Wednesday, October 17, 2012

Lab-meeting on Drosophila evolution: epistatic networks and thermal adaptation

Posted by Erik Svensson

There is now a lot of activity in the Drosophila-lab, with one undergraduate student, one postdoc (Natsu) and yesterday also a PRAO-student (my daughter My). Given this, Jessica and I felt it was time to have a lab-meeting focussed on some interesting new research in evolutionary biology, focussed on the Drosophila-system.

We have therefore picked two recent PNAS-papers for discussion, one more genetic and molecular (dealing with epistasis and gene regulatory networks of starvation resistance and chill coma recovery) and one more macroevolutionary, dealing with the evolution of upper thermal limits in a phylogenetic context. Both have in common a focus on thermal adaptation. You will find Abstracts here and here, and Abstracts and titles below.

In addition, we hope Natsu could bring anbd show some printout pictures of the beatiful Wing Interference Patterns (WIP:s) of Drosophila melanogaster inbred lines. This will just be a taster, however, as Natsu will give a more formal seminar later in November telling the lab-group about the ongoing work and some preliminary results.

Time: Tuesday October 23 at 10.30
Place: "Argumentet", 2nd floor

Epistasis dominates the genetic architecture of Drosophila quantitative traits              


Epistasis—nonlinear genetic interactions between polymorphic loci—is the genetic basis of canalization and speciation, and epistatic interactions can be used to infer genetic networks affecting quantitative traits. However, the role that epistasis plays in the genetic architecture of quantitative traits is controversial. Here, we compared the genetic architecture of three Drosophila life history traits in the sequenced inbred lines of the Drosophila melanogaster Genetic Reference Panel (DGRP) and a large outbred, advanced intercross population derived from 40 DGRP lines (Flyland). We assessed allele frequency changes between pools of individuals at the extremes of the distribution for each trait in the Flyland population by deep DNA sequencing. The genetic architecture of all traits was highly polygenic in both analyses. Surprisingly, none of the SNPs associated with the traits in Flyland replicated in the DGRP and vice versa. However, the majority of these SNPs participated in at least one epistatic interaction in the DGRP. Despite apparent additive effects at largely distinct loci in the two populations, the epistatic interactions perturbed common, biologically plausible, and highly connected genetic networks. Our analysis underscores the importance of epistasis as a principal factor that determines variation for quantitative traits and provides a means to uncover genetic networks affecting these traits. Knowledge of epistatic networks will contribute to our understanding of the genetic basis of evolutionarily and clinically important traits and enhance predictive ability at an individualized level in medicine and agriculture.

Upper thermal limits of Drosophila are linked to species distributions and strongly constrained phylogenetically


Upper thermal limits vary less than lower limits among related species of terrestrial ectotherms. This pattern may reflect weak or uniform selection on upper limits, or alternatively tight evolutionary constraints. We investigated this issue in 94 Drosophila species from diverse climates and reared in a common environment to control for plastic effects that may confound species comparisons. We found substantial variation in upper thermal limits among species, negatively correlated with annual precipitation at the central point of their distribution and also with the interaction between precipitation and maximum temperature, showing that heat resistance is an important determinant of Drosophila species distributions. Species from hot and relatively dry regions had higher resistance, whereas resistance was uncorrelated with temperature in wetter regions. Using a suite of analyses we showed that phylogenetic signal in heat resistance reflects phylogenetic inertia rather than common selection pressures. Current species distributions are therefore more likely to reflect environmental sorting of lineages rather than local adaptation. Similar to previous studies, thermal safety margins were small at low latitudes, with safety margins smallest for species occupying both humid and dry tropical environments. Thus, species from a range of environments are likely to be at risk owing to climate change. Together these findings suggest that this group of insects is unlikely to buffer global change effects through marked evolutionary changes, highlighting the importance of facilitating range shifts for maintaining biodiversity.



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