Variable and sexually conflicting selection on Silene stellata floral traits by a putative moth pollinator selective agent

Conflicting selection is an important evolutionary mechanism since it
impedes directional evolution and helps to maintain phenotypic variation.
It can arise when mutualistic and antagonistic selective agents exert
opposing selection on the same trait and when distinct phenotypic optima
are favored by different fitness components. In this study, we test for
conflicting selection through different sexual functions of the
hermaphroditic plant, Silene stellata during its early and late flowering
season. We find selection is consistently stronger during the early
flowering season, which aligns with the activity peak of the pollinating
seed predator Hadena ectypa. Importantly, we observe sex-specific
selection on petal dimensions to have opposite signs. We propose that the
observed sexually conflicting selection on petal design results from the
negative selection through female function for the avoidance of
oviposition and the subsequent fruit predation by H. ectypa larvae and the
positive selection through male function for pollen export by H. ectypa
adults. The Silene-Hadena interaction has previously been considered to be
largely parasitic. Our findings suggest a trade-off mechanism that could
thwart the evolution of an “escape route” from the nocturnal pollination
syndrome by Silene spp. and contribute to the long-term maintenance of the
Silene-Hadena system.