Researchers at the Natural History Museum at University of Oslo, Norway, were among the first in the world to start analyzing sperm cells to learn more about bird evolution and behavior.
“To understand sexual infidelity in species, interpreting DNA is not enough. We also need to look at the shape and behavior of the sperm cells. Sperm research has opened up a completely new world to us,” says Professor Jan T. Lifjeldto the research-magazine Apollon. “The sperm cells are exposed to fierce competition. The variation in the form and size of sperm cells is smaller in promiscuous species than in species where the female mates with a single male. Today, the fastest sperm cells swim towards the egg at a speed of nearly 0.2 millimetres per second. Because of the competition, the sperm become either longer or faster. To win, they must constantly beat the world record. We wonder why evolution sometimes produces longer sperm cells and sometimes sperm that swim at a higher speed. Long sperm cells don’t necessarily swim faster, but they store more energy, and most likely they also live longer.”
Sperm cells vary greatly from one species to another. In passerines they look like a thin corkscrew. They spin around their longitudinal axis and bore their way through the fluid. In other birds, they look more like tadpoles, winding forward by beating their tail. Some sperm cells have a broad head, while in others the head is more cylindrical.
“Knowledge about sperm cells is essential to understand the large variation in reproductive strategies. Sexual reproduction is also important to understand life on Earth and its biological diversity. Many are making a clear distinction between animals and humans, but we need to regard ourselves also as a product of evolution. This perspective is easily lost if we only study people. We are searching for the general patterns in the biology of sperm cells. This research is therefore important to understand us humans as well,” Lifjeld concludes.