Sperm length predicts female sperm loads in Drosophila species in the wild. Hiroto Kameyama¹, Esra Durmaz², Giovanni Hanna¹, Therese Markow¹. 1) University of California, San Diego, Division of Biological Sciences, 9500 Gilman Dr., La Jolla, CA 92093; 2) Hacettepe University, Faculty of Science, Department of Biology, 06800 Cankaya, Ankara / TURKEY.

   Sperm length in Drosophila varies from .35mm in D. subobscura to 56 mm in D. bifurca. In species characterized by long sperm, males produce far fewer sperm than do those in short sperm species. We predicted that females of the long sperm species should be sperm limited in nature. We tested this prediction by collecting, from nature, females of species with a range of different sperm lengths allowing them to use up their sperm by transferring them to fresh food vials daily and counting the progeny they produced. Species with relatively short sperm, such as D. subobscura, D. pseudoobscura, and D. melanogaster, contained sufficient sperm supply to produce offspring for up to two weeks, while species such as D. hydei, which produces a 23mm long sperm, ran out of sperm after one day and after having produced an average of 20 progeny. We discuss the implications of these observations for reproductive and evolutionary biology.