How much urine can a centimetre-long frog make? The answer: not much.
But that didn’t stop Postdoctoral Research Fellow Lindsay Hogan, from The University of Queensland, in her work to determine the sex of young White-bellied Frogs.
Researcher Lindsay Hogan.
From June to September 2010, Dr Hogan worked with the White-bellied Frogs (Geocrinia alba) in Perth Zoo’s Native Species Breeding Program, collecting urine and faecal pellets to determine their sex. The White-bellied Frogs were part of a rear-for-release program to establish new populations in the wild.
One difficulty that needed to be overcome prior to the first release was determining the sex of the subadult (18 month old) and very small metamorph frogs. White-bellied Frogs are a sedentary species, barely travelling more than a few metres in their entire life, so making sure that both female and male frogs are released together in the same area is a critical factor in the release program.
Dr Hogan says there is no visual way to accurately identify the gender of sexually immature Geocrinia frogs. To overcome this problem, Dr Hogan measured the concentrations of two sex hormones (estrogen and testosterone in both sexes) excreted in the frogs’ urine and faeces in the hope of identifying their sex.
“It wasn’t easy,” Dr Hogan says. “These frogs don’t produce a lot of urine or faeces so we had to get multiple samples from each individual and pool the specimens together to get a large enough sample to test.
“We collected urine from every sub-adult once a week for ten weeks before we had enough urine to run a valid hormone test. We also collected faeces from every sub-adult and metamorph every three days for a period of 10 weeks before we had enough material to test. There were over 80 frogs to collect from so it was time consuming and very fiddly work but rewarding once we saw the results.
White-bellied Frog (Geocrinia alba).
“Just in time for the release, we established that there were six male and six female sub-adults plus 22 male and 23 female metamorph White-bellied Frogs. Twenty-nine metamorphs weren’t sexed as they were either housed in groups – making it difficult to identify which faeces belonged to which animal – or not enough material was collected for analysis.
“A total of 70 frogs were released back into the wild on 13 September in groups of 10. Each group consisted of known males and females, together with some unknowns, so they would have a greater chance of breeding.”
The research is also exciting as it was the first time these techniques have been used on Australian amphibians.
“I have done a lot of work with the reproductive biology of Australian mammals including wombats and dunnarts,” Dr Hogan says. “Applying these techniques to amphibians has opened up a lot more opportunities.”
The second phase of Dr Hogan’s research will be to monitor how the frogs’ hormones affect their reproductive behaviours.
“I’ll be looking at the females to see what their hormones are like during egg development and what happens to them after the eggs are deposited. I will also be investigating how testosterone in the males relates to burrowing and calling. Correlating the hormones with behavioural observations is well studied in mammals but again is something not done before with frogs.
“This research is really at the forefront of amphibian research and will play an important part in the conservation of amphibian species.”
