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.

On wings, genes, exaptations and the evolution of phenotypic novelty in treehoppers

Last week's lab-meeting on kin selection was cancelled, and since this discussion largely seems to be a semantic one and of little direct relevance to our own work on insects, I thought we should instead discuss an insect paper, now when the field season is rapidly approaching. After all, we are not behavioural ecologists and not so focussed on kin selection, but rather field evolutionary biologists, so this paper might be more central to our ongoing work.

The paper is a wonderful example of how evolution acts like a "tinkerer", rather than as an engineer, when novel structures evolve, and that new traits arise from already existing structures/genes as "exaptations", rather than evolve from scratch. In this case, the remarkable morphological structures we will discuss (see above!) are governed by genes which originally coded for wings! The paper I have in mind is a wonderful example of "evo-devo", i. e. the genetic and developmental basis of animal form and it deals with the morphological structures of treehoppers (Homoptera), a diverse insect group characterized by remarkable appendices on their thorax, of unknown adaptive function (see picture above!). The title is: "Body plan innovation in treehoppers through the evolution of an extra wing-like appendage". 

You can downloadthe paper here, and the abstract is found below. Time and place as usual: "Argumentet" at 14.30 on Wednesday May 25. Any fika volunteer?

Body plan innovation in treehoppers through the evolution of an extra wing-like appendage

 Prud'homme B. et al.

Body plans, which characterize the anatomical organization of animal groups of high taxonomic rank1, often evolve by the reduction or loss of appendages (limbs in vertebrates and legs and wings in insects, for example). In contrast, the addition of new features is extremely rare and is thought to be heavily constrained, although the nature of the constraints remains elusive2, 3, 4. Here we show that the treehopper (Membracidae) ‘helmet’ is actually an appendage, a wing serial homologue on the first thoracic segment. This innovation in the insect body plan is an unprecedented situation in 250 Myr of insect evolution. We provide evidence suggesting that the helmet arose by escaping the ancestral repression of wing formation imparted by a member of the Hox gene family, which sculpts the number and pattern of appendages along the body axis5, 6, 7, 8. Moreover, we propose that the exceptional morphological diversification of the helmet was possible because, in contrast to the wings, it escaped the stringent functional requirements imposed by flight. This example illustrates how complex morphological structures can arise by the expression of ancestral developmental potentials and fuel the morphological diversification of an evolutionary lineage.