Static Strategies: Unchanged Sperm Allocation in Ladybird Beetle, Cheilomenes sexmaculata (Coccinellidae: Coleoptera)...

Evolutionary theories propose that males adjust their ejaculate investment in response to the socio-sexual environment they perceive. Specifically, they may increase sperm allocation when facing different intensities of sperm competition (presence of rivals) and reduce investment when they perceive multiple mating opportunities (additional females). To test these predictions, we exposed males to either low intensity (one individual) or high intensity (five individuals) sperm competition and mating opportunity conditions, using an experimental setup that allowed olfactory cues both before and during mating. We also examined whether the number of matings influenced sperm transfer. Contrary to sperm competition theory and the sperm economy model, our results showed that males did not adjust sperm transfer in response to the socio-sexual cues. Sperm allocation remained consistent across treatments, low and high sperm competition, and mating opportunity groups. Similarly, mating latency and copulation duration were not significantly affected by the different socio-sexual environments. However, male body weight decreased under each sperm competition condition, but did not change under the mating opportunities treatment. Moreover, no significant correlation was found between copulation duration and sperm transfer. Our findings suggest that C. sexmaculata males adopt a fixed sperm allocation strategy, unaffected by socio-sexual environment, possibly reflecting an evolutionarily optimized reproductive tactic.