According to a new study performed by Syracuse University researchers, size really does matter when it comes to sex. The size of sperm, that is.

Scott Pitnick, a professor of biology, and co-researcher Gary T. Miller, a post-doctoral research associate, produced a study to be published in the Nov. 8 issue of Science, which examined Drosophilia fruit flies and found that the female reproductive system selects sperm cells of various sizes and shapes to fertilize eggs. This selective process makes females the parent who chooses the variation in offspring.

Marvin Druger, a biology professor in the department of science teaching, said the essence of this study is ‘sexual selection.’

‘Sperm cells have many shapes and sizes. Some have pointed heads, or rounded heads, and some are elongated. Sexual selection at the sperm level leads to a further evolution of the species,’ he said.

Females of most species have a sperm-storing organ in which they store sperm cells of various males they have mated with over the course of a mating season, Druger said.

He added the sperm cells that successfully reach the egg have lengths which correspond with the length of the female storing organ. Females with longer sperm-storing organs choose longer sperm cells. Similarly, females with shorter sperm-storing organs choose shorter sperm cells.

Sperm cells exist in many lengths and dimensions, and until this study, scientists could not explain why such differences existed. The cells evolved differences to compete with each other to fertilize the egg. The amount of sperm produced by an organism was once considered to be the most significant factor of a successful production of a zygote, or the cell formed by the union of sperm and egg. Yet the size of the sperm tail is the deciding factor, Druger said.

William Perez, a freshman biology major, said that he was not surprised by the study because the research is part of biology and evolution.

‘This study shows how females can be selective in reproduction, and in the long run, evolution,’ he said.

Pitnick and Miller’s study explains much in terms of evolution. As the sperm-storing organs of females evolved to greater lengths, the males who produced longer sperm cells were the only males who could successfully mate. These males could thus advance.

‘The genes of males that succeed to mate with the females will be passed on,’ Druger said.

If members of different populations mated, the length of the sperm would not always correspond to the lengths of the sperm-storing organs. This discrepancy in length would have prevented some organisms from mating with others, a prevention that could have led to genetic diversity, he said.

Joseph Fanelli, a senior part-time instructor of Child and Family Studies and professor of Human Sexuality, said the study is very interesting. He agreed that from an evolutionary standpoint, the study brings up two issues.

‘Usually if there is selectivity, my impressions would be that there may be two different factors.’ he said. ‘It could have to do with enhancing reproductive capacity and also could be a little Darwinian, in that it’s not just about species survival, it’s the best surviving, the best of the species.’

Published on November 10, 2002 at 12:00 pm