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. 

Thursday, December 1, 2016

Lab meeting on December 6: Transcriptomics of sexual development without sex chromosomes

Two sexes, one genome: regulatory structure of sex-biased development without sexual chromosomes

Sexual dimorphism poses a challenge for genetically-minded scientists: How can animals with near-identical genomes be so strikingly different? Existing theories rely on selection for sex-linked genes, yet sexual dimorphism is present also in species that lack sexual chromosomes. How do these species induce and maintain different developmental trajectories?

I present the results of my research on the sexual development of the jewel wasp Nasonia vitripennis (Hymenoptera). Nasonia's sex is determined by the number of genome copies received by the zygote and does not show any sex-linked locus within its genome.

I compare the transcriptomes of developing male and female Nasonia in order to detect the mechanistic processes that induce sexual dimorphism throughout development. In particular, I test whether sex-specific differences are present at three molecular levels:
  1. Sub-gene, via alternative splicing
  2. Whole-gene, via differential expression
  3. Between-gene, via higher order transcript-transcript interactions
I show how splicing comprises only a minor portion of between-sex differences, whereas differential expression and sex-biased interactions complement each other and alternate in prevalence throughout development.

Finally, I reconstruct the structural organization of sex-biased developmental sub-networks and compare them to non sex-biased sub-networks. The regulatory architecture of sex-biased sub-networks shows stronger hierarchical organization and preferential integration of new genes in potentially regulatory positions.