Perhaps variety is the very spice of life, but as a matter of producing human life, it could be the bane of existence. That's the indication of a new study in the journal Human Reproduction that found men with wider variation in sperm length, particularly in the flagellum, had lower concentrations of sperm that could swim well. Those with more consistently made sperm seemed to have more capable ones.
"Our study reveals that men who produce higher concentrations of competent swimming sperm also demonstrate less variation in the size and shape of those sperm," said Jim Mossman, a postdoctoral scholar at Brown University and lead author of the paper published in advance online Oct. 28. "It suggests that in some cases, testes are working more optimally to produce high numbers of consistently manufactured sperm, and vice versa."
At the University of Sheffield, where Mossman did his doctoral studies, he and his co-authors measured the heads, midpieces, and flagella of 30 sperm per man, from 103 men randomly selected from a pool of about 500 who were recruited for a larger fertility study. They also measured other characteristics of each man's semen, such as sperm concentration and motility, that the World Health Organization recognizes as important markers of fertility.
"The WHO suggests that measurements should be made on multiple components of sperm, but generally it's only the sperm head that is considered," Mossman said. "No one's ever looked at this before across sperm components. What we show is that measurements on other sperm parts, such as the flagellum that propels the sperm, can provide additional information about the quality and consistency of sperm manufacture."
The result of the novel analysis yielded two overall findings. One was that men who had higher mean flagellum length, total sperm length, and flagellum-to-head length ratios had higher concentrations of motile sperm. But perhaps the more interesting finding was that the greater the inconsistency of length in the sperm a man manufactures, particularly with regard to the flagellum, the lower his concentration of sperm that could swim well.