A study of zebra finches shows sperm with specific head and tail traits get selected to fertilize eggs.
These “super swimmers” tend to have shorter heads with longer tails and are more similar to each other than other inseminated sperm.
Scientists suspect these traits help the sperm swim faster. The bird then stores these sperm before giving them the chance to fertilize her egg.
“Previously it was thought that longer sperm were always more likely to reach the egg. However our study shows that the specific design of sperm is more important than total length alone,” says Nicola Hemmings from the animal and plant sciences department at the University of Sheffield.
“Long tails act as propellers for sperm, but beyond a certain length they seem to become less efficient.
“Shorter heads are also important as they have less surface area to create drag, allowing sperm to swim faster. The tiny subset of ‘super swimmers’ with these traits are better able to reach the egg.”
The research is published in the journal Biology Letters.
Scientists believe that a better understanding of how the shape of sperm and size influences fertilization success in non-human animals such as the zebra finch may suggest new directions for investigating human fertility.
Source: University of Sheffield