BOB HIRSHON (host):
A shark-eat-shark world. I’m Bob Hirshon and this is Science Update.
Sand tiger sharks have a very unusual reproductive strategy. For starters, females have not one uterus, but two. What’s more, the biggest embryo in each uterus gobbles up all of its unborn siblings as it grows. So each uterus produces a single pup, resulting in a litter of two. In a new twist, researchers have discovered that the two surviving pups are almost always sired by the same father, even though the females mate with a number of different males. Stony Brook University marine biologist Demian Chapman led the study.
DEMIAN CHAPMAN (Stony Brook University):
The earliest eggs that are fertilized have the highest probability of reaching that size where the embryo becomes a cannibal. So we think that males that are able to mate first, those are the ones who are going to be most successful.
He says in captivity, males have been observed guarding females, perhaps so they can be the first to fertilize the eggs. I’m Bob Hirshon, for AAAS, the science society.