Thursday, December 15, 2016

Last EXEB-meeting in 2016 on December 20: hard and soft selection revisited

Posted by Erik Svensson

Nathalie and I decided to have a final EXEB-meeting of the year next week anyway, even though nothing was planned. Nathalie will bring "fika", and I will introduce a review paper (hopefully a light read) on "hard" and "soft" selection; two very important concepts that illustrate the difference between ecological and population genetic views of how selection works. Title and Abstract of the paper follows below.

When: Tuesday, December 20 at 10.00
Where: "Darwin, 2nd floor, Ecology Building

 Hard and Soft Selection Revisited: How Evolution by Natural Selection Works in the Real World

by David Reznick ( J Hered doi: 10.1093/jhered/esv07)


The modern synthesis of evolutionary biology unified Darwin’s natural selection with Mendelian genetics, but at the same time it created the dilemma of genetic load. Lewontin and Hubby’s (1966) and Harris’s (1966) characterization of genetic variation in natural populations increased the apparent burden of this load. Neutrality or near neutrality of genetic variation was one mechanism proposed for the revealed excessive genetic variation. Bruce Wallace coined the term “soft selection” to describe an alternative way for natural selection to operate that was consistent with observed variation. He envisioned nature as presenting ecological vacancies that could be filled by diverse genotypes. Survival and successful reproduction was a combined function of population density, genotype, and genotype frequencies, rather than a fixed value of the relative fitness of each genotype. My goal in this review is to explore the importance of soft selection in the real world. My motive and that of my colleagues as described here is not to explain what maintains genetic variation in natural populations, but rather to understand the factors that shape how organisms adapt to natural environments. We characterize how feedbacks between ecology and evolution shape both evolution and ecology. These feedbacks are mediated by density- and frequency-dependent selection, the mechanisms that underlie soft selection. Here, I report on our progress in characterizing these types of selection with a combination of a consideration of the published literature and the results from my collaborators’ and my research on natural populations of guppies.

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