Data from: Constrained evolution of the sex comb in Drosophila simulans

Male fitness is dependent on sexual traits that influence mate acquisition
(pre-copulatory sexual selection) and paternity (post-copulatory sexual
selection), and while many studies have documented the form of selection
in one or the other of these arenas, fewer have done it for both.
Nonetheless, it appears that the dominant form of sexual selection is
directional, although theoretically, populations should converge on peaks
in the fitness surface, where selection is stabilizing. Many factors,
however, can prevent populations from reaching adaptive peaks. Genetic
constraints can be important if they prevent the development of highest
fitness phenotypes, as can the direction of selection if it reverses
across episodes of selection. In this study, we examine the evidence that
these processes influence the evolution of the multivariate sex comb
morphology of male Drosophila simulans. To do this, we conduct a
quantitative genetic study together with a multivariate selection analysis
to infer how the genetic architecture and selection interact. We find
abundant genetic variance and covariance in elements of the sex comb.
However, there was little evidence for directional selection in either
arena. Significant nonlinear selection was detected prior to copulation
when males were mated to non-virgin females, and post-copulation during
sperm offence (again with males mated to non-virgins). Thus contrary to
our predictions, the evolution of the D. simulans sex comb is limited
neither by genetic constraints nor by antagonistic selection between pre-
and post-copulatory arenas, but nonlinear selection on the multivariate
phenotype may prevent sex combs from evolving to reach some fitness
maximising optima.