Male and female genotype and a genotype-by-genotype interaction mediate the effects of mating on cellular but not humoral immunity in female decorated crickets

Sexually antagonistic coevolution is predicted to lead to the divergence
of male and female genotypes related to the effects of substances
transferred by males at mating on female physiology. The outcome of mating
should thus depend on the specific combination of mating genotypes.
Although mating has been shown to influence female immunity in diverse
insect taxa, a male-female genotype-by-genotype effect on female immunity
post-mating remains largely unexplored. Here, we investigate the effects
of mating on female decorated cricket baseline immunity and the potential
for a male-by-female genotype interaction affecting this response. Females
from three distinct genotypic backgrounds were left unmated or singly
mated in a fully reciprocal design to males from the same three genotypic
backgrounds. Hemocytes and hemocyte microaggregations were quantified for
female cellular immunity, and phenoloxidase, involved in melanization, and
antibacterial activity for humoral immunity. In this system, female
cellular immunity was more reactive to mating, and mating effects were
genotype dependent. Specifically, for hemocytes, a genotype-mating status
interaction mediated the effect of mating per se, and a significant
male-female genotype-by-genotype interaction determined hemocyte depletion
post-mating. Microaggregations were influenced by the female’s genotype or
that of her mate. Female humoral immune measures were unaffected,
indicating the propensity for post-mating effects on female is dependent
on the component of baseline immunity. The genotype-by-genotype effect on
hemocytes supports a role of sexual conflict in post-mating immune
suppression, suggesting divergence of male genotypes with respect to
modification of female post-mating immunity, and divergence of female
genotypes in resistance to these effects.