Spatial environmental complexity mediates sexual conflict and sexual selection in Drosophila melanogaster

Sexual selection is an important agent of evolutionary change, but the
strength and direction of selection often vary over space and time. One
potential source of heterogeneity may lie in the opportunity for male–male
and/or male–female interactions imposed by the spatial environment. It has
been suggested that increased spatial complexity permits sexual selection
to act in a complementary fashion with natural selection (hastening the
loss of deleterious alleles and/or promoting the spread of beneficial
alleles) via two (not mutually exclusive) pathways. In the first scenario,
sexual selection potentially acts more strongly on males in complex
environments, allowing males of greater genetic “quality” a greater chance
of outcompeting rivals, with benefits manifested indirectly in offspring.
In the second scenario, increased spatial complexity reduces opportunities
for males to antagonistically harm females, allowing females (especially
those of greater potential fecundities) to achieve greater reproductive
success (direct fitness benefits). Here, using Drosophila melanogaster ,
we explore the importance of these mechanisms by measuring direct and
indirect fitness of females housed in simple vial environments or in vials
in which spatial complexity has been increased. We find strong evidence in
favor of the female conflict‐mediated pathway as individuals in complex
environments remated less frequently and produced more offspring than
those housed in a simpler spatial environment, but no difference in the
fitness of sons or daughters. We discuss these results in the context of
other recent studies and what they mean for our understanding of how
sexual selection operates.