Females of a species generally produce relatively few, large gametes (eggs), while males produce many small gametes (sperm). A general principle in behavioral ecology is that this disparity differences observed between females and males. To understand this principle one must consider the causes of variation in reproductive success for each sex. Successful females, those which best pass their genes to the next generation, are those that most efficiently convert resources into eggs and that have a genetic predisposition to mate with a genetically superior male. A female tends not to benefit from mating with several males, since a single mating can fertilize all of her eggs. By contrast, a male can greatly enhance his reproductive success through several matings. One of the few exceptions to this rule may be Drosophila pachea, a fruit fly endemic to the Sonoran desert that lives only within rotting tissue of senita cactus. Reproductive success of D. pachea males may be limited by the number of sperm they produce. Sperm are huge, 12.5 mm long, and very helical, resembling the spring of a ballpoint pen. Males exhaust their supply of stored sperm after a few copopulations. Additionally, females tend to not receive an adequate supply of sperm to fertilize all of their eggs. Consequently females will remate several times daily. The investigators' research goal is to pattern of sperm production by D. pachea males and to describe male and female mate choice and mating strategy. Studies of the reproductive biology of Drosophila pachea should greatly contribute to the understanding of the evolution of life history traits. Further, because several close relatives of D. pachea are agricultural pests, understanding the mating system of this fly may benefit biological control programs.
