Sunday, April 29, 2012

On speciation, the species problem and the role of species in evolution

This week's lab-meeting will be dedicated to the classical "species problem" in evolutionary biology and the role of species in ecology. We will start off with a brief presentation by Maren Wellenreuther about molecular identification of (putative) hybrid phenotypes between the two calopterygid damselflies (Calopteryx splendens and C. virgo) that she has been working on lately. I will also say a few words about my research trip to Texas, and the remarkable species diversity of odonates in this state (> 260 species in the state of Texas, about five times more than entire Sweden!).

Then, I was thinking we should discuss two recent idéa-articles, which should perhaps be a relatively easy read, and would hopefully be stimulating. One is on the state of the so-called "neutral theory" of species diversity in ecology, and the other is about species concepts and the ephemeral role of species in evolution. Phylogenetic comparative biologist Luke J. Harmon is co-author on both these papers, and one of the other authors is Rampall Etienne, who will be a plenary speaker at our ESF-funded meeting "The role of behaviour in non-adaptive and non-ecological speciation" in August this year. Here you can sign up to this meeting, which is free of charge and will take place on August 18 2012.

Our  lab-meeting  this coming week will take place on May 2, at 13.30 in the seminar room "Argumentet". Below, I provide the abstracts and links to these two interesting articles. You can download them here and here and also by clicking on the Abstract-links below. Enjoy!

The case for ecological neutral theory

Understanding the rate at which new species form is a key question in studying the evolution of life on earth. Here we review our current understanding of speciation rates, focusing on studies based on the fossil record, phylogenies, and mathematical models. We find that speciation rates estimated from these different studies can be dramatically different: some studies find that new species form quickly and often, while others find that new species form much less frequently. We suggest that instead of being contradictory, differences in speciation rates across different scales can be reconciled by a common model. Under the “ephemeral speciation model”, speciation is very common and very rapid but the new species produced almost never persist. Evolutionary studies should therefore focus on not only the formation but also the persistence of new species. 

Thursday, April 26, 2012

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?

Monday, April 16, 2012

On cliff effects, male mate preferences and niche use in Calopteryx

#by Maren Wellenreuther

I am following Erik’s recommendation that we should all start to more actively promote our own research, and will present some of my most recent publications.The first work  that I would like to highlight is a paper that was started in 2007, when Shawn Kuchta and I arrived in Sweden to start our postdocs on the two charismatic Calopteryx damselfly species found in Sweden, C. virgo and C. splendens. We both arrived just at the start of the field season in May 2007 and had never worked on odonates before. It was an exciting time: we were both living at the University's field station in the middle of the forest, which was also used as a military training ground, and so we could relax in the evening after a hard day in the field, while watching the military training tanks and troops drive through the forest and fields outside the station. Shawn had worked for many years on salamanders while I had studied marine fish, and the different view points and ideas that came along with having studied such different study systems made our conversations about science and evolution rich and interesting. Shawn's work on  Calopteryx damselflies is seeking to measure the strength of natural selection acting on the two Calopteryx species (see photograph below), by collecting wings from feeding stations and comparing them to the variation present in natural populations. Although Shawn has left Sweden and is now an Assistant Professor at Ohio University, he is still actively involved in Calopteryx research and is currently writing up this data-so stay tuned for more on this soon!

Calopteryx splendens (left) have wing patches that cover roughly 50% of the wings, while C. virgo have almost fully melanised wings.

At that time that Shawn and I started our work on Calopteryx damselflies in Sweden, another member joined the lab group. Her name is Elodie Vercken, and she was a newly finished postdoc from France who had worked with Jean Clobert on colour morphs and alternative strategies in the common lizard Lacerta vivipara. She is now a researcher at INRA (National Institute for Agronomical Research) in Sophia Antipolis in France.

Elodie Vercken in the field in Sweden catching damselflies fort mate choice experiments.
Together with Elodie, I spent my days out in the field to measure male and female mate choice in different populations, and trying to relate this mate preference data to population ecology and phenotypic traits (sympatry versus allopatry and so on). It was a hot summer and we tried to stay cool while tethering males and females of both species to bamboo sticks and painting their wings to perform mate presentation experiments. It was great fun.
Maren Wellenreuther presenting tethered damselflies in the field

Part of the data that we gathered during that summer was recently used in a modeling paper on cliff-edge effects, which tests the counterintuitive idea that the trait value associated with the maximum of an asymmetrical fitness function is not necessarily the value that is selected for when the trait shows variability in its phenotypic expression.
Vercken E, Wellenreuther M, Svensson EI, Mauroy B (2012) Don't Fall Off the Adaptation Cliff: When Asymmetrical Fitness Selects for Suboptimal Traits. PLoS ONE 7(4): e34889.

From that field season, Elodie, Erik and I also published a paper on male mate preferences in C. splendens, to address the question whether males can distinguish between immigrant and resident females, something previously found for females.
Wellenreuther M, Vercken E and Svensson EI (2010) A role for ecology in male mate discrimination of immigrant females in Calopteryx damselflies? Biological Journal of the Linnean Society 100: 506-518

In addition to these two papers, I further delved into an area that I had investigated extensively during my PhD work: Habitat use and divergence in habitat space between species. The idea was to extent the work that was previously done by our lab and other groups on the habitat use of the two Calopteryx species, by expanding the spatial scale so that broader questions can be asked. To do this, a large data set for the whole of Fennoscandia was generated using field data and museum records, and niche modelling was used to estimate the extent of niche divergence versus conservatism and to identify the most important environmental variables that correspond to niche differences.  The large data set in this paper also allowed us to look into the following question: what is the extent of niche divergence in species that are thought to have primarily evolved through sexual selection on secondary sexual traits? Based on our results, we argue that adaptive niche diversification appears to play a relatively minor role in speciation and evolutionary divergence in species groups such as salamaders, East African cichlids, and odonates where sexual selection on secondary sexual traits is pronounced and a key element of diversification. This work was done in collaboration with Keith W Larson who has excellent modelling skills and likes to analyze large data sets.
Wellenreuther M, Larson K W and Svensson E I. (in press) Climatic niche similarity and geographic range limits in ecologically similar co-existing damselflies Ecology

Maybe Anna Runemark, who is currently finishing her PhD thesis on the Skyros Wall lizard, would like to write the next blog post by telling us about her most recent articles.

Happy Researching!

The abstracts to the papers are posted below. 
Vercken E, Wellenreuther M, Svensson EI, Mauroy B (2012) Don't Fall Off the Adaptation Cliff: WhenAsymmetrical Fitness Selects for Suboptimal Traits. PLoS ONE 7(4): e34889.
Abstract: The cliff-edge hypothesis introduces the counterintuitive idea that the trait value associated with the maximum of an asymmetrical fitness function is not necessarily the value that is selected for if the trait shows variability in its phenotypic expression. We develop a model of population dynamics to show that, in such a system, the evolutionary stable strategy depends on both the shape of the fitness function around its maximum and the amount of phenotypic variance. The model provides quantitative predictions of the expected trait value distribution and provides an alternative quantity that should be maximized (“genotype fitness”) instead of the classical fitness function (“phenotype fitness”). We test the model's predictions on three examples: (1) litter size in guinea pigs, (2) sexual selection in damselflies, and (3) the geometry of the human lung. In all three cases, the model's predictions give a closer match to empirical data than traditional optimization theory models. Our model can be extended to most ecological situations, and the evolutionary conditions for its application are expected to be common in nature.

Wellenreuther M, Vercken E and Svensson EI (2010) A role for ecology in male matediscrimination of immigrant females in Calopteryx damselflies? Biological Journal of the Linnean Society 100: 506-518
Abstract: Sexual selection against immigrants is a mechanism that can regulate premating isolation between populations but, so far, few field studies have examined whether males can discriminate between immigrant and resident females. Males of the damselfly Calopteryx splendens show mate preferences and are able to force pre-copulatory tandems. We related male mate responses to the ecological characteristics of female origin, geographic distances between populations, and morphological traits of females to identify factors influencing male mate discrimination. Significant heterogeneity between populations in male mate responses towards females was found. In some populations, males discriminated strongly against immigrant females, whereas the pattern was reversed or nonsignificant in other populations. Immigrant females were particularly attractive to males when they came from populations with similar predation pressures and densities of conspecifics. By contrast, immigrant females from populations with strongly dissimilar predation pressures and conspecific densities were not attractive to males. Differences in the abiotic environment appeared to affect mating success to a lesser degree. This suggests that male mate discrimination is context-dependent and influenced by ecological differences between populations, a key prediction of ecological speciation theory. The results obtained in the present study suggest that gene-flow is facilitated between ecologically similar populations.

Wellenreuther M, Larson K W and Svensson E I. (in press) Climatic niche similarity and geographic range limits in ecologically similar co-existing damselflies –Ecology
The factors that determine species' range limits are of central interest to biologists. One particularly interesting group are odonates (dragonflies and damselflies), which show large differences in secondary sexual traits and respond quickly to climatic factors, but often have minor interspecific niche differences, challenging models of niche-based species co-existence. We quantified the environmental niches at two geographic scales to understand the ecological causes of northern range limits and the co-existence of two congeneric damselflies (Calopteryx splendens and C. virgo). Using environmental niche modelling, we quantified niche divergence first across the whole geographic range in Fennoscandia and second only in the sympatric part of this range. We found evidence for interspecific divergence along the environmental axes of temperature and precipitation across the northern range in Fennoscandia, suggesting that adaptation to colder and wetter climate might have allowed C. virgo to expand further northwards than C. splendens. However, in the sympatric zone in southern Fennoscandia we found only negligible and non-significant niche differences. Minor niche differences in sympatry lead to frequent encounters and intense interspecific sexual interactions at the local scale of populations. Nevertheless, niche differences across Fennoscandia suggest that species-differences in physiological tolerances limit range expansions northwards, and that current and future climate could have large effects on the distributional ranges of these and ecological similar insects. 

Sunday, April 15, 2012

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?


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.

Monday, April 9, 2012

Praise for the "Oikos" blog

Posted by Erik Svensson

Most of us have very little time to read, unfortunately, including articles and blogs. However, when time is limited, then it becomes crucial to prioritize what to read, so that one can really find the good stuff and learn new things. I have recently enjoyed reading the "Oikos blog", where journal editor and ecologist Jeremy Fox often puts up very readable, provocative and interesting posts.

The Oikos-blog, which is connected to the journal with the same name has consequently often some very high-quality posts about science in general, the field of ecology as well as career advice to students, postdocs and faculty. I can highly recommend it. The Oikos-blog is now on our list of recommended blogs in the right margin of this blog. Go check it out! 

Here are some recent and very interesting posts:

Advice: weak reasons for choosing a research project

Instrumental variables: the key to analyze "natural" experiments

Advice: how to network at conferences

It's the end of NCEAS as we know it (and I feel fine)

Advice: how to choose a PhD program

There are many other interesting posts, but especially the last one should be of interest to our Master's students Anna and John, I think. There is also at least one post with advice for postdocs, but I have not been able to find it again, unfortunately. 

Tuesday, April 3, 2012

Lab-member in the news: Nordén sister duo shows the power of biology studies in Lund

Our Master's student Anna Nordén, who is working with assortative mating in Calopteryx, made it in to the media this week, in the daily newspaper "City". Above, you can see Anna's happy face (well, Anna is actually ALWAYS happy!) when asked about her summer plans. I especially liked that she emphasized that we only work when it is nice outside and that one actually can get PAID to do this kind of stuff (or even get student loans from CSN). But best of all is of course the summary blob in the right corner that says it all: "Ska fånga trollsländor". Cheers to you Anna: you are an excellent ambassador for our research lab!

Remarkably: Anna's sister Elsa Nordén (also a biology student) is also on the front cover of the same issue of City, these Nordén sisters are really media celebrities.

Happy Easter!

Posted by Erik Svensson

I wish all of you, readers and lab-members alike and whereever you are, a Happy Easter. For those of you who are spending part of the holidays in finishing your VR-applications, I hope you can take a few hours break from work.

As for next week, lab-meeting will take place on Wednesday April 11 at 13.30 in "Argumentet". Postdoc Miriam Henze from the "Vision Group" in the Biology Department will tell us a little bit about her ongoing work, progress and recent research results on sensory physiology of the fascinating model organism: the damselfly Ischnura elegans, and how males perceive the three different female colour morphs in this species.

After this, Jessica Abbott wants to have some input on a manuscript she is working on which is about epigenetic inheritance (or the lack thereof) in the charismatic fruitfly Drosophila melanogaster. Jessica will send out a copy of her manuscript later, so that we all can read it well before the meeting and give valuable input to Jessica.