Temporally-balanced selection during development of larval Pacific oysters (Crassostrea gigas) inherently preserves genetic diversity within offspring

Balancing selection is one of the mechanisms which has been proposed to
explain the maintenance of genetic diversity in species across
generations. For species with large populations and complex life
histories, however, heterogeneous selection pressures may create a
scenario in which the net effects of selection are balanced across
developmental stages. With replicated cultures and a pooled sequencing
approach, we show that genotype-dependent mortality in larvae of the
Pacific oyster (Crassostrea gigas) is largely temporally dynamic and
inconsistently in favor of a single genotype or allelic variant at each
locus. Overall, the patterns of genetic change we observe to be taking
place are more complex than what would be expected under classical
examples of additive or dominant genetic interactions. They are also not
easily explained by our current understanding of the effects of genetic
load. Collectively, temporally heterogeneous selection pressures across
different larval developmental stages may act to maintain genetic
diversity in oysters, while also inherently sheltering genetic load within
populations.