The transfer of male cuticular hydrocarbons provides a reliable cue of the risk and intensity of sperm competition in decorated crickets

Theoretically, males should increase their ejaculate expenditure when the
probability of sperm competition occurring (or risk) is high but decrease
ejaculate expenditure as the number of competing ejaculates (or intensity)
increases. Here we examine whether male decorated crickets (Gryllodes
sigillatus) use cuticular hydrocarbons (CHCs) transferred to females by
rival males at mating to assess the risk and intensity of sperm
competition and adjust their ejaculate accordingly. Unmated females and
those perfumed with CHCs extracted from one, three or five males could be
distinguished chemically, providing a reliable cue of the risk and
intensity of sperm competition. In agreement with theory, males mating to
these females increased sperm number with the risk of sperm competition
and decreased sperm number with the intensity of sperm competition.
Similarly, as the risk of sperm competition increased, males produced a
larger and more attractive spermatophylax (an important non-sperm
component of the ejaculate) but there these traits did not vary with the
intensity of sperm competition. Our results therefore demonstrate that
both sperm and non-sperm components of the male ejaculate respond to the
risk and intensity of sperm competition in different ways and that CHCs
provide males with an important cue to strategically tailor their
ejaculate.