Senckenberg Research

Session 3







18. January 2018, 10.30 -12.10 am


10.30-11.00 am

Prof. Thomas Flatt, University of Fribourg, Switzerland

The Genomic Basis of Clinal Adaptation in Drosophila

One of the central goals of evolutionary genetics is to understand how organisms adapt to environmental heterogeneity. A promising approach towards this end is to investigate systematic, gradual phenotypic and genotypic changes along environmental (e.g. climatic) gradients, so-called clines, which are thought to be driven by spatially varying selection.
Over the past 5 years we have been using next-generation sequencing, population genetics and laboratory assays to identify and characterize candidate genes and polymorphisms that might contribute to variation in fitness-related (life-history) traits among populations of the fruit fly, Drosophila melanogaster, situated along a latitudinal cline spanning the North American east coast. Our genomic analyses suggest that spatially varying selection is pervasive and acts on numerous loci and pathways, with many candidates implicated in life-history regulation and exhibiting parallel differentiation along the parallel Australian cline. In my talk, I will focus on our recent work on two clinal polymorphisms, namely an inversion polymorphism that harbors an excess of clinal SNPs and a clinal allele in the insulin signaling transcription factor foxo. In both cases we have experimental evidence that both polymorphisms make a causative contribution to the observed phenotypic clines in fitness-related traits.

11.00-11.20 am

Dr. Martin Kapun, University of Lausanne, Switzerland

Genomic signals of clinal variation in European and North American D. melanogaster

Martin Kapun, Thomas Flatt & The DrosEU consortium

Clines, which are gradual changes of genotypes or phenotypes along environmental transects, are often taken as prima facie evidence for the action of spatially varying selection. However, only due to recent advances in sequencing technology it now becomes possible to compare genome-wide clinal patterns and test for alternative models. With the help of a newly founded population genetics consortium (DrosEU), we, for the first time, conduct genome-wide analyses of clinal genomic variation in D. melanogaster on the yet largely unexplored European continent. These analyses reveal complex demographic patterns and pronounced clinal genetic variation along different geographical transects. Multiple clinal variants, including chromosomal inversions are shared across continents and are also found along a latitudinal temperature gradient at the North American east coast. In particular, we find evidence for steep and temporally stable clinal variation strongly associated with In(3R)Payne, a common cosmopolitan inversion, that cannot be explained by demography alone. To learn more about the potential adaptive effect of this inversion, we compare karyotype-specific genomic variation on multiple different continents. We find genomic regions in the center of the inversion that are in strong linkage disequilibrium with the inversion breakpoints possibly as a result of selection for inversion-specific genetic variation.

11.20-11.40 am

Dr. Ann-Marie Waldvogel, Senckenberg, Germany

The genomic footprint of climate adaptation in Chironomus riparius

Ann-Marie Waldvogel, Andreas Wieser, Tilman Schell, Simit Patel, Hanno Schmidt, Thomas Hankeln, Barbara Feldmeyer, Markus Pfenninger

The gradual heterogeneity of climatic factors produces continuously varying selection pressures across geographic distances that leave signatures of clinal variation in the genome. Separating signatures of clinal adaptation from signatures of other evolutionary forces, such as demographic processes, genetic drift, and adaptation to non-clinal conditions of the immediate local environment is a major challenge. Here, we examine climate adaptation in five natural populations of the harlequin fly Chironomus riparius sampled along a climatic gradient across Europe. Our study integrates experimental data, individual genome resequencing and Pool-Seq data. Common-garden experiments revealed a positive correlation of population growth rates corresponding to the population origin along the climate gradient, suggesting thermal adaptation on the phenotypic level. In a population genomic analysis, we used an FST outlier approach to infer positive selection across the climate gradient, in combination with an environmental association analysis. In total we identified candidate genes as genomic basis of climate adaptation. Enriched functions among these candidate genes involved the apoptotic process and molecular response to heat, as well as functions identified in other studies of climate adaptation in other insects. Our results show that local climate conditions impose strong selection pressures and lead to genomic adaptation despite strong gene flow. Moreover, these results imply that selection to different climatic conditions seems to converge on a functional level, at least between different insect species.

11.40-12.10 am

Dr. Robert Kofler, VetMedUni Vienna, Austria

Influence of temperature on the dynamics of transposable element invasions

The P-element, one of the best understood eukaryotic transposable elements (TEs) recently invaded natural D. simulans populations. We captured a natural D. simulans population from Florida at an early stage of the invasion and set up a replicated experimental evolution study in hot and cold environments. This opens the unprecedented opportunity to study a natural invasion of a TE with the aid of high throughput sequencing technologies in replicated populations evolving at different temperatures. We show that in all replicate populations of a given environment the P-element rapidly spreads with a remarkable consistency. In the hot environment P-element copy numbers increased 16-fold up to generation 20 and attained a stable copy number of about 30 per diploid genome. No further increase could be noted during the next 40 generations of experimental evolution. This plateauing of the invasion was mediated by the rapid emergence of piRNAs against the P-element.
By contrast, at cold conditions the speed of the invasion is much slower, the P-element multiplied 8-fold by generation 40. These differences in the speed of the invasion are likely due to the lower expression of the P-element at cold conditions. We conclude that temperature is a major factor determining the evolution of TEs in their host.