Functional nonequivalence of sperm in Drosophila pseudoobscura.

AUTOR(ES)

Snook, R R

RESUMO

We report on a form of sperm polymorphism, termed polymegaly, that occurs in species of the Drosophila obscura group. Individual males of species in this group characteristically produce more than one discrete length of nucleated, motile sperm. Hypotheses suggested to explain the evolutionary significance of sperm polymorphism have been either nonadaptive or adaptive, with the latter focusing on sperm competition or nutrient provisioning. These hypotheses assume all sperm types fertilize eggs; however, no data have been gathered to test this assumption. We found that two size classes of sperm are produced and transferred to females in approximately equal numbers by the male; only long sperm persist in significant numbers in female sperm storage organs. Furthermore, we used a DNA-specific dye (bisbenzimide) and sperm-specific antibodies to ask if both sperm types fertilize eggs in Drosophila pseudoobscura. Confocal microscopy and immunofluorescent analyses of fertilized eggs using anti-sperm polyclonal antisera demonstrated that only long sperm participate in fertilization. These data falsify those hypotheses in which all sperm types are assumed to be functionally equivalent (fertilize eggs). Any remaining or new hypotheses for the evolutionary significance of polymegaly must incorporate these findings. Several new areas of research are suggested.

Documentos Relacionados

• Virility Deficiency and the Sex-Ratio Trait in DROSOPHILA PSEUDOOBSCURA. I. Sperm Displacement and Sexual Selection
• Four decades of inversion polymorphism in Drosophila pseudoobscura.
• Rare male mating advantage in a natural population of Drosophila pseudoobscura.
• Allelic heterogeneity within allozymes separated by electrophoresis in Drosophila pseudoobscura.
• Evidence for selection by male mating success in natural populations of Drosophila pseudoobscura.