Genotypes and their interaction effects on reproduction and mating-induced immune activation in Drosophila melanogaster

Mating causes considerable alterations in female physiology and behaviour,
and immune gene expression, partly due to proteins transferred from males
to females during copulation. The magnitude of these phenotypic changes
could be driven by the genotypes of males and females, as well as their
interaction. To test this, we carried out a series of genotype by genotype
(G × G) experiments using Drosophila melanogaster populations from two
distant geographical locations. We expected lines to have diverged in male
reproductive traits and females to differ in their responses to these
traits. We examined female physiological and behavioural post-mating
responses to male mating traits, i.e. behaviour and ejaculate composition,
in the short- to mid-term (48 hours) following mating. We then explored
whether a sexually transferred molecule, sex peptide (SP), is the
mechanism behind our observed female post-mating responses. Our results
show that the genotypes of both sexes as well as the interaction between
male and female genotype affect mating and post-mating reproductive
traits. Immune gene expression of three candidate genes increased in
response to mating, and was genotype-dependent but did not show a G × G
signature. Males showed genotype-dependent SP expression in the seven days
following eclosion, but female genotypes showed no differential
sensitivity to the receipt of SP. The two genotypes demonstrated clear
divergence in physiological traits in short- to mid-term responses to
mating, but the longer-term consequences of these initial dynamics remain
to be uncovered.