Thursday, January 26, 2017

Selfing and adaptation

Posted by Jessica Abbott
Physa acuta.Taken by N yotarou.
For next week's group meeting I've chosen a paper that just came out, about the effect of self-fertilization on the rate of adaptation. We expect that in the long term, selfing depletes genetic variance. However in the short term, selfing may produce a more rapid reponse to selection. This study attempts to disentagle effects of contemporary selfing from historical selfing on the rate of adaptation, using experimental evolution in the snail Physa acuta. A commentary on this article is also avaliable here.

Title: Experimental evidence for the negative effects of self-fertilization on the adaptive potential of populations.
Abstract: Self-fertilization is widely believed to be an “evolutionary dead end”, increasing the risk of extinction and the accumulation of deleterious mutations in genomes. Strikingly, while the failure to adapt has always been central to the dead-end hypothesis, there are no quantitative genetic selection experiments comparing the response to positive selection in selfing versus outcrossing populations. Here we studied the response to selection on a morphological trait in laboratory populations of a hermaphroditic, self-fertile snail under either selfing or outcrossing. We applied both treatments to two types of populations: some having undergone frequent selfing and purged a substantial fraction of their mutation load in their recent history, and others continuously maintained under outcrossing. Populations with a history of outcrossing respond faster to selection than those that have experienced selfing. In addition, when self-fertilization occurs during selection, the response is initially fast but then rapidly slows, while outcrossing populations maintain their response throughout the experiment. This occurs irrespective of past selfing history, suggesting that high levels of inbreeding depression, contrary to expectation, do not set strong limits to the response to selection under inbreeding, at least at the timescale of a few generations. More surprisingly, phenotypic variance is consistently higher under selfing, although it quickly becomes less responsive to selection. This implies an increase in non-heritable variance, hence a breakdown of developmental canalization under selfing. Our findings provide the first empirical support of the short-term positive and long-term negative effects of selfing on adaptive potential.
When: Tuesday January 31st, at 10.00.

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