The Role of Prezygotic and Postzygotic, Extragenomic Isolating Mechanisms in Drosophila Population Biology

在果蝇种类中，精子的长度和雌性精子储存器官的进化非常迅速，有些种类产生的精子相对较少，但巨大，可达其体长的20倍。这种不寻常的生殖细胞挑战了我们对性别差异的基本性质和生殖策略进化的理解。这项工作的两个目标是确定(1)这些雄性和雌性特征之间的进化关系；(2)精子和雌性精子储存器官长度变异的功能意义。为此，黑腹果蝇的种群将被人为地选择为更长和更短的精子储存器官。将选择系内的雄性与“相关雄性”系中的雄性进行比较，可以区分多效性和性选择在产生精子长度与雌性精子储存器官长度进化的相关反应中的作用。生产力和精子竞争实验将量化精子长度、女性生殖道形态和女性使用精子模式之间的关系。提出的工作的第三个目标是确定精子长度和雌性生殖道形态的差异在多大程度上导致种群/物种之间的生殖失败。阻止种群间杂交的因素，或“生殖隔离机制”，对物种形成过程至关重要。所选品系之间的互交将决定精子和雌性生殖形态的差异能在多大程度上导致种群间的生殖隔离。在五个密切相关的物种之间的杂交交配中确定精子命运的实验将扩展对生殖隔离机制的分析。将确定每次交配的精子数量、受精卵数量和孵化卵数量，并用于量化所有可能的杂交和对照杂交的精子/雌性和精子/卵子相容性水平。这些研究结果将进一步提高我们目前对交配后、合子前和合子后、基因组外生殖隔离机制的认识，并拓宽我们对果蝇物种形成的认识。

Pitnick 9806649 Among fruitfly species, the length of sperm and of the female's sperm-storage organs have evolved very rapidly, with some species producing relatively few, gigantic sperm, as much as 20 times their body length. Such unusual sex cells challenge our understanding of the fundamental nature of sex differences and of the evolution of reproductive strategy. Two goals of the proposed work are to determine (1) the evolutionary relationship between these male and female traits and (2) the functional significance of variation in sperm and female sperm-storage organ length. To this end, populations of Drosophila melanogaster will be artificially selected for longer and shorter sperm-storage organs. Comparison between males within the selection lines and in "associated male" lines will permit discrimination of the roles of pleiotropy and sexual selection in generating a correlated response in sperm length to female sperm-storage organ length evolution. Productivity and sperm competition experiments will quantify the relationships between sperm length, female reproductive tract morphology, and patterns of sperm use by females. A third goal of the proposed work is to determine the extent to which divergence in sperm length and female reproductive tract morphology contributes to reproductive failure among populations/species. Factors that prevent interbreeding among populations, or "reproductive isolating mechanisms," are critical to the speciation process. Reciprocal crosses among the selected lines will determine the extent to which divergence in sperm and female reproductive morphology can lead to reproductive isolation among populations. Experiments determining the fate of sperm in hybrid matings among five closely related species will extend this analysis of reproductive isolating mechanisms. Number of sperm transferred, eggs fertilized, and eggs hatching per mating will be determined and used to quantify levels of sperm/female and sperm/egg compatibility for all possible hybrid a nd control crosses. Results from these studies will enhance our presently limited understanding of postmating, prezygotic and postzygotic, extragenomic reproductive isolating mechanisms and broaden our perspective on Drosophila speciation.