Drosophila subobscura Short Sperm have no Biochemical Incompatibilities with Fertilization

Drosophila obscura group species produce two distinct sizes of nucleated sperm that differ only in head and tail lenghts. Between both sperm there is no differences in location of the acrosome and flagellum during spermiogenesis where each sperm type develops in its own bundle. Fertile sperm accumulate in the seminal vesicles. Fertilization is exclusively monospermic and in a previous study we suggested that both types of sperm are fertilization-competent on the basis of similar DNA content and storage in females also if morph variations are consistent with a fertilization-related selection for optimal sperm size. This assumption is in agreement with previous studies that demonstrated that only long sperm fertilize eggs. In this study fertilization of Drosophila subobscura is examined using anti-sperm surface -Nacetylhexosaminidases and -L-fucosidase antibodies. Beta hexosaminidases are intrinsic proteins of the sperm plasma membrane in spermomomorphic species of the melanogaster group closely related to Drosophila melanogaster. These enzymes had been previously identified as putative receptors for glycoconjugates of the egg surface, structurally and functionally conserved. Here their localization has been investigated in Drosophila subobscura. Consistent with our previous study, short and long sperm are functionally equivalent. More data are needed to clarify the consequences and adaptative significance of morph variations.