Thoughts and reflections about the nature of selection from a NESCent-meeting in North Carolina

Posted by Erik Svensson

I just returned from a three-day working group meeting at "National Evolutionary Synthesis Centre" (NESCent) in Durham (North Carolina). The working group's topic is "Environmental and demographic determinants of natural selection", and there were 18 participants from the Australia, Canada, Sweden, the US and UK, i. e. a very multantional and scientifically diverse crowd, some of which you see on the pictures above and who you might recognize already. The organizers of this working group are Andrew MacColl, Adam Siepielski, Stephanie Carlson and Tim Coulson, four colleagues whose work I did know very well since before, but this was actually the first time we met IRL.

This working group will perform a meta-analysis and litterature synthesis on a favourite topic of mine: the ecological causes of natural and sexual selection on phenotypic traits in natural populations. I have been interested in this topic since my postdoc, especially the role of density-dependent natural selection on egg size, but also in later years when Tom Gosden and I studied spatial variation in sexual selection and its ecological consequences in the damselfly Ischnura elegans. 

 In spite of several decades of excellent selection studies in natural populations (summarized in a large meta-analysis ten years ago by Joel Kingsolver and colleagues), our knowledge about ecological agents (predators? competitors? parasites? climate?) are still very limited and far from quantitative. This is unfortunate, as natural selection is an ecological process, that might (or might not!) lead to evolutionary change. In fact, and to cite the great population geneticist Ronald Fisher in the famous opening sentence of his landmark volume The Genetical Theory of Natural Selection (published in 1930): "Natural selection is not evolution". Natural selection might lead to evolution - if the traits under selection are heritable and some other conditions are met - but need not to do so, and frequently does not.

Natural selection can for instance also reduce population size and cause extinction - and how often this is the case in nature we do not know. Nor is all evolutionary change due to natural selection - only extreme adaptationists would claim this. Much of evolutionary change can be due to - for instance - genetic drift, gene flow, recombination or simply neutral changes (for non-coding DNA). Thus, evolution and natural selection should not be confused - and one should not forget that one can study natural selection without any knowledge about genetics or the underlying genetic basis of traits under selection (Darwin is a good example of an evolutionist who knew more about natural selection than many molecular geneticists do today).

In this working group, we will search the litterature and add to already existing databases information about selective agents to those published studies where selection on phenotypic traits have been quantified already. Questions that can then be adressed include: How much of the variation in selection gradients can be explained by various environmental factors? What is the role of climatic factors and other abiotic factors vs. biotic factors like predation, competition, food supply or parasites? Do abiotic factors like climate and biotic factors interact - and could they even reinforce each other? We take up the challenge put forward by Michael Wade and Susan Kalisz in their important conceptual paper "The causes of natural selection" from 1990.

The questions are endless - and we know very little about the answers, but they are likely to be important. It is interesting that there is so much to do in this field and in the study of the ecology of selection in the "postgenomic" era, when we realize that the molecular revolution did not, and will not, solve all problems in evolutionary biology, and certainly not these ecological questions about the nature of selection on quantitative traits (whose genetic background is often due to many loci of small effects, resulting in the "missing heritability" problem).

The radical conclusion remains however: we do not need to know anything about neither quantative genetics or molecular genetics to study the ecological causes of selection - as this a question at an entirely different level of organization and  the ecological process of selection does not have anything to do with genetics, as so elegantly clarified and formalized by Lande and Arnold in their classical 1983-paper.

I am happy to have the opportunity to participate in a working group like this, and also impressed by a facility as NESCent - where synthetic work of this kind is funded - to the benefit of not only US scientists but also scientists from other countries. Hopefully, this working group will find some interesting new patterns and move the field forward - and perhaps help us to improve the empirical study of selection. I have already learned a lot - and hope to learn even more in the future. And that, after all, is the goal of science, not only publishing papers - which is of course also nice - but which is only one way of many others to communicate science. This blog post has hopefully also inspired and informed somewhat in that respect.

On "Evolutionary rescue", climate change and evolution of range limits

This week the lab-meeting will focus on  "Evolutionary rescue", which was a topic of a recent scientific conference involving several leading evolutionary biologists and ecologists in France, including leading population geneticist Mark Kirkpatrick who gave a talk entitled: "The evolution of a species’ range by beneficial mutations". 

The organisers of this interesting conference has been kind enough to put up videos on the internet of Mark's talk, which you can find here, as well as two other interesting talks by contributors. This is an excellent way of making it possible for others, like us, who could not take part in this meeting, and also a very environmentally-friendly way of spreading scientific information without necessarily travelling to every meeting you wish to attend.

I suggest that we meet the usual time (13.30 on Wednesday April 15 in "Argumentet") to listen to Mark's talk, and (if we have time), to one or two of the other talks. Thus, there is no need to read any paper before this lab-meeting, just come sharp and alert and be willing to discuss! Hopefully, we can arrange with Machteld's computer to be linked to the Powerpoint-projector so we can see the talk on a large screen. 

 

Lab-meeting on the evolution of plasticity in changing environments

This Wednesday (January 11 2012), we will discuss a relatively recent theoretical and conceptual paper in PLoS Biology entitled "Adaptation, plasticity and extinction in a changing environment: towards a predictive theory".  You can download it here.


Although this paper was published as recently as in 2010, but has already received 79 citations - a sign of a quite an influential paper. This is not surprising as it connects such topics as climate change, thermal adaptation and niche modelling with the evolution of phenotypic plasticity - all very important and central topics in ecology and evoutionary biology. Below you will find the Abstract for the paper. One of the co-authors is legendary evolutionary quantitative geneticist Russel Lande, by the way.

Time: Wednesday, January 11, 2012
Place: "Argumentet"

 

Summary 

Many species are experiencing sustained environmental change mainly due to human activities. The unusual rate and extent of anthropogenic alterations of the environment may exceed the capacity of developmental, genetic, and demographic mechanisms that populations have evolved to deal with environmental change. To begin to understand the limits to population persistence, we present a simple evolutionary model for the critical rate of environmental change beyond which a population must decline and go extinct. We use this model to highlight the major determinants of extinction risk in a changing environment, and identify research needs for improved predictions based on projected changes in environmental variables. Two key parameters relating the environment to population biology have not yet received sufficient attention. Phenotypic plasticity, the direct influence of environment on the development of individual phenotypes, is increasingly considered an important component of phenotypic change in the wild and should be incorporated in models of population persistence. Environmental sensitivity of selection, the change in the optimum phenotype with the environment, still crucially needs empirical assessment. We use environmental tolerance curves and other examples of ecological and evolutionary responses to climate change to illustrate how these mechanistic approaches can be developed for predictive purposes.