Ever since I dwelled in the world of natural selection and genetics, there has been one single question that has intrigued my mind perhaps more than anything else. Namely, how does it come about that there is any genetic variation left in traits under persistent and strong directional selection which is expected erode that variation? I guess this was the very reason why I at the first place choose to jump into quantitative genetics, rather than just play around with allozyme allele frequencies and mtDNA sequences – the tools of the trade in population genetics in early 1990′s.
Yet, the problem turns out to be rather hard one to answer, but some progress have been made. Following up our earlier work with collared flycatchers and general review on heritability of fitness characters, Celine has now – with little help from Jim, John and me – produced an empirical analysis of fitness traits using long-term data on red-billed gulls. In a paper published on the pages of Evolution, this study confirms that that the closer the traits association with fitness (i.e. number of offspring recruiting to the breeding population), the lower the heritability of that trait. Moreover, this seems to be at least partly due lowered additive genetic variance in fitness traits, and not because these traits would just harbor disproportionally much environmental variance.
Céline Teplitsky, James A. Mills, John W. Yarrall, Juha Merilä (2008) Heritability of fitness components in a wild bird population. Evolution (Accepted Article Online: Nov 19 2008 5:51AM). doi: 10.1111/j.1558-5646.2008.00581.x
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Read Frank Doyle’s review of this paper from here (#710: ‘Fitness traits do have lower additive genetic variance. R A Fisher finally wins‘):
http://www.genecomp.com/Sept-Oct_2009.htm