Familiarity dominates relatedness in mate selection in ladybirds

Cuticular and volatile hydrocarbons have been known to act as signatures of sex, species, mating partners and relatives in ladybird beetles. Our aim was to see (1) whether chemical proximity to an individual establishes familiarity and whether this modulates behaviour, and (2) whether ladybirds can detect familiarity or relatedness, and if so, which quality they respond to more favourably. The first experiment investigated whether familiarity can be established in Cheilomenes sexmaculata on the basis of perception of volatile profiles, and the second experiment investigated whether familiarity is stronger than relatedness in determining mate preference. Males and females were housed in an arena which permitted only chemical contact, for 1–10 days, to create familiarity. Females were then given a choice of familiar versus unfamiliar males and were found to preferentially mate with unfamiliar males. The preference for unfamiliar males increased with confinement duration. This preference was also evident in mating as well as in reproductive performance: females mated faster with unfamiliar males and males remained in copula for longer duration with novel females, and higher number of eggs was also laid by females that mated with unfamiliar males. In the second experiment, females were given a choice of related unfamiliar and unrelated familiar males and they preferred the latter, indicating that relatives were not preferred even when they were unfamiliar. When choosing between relatives and familiar individuals, the aversion to relatives was stronger than the affinity for unfamiliar individuals. Bias against mating with relatives is probably a function to prevent inbreeding depression.