Necrophila japonica exhibits indirect flight muscle dimorphisms in both sexes without wing dimorphisms. In general, polymorphisms in flight muscles or wings are maintained by the energetic trade-off between flight capability and reproduction. For examples, flightless females can produce more eggs than flight capable. Furthermore, flight incapable male court females longer and can secure more females than flight capable. However, in N. japonica, flight muscle type was not correlated with reproductive investment and there were few information on mating behavior. Here, we investigated reproductive ability and mating strategy associated with muscle type.

First, we investigated mate choice and competition for securing mates, but males were not choosy and there was no difference in competitive ability. Second, to compare mating success and strategy, we observed a series of mating behavior of each muscle type, and recorded mating duration, insert success and female rejection behavior. Pairs of non-muscled male and non-muscled female showed less frequent female rejection and higher mating success than other pair combinations. In addition, non-muscled males guarded female longer than muscled males. These results indicate that cryptic polymorphism that is indirect flight muscle dimorphisms without wing dimorphism influences mating behavior.