The Evolution of Sex

The 'Evolution' meeting is quickly coming to a close here in Portland. I'm presently blogging from the second last session of the meeting while Marc Johnson gives a fascinating talk on the functional evolutionary loss of sex, via the loss of recombination and segregation, in the evening primrose genus. Among evening primroses (Oenothera) 16% of species have functionally lost the ability to sexually reproduce - but this loss is associated with reciprocal translocations among chromosomes rather than with polyploidy, as it is in most asexual plants. This allows him to study the evolutionary loss of sex independently of the evolution of increased ploidy number. Evidently, asexual species pay a high cost of asexuality in terms of their susceptibility to generalist herbivore insects - although they also exhibit a decreased vulnerability to specialists herbivores (though the underlying mechanism seems a little unclear). In addition, he has found the intriguing, and somewhat counterintuitive, result (but one that had been predicted by some prior theory due to J. Felsenstein) that speciation rates are higher in functionally asexual lineages than in sexual lineages. Extinction also seems slightly elevated in asexual lineages, although this effect was non-significant.