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

(American Society of Naturalists Address)

 

Stevan J. Arnold

Abstract

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.

Visit by Anssi Laurila Wednesday March 30 2011 and seminar on amphibians

This coming Wednesday, Prof. Anssi Laurila from the Department of Population Biology and Conservation Biology at Uppsala University will visit Lund and the Aquatic Ecology Section. Anssi studies phenotypic plasticity, local adaptation and quantitative genetics in amphibians, and will give an invited seminar in "Tanken" on the first floor at 10.00 (March 30 2011), as part of the seminar series organized by Aquatic Ecology. Those of you who are interested should take the opportunity to listen and if you want to meet Anssi and discuss research with him, contact Christer Brönmark (christer.bronmark@biol.lu.se) to make an appointment.

Our lab-meeting this Wednesday will take place in "Argumentet", rather than "Darwin" and it is scheduled another time: 12.30, due to another meeting in the lunch room at 14.00 of the Evolutionary Ecology Section. See previous blogposts for info about which papers to discuss.

How we are evolving and more on the "missing heritability" problem

Although I suggested  we should skip articles for next lab-meeting (Wednesday 22 December), I changed my mind after finding a couple of interesting papers in the popular science magazine Scientific American. Both deal with human evolution and human genetics, and should be an easy read, and are of much principal interest, also to us.

The first one raises the question "How we are evolving" and it discusses the recent recent data obtained from "Next-generation sequencing" that have elucidated the evolutionary history of coding genes in Homo sapiens. It turns out that so-called "selective sweeps" are quite unusual in our genome, i. e. alleles that have quickly increased in frequency in response to local selection pressures and in local environments. Thus, the case of the recent demonstrated selective sweep in the genes affecting haemoglobin production when humans invaded the Tibetan Plateau that we discussed earlier this year, are atypical, and do not seem to be the norm (according to the article in Scientific American).

Instead, it appears that the global distribution of human coding genes more reflects recent migration histories: genes that increased in frequency at a certain place were then carried along to new places as human colonized the Earth. This implies that selective sweeps are rare, and they mainly happen when there is strong and sustained selection that is consistent over relatively long time at a given place. This implies that selection might in general be relative weak, in humans at least. Perhaps humans are able to adapt (culturally) and counteract selection pressures by cultural adaptations, such as clothing, food habits etc., which weakens natural selection in many environments?

The other article in Scientific American deals with the so-called "missing heritability"-problem, i. e. the uncomfortable facts that there are very few genes explaining a substantial amount of variation in diseases. Thus, most large-effect genes are quite rare in the populations, whereas those genes that are common explain only a tiny fraction (in the order of a few percent) of the disease-related variation. This has caused despair among molecular biologists and biomedical researchers, since the huge amount of sequencing data has not solved many of Homo sapiens biomedical problems (contrary to promises in the most enthusiastic heydays of genome sequencing). In spite of thousands of variable SNP:s ("single-nucleotide polymorphisms"), only a few percent of the total amount of variation in human phenotypic traits are explained by these molecular markers. This can either be interpreted as a great disappointment (in relation to promises), a complete failure for molecular biology or a great triumph of quantitative genetics, but as usual, the questions that are raised by these findings might be more interesting than the exact answers. The solution? Well, certainly not to sequence more or try to obtain more SNP:s, but rather to think harder (surprisingly, an underutilized strategy in much of today's science!).

The two articles can be found here and here, and I think you will enjoy both, as they are relatively easy read. Let's have a brief and informal discussion about these papers on Wednesday, after we've had some glögg!

Visit by Thomas F. Hansen and Arnaud Le Rouzic this week

This week our department will be visited by theoretical evolutionary biologist Thomas F. Hansen, who is currently professor at University of Oslo in Norway. I am pleased to host Thomas during his visit to Lund, as I visited his department Centre for Ecological and Evolutionary Synthesis (CEES) in May last year, and it is now my time to take care of him as he visits our department.

Thomas former postdoc Arnaud Le Rouzic will also visit us, and will give a short presentation of his research during our lab-meeting on Wednesday (10.15; Thomas will arrive later, in Wednesday afternoon). During our lab-meeting on Wednesday, I was thinking we should also discuss a paper about evolutionary quantative genetics, authored by Steve Chenoweth et al:

Author(s): Chenoweth SF (Chenoweth, Stephen F.)1, Rundle HD (Rundle, Howard D.)2,3, Blows MW (Blows, Mark W.)1

AMERICAN NATURALIST Volume: 175 Issue: 2 Pages: 186-196 Published: FEB 2010

Abstract: Although divergent natural selection is common in nature, the extent to which genetic constraints bias evolutionary trajectories in its presence remains largely unknown. Here we develop a general framework to integrate estimates of divergent selection and genetic constraints to estimate their contributions to phenotypic divergence among natural populations. We apply these methods to estimates of phenotypic selection and genetic covariance from sexually selected traits that have undergone adaptive divergence among nine natural populations of the fly Drosophila serrata. Despite ongoing sexual selection within populations, differences in its direction among them, and genetic variance for all traits in all populations, divergent sexual selection only weakly resembled the observed pattern of divergence. Accounting for the influence of genetic covariance among the traits significantly improved the alignment between observed and predicted divergence. Our results suggest that the direction in which sexual selection generates divergence may depend on the pattern of genetic constraint in individual populations, ultimately restricting how sexually selected traits may diversify. More generally, we show how evolution is likely to proceed in the direction of major axes of genetic variance, rather than the direction of selection itself, when genetic variance-covariance matrices are ill conditioned and genetic variance is low in the direction of selection.

The paper can be downloaded here. Most of you probably already know that Steve Chenoweth is the postdoc host of Tom Gosden, former PhD-student in our lab.

Also, you should of course not miss the exciting Thursday seminar (18 February at 14.00 in "Blue Hall") by Thomas, also on the theme of quantitative genetics, with the title:

Measuring evolvability and constraints with examples from the evolution of Dalechampia blossoms

We do thus have a very exciting week ahead of us!