Divergence in genetic (co)variances and the alignment of gmax with phenotypic divergence

To better understand the sources of biological diversity in nature, we
need information on the mechanisms underlying population divergence.
Biological systems with patterns of naturally occurring adaptive variation
among populations can provide insight into the genetic architecture of
diverging traits and the influence of genetic constraints on responses to
selection. Using a system of reproductive character displacement in the
North American mushroom-feeding fly Drosophila subquinaria, we assessed
patterns of genetic (co)variance among a suite of chemical signaling
traits and divergence in this pattern among populations. D. subquinaria
exhibits stronger reproductive isolation against the closely related
Drosophila recens in sympatry, where both female mating preferences and
male chemical signalling traits have diverged from the ancestral
allopatric populations. We collected three wild populations from each
region and, in the lab, characterized the phenotypic divergence in these
traits as well as the additive genetic (co)variance structure (G-matrix)
with replicate breeding designs. We found divergence between allopatric
and sympatric D. subquinaria in the shape and size of the G-matrix, and
that the leading axis of genetic variance (gmax) had changed in sympatry
to come into alignment with the primary axis of phenotypic divergence
between the sympatric and allopatric regions.