Evolution of multiple kinds of female sperm-storage organs in Drosophila

Females of all species belonging to the family Drosophilidae have two kinds of sperm-storage organs: paired spherical spermathecae and a single elonga te tubular seminal receptacle. We examined 113 species belonging to the gen us Drosophila and closely allied genera and describe variation in female sp erm-storage organ use and morphology. The macroevolutionary pattern of orga n dysfunction and morphological divergence suggests that ancestrally both k inds of organs stored sperm. Loss of use of the spermathecae has evolved at least 13 times; evolutionary regain of spermathecal function has rarely if ever occurred. Loss of use of the seminal receptacle has likely occurred o nly once; in this case, all descendant species possess unusually elaborate spermathecae. Data further indicate that the seminal receptacle is the prim ary sperm-storage organ in Drosophila. This organ exhibits a pattern of str ong correlated evolution with the length of sperm. The evolution of multipl e kinds of female sperm-storage organs and the rapidly divergent and correl ated evolution of sperm and female reproductive tract morphology are discus sed.