DFG FOR 1078 Natural Selection in Structured Populations

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Seminars 2014

03/02/2014 - John Colbourne - "How Genomic Responses to the Environment Vary"

Environmental Genomics Group, School of Biosciences, University of Birmingham (UK)

colbourneDaphnia, or the water flea, is a sentinel species of freshwater ecosystems. Their populations are defined by the boundaries of ponds and lakes, are sensitive to modern toxicants in the environment, and thus are used to assess the ecological impact of environmental change. Their short generation time, large brood sizes, and ease of laboratory and field manipulation have assured Daphnia’s importance for setting regulatory standards by environmental protection agencies, testing chemical safety, monitoring water quality, and as a model for environmental genomics research. In this study, we take advantage of the animal’s clonality and mature genomics tools to dissect the sources of gene expression variation in the stress response of genetic isolates to six environmentally relevant pollutants, and their binary mixtures. One isolate originates from a natural population that has faced severe chemical challenges for over a century of industrial iron/ore smelting and thus demonstrates evolved tolerance to toxic levels of certain metals. Another isolate originates from a population that has no history of chemical stress and is clearly harmed by metal exposure. By interrogating differential expression of 31,000 annotated genes from 50 comparisons across conditions and between isolates, the current study provides new insights into the functional interactions among genes and environment.

The research was conducted during hands-on training in “Environmental Genomics” – an annual summer course offered at the Mount Desert Island Biological Laboratory.

14/04/2014 - Miguel Gallach - "Recurrent turnover of chromosome-specific satellites in Drosophila"

CIBIV-Vienna, Austria

gallachAbstract: Non-coding repetitive DNA has the ability to adopt specific folding structures that may help cells identify chromosomes. In addition, repetitive DNA elements have also become a major interest among evolutionary biologists since species-specific interactions between chromatin remodeling proteins and repetitive DNA elements are disrupted in hybrids. Remarkably, in Drosophila, the X and dot chromosomes are identified by chromosome-specific binding proteins and they are particularly involved in genetic incompatibilities between closely related species. I found that these two chromosomes are overpopulated by certain repetitive elements that undergo recurrent turnover in Drosophila species. The biology and evolutionary patterns of the characterized satellites suggest that they provide both chromosomes with some kind of structural identity and are exposed to natural selection. The rapid satellite turnover fits some speciation models and may explain why these two chromosomes are typically involved in hybrid incompatibilities.

05/05/2014 - Gerton Lunter - "Inferring demography from whole-genome data"

University of Oxford, UK

lunterAbstract: Genetic data is informative about demography, and holds for instance evidence of past population bottlenecks, admixture and migration. Inferring these from genetic data is however not trivial. Most existing approaches rely on summary statistics, such as site-frequency spectra. More recently, approaches that directly model the process of recombination and coalescence along the sequence have succeeded in inferring past population changes from a single diploid genome. However, extending this approach to multiple samples is not straightforward.

In the talk I will discuss an approach we have been taken, using a fairly recent statistical technique known as particle filters. This approach has the promise to scale to high-dimensional models, and is well suited to this particular inference problem.

12/05/2014 - Fabian Staubach - "Approaches to better understand the role of microbes in the adaptation of metazoans"

University of Freiburg, Germany

fabianstaubachAbstract: Almost all organisms on earth are associated with microorganisms. These microorganisms are important for the evolution of their hosts. However, the role they play for the evolution of their hosts can be very different. On the one hand, disease causing pathogens can exert strong selection pressures on the host that are reflected by fast evolution of host immune genes. On the other hand, microbes that are beneficial for the host have facilitated major adaptations of their host. A prominent example of an adaptation through microorganisms is the protistan microbiota in the gut of termites that facilitates the digestion of wood. I will present approaches to better understand the role of microbes in adaptation using Drosophila and termites as models. 


16/06/2014 - Gerald Wilkinson - "Sexual selection, genomic conflict and speciation in stalk-eyed flies"

University of Maryland, USA, and Wissenschaftskolleg zu Berlin, Germany

wilkinsonAbstract: Speciation occurs when isolated populations diverge sufficiently to cause reproductive isolation. The processes that drive such divergence remain poorly understood. One possibility is sexual selection, which can cause rapid evolution of traits that influence precopulatory or postcopulatory success, but should only cause divergence if populations exhibit differences in mating preferences. An alternative is some type of genomic conflict, such as that responsible for biased transmission of X or Y-bearing sperm, that leads to an arms race between driving and suppressing elements. If coevolution among elements proceeds independently in isolated populations, then heterogametic hybrid sterility or inviability could occur. In this talk, I will present results from a series of studies on stalk-eyed flies that show how sexual selection and genomic conflict operate and interact to cause rapid evolution of reproductive isolation among allopatric populations in southeast Asia. I will also discuss recent genome and transcriptome studies that provide insight into the genetic causes and consequences of the ongoing sex chromosome conflict. The results suggest the genomic landscape, especially of the sex chromosomes, is remarkably dynamic in this extraordinary group of flies.

14/07/2014 - Miltos Tsiantis - "From genes to geometry: towards understanding development and diversification of leaf form"

MPI for Plant Breeding Research, Cologne, Germany

tsiantisAbstract: A key challenge in biology is to understand how diversity in organismal form is generated. Genetic analyses in model systems have identified key regulators that sculpt the body plans of metazoa and seed plants. However, less is known about how the action of such regulators produces particular organ shapes, or how the balance of conservation versus divergence of such form regulating pathways generated the tremendous morphological diversity of multicellular eukaryotes. One impediment to answering these questions is the relative paucity of experimental platforms where genetic tools can be utilized to unambiguously study morphogenesis and its evolution in a genome-wide, unbiased fashion. To circumvent this problem we developed the Arabidopsis thaliana relative Cardamine hirsuta into a versatile system for studying morphological evolution. We aim to understand the molecular mechanisms through which leaf morphology evolved in these species, resulting in simple, undivided leaves in A. thaliana and dissected leaves with distinct leaflets in C. hirsuta. This presentation will discuss our progress towards understanding the genetic pathways that specify dissected versus entire leaf shapes and that regulate the number, position and timing of leaflet production.

01/12/2014 - Andrea Betancourt - "Transposable element dynamics in Drosophila”

VedMedUni Vienna, Austria

betancourtAbstract: Transposable elements are genomic parasites with an evolutionary strategy of increasing their copy number; the success of this strategy can be seen in many eukaryotic genomes, which contain large fractions of transposon derived DNA. Recently, we have begun to acquire an in-depth picture of the population dynamics of transposable elements in Drosophila, with both bursts of transposition and purifying selection against new insertions appear to affect population frequencies of insertions. However, another important process in transposable element evolution -- horizontal transmission between species -- is less wellunderstood. The classic example of a horizontally transmitted element is that of the P-element in D. melanogaster. Recently, we have found that the P-element appears to have recently spread from D. melanogaster into a sister species, D. simulans. P-element appears to have spread quickly in D. simulans, with strains from the same geographic region showing P-element to have increased from low to high frequency within a decade.