pleiotropy
Walsh B & Blows MW 2009 Abundant genetic variation + strong selection = multivariate genetic constraints: a geometric view of adaptation. Annu Rev Ecol Evol Syst 40:41-59.
- the perceived incompatibility between these two observations is a consequence of taking a trait-by-trait approach to the multivariate problem of genetic variation and selection
- the simultaneous presence of widespead genetic variation in, and strong selection on, individual traits indicates that substantial multivariate genetic constraints are likely to be present in natural populations
- mutational target size, rather than any association with the strength of selection, may therefore explain the variation among individual traits in standing genetic variance
- more complex life-history traits are affected by a greater proportion of the genome
- stabilizing selection is far stronger in natural populations than the typical values used in theoretical models to account for the observed levels of genetic variation
- there is currently no compelling explanation for the maintenance of the observed high levels of genetic variation in fitness traits given the established strength of selection
- stasis is more common than evolutionary change in the presence of both ample genetic variance and strong selection
- in isolation the generality of each of these two observations, widespread genetic variance and strong selection, is not in question
- the apparent contradiction of their coexistence rests on a trait-by-trait assessment of quantitative variation and selection
- with a per-trait mutation rate of around 0.1, and a whole-genome mutation rate of around 1, the number of pleiotropically independent traits is likely to be in the order of 10s rather than the 100s or 1000s
- substantial multivariate genetic constraints on the response to selection are present in nature
- bivariate genetic correlations are therefore of little use in isolation in defining genetic constraints in all but the most simple of systems
