Monday, March 31, 2014

Next lab meeting: WIP presentation

Posted by Jessica Abbott on behalf of Qinyang Li

Hello everyone,

Next lab meeting I will present my thesis for the coming defence on Thursday. It would be really nice to hear your comments so I can make some final changes. Also, here is a short fly paper about sexual antagonistic selection on gene expression in Drosophila melanogaster. I think both the topic and method should be of interest in our group.

Evolution under monogamy feminizes gene expression in Drosophila melanogaster

Many genes have evolved sexually dimorphic expression as a consequence of divergent selection on males and females. However, because the sexes share a genome, the extent to which evolution can shape gene expression independently in each sex is controversial. Here, we use experimental evolution to reveal suboptimal sex-specific expression for much of the genome. By enforcing a monogamous mating system in populations of Drosophila melanogaster for over 100 generations, we eliminated major components of selection on males: female choice and male–male competition. If gene expression is subject to sexually antagonistic selection, relaxed selection on males should cause evolution towards female optima. Monogamous males and females show this pattern of feminization in both the whole-body and head transcriptomes. Genes with male-biased expression patterns evolved decreased expression under monogamy, while genes with female-biased expression evolved increased expression, relative to polygamous populations. Our results demonstrate persistent and widespread evolutionary tension between male and female adaptation.

Sunday, March 23, 2014

Lab-meeting on intraspecific assortative mating, disruptive selection and sympatric speciation

Posted by Erik Svensson on behalf of John Waller

This week's lab-meeting will continue on the theme of assorative mating and how it can possibly work together with disruptive selection to cause sympatric speciation. We will discuss two papers by Daniel Bolnick at University of Texas (Austin): one review paper in American Naturalist and one modelling paper in American Zoologist. Abstracts are found below.

Date: Tuesday March 25, 10.30
Place: "Argumentet", 2nd floor, Ecology Building

Assortative mating occurs when there is a correlation (positive or negative) between male and female phenotypes or genotypes across mated pairs. To determine the typical strength and direction of assortative mating in animals, we carried out a meta-analysis of published measures of assortative mating for a variety of phenotypic and genotypic traits in a diverse set of animal taxa. We focused on the strength of assortment within populations, excluding reproductively isolated populations and species. We collected 1,116 published correlations between mated pairs from 254 species (360 unique species-trait combinations) in five phyla. The mean correlation between mates was 0.28, showing an overall tendency toward positive assortative mating within populations. Although 19% of the correlations were negative, simulations suggest that these could represent type I error and that negative assortative mating may be rare. We also find significant differences in the strength of assortment among major taxonomic groups and among trait categories. We discuss various possible reasons for the evolution of assortative mating and its implications for speciation.

Current Zoology    2012, 58(3): 484 - 492

The term 'assortative mating' has been applied to describe two very different phenomena: (1) the tendency for individuals to choose phenotypically similar mates from among conspecifics; or (2) the tendency to prefer conspecific over hete- rospecific mates (behavioral reproductive isolation). Both forms of assortative mating are widespread in nature, but the relationship between these behaviors remains unclear. Namely, it is plausible that a preference for phenotypically similar conspecifics incidentally reduces the probability of mating with phenotypically divergent heterospecifics. We present a model to calculate how the level of reproductive isolation depends on intraspecific assortative mating and the phenotypic divergence between species. For empirically reasonable levels of intraspecific assortment on a single trait axis, we show that strong reproductive isolation requires very substantial phenotypic divergence. We illustrate this point by applying our model to empirical data from threespine stickleback Gasterosteus aculeatus and Darwin’s Finches (Geospiza spp). We conclude that typical levels of intraspecific assortment cannot generally be extrapolated to explain levels of interspecific reproductive isolation. Instead, reproductive isolation between species likely arises from different mate choice behaviors, or multivariate assortative mating  

Friday, March 14, 2014

Lab-meeting about phenotypic evolution, the ongoing synthesis and assortative mating

Posted by Erik Svensson

This coming lab-meeting (Tuesday March 18, 10.30), I wanted to discuss a recent general research overview and perspective by evolutionary biologist Stevan J Arnold. It is about the ongoing synthesis in evolutionary biology, but it takes a longer historical perspective. It is the "American Society of Naturalist's Adress", and it is published in the same journal. Hopefully, you will get some feeling for where evolutionary quantitative genetics is today, where it has evolved from, and where it will go in the future. Hopefully, you will also agree that this is still a very dynamic and exciting research approach that will continue to provide many new insights in the genomic and postgenomic era, as it is a synthetic approach that adresses questions that cannot and will never be answered by molecular approaches alone.

You will find the title, the abstract and a link to the article below. Related to this article, I will also spend a few minutes showing some simulation results of what disruptive selection gradients are useful for, and how they can be used to say something about the future.

Phenotypic Evolution: The Ongoing Synthesis


I explore the proposition that evolutionary biology is currently in the midst of its greatest period of synthesis. This period, which I call the Ongoing Synthesis, began in 1963 and continues at the present time. I use analysis of citations, conduct, and content to compare the Ongoing Synthesis to widely recognized periods of synthesis in the nineteenth and twentieth centuries. To compare content, I focus on phenotypic evolution and compare current efforts with George Gaylord Simpson’s struggle to understand evolution in deep geological time. The essence of current effort is captured by the question, What is the best model for phenotypic evolution? Although many investigators are actively engaged in answering this question, I single out two examples of my own collaborative work for emphasis here. These two studies share three important characteristics: diagnosis of evolutionary pattern using massive data sets, validation of model parameter values using compilations of estimates (e.g., heritability, stabilizing selection, distance to an intermediate optimum), and identification of evolutionary process using alternative models of stochastic evolution. Our primary findings (discovery of the blunderbuss pattern and the result that rare bursts of evolution carry lineages out of established adaptive zones) compare favorably with important insights from the Modern Synthesis.

Friday, March 7, 2014

Sampling flies above the artic circle in Norway

# posted by Maren Wellenreuther

Hanna and I are in northern Norway to sample populations of seaweed flies (Coelopa frigida). As the name indicates, these flies live on seaweed that has been washed up on the shore and form wracks. The temperature in these wrackbeds can easily be 30 degrees above the ambient temperature and it is therefore no surprise that you can find these flies thriving year round, even in these northern latitudes. We are interested in how the flies manage to survive in different habitats (e.g. gradients in salinity, exposure, extremes of temperatures), and are planning to compare populations in southern Sweden with populations in northern Norway. Comparisons will entail genomic and transcriptomics analyses of adult and larval life stages, and experiments testing fitness in different habitats. 

We arrived on Tuesday and have been studying the maps of the coastline to find stretches that are exposed to ocean swell, which is needed for the accumulation of wrack. The expansive fjords that characterize the landscape in this part of Scandinavia make is hard to get to the outer coast, and the journey from one side to the fjord to the other typically leads over numerous tunnels and bridges that seem to disappear in the sky. Snow covered mountains are framing the view wherever we go and the temperatures that we have experienced during the days have ranged from -15 to  +7. All in all, this part of the world is full of extremes and stunning beauty.

Yesterday we found our first population. We traveled all day to an exposed stretch of coastline north of the town Bodo, which is only accessible with a short ferry journey. At the very end of the fjord we found an 80 cm deep wrack, and surely enough, seaweed flies were abundant at that site too. It had just been raining heavily with gale force winds, so all adults were hiding among the wrack.

The flies were cold and did not move at all, which made sampling easy, because we could literally pick the flies up by hand and drop them into the Eppendorf’s. At the end of the sampling the rain and wind stopped, and within minutes all the flies came out and ‘basked’ in the light.

All the best to Lund and happy greetings from the Lofoten!