Studying female reproductive tracts and sperm in diving beetles (Dytiscidae), researchers from the University of Arizona and Syracuse University have obtained a glimpse into a bizarre and amazing world of sperm that can take on a variety of forms including joining together into conglomerates that navigate the twisted mazes of the female reproductive tract.
Analyses of the evolutionary relationships among diving beetles reveal that sperm form appears to follow function dictated by female reproductive organs.
"Our findings show that sexual selection isn't always all male-male competition," said Dawn Higginson, the study's lead author who is a postdoctoral research associate at the University of Arizona's Center for Insect Science, who did much of the work for this study with her doctorate advisor Scott Pitnick, a professor of biology at Syracuse University in Syracuse, N.Y.
"Rather than standing at the sidelines, it appears that females can take the lead in driving the evolution of male sexual traits," Higginson said.
The study results will be published the week of Feb. 6 in the journal Proceedings of the National Academy of Sciences.
Unlike most mammals in which fertilization involves large numbers of simple-built, individual sperm cells racing for the egg through a rather straightforward female reproductive tract, many other animal groups, especially invertebrates such as mollusks and insects, have evolved complex anatomical variations in both sperm and female reproductive organs.
According to Pitnick, sperm shape does not show much variation in species whose eggs are fertilized after they have left the female, such as most fish, for example.
"But once internal fertilization evolves, something happens and evolution goes crazy," he said. "In almost every animal group with internal fertilization that has been looked at, sperm have evolved into a real diversity of forms."'/>"/>
|Contact: Daniel Stolte|
University of Arizona