Visit by US colleague Eben Gering next week: invasion biology and colour evolution of damselflies and chickens

 


Posted by Erik Svensson

Next week (October 12-16), our colleague Dr. Eben Gering from Michigan State University in the US will visit EXEB and the Biology Department. Some of you have already met Eben before, and he visited three years ago during the ISBE Congress in Lund 2012. Eben obtained his PhD at University of Texas (Austin), under the supervision of Prof. Molly Cummings. His thesis-research focused on mechanisms of colour polymorphism maintenance in damselflies and island biogeography. He studied the damselfly Ischnura ramburi (a congener to Ischnura elegans, which we are working on in our lab), and he performed much of his field work on Hawaii.

Currently, Eben is a postdoc at MSU, but he collaborates with a Swedish research group working on chicken genomics at Linköping University, particularly Dominic Wright. On his way to Linköping, Eben thus stops by in Lund and he will participate in our lab-meeting on Tuesday next week (announced in a separate blog post). He will give next week's Thursday seminar on October 15 (13.15) in the "Blue Hall", which will contain data about colour evoution in both damselflies and chickens and a discussion about the evolutionary and genomic consequences of feralization (the opposite of domestication).  

If you are interested in meeting with Eben and discuss his or your research, please contact me (erik.svensson@biol.lu.se), so we can set up a meeting. We also plan to go out for beers at least one evening (tentatively on Wednesday October 14, to "Inferno"), and everybody who wants to attend are most welcome to join in. Below follows more information and an Abstract about Eben's talk.

A tale of two invasions: rapid evolution of color polymorphism in invasive damselflies and chickens

"Darwin and Wallace each struggled to explain the variation in evolution’s color palette. In Darwin’s view, colorful ornaments were a common outcome of sexual selection, whereas Wallace ascribed them to natural selection. A century later, we recognize that both forms of selection interact in complex ways to determine color phenotypes. Here I will describe two case studies of color evolution within invasive populations. Species invasions provide unique opportunities to characterize how traits respond to novel (and often extreme) forms of selection. Surprisingly, our syntheses of historical, genetic and experimental data from invasive chickens and damselflies suggest that density-dependent selection promoted color variability in both groups via very different mechanisms. In damselflies, color polymorphism allowed females to adapt to changes in social environment that ensued invasive spread.  In chickens, plumage variation that resulted from hybridization collapsed during colonization of marginal habitats. While our understanding of these complex systems is far from complete, patterns seen thus far reveal how demographic features of biotic invasions could facilitate rapid evolution by both Darwinian and Wallacian mechanisms." 

Genetic basis of pigmentation loss and eye evolution in Asellus aquaticus

People in this lab are probably well aware of the interesting freshwater isopod Asellus aquaticus, who has contributed to two PhD-theses in our group by Fabrice Eroukhmanoff and Kristina Karlsson. Fabrice has published two thesis-papers on the quantitative genetic basis of ecotype divergence in body size and pigmentation, in Molecular Ecology and Journal of Evolutionary Biology (forthcoming).

What we demonstrated in these papers was that both morphological traits (size-traits) and pigmentation had significant additive genetic basis, both between and within populations. What we did not show, however, was the specific molecular-genetic basis of these heritable traits, i. e. which loci, how many and their genomic locations. That was not our goal, however, and Asellus aquaticus has not been a major model organism in molecular genetics.

But things seems to change. A forthcoming paper in PNAS by a US-based group presents a genome-wide linkage map involving 117 markers for Asellus aquaticus, and discuss the genetic mechanisms behind loss-of-pigmentation phenotypes and loss-of-vision phenotypes among blind, pale and cave-dwelling populations of this enigmatic species. The abstract is found below. I predict that the findings in that study will also have implications for ecotype divergence within lakes, such as between the ecotypes we have studied in southern Sweden.

Genetic basis of eye and pigment loss in the cave crustacean, Asellus aquaticus

Protas ME, Trontelj P, Patel NH.

Department of Molecular and Cell Biology, Center of Integrative Genomics, and Department of Integrative Biology, University of California, Berkeley, CA 94720-3200.

Abstract

Understanding the process of evolution is one of the great challenges in biology. Cave animals are one group with immense potential to address the mechanisms of evolutionary change. Amazingly, similar morphological alterations, such as enhancement of sensory systems and the loss of eyes and pigmentation, have evolved multiple times in a diverse assemblage of cave animals. Our goal is to develop an invertebrate model to study cave evolution so that, in combination with a previously established vertebrate cave system, we can address genetic questions concerning evolutionary parallelism and convergence. We chose the isopod crustacean, Asellus aquaticus, and generated a genome-wide linkage map for this species. Our map, composed of 117 markers, of which the majority are associated with genes known to be involved in pigmentation, eye, and appendage development, was used to identify loci of large effect responsible for several pigmentation traits and eye loss. Our study provides support for the prediction that significant morphological change can be mediated through one or a few genes. Surprisingly, we found that within population variability in eye size occurs through multiple mechanisms; eye loss has a different genetic basis than reduced eye size. Similarly, again within a population, the phenotype of albinism can be achieved by two different genetic pathways-either by a recessive genotype at one locus or doubly recessive genotypes at two other loci. Our work shows the potential of Asellus for studying the extremes of parallel and convergent evolution-spanning comparisons within populations to comparisons between vertebrate and arthropod systems.

Day 2: Genomics of speciation

The second day at Kristineberg has mainly been devoted to the genomic basis of speciation and the genetics of postzygotic isolation. Interesting talks by Michael Nachman, Hopi Hoekstra, Axel Meyer and Dave Presgraves. In general, though, it has been a bit too much about postzygotic isolation, though, to my taste. This, however, reflects that it is a meeting that was organized by Hans Ellegren, whose main interests are in these genomic aspects of speciation and evolution.

Again, my general feeling from yesterday remains: the field of speciation have reached the phase of "normal science", where there are not that many exciting discoveries or new concepts, but rather a lot of "problem solving" and filling in of the gaps. This might not necessarily be a bad thing: when fields are too hot and fast moving, the best science is not necessarily made because people tend to jump on bandwagons and reflect very little once they are on those bandwagons.

I had an interesting lunch discussion with Trevor Price today about the role of learning in evolution, particularly the role of learned mate preferences. This was quite refreshing, since Trevor thinks learning is extremely important and underestimated in the speciation process (as I also believe). When I first brought up the issue of learned mate preferences in on of our lab-meetings about 1 1/2 years ago, I saw mainly a lot of blank faces in the room, but I am more convinced than ever that this is one of the most exciting areas of speciation research in the future (and our coming postdoc Machteld Verzijden would probably agree, I suspect). It is also a natural area where field ecologists and behavioural ecologists could make important contributions and add to a more balanced picture of the speciation process than we would have had if we only relied on genomics data from Drosophila-research.

Another general reflection of this meeting is how large resources many research groups in the US have, compared to us in Sweden. This is particularly evident when it comes to genomic studies, such as large-scale DNA-sequencing efforts, transcriptomics, "454" and microarrays. All these techniques cost a lot of money, more money than we can ever dream of getting in Sweden with the current research financing system. So how then to seriously compete with these groups?

Perhaps the correct answer is not to try to compete at all, but rather try to specialize in areas where these groups are weaker, and not be too frustrated that we do not have access to similar large-scale genomic resources. Our main strength in Lund is our ecological and experimental tradition, not primarily our skills in genomics. This is also where we have to profile and advertise ourselves in the future, as this is an area that separates from other departments. In that sense, we have to push or Linnaeus-programme CAnMOVE in the future and emphasize the strong Lund research tradition of animal movement, dispersal and migration (and the consequences thereof).

Hans Ellegren, the organizer of this meeting, actually suggested that we in Lund should organize a similar meeting about animal movement in the future, and this seems like an excellent idéa. If there is something I think has been missing at this meeting, it is the field experiments and studies on animals in their natural environments, including mate preferences in the wild and dispersal behaviours.