Giant Sperm Is Ancient Evolutionary Tool, Study Finds

Size does matter, at least for the seed shrimp.

The tiny creatures’ giant sperm are an evolutionary strategy that stretches back at least a hundred million years, scientists discovered in a new study.

The giant sperm can be up to ten times the animals’ body lengths. By comparison an average sperm from a man is around 0.002 inch (0.05 millimeter) long, less than a thirty-thousandth of his height.

To find out whether giant sperm is an ancient adaptation, researchers x-rayed the innards of five well-preserved seed shrimp, or ostracods, from hundred-million-year-old sediment from Brazil. Although the giant sperm had rotted away, the scientists could still see the remains of perhaps the ultimate male organ: a sperm pump, used to push the giant

“Only [shrimp] that produce giant sperm have this organ,” study co-author Robin Smith, of Lake Biwa Museum in Japan, said by email.

Furthermore, two female specimens also found in the sediment had huge reproductive cavities.

“These sperm receptacles only inflate when they carry sperm, meaning the [two] females must have mated only shortly before they died,” said lead study author Renate Matzke-Karasz, of Ludwig Maximilians University in Munich, Germany.

nationalgeographic.com