Evolutionary significance of promiscuity in an aphidophagous ladybird,Propylea dissecta(Coleoptera: Coccinellidae)

The short- and long-term consequences of monogamy and promiscuity in an aphidophagous ladybird,Propylea dissecta(Mulsant) in terms of reproductive performance and offspring fitness were investigated. Promiscuous females were more fecund and laid more viable eggs than monogamous ones. Amongst promiscuous females, those mated with multiple males (freedom for mate choice) had significantly higher reproductive output than those mated daily with a new unmated male. The increased reproductive output of females mated with an unmated male each day in comparison to monogamous ones might possibly be a result of their increased ejaculate size. The further increase in reproductive output, when a female was allowed to choose a mate, may be because of repeated preferential mating with the fitter males. Results on long-term consequences of promiscuity revealed faster development and increased survival in offspring of promiscuous females at 25, 27 and 30%C. The percent adult emergence was more strongly influenced than development by the mating regime. There were no statistically significant differences in survival of offspring of promiscuous females (mate choice) at the three temperatures, while the percent survival of offspring of monogamous females differed significantly. Offspring of promiscuous females (mate choice) were fittest in terms of development and survival, which indicates their probable better genetic constitution and subsequently that of chosen mates. Thus, promiscuity has both short- and long-term benefits and is advantageous to ladybirds. The presence of long-term benefits in terms of fitter offspring probably indicates the evolutionary rationale behind the prevalence of promiscuity in ladybirds.