Solved: the problem of the cross-dressing frogs

By Rebecca McLeod 03/11/2009 4


The global plight of amphibians received a lot of attention last year — the official Year of the Frog. Just in case you missed it, amphibians are currently undergoing a worldwide extinction crisis, with 32% of all species threatened with extinction. The reasons for this sorry state of affairs are believed to be many — loss of habitat, increased incidence of disease, competitive exclusion from introduced species, climate change, increased UV radiation, pollution, predation, and overexploitation.

But I don’t want this to be yet another story documenting the alarming state of our global ecosystem. Recently I attended a very inspiring seminar given by Jen Germano — and it gave me hope that innovative approaches to conservation might just lead to some species recovering to healthy levels. Germano is a doctoral student at Otago University who is about to submit her PhD thesis under the supervision of Drs Phil Bishop and Alison Cree, and in collaboration with Landcare Research scientist Dr Frank Molinia.

A Maud Island frog (Leiopelma pakeka)
A Maud Island frog (Leiopelma pakeka)

Germano has spent the past 5 years focusing on ways to improve the success of conservation efforts for New Zealand native frogs (genus Leiopelma). New Zealand currently has 4 species of native frog — all classified as endangered – and 3 species that are believed to be extinct. Our frogs are from an archaic lineage and have a few traits that set them apart from those inhabiting other parts of the globe. Most notably, New Zealand native frogs do not have external eardrums, and therefore do not croak, instead communicating with chemical signals. There is also no easy way to tell males and females apart — there are no colour, size, or other morphological differences between sexes (hence the crass but attention-grabbing headline!), and this has posed problems for those trying to save them.

Jen Germano with some Maud Island froglets (babies)
Jen Germano with some Maud Island froglets (babies)

A proactive approach is being taken to frog conservation in this country, and many organizations are involved with efforts to breed and translocate frogs, to encourage sustainable populations. With other endangered species captive breeding populations have provided a form of ’insurance’, but one major problem has arisen for NZ frogs — whilst our zoos have put a great deal of effort into starting captive frog colonies, they haven’t been able to successful breed any of the native frogs. This setback led Germano to develop a method for telling apart males and females based on hormone levels in their urine. The method is relatively non-invasive, and has allowed Germano and her colleagues to sex Maud Island frogs with 94% certainty. The ability to identify the sex of our native frogs is a big leap forward for captive breeding and translocation programs, as now they will be able to provide even sex ratios, which will hopefully lead to higher breeding success. Germano has been passing on her skills to staff at Auckland Zoo and Orana Park, where captive breeding programs are underway.

Germano explains that until recently, very little was known about the basic life history of our native frog species. ’While I was working on frog translocations for my Masters project, I saw many of the problems that other scientists were facing when working with these frogs and it was obvious that there were huge gaps in the knowledge that we had for the basic biology of our endemic species and in the information that managers and scientists needed to conserve them.’ A large part of Germano’s thesis involved determining the breeding season of Maud Island frogs — and surprisingly she found it is likely to occur in mid winter. Germano has also discovered that Maud Island frogs have incredibly low sperm counts, which may also help to explain why their numbers are so low.

With her PhD thesis soon to be submitted, Germano will be heading to Memphis Zoo in the USA to begin a position as a postdoctoral researcher in amphibian reproductive biology. But she can leave with the satisfaction of knowing that the Maud Island frogs and those working to save them in a much better position than when she began her studies.

The largest remaining population of native frogs in NZ exists on Maud Island, a predator-free island in the Marlborough Sounds.
The largest remaining population of native frogs in NZ exists on Maud Island, a predator-free island in the Marlborough Sounds.

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