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Ancient frogs threatened by fungus

Archey's frog

Ancient lineage - Archey's frog, Leiopelma archeyi, from the Coromandel Peninsula on the North Island. (Pic: Dan Buckhholz)

A unique and ancient lineage of frogs living in New Zealand is under threat from a deadly fungus.

The chytrid fungus, which was discovered in Australia and Central America in 1998, has caused unprecedented numbers of frog deaths in those countries. It was was first found in New Zealand in November 1999, but in an introduced species of Australian bell frog. It has now been discovered in native New Zealand species.

"What we were afraid of all along was that they would jump species into the native population," said Dr Bruce Waldman, a zoologist at the University of Canterbury in Christchurch.

"It seems quite likely this has happened through the human movement of those frogs."

New Zealand's four native species of frog, which all belong to the genus Leiopelma, are among the rarest frogs in the world. They are the living representatives of the most ancient lineage of frogs, closely resembling the fossils of frogs that lived 200 million years ago.

Dr Waldman said this week that the chytrid fungus was first found in one of the four species, the Archey's frog (Leiopelma archeyi), in September last year.

Since then, researchers have found sick and dying specimens in each of the three major populations of Archey's frogs in New Zealand.

When infected, the frogs show strange motor behaviours. At first, their movement is unbalanced. Then they become immobile and are paralysed in unnatural positions.

How the fungus attacks is still a mystery. One possibility is that the fungus suffocates the frog by impeding breathing through the skin. Alternatively, the fungus might secrete a poison that paralyses the frog, or cause a reaction in the immune system that poisons the frogs.


Like their 200-million-years-old cousins, the Leiopelma frogs have nine vertebrae in front of the sacrum (modern frogs have eight), and retain tail-wagging muscles as adults. Their ribs are floating, not attached to the spine.

The only other frog in the world that has this ancient morphology is the Pacific North West frog, Ascaphus truei, which was originally placed in the same family as the Leiopelma species. They have recently been split into separate families.

Three of the four species do not have a tadpole stage — they emerge from their eggs as froglets — though this characteristic is shared by some modern frogs, said Dr Waldman.

The native frogs are long-lived, with some individuals known to survive as long as 30 years, but because they do not reproduce every year, their populations are vulnerable. When they do breed, clutch sizes are small, at only four or five eggs.

"They have a very slowly reproducing population, so if they get wiped out by disease they might not come back very quickly," Dr Waldman explained.

"They are not typical frogs in terms of their ecology and life history."

There is no monitoring scheme in New Zealand to go out and find frogs infected by the chytrid fungus, but the researchers have taken several frogs out of the wild and brought them back to good health.

Sick animals sometimes move away from the water, possibly in an attempt to cure themselves, Dr Waldman speculated.

The fungus does not survive dry conditions or temperatures over 30 degrees Celsius, he said, making sick frogs relatively easy to treat.

The Native Frog Recovery Group in New Zealand has not decided yet what to do with the frogs that have been cured. They may try to find areas free of the fungus to relocate them.

Ultimately, however, the native species' best prospects for survival would be genetic variation in the population, Dr Waldman said. If present, it may enable frog populations to develop resistance to the fungus.

"We are putting a lot of hope into that."