Thursday, January 19, 2017

Sex-biased gene expression

Next week we will discuss the following paper by Cheng & Kirkpatrick for EXEB meeting:

"Sex specific selection and sex-biased gene expression in humans and flies"

Sexual dimorphism results from sex-biased gene expression, which evolves when selection acts differently on males and females. While there is an intimate connection between sex-biased gene expression and sex-specific selection, few empirical studies have studied this relationship directly. Here we compare the two on a genome-wide scale in humans and flies. We find a distinctive “Twin Peaks” pattern in humans that relates the strength of sex-specific selection, quantified by genetic divergence between male and female adults at autosomal loci, to the degree of sex-biased expression. Genes with intermediate degrees of sex-biased expression show evidence of ongoing sex-specific selection, while genes with either little or completely sex-biased expression do not. This pattern apparently results from differential viability selection in males and females acting in the current generation. The Twin Peaks pattern is also found in Drosophila using a different measure of sex-specific selection acting on fertility. We develop a simple model that successfully recapitulates the Twin Peaks. Our results suggest that many genes with intermediate sex-biased expression experience ongoing sex-specific selection in humans and flies.

See you in Darwin at 10am!

Friday, January 13, 2017

Domestication syndrome in mammals

Hej hej!

Tobias will be teaching in Czech Republic next Tuesday (Jan 17), so I'm jumping the queue ;-)
I would like to discuss the following paper:

I think the authors are putting forward a very original idea that is worth while following up! In a nutshell: they suggest that a concerted response of neural crest cells is underlying the suite of traits that domesticated mammals have in common: floppy ears, smaller teeth, increased docility and tameness, curly tail, smaller brains etc.

See you in Darwin's at 10 am on Tuesday!

Charles Darwin, while trying to devise a general theory of heredity from the observations of animal and plant breeders, discovered that domesticated mammals possess a distinctive and unusual suite of heritable traits not seen in their wild progenitors. Some of these traits also appear in domesticated birds and fish. The origin of Darwin’s “domestication syndrome” has remained a conundrum for more than 140 years. Most explanations focus on particular traits, while neglecting others, or on the possible selective factors involved in domestication rather than the underlying developmental and genetic causes of these traits. Here, we propose that the domestication syndrome results predominantly from mild neural crest cell deficits during embryonic development. Most of the modified traits, both morphological and physiological, can be readily explained as direct consequences of such deficiencies, while other traits are explicable as indirect consequences. We first show how the hypothesis can account for the multiple, apparently unrelated traits of the syndrome and then explore its genetic dimensions and predictions, reviewing the available genetic evidence. The article concludes with a brief discussion of some genetic and developmental questions raised by the idea, along with specific predictions and experimental tests.

Friday, January 6, 2017

Happy New Year and new EXEB-schedule for 2017

Posted by Erik Svensson 
The year 2016 might have been a depressing year on the world political front, but at least it was very good when it comes to our very stimulating EXEB-meetings and other scientific activities in the Biology Department. Above, I have posted some pictures of EXEB-members from the Christmas Meeting of the Evolutionary Ecology Unit.
Below is the schedule for EXEB-meetings in spring 2017, based on input from those of you who responded to my Doodle-poll. For some of you, I have put two or three names at some dates, meaning that you can share the task in between you. As before, we should strive for a nice mixture between journal club, informal talks by ourselves or temporary visitors and general discussions about various topics. Also, as before, it is the person responsible for a Tuesday meeting that is responsible to finding a substitute, should (s)he not be able to make it. Also, as before, the blogpost announcing the meeting should be put up the week before, e. g. on Thursday or Friday,  so that the rest of the group has time to download and read the paper, if will be an article discussion.
As I will be travelling and doing field work with Beatriz Willink this winter (January 12 - February 24), I have made our two "brutal" and highly qualified postdocs Stephen De Lisle and Nathalie Feiner responsible for "policing" these meetings, and they will make sure to remind the persons responsible to do their work and put up the blog post in time. And of course remind them to bring fika!


First EXEB-meeting of 2017: "Countdown to 150" and a discussion about why mountain tops are higher in the tropics

Posted by Erik Svensson

Next week - on January 12 2017 - I am leaving together with Beatriz Willink and Hanna Bensch for a field expedition to Cameroon in Africa, where will study and collect odonates in various habitats. Given our coming field expedition to the tropics, and given that the journal ecological and evolutionary journal American Naturalist celebrates its 150th year anniversary by reminding us about some of the classical and highly-cited papers that have been published in this journal, I wanted to take the opportunity to present one such classic paper on Tuesday and discuss it with the group. The paper I am thinking of is Daniel Janzen's classical one entitled "Why mountain passes are higher in the tropics", and you can find it here.

(Full disclaimer: American Naturalist is my favourite journal, and I am member of the editorial board since several years. I especially like the journal's mix of ecology and evolution, and the aim to contribute to synthesis in biology. And of course that natural history is explicitly acknowledged as important, especially if combined with evolutionary theory. Natural history will continue to be important, in spite of being declared dead by some). 

The paper was published in 1967, i. e. the same year as I was born in Sweden. Janzen was (is) a famous US-based ecologist and evolutionary biologist who is also based in Costa Rica, where he has done a lot of interesting research and made contributions to tropical conservation.

Viktor Nilsson-Örtman will bring fika.
Time: Tuesday, January 10, 10.00
Where: "Darwin", 2nd floor "Ecology Building"

Thursday, December 15, 2016

Last EXEB-meeting in 2016 on December 20: hard and soft selection revisited

Posted by Erik Svensson

Nathalie and I decided to have a final EXEB-meeting of the year next week anyway, even though nothing was planned. Nathalie will bring "fika", and I will introduce a review paper (hopefully a light read) on "hard" and "soft" selection; two very important concepts that illustrate the difference between ecological and population genetic views of how selection works. Title and Abstract of the paper follows below.

When: Tuesday, December 20 at 10.00
Where: "Darwin, 2nd floor, Ecology Building

 Hard and Soft Selection Revisited: How Evolution by Natural Selection Works in the Real World

by David Reznick ( J Hered doi: 10.1093/jhered/esv07)


The modern synthesis of evolutionary biology unified Darwin’s natural selection with Mendelian genetics, but at the same time it created the dilemma of genetic load. Lewontin and Hubby’s (1966) and Harris’s (1966) characterization of genetic variation in natural populations increased the apparent burden of this load. Neutrality or near neutrality of genetic variation was one mechanism proposed for the revealed excessive genetic variation. Bruce Wallace coined the term “soft selection” to describe an alternative way for natural selection to operate that was consistent with observed variation. He envisioned nature as presenting ecological vacancies that could be filled by diverse genotypes. Survival and successful reproduction was a combined function of population density, genotype, and genotype frequencies, rather than a fixed value of the relative fitness of each genotype. My goal in this review is to explore the importance of soft selection in the real world. My motive and that of my colleagues as described here is not to explain what maintains genetic variation in natural populations, but rather to understand the factors that shape how organisms adapt to natural environments. We characterize how feedbacks between ecology and evolution shape both evolution and ecology. These feedbacks are mediated by density- and frequency-dependent selection, the mechanisms that underlie soft selection. Here, I report on our progress in characterizing these types of selection with a combination of a consideration of the published literature and the results from my collaborators’ and my research on natural populations of guppies.

Thursday, December 8, 2016

Visitor statistics to the EXEB-blog: the mystery of May 2016

Posted by Erik Svensson

The EXEB-blog has been running since 2009, and I occasionally check the number of visitors. I do not post as much as I did in the past, and nowadays it is mainly our forum for announcing EXEB seminars.  I used to hope that we could use it more actively, for outreach and scientific discussion posts, but as many seem to be unwilling to contribute I have more or less given up on that. 

However, I note that we do still have quite many visitors who are interested in our lab-meetings and seminars, and I guess it is good to have a presence in the bloggosphere. At the present moment, we have had over 300 000 visitors over these 7 years, and the average number of visitors per month hovers between 8000 and 12 000 per month. Naturally, some posts attract more visitors, such as the one when we discussed a PNAS-paper with the title "How does penis size influence male attractiveness in humans?" 

Something strange happened to our visitor number in May 2016, however (check visitor graph above). Suddenly, the visitor number jumped up almost fourfold to about 40 000 visitors, and remained high during the summer. As this is normally quite a slow period for the blog with no regular meetings, I find it interesting but difficult to explain. Was it simply some robots that scanned our blog then, or were there suddenly an extreme interest in the research activities of EXEB? Well, we will probably never get to know the answer, but it is at least fascinating to think of what it could have been that caused this spike of visitors!!!

Tuesday, December 6, 2016

Welcome and congratulations to two new incoming postdocs: Maarit Mäenpää and Masahito Tsuboi!

Posted by Erik Svensson

I feel very lucky that young and talented postdocs who are interested in joining my group have recently been succesful in terms of obtaining external scholarships. Here, I would like to welcome two new incoming postdocs who will officially join my lab next year (2017) and hence become part of the EXEB-environment. First, it is Maarit Mäenpää, who recently defended her PhD at Edinburgh University and who obtained a two-year postdoc grant from Emil Aaltonen Foundation in Finland. 

Second, and only a couple of days after Maarit found out about her postdoc grant, we found out that Masahito Tsuboi, who visited EXEB in August 2016 and gave a research talk on one of our Tuesday meetings, got a three-year postdoctoral position from the Swedish Research Council (VR). Masahito will spend two years abroad in Oslo (Norway) and Florida (US) in the laboratories of Prof. Thomas Hansen and Prof. David Houle, working on stasis and evolution of insect wing morphology, complemented with field work in Sweden and on odonates. 

Presentations follow below

 Maarit Mäenpää

Maarit I. Mäenpää

I am an evolutionary biologist, with a background in experimental research, and a deep interest in the role of different types of interactions – both ecological and social – on evolutionary processes. My research so far has focused on different aspects of life history evolution, from large scale geographic patterns in body size of geometrid moths, to the individual level effects of parent-offspring communication to the life history traits of a species of burying beetle. In Lund, I’m going to investigate phenotypic plasticity and trait canalization in genital morphology of the damselfly Ischnura elegans. My aim is to uncover the potential association of trait variation with assortative mating, and to thus explore a potential mechanism for evolutionary stasis and rapid divergence of traits. I will be using a combination of experimental and correlational approaches, in order to investigate both the existing patterns of trait variation, and to understand the underlying processes affecting it.

 Masahito Tsuboi


I am an evolutionary biologist interested in macroevolution. I have a background in phylogenetic comparative study of brain size evolution in teleost fish, where I enjoyed the effectiveness of phylogenetic comparative approach to investigate evolutionary questions in across-species, macroevolutionary time scales. However, this experience also revealed a frustrating lack of our current understanding in how evolutionary processes at macro scales are related to those at population or species levels (microevolutionary time scales). In the coming three years at EXEB, I will investigate the role of multivariate genetic constraints as the hypothetical “bridge” between micro- and macroevolution. I will do so by combining phylogenetic comparative methods with theories of evolutionary quantitative genetics.