Ingested spermatophores accelerate reproduction and increase mating resistance but are not a source of sexual conflict

Abstract

Seminal products transferred during copulation can have substantial effects on females, including accelerated oviposition, decreased mating receptivity and shorter life span. This study addresses two sets of hypotheses about ingested seminal products: (1) whether they act as nutrition or have effects like those of seminal proteins and (2) whether they harm females (implying sexual conflict). We studied the ladybird beetle Adalia bipunctata , the females of which consume a spermatophore after mating. To examine the effect of spermatophore feeding on short-term reproduction, we combined a spermatophore treatment (allowing or preventing ingestion) with a diet manipulation. If spermatophores serve only as food, then low-food females are expected to show the strongest response; if spermatophores contain signalling proteins, the effect should be of similar magnitude across food treatments. Feeding on a single spermatophore affected females in two ways. The ‘allow’ group oviposited significantly faster than the ‘prevent’ group, but this response was independent of female diet, suggesting that spermatophores act as signals rather than as nutrition. In a second experiment, spermatophore consumption increased female remating resistance. In a long-term experiment, the continued ingestion of multiple spermatophores had no detectable effect on female life span, lifetime reproductive success or lifetime remating behaviour. The absence of such costs does not support the hypothesis of sexual conflict over spermatophore ingestion. Overall, the results imply that spermatophores have a signalling function but provide little, if any, nutritional value or long-term effect on fitness. Direct evidence that spermatophore function is shaped by sexually antagonistic coevolution is still lacking.