Sexually antagonistic coevolution of the male nuptial gift and female feeding behaviour in decorated crickets

The evolution of nuptial gifts has traditionally been considered a
harmonious affair, providing benefits to both mating partners. There is
growing evidence, however, that receiving a nuptial gift can be actively
detrimental to the female. In decorated crickets (Gryllodes sigillatus),
males produce a gelatinous spermatophylax that enhances sperm transfer but
provides little nutritional benefit and hinders female post-copulatory
mate choice. Here, we examine the sexually antagonistic coevolution of the
spermatophylax and the female feeding response to this gift in G.
sigillatus maintained in experimental populations with either a
male-biased or female-biased adult sex ratio. After 25 generations, males
evolving in male-biased populations produced heavier spermatophylaxes with
a more manipulative combination of free amino acids than those evolving in
female-biased populations. Moreover, when the spermatophylax originated
from the same selection regime, females evolving in male-biased
populations always had shorter feeding durations than those evolving in
female-biased populations indicating the evolution of greater resistance.
Across populations, female feeding duration increased with the mass and
manipulative combination of free amino acids in the spermatophylax
suggesting sexually antagonistic coevolution. Collectively, our work
demonstrates a key role for interlocus sexual conflict and sexually
antagonistic coevolution in the mating system of G. sigillatus.