Data from: Male butterflies use an anti-aphrodisiac pheromone to tailor ejaculates

1. When females mate with multiple partners, the risk of sperm competition
depends on female mating history. To maximize fitness, males should adjust
their mating investment according to this risk. In polyandrous butterflies
males transfer a large, nutritious ejaculate at mating. Larger ejaculates
delay female remating and confer an advantage in sperm competition. 2. We
test if male ejaculate size in the butterfly Pieris napi (Lepidoptera)
varies with female mating history and thus sperm competition, and whether
males assess sperm competition using the male-transferred anti-aphrodisiac
Methyl salicylate (MeS) as a cue. 3. Both sexes responded physiologically
to MeS in a dose-dependent manner. Males; however, were more sensitive to
MeS than females. 4. Ejaculates transferred by males mating with
previously mated females were on average 26% larger than ejaculates
transferred by males mating with virgin females, which conforms to sperm
competition theory and indicates that males tailored their reproductive
investment in response to sperm competition. Furthermore, ejaculates
transferred by males mating with virgin females with artificially added
MeS were also 26% larger than ejaculates transferred to control virgin
females. 5. Male-transferred anti-aphrodisiac pheromone not only functions
as a male deterrent, but also carries information on female mating history
and thus allows males to assess sperm competition.