Heterozygote advantage and pleiotropy contribute to intraspecific color trait variability

The persistence of intrapopulation phenotypic variation typically requires
some form of balancing selection since drift and directional selection
eventually erode genetic variation. Heterozygote advantage remains a
classic explanation for the maintenance of genetic variation in the face
of selection. However, examples of heterozygote advantage, other than
those associated with disease resistance are rather uncommon. Across most
of its distribution, males of the aposematic moth Arctia plantaginis have
two hindwing phenotypes determined by a heritable one locus-two allele
polymorphism (genotypes: WW/Wy = white morph, yy = yellow morph). Using
genotyped moths we show that the presence of one or two copies of the
yellow allele affects several life-history traits. Reproductive output of
both males and females, and female mating success are negatively affected
by two copies of the yellow allele. Females carrying one yellow allele
(i.e. Wy) have higher fertility, hatching success, and offspring survival
than either homozygote, thus leading to strong heterozygote advantage. Our
results indicate strong female contribution especially at the
postcopulatory stage in maintaining the color polymorphism. The interplay
between heterozygote advantage, yellow allele pleiotropic effect and
morph-specific predation pressure may exert balancing selection on the
color locus, suggesting that color polymorphism may be maintained through
complex interactions between natural and sexual selection.