I know many of you are probably enjoying your vacations right now, but given the bad weather Europe is experiencing at the moment, I thought I could suggest a couple of papers that might eb of interest to you during a rainy day...
First, Erik, Anders and I recently published the last two "isopod" papers included in my thesis, one dealing with reproductive barriers and adaptive divergence, mainly assessing the role and importance of assortative mating and migration modification during ecotype divergence in aquatic isopods:
Eroukhmanoff, F., Hargeby, A., & E. I. Svensson. 2011. The importance of different reproductive barriers during phenotypic divergence in isopod ecotypes. Evolution DOI: 10.1111/j.1558-5646.2011.01327.x.
ABSTRACT: The question of how diverging populations become separate species by restraining gene flow is a central issue in evolutionary biology. Assortative mating might emerge early during adaptive divergence, but the role of other types of reproductive barriers such as migration modification have recently received increased attention. We demonstrate that two recently diverged ecotypes of a freshwater isopod (Asellus aquaticus) have rapidly developed premating isolation, and this isolation barrier has emerged independently and in parallel in two south Swedish lakes. This is consistent with ecological speciation theory, which predicts that reproductive isolation arises as a byproduct of ecological divergence. We also find that in one of these lakes, habitat choice acts as the main barrier to gene flow. These observations and experimental results suggest that migration modification might be as important as assortative mating in the early stages of ecological speciation. Simulations suggest that the joint action of these two isolating barriers is likely to greatly facilitate adaptive divergence, compared to if each barrier was acting alone.
and the other one involving the role of genetic constraints and genetic variation in adaptation to a novel habitat, specifically the influence of the G-matrix and its evolution during such processes:
Eroukhmanoff, F. & E.I. Svensson. 2011. Evolution and stability of the G-matrix during colonization of a novel environement. Journal of Evolutionary Biology 24: 1363-1373.
ABSTRACT: Populations that undergo a process of rapid evolution present excellent opportunities to investigate the mechanisms driving or restraining adaptive divergence. The genetic variance–covariance matrix (G) is often considered to constrain adaptation but little is known about its potential to evolve during phenotypic divergence. We compared the G-matrices of ancestral and recently established ecotype populations of an aquatic isopod (Asellus aquaticus) that have diverged in parallel in two south Swedish lakes. Phenotypic changes after colonization involved a reduction in overall size, lost pigmentation and changes in shape. Comparisons between G-matrices reveal close similarity within the same ecotype from different lakes but some degree of differentiation among ecotypes. Phenotypic divergence has apparently not been much influenced by the orientation of G. Additive genetic variation in the newly colonized habitats has also decreased substantially. This suggests that a process of adaptation from standing genetic variation has occurred and has probably facilitated phenotypic divergence.
Finally, I wanted to draw your attention on two recently published papers on the sparrow species complex (House-Spanish-Italian) originating from my new research group in Oslo, with my postdoc host Glenn-Peter Saetre and two of his PhD students Jo Hermansen and Tore Elgvin among others. These two papers present in detail molecular and phenotypic evidence for one of the first reported cases of hybrid speciation in birds and discuss a role for sex chromosomes, which we know has been a hot topic in birds in relation with mate choice and hybridization/speciation. These two papers will soon appear in a new issue of Molecular Ecology along with some Perspective piece but they are already available online:
Hybrid Speciation in sparrows I: phenotypic intermediacy, genetic admixture and barriers to geen flow. Jo S. Hermansen et al. Molecular Ecology DOI: 10.1111/j.1365-294X.2011.05183.x
Hybrid Speciation in sparrows II: a role for sex chromosomes? Tore O. Elgvin et al. Molecular Ecology DOI: 10.1111/j.1365-294X.2011.05182.x