Whale sharks can produce many offspring from single mating session

Washington, Aug 25 (ANI): A new paternity study on female whale sharks has shown that these ocean-roaming giants can continue to produce many offspring from a single mating session.

The results of the study, by University of Illinois at Chicago biologist Jennifer Schmidt, suggests that female whale sharks store sperm after a single mating event, and subsequently fertilize their own eggs as they are produced.

Schmidt, a UIC associate professor of biological sciences, determined paternity of 29 frozen embryos saved from a female whale shark caught off the coast of Taiwan in 1995.

The embryos, studied in collaboration with Professor Shoou-Jeng Joung at the National Taiwan Ocean University, are extremely rare.

The pregnant shark carried a surprisingly large number of embryos -- 304 -- still in the uterus and representing a spectrum of age and development stages ranging from being still egg-encased to developed, near-term animals.

The researchers spent several years developing DNA genetic markers to study whale sharks, initially for population genetics, but in this study the tool was used to determine paternity.

Shark reproduction is still an emerging science, but what is known suggests that most broods are sired by more than one male.

But that is not what Schmidt found with this particular female whale shark.

"These differently aged embryos -- itself unusual across animal species -- had the same father. We have to be very cautious in drawing conclusions from a single litter, but the data suggest female whale sharks store sperm after a single mating event, and subsequently fertilize their own eggs as they are produced," said Schmidt.

If the finding can be supported from analysis of other whale shark litters, Schmidt said: "it would suggest that there is no whale shark breeding ground where large numbers of animals meet to mate, but rather that mating occurs as an isolated event." (ANI)