A fuzzy face popped up on my Facebook feed: possum volunteers wanted! I was sold, and started volunteering the very next week. From February onwards I have been helping to care for the brushtail possums that are the focus of Sarah Buchan’s Honours research project.
Brushtail possums are found all over Australia (ALA), stealing fruit and sneaking into rooves. However, there is more to these mischievous marsupials than meets the eye. These possums have a super power: the ability to consume poison! Possums regularly consume toxic plant secondary metabolites (PSMs) when eating gum leaves (McLean, 2007). Enzymes in their liver break down the PSMs the possums can even develop a resistance to them over time (McLean, 2008).
But what happens when climate change is introduced to the equation? Sarah Buchan and the Foley Lab at ANU are testing the temperature dependant toxicity hypothesis as suggested by Moore et al (2015). Animals have the lowest metabolic rate when their body is in the thermoneutral zone (figure?), and colder or hotter and the animal must use energy to keep its core temperature stable. Liver function decreases as ambient temperature increases beyond this thermoneutral zone, and detoxifying PSMs creates more heat than usual. Sarah has predicts that “food intake will significantly decrease when the animals experience hot [ambient temperature] and that some compounds will show evidence of temperature dependent toxicity.”
We had 12 marsupial ‘guinea pigs’, each in their own roomy cage ready to get eating!
By the time I started volunteering, the brushies had already been acclimatised to the cages and their basal diet of fruit, veg and 11 secret forms of fibre. The possums were also introduced to the PSMs being used so they could recognise them during the experiment.
The first experiment looked at how ambient temperature affects how much the brushies eat when different PSMs are mixed into their basal diets. Some of these PSMs deter herbivory by limiting taste while others limit the animal’s metabolism. Sarah predicted that if reduced liver function is the real cause of temperature dependant toxicity then “only PSMs that deter feeding due to constraints on the liver metabolism should show significant temperature dependent patterns of food intake”.
The second experiment looked at how dietary thermogenic uncoupling agents (break down PSMs but raise the body temperature) influence how much brushies eat at different ambient temperatures. Sarah predicted that our possums would “avoid a diet containing thermogenic uncoupling agents at hot [ambient temperature] treatments in order to avoid hyperthermia” and that “brushtail possums will prefer diets with thermogenic uncoupling agents at low [ambient temperature] to gain an energetic advantage when maintaining homeostasis.”
The third experiment looked at temperature events and their effect on brushtail feeding. Are cool nights important? Do ongoing high temperatures affect how much brushies eat? Sarah predicts that temperature dependant toxicity “will cause brushtail possums to reduce their intake of PSMs under hot [ambient temperatures]” and that “cool night-time temperatures are critical to the feeding decisions of nocturnal species such that cool night time temperature may offset the effect of a hot day hence allowing the possums to maintain intake of PSMs.”
By looking at how brushtail possums respond to plant secondary metabolites at various ambient temperatures, we may be able to better understand how climate change will affect our native herbivores.
During the experiment I helped to prepare the possum diets and feed them out. I also had the glamourous job of cleaning up after the possums (believe me, you learn to identify them by smell!). We also weighed the possums, moved them between treatment rooms, and collected branches for them to munch on!
I was also lucky enough to help Sarah release a possum (goodbye Old Man Poss!) after he had graduated the program, and try and trap his replacement. After spending a night running around campus with traps and peanut butter, we finally caught a male possum! Turns out it was just Old Man back for more peanut butter.
I learnt that field work is fun yet tiring, caring for possums is a full time job, and that Sarah can track down possums with her nose! The most astounding discovery I made was the sheer amount of time and effort that goes into an Honours research project. I feel a new sense for respect for the researchers out there who give up their lifestyle to discover more about our natural world. Even though Sarah’s experiment phase is over, I am still volunteering with the possums. There is still much more to learn from these cute and devious little individuals. And who could stay away from such a charismatic creature?
Bronte Sinclair (u5564719)
Want to know more about brushes? Check out their Arkive page.
What does climate change mean for our future? Dr Anne Fowler has some suggestions.
What can we do? WWF has got a plan.
The experiments have been approved by the ANU Animal Experimentation Ethics Committee and conform with Australian Code for the Care and Use of Animals for Scientific purposes 8th edition (2013).
Dearing (2012). Temperature-dependent toxicity in mammals with implications for herbivores: a review. Journal of Comparative Physiology B, Volume 183: 43-50.
McLean S, Boyle R, Brandon S, Davies N & Sorensen J (2007). Pharmacokinetics of 1,8-cineole, a dietary toxin, in the brushtail possum (Trichosurus vulpecula): Significance for feeding. Xenobiotica, Volume 37: 903-922.
McLean S, Brandon S, Boyle R & Wiggins N (2008). Development of Tolerance to the Dietary Plant Secondary Metabolite 1,8-cineole by the Brushtail Possum (Trichosurus vulpecula). Journal of Chemical Ecology, Volume 34: 672–680.
Moore B, Wiggins N, Marsh K, Dearing M & Foley W (2015). Translating physiological signals to changes in feeding behaviour in mammals and the future effects of global climate change. Animal Production Science, Volume 55: 272-283.
Wearing M (2012). Temperature-dependent toxicity in mammals with implications for herbivores: a review. Journal of Comparative Physiology B, Volume 183: 43-50.