Antagonistc pleiotropy & maintenance of variation

Antagonistic pleiotropic effects reduce the potential adaptive value of the FRIGIDA locus:

....Here we investigate the importance of pleiotropy and epistasis in determining the adaptive value of a candidate gene using the gene FRI (FRIGIDA), which is thought to be the major gene controlling flowering time variation in Arabidopsis thaliana. The effect of FRI on flowering time was analyzed in an outbred population created by randomly mating 19 natural accessions of A. thaliana. This unique population allows the estimation of FRI effects independent of any linkage association with other loci due to demographic processes or to coadapted genes. It also allows for the estimation of pleiotropic effects of FRI on fitness and inflorescence architecture. We found that FRI explains less variation in flowering time than previously observed among natural accessions, and interacts epistatically with the FLC locus. Although early flowering plants produce more fruits under spring conditions, and nonfunctional alleles of FRI were associated with early flowering, variation atFRI was not associated with fitness. We show that nonfunctional FRI alleles have negative pleiotropic effects on fitness by reducing the numbers of nodes and branches on the inflorescence. We propose that these antagonistic pleiotropic effects reduce the adaptive value of FRI, and helps explain the maintenance of alternative life history strategies across natural populations of A. thaliana..

The implication here seems to be that there different genetic architectures which lead to alternative phenotypes which exhibit the same fitness value. This means that the various polymorphisms within the population may lead to multiple adaptive equilibria, maintaining phenotypic variation and the ergo the genetic variation extant within the population. Even though A. thaliana is a plant I think that the basic principles may also operate within our own species and so explain some of the behavioral and physical variation we see all around us. This should also make us cautious about one-size-fits-all adaptive explanations which ignore why variation would remain within the population.