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.

Welcome to Alfredo Rago, new postdoc in Tobias Ullers lab and in the EXEB environment

 Posted by Erik Svensson

My aim is to understand how regulatory networks evolve to integrate genetic, developmental and environmental factors. I focus on how phenotypic evolution can be caused by changes in the interactions between groups of heterogeneous components rather than by individual genes. My methods include integrative analyses of heterogeneous high-throughput datasets based on theoretical evolutionary modelling.

I am using simulations of environmental and genetic networks to explain the evolution of phenotypic plasticity. I aim to provide a theoretical backbone for empirical studies on how environmental interactions affect the structure of developmental regulation and to understand which regulatory architectures evolve to dampen, propagate or interpret environmental inputs.

Symposium on phenotypic plasticity in Lund: November 26-27 2012

Posted by Erik Svensson

Next week there will be no lab-meeting as there will instead be an exciting international symposium in our department on the evolution of phenotypic plasticity: November 26-27 (two full days). The program looks very exciting, with some wellknown researchers and international guests. For more information, contact Johan Hollander (johan.hollander@biol.lu.se).

Also, the week after there will not be a regular lab-meeting, as the Evolutionary Ecology Unit will have its annual "Christmas Meeting" between December 4 and 5. There will be research talks, social activites and Christmas Dinner. If you are affiliated with the Evolutionary Ecology Unit and would like to participate, contact Anne Fogelberg (anne.fogelberg@biol.lu.se) or Per Lundberg (per.lundberg@biol.lu.se).

Lab-meeting on the evolution of plasticity in changing environments

This Wednesday (January 11 2012), we will discuss a relatively recent theoretical and conceptual paper in PLoS Biology entitled "Adaptation, plasticity and extinction in a changing environment: towards a predictive theory".  You can download it here.


Although this paper was published as recently as in 2010, but has already received 79 citations - a sign of a quite an influential paper. This is not surprising as it connects such topics as climate change, thermal adaptation and niche modelling with the evolution of phenotypic plasticity - all very important and central topics in ecology and evoutionary biology. Below you will find the Abstract for the paper. One of the co-authors is legendary evolutionary quantitative geneticist Russel Lande, by the way.

Time: Wednesday, January 11, 2012
Place: "Argumentet"

 

Summary 

Many species are experiencing sustained environmental change mainly due to human activities. The unusual rate and extent of anthropogenic alterations of the environment may exceed the capacity of developmental, genetic, and demographic mechanisms that populations have evolved to deal with environmental change. To begin to understand the limits to population persistence, we present a simple evolutionary model for the critical rate of environmental change beyond which a population must decline and go extinct. We use this model to highlight the major determinants of extinction risk in a changing environment, and identify research needs for improved predictions based on projected changes in environmental variables. Two key parameters relating the environment to population biology have not yet received sufficient attention. Phenotypic plasticity, the direct influence of environment on the development of individual phenotypes, is increasingly considered an important component of phenotypic change in the wild and should be incorporated in models of population persistence. Environmental sensitivity of selection, the change in the optimum phenotype with the environment, still crucially needs empirical assessment. We use environmental tolerance curves and other examples of ecological and evolutionary responses to climate change to illustrate how these mechanistic approaches can be developed for predictive purposes.

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.

Recently we have published two studies based on the isopod system of Asellus aquatics. This species occurs in two ecotypes, which resides in different habitats. As the ecotypes are present in several Swedish lakes, this system has been studied in depth with regard to parallel evolution. Our new articles address differences in mating behavior between the ecotypes. As other crustaceans, A. aquaticus exhibits precopulatory mate guarding where the male captures a female before she is receptive and carries her beneath him until she is ready to mate. This behavior is target for sexual conflict in several isopods as the optimal initiation of pairbonding may differ between the sexes.

One of our articles, published in the latest number of Journal of Evolutionary Biology, deals with differences between the ecotypes in mate guarding duration, but also in differences in female survival and offspring production. Among other things, we found a pattern of parallel evolution in these traits. The other article, published in open access journal PLoS ONE, deals with differences in mating propensity between the ecotypes and how this is affected by demographic factors. Here, we found that the novel ecotype seem to have evolved a plastic behavior as response to sex ratio, in contrast to the ancestral ecotype.

You could find both abstracts below, and both articles are included in Kristina Karlsson Green’s thesis that will be defended on next Friday.

Parallel divergence in mate guarding behaviour following colonization of a novel habitat

K. Karlsson, F. Eroukhmanoff, R. Härdling & E.I. Svensson

Abstract

Ecological factors can have profound effects on mating system and mating behaviour. We investigated the effect of altered ecological conditions, following colonization of a novel habitat, on precopulatory mate guarding in a freshwater isopod (Asellus aquaticus). This isopod occurs in two different ecotypes, which coexist within several different lakes in Sweden but which utilize different habitats. These ecotypes have rapidly (ca. 40 generations) diverged in parallel among lakes in several phenotypic characters, presumably as a response to different predatory pressures. Here, we demonstrate that also mate guarding characteristics have diverged in parallel between the ecotypes in different lakes. This is one of the few studies reporting parallel evolution of mating behaviour. Furthermore, our results also indicate a potential sexual conflict, as the length of mate guarding appears to lower components of female fitness. We discuss how novel environments might have strong and rapid effects on mate guarding dynamics and mating behaviour.

Phenotypic Plasticity in Response to the Social Environment: Effects of Density and Sex Ratio on Mating Behaviour Following Ecotype Divergence

Kristina Karlsson^*, Fabrice Eroukhmanoff, Erik I. Svensson

Abstract

The ability to express phenotypically plastic responses to environmental cues might be adaptive in changing environments. We studied phenotypic plasticity in mating behaviour as a response to population density and adult sex ratio in a freshwater isopod (Asellus aquaticus). A. aquaticus has recently diverged into two distinct ecotypes, inhabiting different lake habitats (reed Phragmites australis and stonewort Chara tomentosa, respectively). In field surveys, we found that these habitats differ markedly in isopod population densities and adult sex ratios. These spatially and temporally demographic differences are likely to affect mating behaviour. We performed behavioural experiments using animals from both the ancestral ecotype (‘‘reed’’ isopods) and from the novel ecotype (‘‘stonewort’’ isopods) population. We found that neither ecotype adjusted their behaviour in response to population density. However, the reed ecotype had a higher intrinsic mating propensity across densities. In contrast to the effects of density, we found ecotype differences in plasticity in response to sex ratio. The stonewort ecotype show pronounced phenotypic plasticity in mating propensity to adult sex ratio, whereas the reed ecotype showed a more canalised behaviour with respect to this demographic factor. We suggest that the lower overall mating propensity and the phenotypic plasticity in response to sex ratio have evolved in the novel stonewort ecotype following invasion of the novel habitat. Plasticity in mating behaviour may in turn have effects on the direction and intensity of sexual selection in the stonewort habitat, which may fuel further ecotype divergence.

Updated Wednesday-plans for lab-meeting on October 6

On Wednesday, our lab-meeting will start one hour later, at 11.15, as there is an interesting seminar that starts at 10.00 in the Limnology Section's seminar room "Tanken" (first floor). The talk will be given by Dr. Martin Lind, former PhD-student in Umeå in the laboratory of Frank Johansson, and currently a VR-postdoc at Sheffield University (UK). The title of Martins talk is:

"Local adaptation, gene flow, cost and benefits of phenotypic plasticity"

After the seminar, we walk back to the 2nd floor, and start  our regular lab-meeting at 11.15, i. e. one hour later than usual. This lab-meeting will take place in "Darwin", as has previously been announced. Hopefully, Martin will join us and provide some input on the papers. We will discuss one paper on niche conservatism in North American Jays, and one manuscript of ours that has already been sent out by Maren Wellenreuther. Send Maren an e-mail if you have not yet received this manuscript (maren.wellenreuther@zooekol.lu.se).

Lab-meeting on phenotypic plasticity, learning, sexual selection and mate preferences

This coming Wednesday (26 May), I wish to discuss a recent TREE-article by Charlie Cornwallis and Tobias Uller that recently came out. The title of this article is Towards an evolutionary ecology of sexual traits. I was one of the reviewers on this article, and I think they have some interesting things to say. Whether you agree or not with their general message, I think this paper should stimulate some discussion.

Also, postdoc Machteld Verzijden might send out one of her manuscripts about mate preference evolution in fish, that she want some input on. If she is able to finish this manuscript, she will send it out by e-mail to the group tomorrow (Tuesday).

Any fika-volunteer?

Lab-meeting on Tuesday 9 March at 13.00 on sexual dimorphism and sex-specific selection

Lab-meeting this coming week will be on Tuesday afternoon (13.00-15.00), not on our usual time on Wednesday mornings. We will discuss a recent paper in Evolution by our Dartmouth colleagues Robert Cox and Ryan Calsbeek on sexual size dimorphism and sex-specific selection in Anolis-lizards:

SEX-SPECIFIC SELECTION AND INTRASPECIFIC VARIATION IN SEXUAL SIZE DIMORPHISM Robert M. Cox and Ryan Calsbeek Sexual size dimorphism (SSD) is thought to evolve due to sex differences in selection on body size, but it is largely unknown whether intraspecific variation in SSD reflects differences in sex-specific selection among populations. We addressed this question by comparing viability selection between two island populations of the brown anole lizard (Anolis sagrei) that differ in the magnitude of male-biased SSD. On both islands, females experienced stabilizing selection favoring intermediate size whereas males experienced directional selection favoring larger size. Thus, sex-specific selection matched the overall pattern of male-biased SSD, but population differences in the magnitude of SSD were not associated with local differences in selection. Rather, population differences in SSD appear to result from underlying differences in the environmental potential for a rapid growth, coupled with sex-specific phenotypic plasticity. Males grew more slowly on the island with low SSD whereas growth of females did not differ between islands. Both sexes had substantially lower mass per unit length on the island with low SSD, suggesting that they were in a relatively poorer energetic condition. We propose that this energetic constraint disproportionately impacts growth of males due to their greater absolute energy requirements, thus driving intraspecific variation in SSD.

This paper should be of interest because of its links to sexual conflict, and incidentally, Bob and Ryan also has a Science-paper that will soon come out on how females manipulate offspring sex depending on the sire's body size in an adaptive fashion, i. e. a resolution of intralocus sexual conflict that you can read more about in this previous blogpost on one of my recent papers on another lizard species (Uta stansburiana).

When to meet? Tuesday March 9, 13.00
Where: "Darwin" room, 2nd floor, Ecology Building

Any fika-volunteer?