When a Zoos Victoria team had difficulties breeding some of their critically endangered mountain pygmy-possums, they decided to investigate the animals’ hormone levels. A lot is known about hormones in humans and domestic animals, but it was the first time anyone had looked at pygmy-possum hormones – and, in fact, one of the first times a non-invasive hormone approach had been used in any marsupial conservation program.
It was a serendipitous moment that ultimately fuelled a revolutionary new Melbourne-based program now helping to save some of Australia’s most endangered creatures from extinction, by applying the scientific discipline of wildlife endocrinology. At the program’s helm are two reproductive biologists who were on that original team: Dr Marissa Parrott, Senior Conservation Biologist in the Wildlife Conservation and Science team at Zoos Victoria, and Dr Kerry Fanson, who leads the Wildlife Conservation and Reproductive Endocrinology Lab (WiCRE) at Melbourne’s La Trobe University.
Wildlife endocrinology is simply the study of hormones in wild animals, and during the past two decades it has successfully underpinned breeding programs for many exotic species – from tigers and elephants to pandas – in zoos around the world. But until now, it’s rarely been used in Australia to help recover declining populations of native species, and its potential is huge.
To understand this, it’s necessary to appreciate the role played by hormones, which are chemical messages produced inside all animals and detectable in biofluids such as saliva and urine, and in faeces. “They underlie every part of animal health, behaviour and reproduction,” Marissa says. “Knowing what healthy baseline levels of hormones are allows us to identify [physiological] problems and look for solutions, which is important in endangered and critically endangered species.”
That’s because when a species’ population falls to desperately low levels it usually means a captive breeding program is needed to save it, but this is unfortunately often viewed as a last resort. “But by the time a species is brought in to start a captive breeding program, it usually has low genetic diversity because its populations are so reduced, and that often leads to health and hormone issues that cause low fertility and low fecundity,” Marissa says.
And that’s exactly what’s happened with a key population of the mountain pygmy-possum.
Pygmy-possum breeding success
With fewer than 2000 of the critically endangered possums now estimated to survive in the wild, inbreeding – which leads to a loss of genetic diversity – is a major issue. The species has a complex life history. The mountain pygmy-possum’s natural distribution range is limited to Australia’s alpine areas and it is the only Australian marsupial that hibernates for around six months a year beneath a thick layer of snow. Its survival is also closely tied to the life cycle of its major food source – the migratory bogong moth, which is also endangered.
When Zoos Victoria began its mountain pygmy-possum breeding program almost two decades ago, wild-caught females were brought in to mate with wild-caught males from a different population. The males were genetically robust and had already proven to be successful in the breeding stakes. But the new females came from an extremely small inbred wild population and some weren’t becoming pregnant.
“We looked at hormone levels in our breeding females that had successfully raised young and compared them with the females that hadn’t bred,” Marissa says.
Kerry elaborates: “We found that successfully breeding females had really nice clear cycles, whereas the unsuccessful breeders didn’t have any progesterone cycles – they didn’t seem to be ovulating when they should have been.”
In response, the team refined the care and management of the possums, including their diet and social system. When further wild-caught females from genetically healthy populations were introduced to the breeding program, all of them successfully bred and raised young.
The zoo’s breeding success rate for mountain pygmy-possums is now up to 100 per cent.
Building a database
Leadbeater’s possum is another critically endangered species that’s now having its hormones scrutinised and documented by the team. It has a vastly different reproductive strategy from the pygmy-possum. But there also appear to be treatable hormone imbalances in animals that have been failing to reproduce, and the team was able to breed the first Leadbeater’s babies in the new conservation breeding program last year.
“At the moment we’re looking at what’s happening with females that are reproducing versus those not reproducing, as we did in the pygmy-possums,” Marissa says, explaining that for female Leadbeater’s the current focus is on the hormone progesterone. One of the major challenges is recognising and understanding individual differences in animals’ physiology –not all females are the same. “We found that female Leadbeater’s in this population have seasonal changes in reproduction. For some females, the window of reproductive activity is quite long, whereas other females have a restricted window of breeding opportunity. But our next step is working with male samples and looking at testosterone.”
The Tasmanian devil is another endangered marsupial species that’s so far been a focus for the project, and the New Holland mouse, also known as the pookila, a native mouse that’s now extinct from large parts of its former range, is another.
The project is still in its early stages. Currently it’s focused mainly on building a database of what are normal and abnormal hormone levels for some endangered and critically endangered species – mostly mammals, although some work has begun on frogs that, as a group globally, have suffered significant declines.
This work alone is of massive interest simply because it’s never been done before. It will help flesh out what makes our native animals function and inform conservation breeding programs. But what makes this project particularly exciting are the ways in which this vast bank of knowledge will ultimately be used in the field.
Non-invasive approach
Unlike a lot of animal research that requires live specimens to be captured and handled, endocrinology can be a non-invasive science. Hormone levels can be detected from biofluids, hair, feathers and scales, so urine and gland secretions used to scent-mark territories, and faeces left at regular latrine sites – like those used by devils – can be sampled in the field without even needing to see an animal.
“Non-invasive hormone monitoring has a couple of unique benefits for understanding the physiology and behaviour of Australia’s unique endangered wildlife,” Kerry says. She explains that for mountain pygmy-possums, urine – which is easy to collect in captive populations – has so far been the preferred sample type for the project.“ But for Leadbeater’s possums, Tassie devils and pookila, we’re largely using faeces because it’s so much easier to collect without even seeing the animals.”
To collect hormone samples as non-invasively as possible in frogs, the team is developing special capabilities that involve placing a small patch of filter paper onto the frog’s back to pick up skin secretions without hurting it. “Yes, you would have to first find the frogs to do that,” Kerry says. “But for all these species, we’re currently using captive-based populations to establish a critical foundation of knowledge about what their normal reproductive physiology is, and from that we’ll be able to develop biomarkers.”
The sorts of physiological conditions for which researchers are hoping to develop biomarkers include, for example, reproductive health, pregnancy and lactation. Having this sort of capability would allow researchers to identify situations such as whether or not a wild population of an endangered animal was successfully breeding. This could be done without exposing animals, or mothers and offspring, to a potentially stressful experience.
Taking this sort of application even further: Zoos Victoria already has a team of highly trained wildlife-detection dogs that can detect the presence (or absence) of particular species without the need for trapping or tagging. The dogs have also been trained to detect scents associated with reproductive status and cycling in Tasmanian devil faecal samples. It’s a world first using detection dogs to track reproductive cycles in a conservation breeding program and may be adaptable to wild populations.
“It’s an exciting time in the field of wildlife endocrinology. Much of the groundwork has been laid, so now we can start applying these methods to generate meaningful insights for wildlife conservation,” Kerry says. “It’s revolutionising what we can do. That’s why this new partnership between my lab and Zoos Victoria is so important, because they are on the ground with the animals, either for captive breeding or in the field, and we are able to turn those samples they collect into meaningful insights about reproductive biology, how healthy a population is and how the animals perceive their environment.”
Relevance to human reproduction
Perhaps, however, the most remarkable aspect of Kerry and Marissa’s work is how it’s informing our understanding of human reproduction and potential infertility issues. Their work together – first in mountain pygmy-possums, but now also in devils and Leadbeater’s – has, for example, revealed a new role for the group of hormones called glucocorticoids. These have widely and traditionally been thought of as stress hormones.
“But they’re not!” Kerry says. “They do so many different things to the body.” When Kerry and Marissa were studying mountain pygmy-possums, they found that cortisol, a type of glucocorticoid, consistently increased before ovulation. At first, this was counter-intuitive, because everyone thought that elevated glucocorticoid levels should inhibit reproduction.
“But we’ve been looking a lot more closely at reproduction and glucocorticoids in other species and found that they increase during important reproductive events: when females become reproductively mature, before they ovulate and throughout pregnancy,” Kerry says. These insights have come from the endocrinology studies done by her and Marissa.
“If glucocorticoids increase at all these critical stages in female reproduction and promote successful outcomes, we need to change our thinking about how glucocorticoids affect reproduction. We are really driving this paradigm change together,” Kerry says. “We found that in mountain pygmy-possums, cortisol [one of the glucocorticoids] increases just before the female ovulates and that it’s followed by an increase in progesterone. That will be really useful for giving us another tool to first diagnose and then potentially treat reproductive failure.”
And that is likely to not just be limited to these three mammal species, but to all mammals.
Not surprisingly, researchers in the areas of fertility and IVF have begun looking at how this might be relevant to treating infertility in humans.
