today has been theory and genetics of speciation, with some great contributions from evolutionary theoreticians Michael Turelli (University of California, Davies) and Sergey Gavrilets (University of Knoxville, Tennesse). Turelli talked about Haldane's rule and the genetics of postzygotic isolation, and Gavrilets presented models for the tempo and mode of adaptive radiations. Although some of these topics have been presented before by these two leading theoreticians, it is always nice to get un update.

Gavrilets have apparently got a big grant from the National Science Foundation (NSF) to set up a centre for mathematical and biological synthesis in Knoxville, similar to the ecological synthesis centre in Santa Barbara and the evolutionary synthesis centre in North Carolina. Worth checking up: there will be funding opportunities for both postdocs and workshops.

More "naturalistic" talks were given by Trevor Price (University of Chicago) and Jim Mallet (London) about bird and butterfly speciation, respectively. Trevor presented some idéas and phylogenetic patterns on bird diversification in the Himalayas, which challenges the current ecological speciation paradigm, which has almost been taken a bit too much for granted based on a few well-investigated model systems such as the Galápagos finches. Mallet questioned the views by Ernst Mayr about the reality of species and argued that Darwin's view on species was more realistic than some of the views that were advocated by Mayr and other architects of the so-called "Modern Synthesis" in the 1940'ties. In particular, Mallet argued that some of their idéas about reproductive isolation evolving to protect the "genetic integrity" of species relied on naive group-selectionism.

Two swedish contributions were by Kerstin Johannesson (parallell evolution of reproductive isolation in Littorina-snails) and Anna Qvarnström (genetics of speciation in Ficedula-flycatchers). In general, I would say that this meeting has been good to get updated on the classical concepts and discussion topics, although there has not been many surprising news. In that sense, I have the feeling that perhaps the field of speciation might have reached a plateau (perhaps temporary) where it has now entered what science philosopher Thomas Kuhn would call "normal science" or "problem solving". Perhaps I am wrong, but I have the distinct feeling that we need some new idéas to focus on, as the classical allopatry-sympatry controversy seems to fade away and people loose interest. To me, the most thought-provoking talk today was the one by Trevor Price, although I do not necessarily agree with everything he had to say. In any case, his book "Speciation in birds" is highly recommendable.

Hopefully, I will be able to publish another bloggpost tomorrow about the genomic aspects of speciation, which will be discussed tomorrow. Food here is excellent, by the way.

Visit by Finnish colleagues this week

As you hopefully already know, Drs. Katja Tynkkynen and Janne Kotiaho from University of Jyväskylä in Finland will visit our department and our research group this week. They will arrive tomorrow (Tuesday), and will participate in our lab-meeting on Wednesday morning (10.15). Maren will provide some "fika".

We will discuss two papers suggested by Janne, that have already been sent out to you. Please contact me or anyone else in the group if you have not got these papers, so that you are prepared for Wednesday morning. Both papers deal with species concepts and speciation, one with Lamarck's species concept, the other with definitions of sympatric speciation.

The title of the papers for the seminar are:

Jean-Baptiste Pierre Antoine de Monet, Chevalier de Lamarck

On classification and evolution

Philosophie zoologique, ou exposition des considérations
relatives à l'histoire naturelle des animaux.

(Zoological Philosophy. An Exposition with
Regard to the Natural History of Animals)
by J.B. Lamarck
1809
Translated by Hugh Elliot

Macmillan, London 1914
Reprinted by University of Chicago Press, 1984

And:

Fitzpatrick et al. 2008. What, if anything is sympatric speciation? 2008.
J. Evol. Biol. 21:1452-1459.



After the lab-meeting, I will bring Janne for a lunch on Wednesday together with Susanne Åkesson, Anders Brodin, Anders Hedenström and Dennis Hasselquist. We will plan the International Behavioural Ecology Congress (ISBE) that will take place in Lund 2012, and we would like to get some feedback and advices from Janne about his experiences when he arranged the ISBE-meeting in Jyväskylä a few years ago. I hope the rest of you can take care of Katja during Wednesday lunch. The afternoon will be set aside for scientific discussions in the "Darwin"-room, where Katja will present some of her work.

On Thursday (19/3), Janne will present a talk about the history of sexual selection, that will take place in the "Blue Hall" (bottom floor in the Ecology Building) at 14.00. The title of this talk is:

"The past and present of the theory of sexual selection through mate choice"

Janne has promised to present a historical overview about the intellectual roots of the idéa of sexual selection through female choice, and the (possible) role of the feminist movement in affecting its scientific acceptance in the early 1980'ties, more than hundred years after it was originally developed by Charles Darwin.

This is likely to be a fun, and perhaps also controversial talk, so do not miss it! Janne has promised to "discuss some of the slightly less pleasent aspects of the current scientific enterprise through some examples stemming from sexual selection.". We are indeed looking forward to this.