A courtship behavior that makes monandrous females polyandrous

Females of many animal species mate several times with different males (polyandry), whereas females of some species mate with a single male (monandry) only once. Little is known about the mechanisms by which these different mating systems evolve. Females of <i>Drosophila prolongata</i> mate serially, unlike <i>D. melanogaster</i> females that refuse to remate for several days after their first mating (remating suppression, RS). Nevertheless, interestingly, non-virgin <i>D. prolongata</i> females refuse to remate with males that are prohibited from performing their species-specific courtship behavior, leg vibration (LV), suggesting that LV overrides RS making it cryptic in <i>D. prolongata</i>. In this study, we examined how long this cryptic RS persists. Surprisingly, it was sustained for at least two weeks, showing that RS is substantially augmented in <i>D. prolongata</i> compared to that of <i>D. melanogaster</i>. The two most closely related species to <i>D. prolongata</i>, <i>D. rhopaloa</i> and <i>D. carrolli</i>, do not perform LV and showed augmented RS, supporting the idea that augmented RS could have evolved before LV was acquired. These results suggested that <i>D. prolongata</i> females are intrinsically monandrous, whereas the newly evolved courtship behavior makes them polyandrous. This is a rare case in which a proximate mechanism of polyandry evolution from monandry is demonstrated.