Thursday, October 31, 2013

Is there room for punctuated equilibrium and species selection in macroevolution?

Posted by Erik Svensson

Next week (Tuesday November 5, 2013 at 10.30) I want to discuss a classical question in macroevolution that was originally suggested by paleontologists Niles Eldredge and Stephen Jay Gould in 1973, but which has gained increased interested with the explosion of molecular phylogenetic information and improved comparative methods: punctuated equilbrium and species selection. A recent TREE-article take a critical look at the evidence, and it should hopefully be an interesting read and stimulate discussion.

The first TREE-article seems critical towards the prospects for punctuated equilibrium, so as a complement (optional reading) I also post a link to an empirical study on extant mammalian body size variation by Folmer Bokma, which is suggestive of punctuated equilbrium. Enjoy that too!


Is there room for punctuated equilibrium in macroevolution?

Friday, October 25, 2013

Lab meeting 29/10: More about inversions

#posted by Maren Wellenreuther

Hi lab members,
let's have a little follow up from last weeks paper and discuss inversions a bit more-they are cool! Kirkpatrik wrote 2010 a neat paper with the title 'How and Why Chromosome Inversions Evolve' and I think that would provide a good basis to get a general idea of their relevance in evolution, and particular in adaptation.

The link to the paper is below:

Wednesday, October 23, 2013

New paper on the influence of epigenetic effects on sex-specific fitness

Male Drosophila melanogaster.
Photo by André Karwath

Posted by Jessica Abbott.

Some colleagues and I published a paper in PLoS One a couple of months ago that I'd like to highlight here. We used male-limited X-chromosome evolution to investigate the influence of epigenetic effects on sex-specific fitness. The main aim of this experiment was actually to look for specialization of the X for male fitness as a result of the experimental evolution, but as a side effect we were able to look for imprinting effects. The experimental males received their sex chromsomes from the "wrong" parent (i.e. they had paternally inherited X's and maternally inherited Y's), which initially decreases male fitness, but which our experimental evolution lines were able to adapt to over time. We had thought that genomic imprinting was a possible explanation for this pattern, but an analysis of gene expression data suggested that the likely cause was rather maternal effects and coevolution between the sex chromosomes.

Epigenetics and Sex-Specific Fitness: An Experimental Test Using Male-Limited Evolution in Drosophila melanogaster. PLoS One 8(7): e70493.
By Jessica K. Abbott, Paolo Innocenti, Adam K. Chippindale, & Edward H. Morrow

Abstract: When males and females have different fitness optima for the same trait but share loci, intralocus sexual conflict is likely to occur. Epigenetic mechanisms such as genomic imprinting (in which expression is altered according to parent-of-origin) and sex-specific maternal effects have been suggested as ways by which this conflict can be resolved. However these ideas have not yet been empirically tested. We designed an experimental evolution protocol in Drosophila melanogaster that enabled us to look for epigenetic effects on the X-chromosome–a hotspot for sexually antagonistic loci. We used special compound-X females to enforce father-to-son transmission of the X-chromosome for many generations, and compared fitness and gene expression levels between Control males, males with a Control X-chromosome that had undergone one generation of father-son transmission, and males with an X-chromosome that had undergone many generations of father-son transmission. Fitness differences were dramatic, with experimentally-evolved males approximately 20% greater than controls, and with males inheriting a non-evolved X from their father about 20% lower than controls. These data are consistent with both strong intralocus sexual conflict and misimprinting of the X-chromosome under paternal inheritance. However, expression differences suggested that reduced fitness under paternal X inheritance was largely due to deleterious maternal effects. Our data confirm the sexually-antagonistic nature of Drosophila’s X-chromosome and suggest that the response to male-limited X-chromosome evolution entails compensatory evolution for maternal effects, and perhaps modification of other epigenetic effects via coevolution of the sex chromosomes.

Friday, October 18, 2013

Effects of sexual selection and viability selection on a chromosomal inversion polymorphism

#posted by Maren Wellenreuther

Dear all,
sorry for the late posting. At next week's EXEB lab meeting we will dive into the world of seaweed flies and discuss a recent paper by Edward and Gilburn on the interaction of sexual selection and viability selection on the maintenance of a large chromosomal inversion polymorphism. Hanna Rosenquist will present the paper.

Evolution. 2013 Jan;67(1):295-302. doi: 10.1111/j.1558-5646.2012.01754.x. Epub 2012 Aug 27.
Male-specific genotype by environment interactions influence viability selection acting on a sexually selected inversion system in the seaweed fly, Coelopa frigida.
Edward DA, Gilburn AS.

In the seaweed fly, Coelopa frigida, a large chromosomal inversion system is affected by sexual selection and viability selection. However, our understanding of the interaction between these two selective forces is currently limited as research has focused upon a limited range of environments. We allowed C. frigida larvae to develop in two different algae, Fucus and Laminaria, and then measured viability and body size for each inversion genotype. Significant male-specific genotype-by-environment interactions influenced viability and body size. For males developing in Laminaria, the direction of viability selection acts similarly on the inversion system as the direction of sexual selection. In contrast, for males developing in Fucus, viability selection opposes sexual selection. These results demonstrate that through considering viability selection in different environments, the costs and benefits associated with sexual selection can be found to vary.

Thursday, October 17, 2013

New PhD student: Anna Nordén

My name is Anna Nordén and I started as a PhD student in the Section for Evolutionary Ecology in May this year. I am working on intralocus sexual conflict in a hermaphroditic flatworm under the supervision of Dr Jessica Abbott. My project focuses on the role of sexual antagonism in maintaining standing genetic variation in populations. To investigate this, I will measure the response to sex-limited evolution through experiments using a synthetic sex chromosome in the hermaphroditic free-living marine flatworm Macrostomum lignano.

Before, I have worked on assortative mating and sexual selection in Calopteryx damselflies under the supervision of Prof Erik Svensson at Lund University, and on the co-evolutionary relationship between the moth Greya politella and its host plant Lithophragma parviflorum under the supervision of Prof John Thompson at University of California, Santa Cruz.

Wednesday, October 16, 2013

On linking ecology to sexual selection

Together with John Waller, I have a paper that is now out in American Naturalist as an E-article, meaning that it is "Open Acess" and possible for anyone to download. Go here, if you would like to download a PDF of this paper. I am very much in favour of the OA-model of publishing, and I certainly hope that the publication fees we paid will also result in more citations.

This study, which was fun to do and write up, takes a look at the important link between ecology and sexual selection. We were interested in the functional significance and evolutionary consequences of wing pigmentation in calopterygid damselflies, and we used a mixture of comparative phylogenetic analyses and field studies using thermal imaging to adress this issue. In particular, we wanted to see if there was any obvious thermal benefit of male wing pigmentation, which also has important functions in sexual selection, male-male competition and species recognition. Turns out that the evidence for such a thermal benefit is mixed, although there is a clear biogeographic signature in the sense that pigmented clades are more common in northern regions and temperate climates.

Wing pigmentation is also significantly associated with eleved speciation and extinction rates, using so-called BiSSE-analyses ("Binary Speciation and Extinction") as implemented in Diversitree. This latter result provides comparative support to our previous experimental work demonstrating that wing pigmentation functions as a species recognition character between C. splendens and C. virgo, and suggest that wing pigmentation is generally involved across the entire group as a promoter of speciation, although most species formed by such non-ecological sexual selection tend to go extinct fairly soon after they have formed.

In general, I think there are too few studies where comparative approaches and field experiments are combined, as both have strength and weaknesses and inferences could be stronger if they are combined (Disclaimer: in case some sensitive theoretical ecologist reads this post, I do of course also think there are other interesting and useful research approaches, such as mathematical models).

Ecology and Sexual Selection: Evolution of Wing Pigmentation in Calopterygid Damselflies in Relation to Latitude, Sexual Dimorphism, and Speciation

American Naturalist (in press, November 2013)


Our knowledge about how the environment influences sexual selection regimes and how ecology and sexual selection interact is still limited. We performed an integrative study of wing pigmentation in calopterygid damselflies, combining phylogenetic comparative analyses, field observations and experiments. We investigated the evolutionary consequences of wing pigmentation for sexual dimorphism, speciation, and extinction and addressed the possible thermoregulatory benefits of pigmentation. First, we reconstructed ancestral states of male and female phenotypes and traced the evolutionary change of wing pigmentation. Clear wings are the ancestral state and that pigmentation dimorphism is derived, suggesting that sexual selection results in sexual dimorphism. We further demonstrate that pigmentation elevates speciation and extinction rates. We also document a significant biogeographic association with pigmented species primarily occupying northern temperate regions with cooler climates. Field observations and experiments on two temperate sympatric species suggest a link between pigmentation, thermoregulation, and sexual selection, although body temperature is also affected by other phenotypic traits such as body mass, microhabitat selection, and thermoregulatory behaviors. Taken together, our results suggest an important role for wing pigmentation in sexual selection in males and in speciation. Wing pigmentation might not increase ecological adaptation and species longevity, and its primary function is in sexual signaling and species recognition.

Sunday, October 13, 2013

Next meeting: should scientific inquiry be limited?

Posted by Jessica Abbott

Sorry for the late post, but it took a while to figure out who would host the next lab meeting.  A number of members won't be able to make it, unfortunately, so I thought we could just have a short meeting to discuss a short article, the recent Nature news feature

Ethics: taboo genetics

This article deals with a number of topics (such as IQ and race) where investigations of the genetic basis of these traits is controversial.  I thought this would be something fun to talk about!

Tuesday the 15th of October at 10.30 in Argumentet, as usual.

Monday, October 7, 2013

The Progressive Loss of Syntactical Structure in Bird Song along an Island Colonization Chain

Posted by Machteld

A long, long, time ago, in a land not that far away from here, I worked on birds. Bird song, to be exact; learned bird song, to be even more exact. Why do songbirds sing the way they do? Why is it so consistent in some species, and why do other species have dialects?

It may be more easy to understand how geographical variation occurs in learned birdsong, than to understand the absence of it. Mistakes can occur in the learning process (cultural mutations), the transmission of the sound is different in some places putting natural selection on the song frequencies, and perhaps other species interfere with the vocal communication. These are all good reasons why the song of a species might differ between places.  However, most songbird species – all of which learn their song, show a high consistency of species specific song.  How do they do that?

Although the particular notes in songs differ between songs, one individual may even have several songs, and between males within a species there will be variation; there is a certain overall structure, which makes a great tit song recognizable from a blue tit’s song or a chaffinch’s song. This is called the ‘syntax’ of bird song, where each note is a ‘syllable’ in the analogy with human speech.
One explanation for how birds maintain their species’ typical song, even if the particular notes (syllables) in the song differ over time and distance is that birds have a filter, or bias, for what kind of song they learn. If you think about it, this makes some sense, since young birds learning their song will hear lots of sounds and bird song from other species. A pre-set bias will give them some guidelines of which songs to learn.  

But clearly, there is variation between species in syntax, so how did this evolve? One would think that, after so many years of biologists studying bird song (and they’ve been at it for decades – ever since the Bell Telephone Laboratories made it possible to make sounds visible on paper in the 40’s) there would have been some good handle on this issue. Not so, unfortunately. One particular technical problem that has bothered progress is that syntax is hard to quantify. There have been attempts, but this always ended in semantic debates about definitions, and well, very little progress is made when that happens.
A chaffinch male, picture taken from
Well, there is where this paper comes in. This is a study on the song of chaffinches. A bird that has been the focus of bird song studies ever since the beginning (1954).  This is a very common bird throughout Europe (and also in other parts of the world, having been deliberately exported on a few occasions), and lives on the mainland of Europe, but also on almost all of the islands in the periphery of the continent in the Atlantic, such as Britain, the Azores, the Canary islands). The nice thing is that the colonization route of the chaffinch to those islands had been figured out already quite a while ago, so that we had a repeated evolutionary experiment at our hands, not unlike the finches at the Galapagos. They first colonized the Azores, then went on to the Canary Islands, with Gran Canaria the last island to get colonized by the finches. 

Many, many, many, many, recordings of chaffinches later, on all those wonderful locations (which I was lucky to be part of on some of those locations, such as the little gem of an island El Hierro), we created a database of chaffinch song in Europe.

That was the practical part. Then the hard statistics came in. I am not going to try to explain this here in detail, but in essence, per population, the songs were analyzed to see which were the ‘atoms’, or the parts that always occurred as a unit, such as a syllable (song note) or group of syllables. Then, zoom out, and repeat this process: which units (classes of syllables) always occur together. You can see how you can start to quantify things this way. The more you can cluster units within units within units, the higher the redundancy in the syntax of a song, i.e. the more stereotypical a song is.
Mainland Europe chaffinch song is highly stereotypical. Songs sung by birds in Holland and Spain follow very much the same syntax. This starts to differ once you get on to the islands, first the Azores, then the Canary Islands, where this structure starts to fall apart, until at the last island, Gran Canaria, there is almost no syntactical structure to be found. Clearly, with every colonization event, syntactical structure in the song disappeared a little.

Why did this happen? There are a few possible explanations, and read the paper for those, but one thing that we argue is that populations that go through bottle necks, such as at each colonization event, there is strong selection to recognize anything that might possibly be a conspecific. The learning biases that I mentioned in the beginning were thus selected to become less restrictive, i.e. less biased. A wider range of songs passed for species’ specific song. If this happens a enough times, you end up with no structure in your song. Which is what you find in Gran Canaria. 

And now this work has resulted in a wonderful publication, in Current Biology, available online, but in press still: 

Friday, October 4, 2013

Non-genetic inheritance

Posted by: Machteld

Next week's lab meeting will be about non-genetic inheritance, since this is the topic of a workshop I will be attending (as will Jessica) this December. This is a good moment to start reading up on it, and since this is a broadly written paper on the topic, this might be a great introduction to all of you as well, so you might have some idea what Jessica and I will be working on during that workshop :).

Since it is published in an open access journal, I've linked the paper here, for everyone's convenience.

Non-genetic Inheritance in Evolutionary Theory: a Primer

By Tobias Uller and Heikki Helanterä

Evolutionary biology traditionally equates inheritance with transmission of genes from parents to offspring. However, recent literature calls for considering ‘non-genetic inheritance’ in evolutionary theory. These calls have met with substantial scepticism. What is more, they appear to have caused further confusion both with respect to what inheritance is and what types of inheritance mechanisms are evolutionarily consequential. Building on previous work, we make use of the Price Equation to outline a general discussion of how non-genetic inheritance can affect phenotypic change within populations, exemplified by epigenetic inheritance. This shows that integrating non-genetic inheritance in evolutionary theory will require specific attention to the developmental processes that shape the relationship between the fitness of parents and the phenotype of their offspring.

See you all on Tuesday!