Detecting independence in viability selection on two traits

Abstract

Any study of interdependence of viability selection on multiple traits (or gene loci) decisively rests on the applied measure of viability selection. An appropriate measure is obtained by normalizing the survival probabilities by their maximum. A necessary and sufficient characterization of independent operation of viability selection on two traits is given. The characterization comprises both simultaneous and successive selection, and it takes account of the bias introduced by stochastic association between the traits. It is proven that every type of independent selection on two traits can be represented in the form of two successive and independent selection steps (sequential selection). The relations between independent viability selection and the resulting population reduction (the selection load) are established. An analysis of published data on viability selection in beech revealed unexpectedly large amounts of selective interaction between two enzyme loci. The considerable accompanying increase in genetic load adds an interesting aspect to the selectionist-neutralist debate.