DFG FOR 1078 Natural Selection in Structured Populations
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Seminars 2010

25/01/10 - Dr. Oscar Gaggiotti - "Disentangling the effects of evolutionary, demographic and environmental factors influencing the genetic structure of natural populations"

University of Grenoble, France

gaggiottiAbstract: The spatial structuring of intraspecific genetic diversity is the result of random genetic drift, natural selection, migration, mutation, and their interaction with historical processes. The contribution of each has been typically difficult to estimate, but recent advances in statistical genetics have provided valuable new investigative tools to tackle such complexity. During the talk I will explain how we can capitalise on such advances in order to develop a statistical framework that allows us to disentangle the effects of selective forces and demographic processes. The use of this framework will be illustrated with an application to the study of a widely distributed and abundant marine pelagic fish of economic importance, Atlantic herring (Clupea harengus)

31/05/10 - Dr. Arndt Telschow - "The role of Wolbachia and other reproductive parasites in eukaryotic evolution"

Westfälische Wilhelms University, Germany

telschowAbstract: Reproductive parasites are cytoplasmically inherited endosymbionts that manipulate the host reproductive system to their own advantage but to the disadvantage of their host. Common forms of reproductive parasitism are cytoplasmic incompatibility, male-killing, feminization, and parthenogenesis induction. Well-studied reproductive parasites belong to the bacterial groups Wolbachia, Rickettsia, Spiroplasma, and Cardinia. The wide distribution of these bacteria among arthropods, with Wolbachia estimated to infect 20–70% of all insect species, make the study of reproductive parasitism an important topic in evolution and ecology. In the first part of the presentation, it is discussed how reproduction parasites modify host gene flow and promote speciation. A mathematical modelling approach is used and analytical results for gene flow modification are presented. The results support the view that Wolbachia can promote host speciation, and, further, suggest strong impact of reproductive parasites on host gene flow. In the second part, results from the Nasonia genome project are presented which suggest horizontal gene transfer between Wolbachia, Nasonia, and pox viruses. These results suggest an important role of reproductive parasites in eukaryotic evolution.

07/06/10 - Prof.Tadeusz J. Kawecki - "Evolutionary biology of learning: lessons from fruit flies"

Université de Lausanne, Switzerland

kaweckiAbstract: Learning allows an animal to develop, within its lifetime, an adaptive response to a completely novel situation. The ability to learn is thus one of the top achievements of biological evolution. While the benefits of learning are relatively well understood, a number of questions remain open. How readily can evolution lead to improvements in learning ability? What would the resulting costs or trade-offs be? What is the nature of genetic variation affecting learning? How does learning affect evolutionary change? We address these questions using experimental evolution as the approach and Drosophila as the study system. The talk with review the insights into the above questions produced by this research program.top

14/06/10 - Dr. Lino Ometto - "One genotype for three phenotypes: the evolution of gene expression in ants"

Centro Ricerca e Innovazione Fondazione Edmund Mach, Italy

omettiAbstract: Ants are a remarkable example of equivalent genotypes developing into divergent and discrete phenotypes. With few exceptions, any fertilized (diploid) egg has the potential to develop into either a fertile queen or a sterile worker depending upon environment-induced differentiation in gene expression. In contrast, the differentiation between males and females depends upon whether eggs are fertilized, with fertilized eggs giving rise to females and unfertilized (haploid) eggs giving rise to males. Moreover, because of their highly specialized social roles, ant castes represent phenotypic targets of natural selection on colony efficiency. To obtain a comprehensive picture of the relative contributions of sex, caste and species divergence to gene expression evolution we investigated gene expression patterns in queens, workers, and males of two species of fire ants, Solenopsis invicta and S. richteri in fire ants. Our results highlight the role of differential gene expression in species where distinct phenotypes are not merely the result of sexual dimorphism. Workers have a considerable number of genes that are specifically up- or down-regulated compared with males and queens. Moreover, workers also have more genes significantly differentially expressed between species than do the other castes. Thus, much of the evolution of gene expression in ants may occur in the worker caste despite the fact that these individuals are largely or completely sterile. This can be explained by a combination of factors, including adult workers experiencing the most diverse environments and exhibiting the broadest behavioral repertoires.

21/06/10 - Dr. Claudie Doums - "The pros and cons of combining sex and thelytokous parthenogenesis in the mediterranean ant Cataglyphis cursor"

Université Pierre & Marie Curie, France

doumsAbstract: The evolution of sex remains one of the major unsolved evolutionary paradoxes despite the intensive research effort devoted to this subject for more than 30 years. The main assumption of most of the models on the evolution of sex is that sexual and asexual individuals are equivalent. However, this hypothesis of all else being equal is often violated, when sex is lost. This is especially true in social organisms in which asexuality induces major changes in the genetic relatedness among group members hence affecting the potential reproductive conflicts among them. We studied the evolution of parthenogenesis in the ant Cataglyphis cursor. This species present a peculiar reproductive system characterized by a conditional use of thelytoky by the queen only for producing the new queens. The queen still uses sexual reproduction to produce workers and mate with a large number of males, thus maintaining a high genetic diversity among workers within the colony. Moreover, workers are also known to use thelytokous parthenogenesis in queenless colonies under laboratory conditions. In this study, we first investigated the frequency of sexually and parthenogenetically produced young queens in two natural populations and tested whether these two types of queens differed by some morphological and physiological parameters. In the second part, we analysed the importance of worker reproduction in the field and of worker reproductive competition in the laboratory in orphaned colonies. Our results show that half of the young queens are parthenogenetically produced in the field but do not differ from sexually produced queens except by their high level of inbreeding. Moreover, our results suggest that worker reproduction is not very important in natural population so that parthenogenesis probably evolved for increasing gene transmission of the queen and avoiding intra-colonial conflicts rather than for allowing worker to reproduce.

28/06/10 - Prof. Richard Nichols - "Geographic patterns in genetic data: can we make sense of an imperfect world?"

University of London, UK

nicholsAbstract: Simple models of subdivided populations make predictions about the amount of genetic divergence between populations of the same species and the time over which such divergence would accumulate. They can also be used to explain why the genetic divergence between species may differ among loci. However, the history and ecology of most real species have important differences from this simplistic model. In particular the density and geographic range of most species has altered dramatically since the last ice age. I will argue that, with care, we can still make relatively concrete inference about the demography, history and selection acting on a species from its genetic patterns.top

19/07/10 - Andreas Wollstein -  "Demographic Parameter Estimation from Ascertained Single Nucleotide Polymorphisms"

Department of Forensic Molecular Biology, Erasmus University Medical Center, Rotterdam, The Netherlands
Cologne Center for Genomics (CCG), University of Cologne, Cologne, Germany

Abstract:Certain patterns of genetic variation across human populations are well known to reflect past migration events, and allow us to learn about the evolution of the human species and contrast this with archaeological evidence. For a precise inference a sufficient amount of sequence data is necessary but often unavailable. Most currently favoured genotyping technologies suffer from the discovery bias of the used variation, that is for example from a much lower sample size or a distantly related population than the population of interest. Here, I present a novel approach to estimate demographic parameters accounting for the discovery bias using Approximate Bayesian Computation. I will further present an application of this new methodology to reveal the demographic history of Oceania, one of the most recent populated parts of the world whose history is currently highly debated.

25/10/10 - Prof. Laura Rose - "Molecular evolution of disease resistance genes in wild tomatoes"

LMU Munich and Heinrich-Heine-Universität, Düsseldorf

roseAbstract: I will describe our investigations of the evolutionary history of five genes in a defense signaling pathway in wild tomatoes. Pathway theory predicts that genes that function downstream in the pathway, which serve as convergence points for upstream signals, should show greater evolutionary constraint. We find that two of the upstream genes evolve under strong evolutionary constraint, while the other genes, which operate further downstream in the pathway, show evidence of balancing selection. This counterintuitive observation may be likely in pathways involved in pathogen defense. Pathogens may specifically target downstream positions in resistance pathways to manipulate or nullify host resistance. However, plants also express pathogen specific receptors that function upstream in resistance pathways and activate the resistance responses upon pathogen detection. Therefore, it is likely that genes throughout defense pathways serve as targets for coevolution between hosts and pathogens.

16/11/10 - Prof. Eörs Szathmáry - "Evolution and the Origin of Life"

The Parmenides Foundation Pullach/München Collegium Budapest(Institute for Advanced Study)

szathmaryAbstract:Life is a symbiosis between templates, metabolism and membranes. The question is how such systems could have self-assembled in early chemical and biological evolution. Synthesis of organics can be achieved by various means, but we should also enquire about the origin of chemical supersystems, out of which some will show characteristics of life. The main problem of the origin of life is the notorious presence of side reactions. In contemporary living systems enzymes are sufficient to ensure that required reactions win over side reactions, but of course one cannot start with enzymes in the earliest times. Spontaneous degradation of molecules, high mutation rates, nucleotide elongation competing with replication, and tar formation are all plagues to our understanding how life could have originated. The RNA world idea at least helps us separate the very problem of the origin of life from that of the genetic code. Snags are that we do not know where RNA came from and we still do not have a functioning replicase ribozyme. Even if the replication problem is solved, we still need to solve the earliest appearances of intragenomic conflict. I shall analyze various models and offer a few conclusions regarding the first major transitions in the history of life.

29/11/10 - Prof. Hans Stenoien - "Phylogeography of peat mosses (Sphagnum): globetrotters or unmoving sphinxes from the past?"

Norwegian University of Science and Technology, Trondheim, Norway

stenoienAbstract: Genetic and morphological similarity between populations separated by large distances may be caused by frequent long-distance dispersal or retained ancestral polymorphism. The frequent lack of differentiation between disjunct conspecific moss populations on different continents has traditionally been explained by the latter model, and has been cited as evidence that many or most moss species are extremely ancient and slowly diverging. Peat mosses (genus Sphagnum) constitute a major part of northern hemisphere wetland and mire biodiversity. Recent studies show that despite the ancient divergence between Sphagnum and other mosses, and despite their widespread occurrence, high diversity and ecological importance, extant Sphagnum species are surprisingly young. On the other hand, highly disjunct populations often show high genetic similarity, even in species seemingly lacking means for long-distance dispersal. Here I will present results from recent studies on Sphagnum phylogeography.