Friskier frogs: endangered species gets a sex appeal boost
Australian researchers are applying a sex hormone to the skin of the critically endangered northern corroboree frog in a world-first treatment to encourage females to accept less desirable mates in captivity.
A trial conducted by the University of Wollongong and Taronga zoo found that, by administering the hormone to both a male and female frog before pairing them off, researchers could increase the chance that they would accept their allocated partner from about 22% to 100%.
In a world-first, the researchers put a few drops of the synthetic gonadotrophin-releasing hormone on the frog’s stomach instead of using the accepted technique of injecting the hormone under the skin.
It is the same type of hormone used in IVF.
“Because frogs have highly permeable skin, the hormone gets absorbed straight in,” lead researcher Dr Aimee Silla said. “It’s extremely safe to use and we are really pleased with the outcome of these trials because we’re hoping that this method of application will be adopted by other amphibian breeding programs globally.”
Taronga zoo’s northern corroboree frog population is drawn from a genetically isolated wild population in the northern Brindabella Range, on the border of New South Wales and the Australian Capital Territory.
Protecting the genetic integrity of the wild population is a key aim of the captive breeding program.
Frogs bred in the zoo are released into the ranges to boost the wild population, which currently stands at around 200. It is the larger of the three known wild populations of northern corroboree frog.
Since the hormone therapy program began in 2014, about 800 offspring – a mix of eggs, tadpoles and juvenile frogs – have been released.
Without hormone therapy, the frogs usually rejected paired partners and were instead introduced to prospective mates in large groups, allowing them to pair off on their own.
Unfortunately, Silla said, only about one third of the males were chosen to mate.
“The females are given that opportunity to choose the mate that they think is most desirable, and that’s where we are seeing those mating biases and only a couple of individuals getting those matings,” she said.
“From a genetic management perspective, we would really like to identify particular males that are genetically important and be able to have a larger representation of those genes in the offspring being produced.”
Applying the hormone, she said, just makes the frogs more amenable to zookeeper matchmaking.
“If we supply both the male and the female with these reproductive hormones, it just encourages them to breed with the mate that we have given them and their mate becomes more attractive because they’re more receptive to breeding,” she said.
Taronga Conservation Society Australia herpetofauna superviser Dr Michael McFadden said the hormone trial also had benefits for frog health because it reduced the number of female frogs that re-absorbed their eggs after an unsuccessful breeding season.
He said he hoped the program would be expanded to other threatened amphibian species.
Among them is the southern corroboree frog, which lives in tiny pockets of Kosciuszko national park and is currently facing increased threats due to a New South Wales government plan to protect feral horses.