Parthenogenesis as an alternative reproductive strategy in Drosophila. Chia-chen Chang1, Shu Fang2, Chau-Ti Ting3, Hwei-yu Chang1,2. 1) Department of Entomology, National Taiwan University, Taipei, Taiwan 10617, ROC; 2) Biodiversity Research Center, Academia Sinica, Taipei, Taiwan 11529, ROC; 3) Department of Life Science, Genome and Systems Biology Degree Program, Institute of Ecology and Evolutionary Biology, Institute of Zoology, and Research Center for Developmental Biology and Regeneration Medicine, National Taiwan University, Taipei, Taiwan.

   Parthenogenesis has independently evolved multiple times in Drosophila lineages, and most of them are facultative. Given that most Drosophila species reproduce bisexually, the facultative parthenogenesis is not an adaptive reproductive strategy in long-term evolution. Nonetheless, some characteristics for the facultative parthenogenesis may be temporarily advantageous. To test this idea, we investigated several fitness components of a parthenogenetic strain in D. albomicans compared to their bisexual counterparts. The fertility of the parthenogenetic strain was low, only 10% via parthenogenesis and 60% via sexual reproduction compared with a bisexual strain. Females from the parthenogenetic strain produced both parthenogenetic and sexual offspring after mating. The number of parthenogenetic offspring produced by mated females was comparable with that by virgin females, suggesting that parthenogenetic ability was not obviously disturbed by mating. We also found that 70% of F1 offspring produced via bisexual reproduction could perform parthenogenesis albeit their fertility was extremely low. Genetic variation of the parthenogenetic strain might be extreme low because gamete duplication was the predominant mechanism (91.8%). Despite the low fertility, several features including producing both parthenogenetic and sexual offspring after mating, high parthenogenetic capability of sexually produced F1 females, and multiple mechanisms for diploidization, might explain why the facultative parthenogenesis could be maintained in the population. Our findings suggest that facultative parthenogenesis is an alternative reproductive strategy.