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.

EXEB meeting on Tuesday April 15: Visit by Wiebke Feindt and talk about comparative transcriptomics in Neotropical damselflies

Posted by Erik Svensson

 For next week's EXEB-meeting, I am pleased to welcome Wiebke Feindt from ITZ Division of Ecology & Evolution in Hannover (Germany). Wiebke is currently doing a PhD on evolution, conservation genetics and comparative transcriptomics of Neotropical odonates. She is particularly interested in the charismatic genus Megaloprepus, which contains the largest damselflies in the world and which are often called "Helicopter damselflies". Below is the title of Wiebke's talk and a brief Abstract.

Odonate speciation in the Neotropics: New insights into the genus Megaloprepus

In an ever-changing world flying insects play a significant role for studying speciation. As the world’s largest living odonate species, Megaloprepus caerulatus is an excellent model organism to investigate this crucial point of evolution. Despite its niche conservatism, a strong genetic differentiation and a morphometric separation into four distinct clusters was detected. On this basis, ongoing comparative transcriptomics may further contribute to elucidate the complex evolutionary processes and causal interplays of speciation.

Time: Tuesday, March 15, 2016, at 10.00

Locale: "Argumentet", 2nd floor, Ecology Building

Lab-meeting on intralocus sexual conflict and transcriptomics

It is time for the fall's first lab-meeting, and what could possibly be a better start than to discuss a paper about how intralocus sexual conflict might (or might not!) leave a transcriptomic signature in the organism? The study I wish to discuss is a relatively new paper in PLoS Biology by Paulo Innocenti and Ted Morrow. The authors combined quantitative-genetic fitness assays in the fruitfly (Drosophila melanogaster) to investigate sex-biased gene expression and its links to intralocus sexual conflict, i. e. the developmental conflict that arises between male and female phenotypes, that arises due to the fact that both sexes share a common gene pool.

We have discussed intralocus sexual conflict and its consequences in previous lab-meetings, and some of our recent lab-publications that are relevant to this topic can be found here (lizards) and here (damselflies). The authors of the current study used microarrays to study sex-specific transcripts, a technique which is now rapidly replaced by "454-sequencing" and other methods in this rapidly moving field of molecular biology.

The time and place for the lab-meeting is as usual: Wednesday August 15 at 10.15 in the "Darwin Room" (2nd floor, Ecology Building). Fika volunteers are encouraged to step forward. Below, I have put an abstract to the paper which can be downloaded here, and you can also find an interesting short comment by Robin Meadows, also published in PLoS Biology.

Abstract 

When selective pressures differ between males and females, the genes experiencing these conflicting evolutionary forces are said to be sexually antagonistic. Although the phenotypic effect of these genes has been documented in both wild and laboratory populations, their identity, number, and location remains unknown. Here, by combining data on sex-specific fitness and genome-wide transcript abundance in a quantitative genetic framework, we identified a group of candidate genes experiencing sexually antagonistic selection in the adult, which correspond to 8% of Drosophila melanogaster genes. As predicted, the X chromosome is enriched for these genes, but surprisingly they represent only a small proportion of the total number of sex-biased transcripts, indicating that the latter is a poor predictor of sexual antagonism. Furthermore, the majority of genes whose expression profiles showed a significant relationship with either male or female adult fitness are also sexually antagonistic. These results provide a first insight into the genetic basis of intralocus sexual conflict and indicate that genetic variation for fitness is dominated and maintained by sexual antagonism, potentially neutralizing any indirect genetic benefits of sexual selection.

Author's summary

Males and females of many species are different: many of these differences are thought to have evolved because the sexes often have needs and strategies that do not coincide. For example, in fruit-flies, females may do best by concentrating their efforts in acquiring resources to be able to lay more eggs, while males would benefit most from increasing their mating and fertilization success. Such differences generate a sexual “conflict of interests”, and since as a general rule each behavioural, morphological or physiological characteristic is regulated by the same set of genes in the two sexes, this conflict takes place ultimately at the genetic level. In our study, we combined data on the reproductive success of different lines of fruit-flies with their gene expression profiles. We show that a large proportion of genes that contribute to male fertilization success are detrimental for female fecundity, and vice-versa. These results indicate that an optimal genotype for both sexes does not exist: many genes maintain different variants because they have opposite effects in males and females, perhaps helping to explain how genetic diversity is maintained in the face of selection.

Citation: Innocenti P, Morrow EH (2010) The Sexually Antagonistic Genes of Drosophila melanogaster. PLoS Biol 8(3): e1000335. doi:10.1371/journal.pbio.1000335