fighting extinction

Our First Mammalian Casualty: The Extinction of the Bramble Cay Melomys

Not too long ago, I wrote a piece on our native rodents. Before I wrote that article I, like 80% of the people I’ve met, was… not a fan, to put it nicely. Researching our native species and their amazing relationship with our continent completely switched my brain around. I couldn’t believe that, in just one-fifth of Australia’s history as an isolated continent, our number of native rodent species grew from zero to sixty. I couldn’t believe that we actually had mice that used pebbles in their burrows! And some of our native rodents hopped like our marsupial species - I mean, that’s crazy, right? That is actually amazing. I couldn’t believe that there was all this diversity right at my feet and I had literally no idea.

There have been no sightings of the Bramble Cay melomys since 2009.

There have been no sightings of the Bramble Cay melomys since 2009.

Up until a few days ago, I also had no idea about another native rodent species, the mosaic-tailed rat, which was also known as the Bramble Cay melomys, or Melomys rubicola. Reddish-brown and small-eared, it had a tail scaled in a mosaic pattern, distinctive for the genus. The species was found only on Bramble Cay, a small vegetated coral cay in the Torres Strait. The species shared its home with sea turtles, shore birds, and a single lighthouse, the only artificial structure. In 1978, hundreds of Bramble Cay melomys were thought to have lived on Bramble Cay, foraging at night and burrowing through logs and debris. Numbers declined rapidly in the 1990s and 2000s, directly correlated with rising sea levels. In just ten years, 97% of their habitat was completely wiped out. In the last month, this native rodent, the only mammal endemic to the Great Barrier Reef, has been confirmed to be extinct. Not only that, it is the first mammal confirmed to be driven to extinction due to climate change.

For a lot of people, climate change probably doesn’t seem very real. I know in the past it has seemed rather abstract to me. I’ve learnt about it since I was in primary school, and it seems to have followed me as I’ve aged – discussed by teachers, lecturers, scientists, and politicians. There have been movies and documentaries, papers and popular books written about the phenomenon, warning me of what was to come. Still, I had always been able to distance myself from the reality of climate change – based in Melbourne, I’m relatively protected from the realities faced by so many other people and species. But when I recently read about the Bramble Cay melomys and discovered that scientists had recorded the first mammal to go extinct from climate change – and that this mammal was native to Australia – climate change no longer seemed like a far-off thing. Climate change is not ‘coming’ – it has arrived in full force, and it has claimed its first mammalian casualty here, in Australia.

The only artificial structure on the island, the Bramble Cay lighthouse sticks out amongst flocks of nesting seabirds.  Image: Natalie Waller via  The Conversation

The only artificial structure on the island, the Bramble Cay lighthouse sticks out amongst flocks of nesting seabirds. Image: Natalie Waller via The Conversation

Australia is home to so many endemic species, each of them amazing. From kangaroos to wombats, platypus to green tree frogs, the sheer number of species is difficult to think about. But now we are home to one less. We may not notice one species, the only mammal in the Great Barrier Reef, as it slipped away from us due to human-induced climate change – but we will miss the approximate one-sixth of all species on the planet that are estimated to disappear if we keep refusing to act. There are opportunities we can take to minimise the damage we’re causing and reduce our carbon footprint. Getting involved in charities like Cool Earth and Conservation Volunteers Australia are good places to start to learn how to give back.  

It is too late for the Bramble Cay melomys, but we owe it to our other native species to try.


Mary Shuttleworth

Mary Shuttleworth is a Masters graduate from the University of Melbourne, where she pursued her interests in ecology and parasitology. She is interested in science communication, education and community engagement.

Find her on Twitter at @muttersworth.


Banner image courtesy of Natalie Waller via The Conversation.

The Lady's Choice

Only if we understand can we care.

That sentence is the beginning of a quote from beloved conservationist Jane Goodall. It is also the beginning of an idea, growing amongst people in science; an idea that leads biologists away from the forests and deserts of their research and into lecture theatres and radio studios. Our own understanding is not enough. Our own knowledge, sifted and harvested from thousands of hours’ worth of data and records and testing, can no longer rest amongst just those who share in our pursuits. It is the public who matter.

Twice a month, the Royal Society of Victoria takes aim at just this idea with free, open lectures. Ranging through a banquet of scientific disciplines, speakers are chosen to bring information about their work to anyone interested. For those who attended in late February the topic was the encroaching extinction of Victoria’s most vulnerable animals, brought by Dr Marissa Parrott of Zoos Victoria.

When an animal becomes vulnerable, through predation or habitat loss or any other unfortunate cause, the challenge for conservationists is maintaining enough genetic diversity to ensure future recovery. Many times over, isolated populations have shown that an increase in inbreeding leads to a decrease in health. A population of one male and one female will often struggle to survive, no matter how fertile they are.

Socially, the aversion to incestuous relationships is deeply ingrained in a number of societies. From a biological viewpoint this is highly beneficial, for two important reasons. Firstly, inherited disadvantages are much more prevalent in inbred populations – if both parents are hiding some faulty gene received from a common ancestor, then the chance of their offspring receiving two bad copies and no good ones becomes very real.

The helmeted honeyeater. Image: Trent Browning / Zoos Victoria

The helmeted honeyeater. Image: Trent Browning / Zoos Victoria

Secondly, even if all genetic information is functioning normally, the lack of variety means that the species won’t be as capable of coping with surprises. This may be the ability to adapt to changes in the environment, such as temperature and water availability, but immunity is also a major concern. The major histocompatibility complex (MHC) protects mammals from infection by anticipating what bacteria or viruses might look like, building from a combination of variable genes. A greater variety in these genes means a greater number of threats that a species is prepared for, while a limited gene pool is less likely to be ready for rare and new pathogens. It’s like a game of poker with half the deck missing; if there are no aces in the pile, there’s no chance of playing a royal flush when you need to.

Historically, this has made captive breeding programs a very mathematical process. Introducing genetically dissimilar individuals ensures that offspring are biologically equipped with the best chance they could have, and zoos have developed extensive stud books to keep track of family trees. However, developing the acquaintance between the male and female often takes time; slow breeding and small brood sizes were once seen as common.

The agile antechinus ( Antechinus agilis ). Image: John Gould

The agile antechinus (Antechinus agilis). Image: John Gould

Dr Parrott’s work with dunnarts, Antechinus and other marsupial species introduced a different method. She showed that when a female was able to select her own partner, it took less time for the pair to begin reproducing, gave rise to a greater number of pregnancies, and all with decreased aggression between the female and the male. On the surface, this seems like an easy and more certain way of increasing the success of breeding programs. However, the limited resources of conservation strategies mean that every angle needs to be considered and every variable controlled to best create genetically fit and well-adjusted populations. If the female was allowed to choose her own mate from a group of genetically suitable suitors provided by zoo staff, what was the risk of her choosing a bad match?

The dilemma was a strong one. It’s been shown that mammals are more comfortable socialising with individuals they’ve met before, and particularly with family. Dr Parrott and her collaborators’ work with Tasmanian devils at Healesville Sanctuary showed that introducing young devils to one another – growing used to the smells, sounds, and personalities of new animals – led to greater interactions, more activity and increased denning with their conspecifics. While socialising young devils appears to produce more socially competent animals as adults, further research showed that their interest in novel or familiar animals was similar; a good outcome for breeding programs that introduce a variety of potential mates. However, could some females be selecting males that appear familiar, and risk all the complications of inbreeding?

No, it turns out. Not at all. In her 2015 paper, Dr Parrott shows that female Antechinus were perfectly capable of distinguishing between related and unrelated males, and acting accordingly. Her earlier research on the species shows that it largely comes down to scent – among other cues, with a possibility that the MHC produces chemical traces that change how a male smells to a female. Multiple tests showed that females are more interested in those who smell different to themselves, making more frequent and longer visits to males that were genetically dissimilar. Males that were genetically dissimilar to females secured more matings and sired the highest proportion of young. While it’s not yet clear which range of specific cues other than genetic dissimilarity are providing the information, the result is inarguable – the lady knows best. In a system where multiple matings almost always produce a litter with more than one father, offspring were found to have come from genetically distant males around 9 out of 10 times.

With the limited resources available to conservation programs, understanding how to best produce a robust population is crucial. Zoos Victoria’s Fighting Extinction plan has committed to a magnificent goal: that no Victorian terrestrial vertebrates will go extinct on their watch. Ever. This includes 20 high priority species, as well as a watchlist of other vulnerable animals. But the programs aren’t just about breeding and habitat monitoring – we come into them as well, in the small changes we can make to our daily lives. The fantastic Wipe for Wildlife campaign is one such example, calling for the simple change to recycled toilet paper - with its very own superhero. And there’s the Love Your Locals campaign – helping children and adults alike to discover who they’re sharing Victoria with, before we’re left alone.

Only if we understand can we care.
Only if we care will we help.
Only if we help shall they be saved.
— Jane Goodall

Paul Jones

Paul works in science education and has been a teaching member of Monash University's Department of Biology since 2010. He is interested in community engagement and sustainable urban development.

Possum Tragic: Victoria's Vanishing Vertebrate

Deep in the Australian bush, a pair of possums set out on an adventure that will take them across the continent. Grandma Poss makes her granddaughter Hush invisible to keep her safe from predators, but when Hush decides she wants to be seen, Poss must work her bush magic to make her visible again.

Possum Magic, written by Mem Fox and illustrated by Julie Vivas, first appeared on shelves more than thirty years ago. Over the course of three decades this charming piece of children’s literature has worked its way into the country’s collective imagination. With a magical narrative and a host of native characters, Possum Magic has become a pivotal part of childhood in Australia.

Yet this whimsical tale of a disappearing possum is not as far from reality as we may think. Though species like Ringtail and Brushtail Possums are a common sight in Melbourne’s parks and gardens, elsewhere in Victoria their relative, the mountain pygmy possum, is in danger of extinction.

The mountain pygmy possum is just one species currently under threat of extinction.  Image: Matt West

The mountain pygmy possum is just one species currently under threat of extinction. Image: Matt West

At Mount Buller, one of only three populations of mountain pygmy possum in the world is dwindling to invisibility. Australia’s only hibernating marsupial measures up to 29cm from the top of its head to the tip of its tail, and weighs between 30 to 60 grams. Confined to alpine and subalpine regions due to their dependence on winter snow, there are very few populations left in Australia (two in Victoria and one in New South Wales) and less than 2,000 individuals remaining today.

Hibernation is a vital part of life for the mountain pygmy possum.   Image:   Matt West

Hibernation is a vital part of life for the mountain pygmy possum.  Image: Matt West

In 1996, it was estimated that there were 300 adult female mountain pygmy possums at Mount Buller. Over the years their population has fallen rapidly, and in 2007 it was estimated that there were as few as 30 adults surviving. Habitat destruction is one of the key reasons for the dramatic decline in their numbers; the growth of the ski resort at Mount Buller, for example, has negatively impacted on the mountain pygmy possum population. Climate change is affecting snowfall and disrupting hibernation, while wildfires are damaging to their habitats.

This species is now estimated to inhabit a total range of less than seven square kilometres. As the snowline recedes across the country, their numbers continue to fall. Surprisingly, the first record of the species was discovered in 1894: a fossil found in the Wombeyan Caves, New South Wales. For the best part of a century, it was the only evidence that the creatures had ever existed. A living specimen wasn’t found until 1966. Now, nearly fifty years later, we are on the brink of losing them forever. Like Grandma Poss, we need to work some bush magic before our possums vanish completely.

Let us hope that the unique mountain pygmy possum does not disappear like little Hush.  Image: Julie Vivas

Let us hope that the unique mountain pygmy possum does not disappear like little Hush. Image: Julie Vivas

Mem Fox’s earlier drafts of her most famous work featured mice in the leading roles. It wasn’t until late in the process that Hush and her Grandma became possums. Would the tale of Hush the vanishing mouse have become as integral to the Australian psyche? Likely not. The true value of Mem Fox’s and Julie Vivas’ work is to be found not only in the telling of a magical and memorable story, but in reminding children and adults that there is magic to be found in the bush.

 

Banner image courtesy of Julie Vivas