Heritability and Sexual Selection

EFFECT OF SEXUAL SELECTION ON HERITABILITY OF TRAITS

Strong directional selection usually exhausts additive genetic variance for a trait (in this context, this means traits governed by polygenic inheritance, or QTL's) in three to five generations. After that there is no further response to selection and the remaining phenotypic variation is either environmental or non-additive genetic variation. In theory, sexual selection, on a trait, such as antler size, should rapidly eliminate the additive genetic variance for the trait. In other words, the trait will be genetically fixed. In practice, many traits that seem to be under strong sexual selection still have considerable residual heritability. (Pomiankowski, A. and A. P. Moller, 1995)

Hypotheses for why this might be:

sexual selection is strong only under extreme environmental conditions in which survivorship is low, thus variation is maintained during periods of relaxed selective forces.
Interactions (eg linkage effects, viability effects) with other traits put the brakes on sexual selection before the additive variation is exhausted.
Mate choice relies on many factors, rather than one trait; when selection is acting an multiple traits, variation will remain in each of the traits.
Counterbalancing selection maintains additive genetic variance by putting a limit on how elaborate a signal can be (Zuk, M. and G. R. Kolloru. 1998).

These models have fallen from favor as the handicap principle has become more generally accepted, but could explain some outlandish sexually selected traits.

Lande, R. 1976. Models of speciation by sexual selection on polygenic traits. P. N. A. S. (USA) 78:3721-25.

Pomiankowski, A. and A. P. Moller, 1995, A resolution of the lek paradox. Proc. Roy. Soc. London, B. 260:21-29

Zuk, M. and G. R. Kolloru. 1998. Exploitation of sexual signals by predators and parasitoids. Quart. Rev. Biol. 73:415-438. Runaway model (Fisher) Female preference need not rely on a fitness-correlated trait.