Tuesday, May 24, 2011
Sunday, May 22, 2011
Last week's lab-meeting on kin selection was cancelled, and since this discussion largely seems to be a semantic one and of little direct relevance to our own work on insects, I thought we should instead discuss an insect paper, now when the field season is rapidly approaching. After all, we are not behavioural ecologists and not so focussed on kin selection, but rather field evolutionary biologists, so this paper might be more central to our ongoing work.
The paper is a wonderful example of how evolution acts like a "tinkerer", rather than as an engineer, when novel structures evolve, and that new traits arise from already existing structures/genes as "exaptations", rather than evolve from scratch. In this case, the remarkable morphological structures we will discuss (see above!) are governed by genes which originally coded for wings! The paper I have in mind is a wonderful example of "evo-devo", i. e. the genetic and developmental basis of animal form and it deals with the morphological structures of treehoppers (Homoptera), a diverse insect group characterized by remarkable appendices on their thorax, of unknown adaptive function (see picture above!). The title is: "Body plan innovation in treehoppers through the evolution of an extra wing-like appendage".
You can downloadthe paper here, and the abstract is found below. Time and place as usual: "Argumentet" at 14.30 on Wednesday May 25. Any fika volunteer?
Body plans, which characterize the anatomical organization of animal groups of high taxonomic rank1, often evolve by the reduction or loss of appendages (limbs in vertebrates and legs and wings in insects, for example). In contrast, the addition of new features is extremely rare and is thought to be heavily constrained, although the nature of the constraints remains elusive2, 3, 4. Here we show that the treehopper (Membracidae) ‘helmet’ is actually an appendage, a wing serial homologue on the first thoracic segment. This innovation in the insect body plan is an unprecedented situation in 250 Myr of insect evolution. We provide evidence suggesting that the helmet arose by escaping the ancestral repression of wing formation imparted by a member of the Hox gene family, which sculpts the number and pattern of appendages along the body axis5, 6, 7, 8. Moreover, we propose that the exceptional morphological diversification of the helmet was possible because, in contrast to the wings, it escaped the stringent functional requirements imposed by flight. This example illustrates how complex morphological structures can arise by the expression of ancestral developmental potentials and fuel the morphological diversification of an evolutionary lineage.
Thursday, May 12, 2011
Monday, May 9, 2011
In our next lab-meeting, we will dive in to the recent controversy over kin selection and its utility in explaining the evolution of eusociality in social insects. This controversy started with a provocative paper in "Nature" by Martin Nowak, Corina Tarnita and Edward O. Wilson, which you can download here. Basically, these three authors argue that kin selection is neither necessary nor sufficient to explain the evolution of eusociality, but that standard natural selection theory is sufficient. It is not surprising that this paper has been met by an outcry from many researchers in social evolution, and they have got a severe criticism in this paper, with a lot of different co-authors. Nowak et al. defend themselves against the many critics here.
Who is right? Well, it is up to us to make up our own opinion, after we have read these three papers! We will meet on Friday May 13 at 10.30 in "Argumentet" to discuss these three rather short papers.
For those of you who are interested more in this debate and want some different viewpoints, I can recommend this blogpost by Jerry Coyne who, not surprisingly, is very critical of Nowak et al. So is Richard Dawkins. For a counterpoint and an interesting perspective from a classical proponent of group selection, I can recommend this blogpost by David Sloan Wilson, who criticizes both camps, i. e. both Nowak et al. and their critics, and suggest that both have misunderstood the real issues at stake! David Sloan Wilsons blogpost has the challenging and provocative title: "137 Co-authors Can't Be Wrong - and That's The Problem".
It is certainly a sign of a healthy research field that things like these are intensively debated, and shows that evolutionary biology is as vibrant and exciting as ever, with some fundamentally important controversies that needs to be discussed.
Monday, May 2, 2011
When I was a PhD-student in Sweden in the nineties, one of the most ugly words you could say was "group selection", and the so-called "selfish-gene paradigm" of Richard Dawkins was taken as almost a religious truth. These were the days when behavioural ecology ruled much of of the scentific activities in biology in Scandinavia and Britain. Lower-level selection of selfish genes was assumed to be either the only or at least the major evolutionary force that would explain all adaptation and biological diversity. Higher-level selection, on goups, demes, populations or species, was either deemed impossible or dismissed as unimportant.
This remarkable dogmatic reductionism in Scandinavian behavioural ecology seems, in the aftermath, as both dogmatic and not very well supported by either theory or empirical evidence. Even the great population geneticist R. A. Fisher did actually believe in group selection, and for him it was mainly an empirical issue how strong it was, compared to lower-level selection of individuals and genes.
However, one thing is certain: scientific paradigms change, and clearly group-selection (or rather multi-level selection) is on the rise again. This week's lab-meeting (Wednesday May 4), we will discuss a relatively recent TREE-paper on how molecular phylogenies might be used to study the process of species selection in a statistically rigorous and empirical way. Increasing evidence suggest that macroevolutionary trends, such as increases or decreases in diversity, speciation and extinction can simply not be extrapolated from lower-level selection processes, challenging the selfish-gene paradigm. Below, you will find an abstract and a link to the paper.
Time as usual: 13.30 on Wednesday (May 4) afternoon. Place: Probably "Argumentet".
Rabovsky, M. L. & MacCune, A. R.
Trends Ecol. Evol. 25: 68-74
Abstract: Species selection as a potential driver of macroevolutionary trends has been relegated to a largely philosophical position in modern evolutionary biology. Fundamentally, species selection is the outcome of heritable differences in speciation and extinction rates among lineages when the causal basis of those rate differences can be decoupled from genotypic (within-population) fitnesses. Here, we discuss the rapidly growing literature on variation in species diversification rates as inferred from molecular phylogenies. We argue that modern studies of diversification rates demonstrate that speciesselection is an important process influencing both the evolution of biological diversity and distributions of phenotypic traits within higher taxa. Explicit recognition of multi-level selection refocuses our attention on the mechanisms by which traits influence speciation and extinction rates.