Evolution under these conditions is called frequency-dependent selection
. Some phenotypes become "fitter" as they become more common (positive frequency-dependent selection
(2009) reported frequency-dependent selection
by avian predators for the more common of the color morphs in P.
This occurred through frequency-dependent selection
, where the fitness of one particular phenotype depended on the distribution of other phenotypes in the population.
Codon bias and frequency-dependent selection
on the hemagglutinin epitopes of influenza A virus.
The causes for this change are discussed in relation to frequency-dependent selection
and density/social stress hypotheses.
There are several mechanisms by which frequency-dependent selection
might be achieved.
(2) There may be pest-by-control-agent genotype interactions, leading to frequency-dependent selection
, and a reduced overall rate of selective advance.
In the case of haploid organisms such as bacteria, balancing selection would take the form of frequency-dependent selection
rather than overdominant selection.
As mentioned in the introduction, two selection pressures against hybrids are likely: frequency-dependent selection
for warning coloration and abiotic selection on either side of an aridity gradient centered in the hybrid zone (Jiggins et al.
Various forms of frequency-dependent selection
have long been hypothesized to maintain genetic polymorphisms in natural populations (Cain and Sheppard 1954, Fisher 1958, Haldane and Jayakar 1963, Ayala and Campbell 1974, Levin 1988, Hori 1993).
Under these conditions, fecundity selection is expected to reinforce the frequency-dependent selection
typical of SI systems, and this may lead to an increase in the number of alleles maintained in natural populations.
The non-zero equilibrium value of the variance is determined by frequency-dependent selection
, which is operating because the fitness of a phenotype decreases if more individuals of the same phenotype are present.