On linking ecology to sexual selection

Together with John Waller, I have a paper that is now out in American Naturalist as an E-article, meaning that it is "Open Acess" and possible for anyone to download. Go here, if you would like to download a PDF of this paper. I am very much in favour of the OA-model of publishing, and I certainly hope that the publication fees we paid will also result in more citations.

This study, which was fun to do and write up, takes a look at the important link between ecology and sexual selection. We were interested in the functional significance and evolutionary consequences of wing pigmentation in calopterygid damselflies, and we used a mixture of comparative phylogenetic analyses and field studies using thermal imaging to adress this issue. In particular, we wanted to see if there was any obvious thermal benefit of male wing pigmentation, which also has important functions in sexual selection, male-male competition and species recognition. Turns out that the evidence for such a thermal benefit is mixed, although there is a clear biogeographic signature in the sense that pigmented clades are more common in northern regions and temperate climates.

Wing pigmentation is also significantly associated with eleved speciation and extinction rates, using so-called BiSSE-analyses ("Binary Speciation and Extinction") as implemented in Diversitree. This latter result provides comparative support to our previous experimental work demonstrating that wing pigmentation functions as a species recognition character between C. splendens and C. virgo, and suggest that wing pigmentation is generally involved across the entire group as a promoter of speciation, although most species formed by such non-ecological sexual selection tend to go extinct fairly soon after they have formed.

In general, I think there are too few studies where comparative approaches and field experiments are combined, as both have strength and weaknesses and inferences could be stronger if they are combined (Disclaimer: in case some sensitive theoretical ecologist reads this post, I do of course also think there are other interesting and useful research approaches, such as mathematical models).

Ecology and Sexual Selection: Evolution of Wing Pigmentation in Calopterygid Damselflies in Relation to Latitude, Sexual Dimorphism, and Speciation

American Naturalist (in press, November 2013)

Erik I. Svensson* and John T. Waller

Evolutionary Ecology Unit, Department of Biology, Lund University, SE-223 62 Lund, Sweden

Abstract

Our knowledge about how the environment influences sexual selection regimes and how ecology and sexual selection interact is still limited. We performed an integrative study of wing pigmentation in calopterygid damselflies, combining phylogenetic comparative analyses, field observations and experiments. We investigated the evolutionary consequences of wing pigmentation for sexual dimorphism, speciation, and extinction and addressed the possible thermoregulatory benefits of pigmentation. First, we reconstructed ancestral states of male and female phenotypes and traced the evolutionary change of wing pigmentation. Clear wings are the ancestral state and that pigmentation dimorphism is derived, suggesting that sexual selection results in sexual dimorphism. We further demonstrate that pigmentation elevates speciation and extinction rates. We also document a significant biogeographic association with pigmented species primarily occupying northern temperate regions with cooler climates. Field observations and experiments on two temperate sympatric species suggest a link between pigmentation, thermoregulation, and sexual selection, although body temperature is also affected by other phenotypic traits such as body mass, microhabitat selection, and thermoregulatory behaviors. Taken together, our results suggest an important role for wing pigmentation in sexual selection in males and in speciation. Wing pigmentation might not increase ecological adaptation and species longevity, and its primary function is in sexual signaling and species recognition.

On blogging, tweeting and non-ecological speciation

One of the reasons to have a scientific blog, whether an individual-based or a group-based one like ours, is that you might increase the attention to your research, and hopefully also increase the interest in your work, boost your citation rates and perhaps become more succesful as a scientist in grant applications. But is there any real evidence for this, or is it pure wishful thinking? As a matter of fact, some quantitative evidence is starting to accumulate now, that blogging and tweeting does increase the interest in your work, as judged by increasing number of downloads. Thus, unlike many other scientists who might consider blogging waste of time, I think it is a mistake to dismiss social media in the scientific process these days.

In the spirit of this, and with the hope to increase the interest in my research, I post my latest article that is published in Organisms, Diversity & Evolution and which is entitled: "Non-ecological speciation, niche conservatism and thermal adaptation: how are they connected?" It is a critical review of the current state of ecological speciation theory, its assumptions and limitations, and with a discussion about some alternatives to ecological speciation. Download it, read it or cite it (or do it all!)! I also present some thermal image data on the thermal niches of two sympatric calopterygid damselflies: Calopteryx splendens and C. virgo.

This paper was fun to write, and it largely grew out of discussions I had with Andrew Hendry and some other folks at Uppsala last year, when I visited the Evolutionary Biology Centre (EBC) in conjunction with the PhD-student defence's of Niclas Vallin and Paolo Innocenti. The Abstract and paper details are given below. Now, perhaps Maren Wellenreuther and Anna Runemark will post about some other recent lab-publications that have come out recently?

Abstract

During the last decade, the ecological theory of adaptive radiation, and its corollary “ecological speciation”, has been a major research theme in evolutionary biology. Briefly, this theory states that speciation is mainly or largely the result of divergent selection, arising from niche differences between populations or incipient species. Reproductive isolation evolves either as a result of direct selection on mate preferences (e.g. reinforcement), or as a correlated response to divergent selection (“by-product speciation”). Although there are now many tentative examples of ecological speciation, I argue that ecology’s role in speciation might have been overemphasised and that non-ecological and non-adaptive alternatives should be considered more seriously. Specifically, populations and species of many organisms often show strong evidence of niche conservatism, yet are often highly reproductively isolated from each other. This challenges niche-based ecological speciation and reveals partial decoupling between ecology and reproductive isolation. Furthermore, reproductive isolation might often evolve in allopatry before ecological differentiation between taxa or possibly through learning and antagonistic sexual interactions, either in allopatry or sympatry. Here I discuss recent theoretical and empirical work in this area, with some emphasis on odonates (dragonflies and damselflies) and suggest some future avenues of research. A main message from this paper is that the ecology of species differences is not the same as ecological speciation, just like the genetics of species differences does not equate to the genetics of speciation.

Keywords  Mike May Festschrift – Calopteryx – Learning – Learned mate preferences – Niche – Sexual conflict – By-product speciation – IR-camera – Thermal imaging – Ectotherms – Sexual isolation