World Wildlife News

Female sharks can reproduce without having sex, scientists have found. A female hammerhead shark has given birth without mating with a male and its offspring has no paternal DNA.

An international team of researchers from Queen’s University Belfast, the Guy Harvey Research Institute at Nova Southeastern University in Florida and the Henry Doorly Zoo in Nebraska has found evidence that sharks can reproduce asexually by an unusual method known as “parthenogenesis”. This is the first scientific report of asexual reproduction in sharks.

Head of the Queen’s research team and study co-author, Dr Paulo Prodöhl, from the School of Biological Sciences, said: “The findings were really surprising because as far as anyone knew, all sharks reproduced only sexually by a male and female mating, requiring the embryo to get DNA from both parents for full development, just like in mammals.”

“The discovery that sharks can reproduce asexually by parthenogenesis now changes this paradigm, leaving mammals as the only major vertebrate group where this form of reproduction has not been seen.”

The long-term study was prompted by the unexpected birth of a baby hammerhead shark in an aquarium at the Henry Doorly Zoo in December 2001. The astonishing thing about the birth was that none of the three candidate mother hammerheads in the tank, all of whom been caught in Florida waters as babies themselves, had been exposed to any male hammerhead sharks for the three years since their captivity.

More to follow on Science Daily

Hordes of giant mice are devouring endangered seabird chicks on a remote South Atlantic island and may be pushing some of the birds to extinction, scientists report. The carnage has harmed the breeding success of endangered Tristan albatrosses and threatened Atlantic petrels on Gough Island, a British territory a thousand miles (1,600 kilometers) off the coast of South Africa.

The birds’ sole breeding ground is home to 22 bird species 10 million birds in total and is considered the world’s most important seabird colony.

Common house mice were introduced to the island more than a century ago. Now three times larger than normal mice, the invasive rodents likely number more than a million.

Video cameras revealed one pack of ten mice feeding on a Tristan albatross chick’s wounds as it nested on the ground. Footage also showed mice devouring Atlantic petrel and great shearwater chicks.

The birds did not fight off their attackers, even as some mice fed inside the body cavity of one albatross chick.

Researchers say the footage provides the first hard evidence that mice previously thought harmless to seabirds are willing to attack prey more than 300 times their weight.

“Like a House Cat Attacking a Hippo”

Nearly three feet (one meter) tall, a Tristan albatross chick can weigh up to 22 pounds (10 kilograms), or about as much as a turkey. Gough Island mice weigh just 1.2 ounces (35 grams) on average.

Geoff Hilton, a U.K.-based biologist with the Royal Society for the Protection of Birds and study co-author, has compared the mismatch to a house cat attacking a hippopotamus.

Hilton and his colleagues say that while the seabird chicks can defend themselves from other birds, the chicks don’t appear to be programmed to fend off novel predators like mice.

Ross Wanless, a Ph.D. candidate at the University of Cape Town, led the study, published in the online edition of the journal Biology Letters.

Sean Markey
for National Geographic News