Postdoc
Ph: 520 626 1727
Office: BSW 121
Very generally, I am interested in what (evolutionary) solutions exist to deal with environmental variability. And there seems to be a lot of solutions, only a few of which I have studied (yet).
During my PhD, I studied the local adaptation of dormancy strategies, both theoretically and in the field, the latter by means of experiments in two populations of the chestnut weevil, Curculio elephas.
My current research as a post-doc is about the evolution of evolvability by means of the preadaptation of cryptic genetic variation. Within this general framework, I am interested in the evolution of the rate of “errors” in protein synthesis (e.g. a codon stop read-through). Error rates are generally considered to be the result of a selective trade-off between the costs of errors and the benefits of a high speed of protein synthesis. Due to the negative consequences of errors, one may postulate that selection on processes involved in protein synthesis would favor accuracy. We found it to be otherwise…
We designed a model based on the evolution of the frequency of stop codon readthrough, whereby a RNA sequence in the 3′UTR is translated into an amino-acid sequence. Readthrough can decrease individual fitness (e.g. if the elongated protein does not fold) or not (if the elongated protein is benign). We found that the evolution of readthrough frequencies is highly dependent of the population size (Rajon & Masel, 2011). This is because selection against cryptic deleterious 3′UTR sequences is more efficient in large populations. With fewer deleterious cryptic sequences among the 3′UTRs, readthrough errors throughout the genome have a less negative effect, which drives the evolution of the cost of errors/accuracy trade-off towards a higher error rate. More errors mean more selection on cryptic sequences, so there is a positive feedback between selection against deleterious sequences and the error rate, which ultimately leads to the evolution of an error rate high enough to efficiently purge deleterious cryptic sequences. This doesn’t happen in small populations, where selection is never efficient enough to eliminate deleterious sequences, and where a low error rate evolves (as it hides the junk in the 3′UTR). In populations of intermediate sizes, the outcome depends on the initial genotype: a low error rate evolves when the number of deleterious sequences in the 3′UTRs is above a certain threshold, and a high error rate evolves otherwise. This has interesting consequences: for example, a large population (where deleterious sequences are efficiently eliminated) will keep its high error rate and its clean 3′UTRs if it decreases in size across a certain range.
One of my current projects is to bring environmental variability into this evolutionary game. As we have shown (Rajon & Masel, 2011), a high error rate has the advantage of selecting against unconditionally deleterious cryptic mutants. After an environmental change, lineages formerly subject to frequent errors could therefore contain cryptic variants that are more likely to be adapted to the new conditions encountered. When these sequences can become permanently expressed (e.g. after a mutation of the stop codon in the example of readthrough errors), this increases evolvability. I am currently designing a model that will determine in which conditions the rate of errors might increase due to its evolvability properties.
Publications:
- Venner, S., Pélisson P-F., Bel-Venner M-C., Débias F., Rajon, E., & Menu, F. (2011). Coexistence of Insect Species Competing for a Pulsed Resource: Toward a Unified Theory of Biodiversity in Fluctuating Environments PLoS One, 6(3), e18039. (PubMed)
- Rajon, E., & Masel, J. (2011). Evolution of molecular error rates and the consequences for evolvability. Proc. Natl. Acad. Sci. USA, 108(3), 1082-7. (PubMed)
- Menu, F., Ginoux, M., Rajon, E., Lazzari, C. R., & Rabinovich, J. E. (2010). Adaptive Developmental Delay in Chagas Disease Vectors: An Evolutionary Ecology Approach. PLoS Negl Trop Dis, 4(5), 691. (PubMed)
- Rajon, E., Venner, S., & Menu, F. (2009). Spatially heterogeneous stochasticity and the adaptive diversification of dormancy. J. evol. biol., 22, 2094-2103.