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Professor Marilyn Renfree was interviewed in 2000 for the Australian Academy of Science's '100 Years of Australian Science' project funded by the National Council for the Centenary of Federation. This project is part of the Interviews with Australian scientists program. By viewing the interviews in this series, or reading the transcripts and extracts, your students can begin to appreciate Australia's contribution to the growth of scientific knowledge.
The following summary of Renfree's career sets the context for the extract chosen for these teachers notes. The extract covers how she came to work on honey possums. Use the focus questions that accompany the extract to promote discussion among your students.
Marilyn Renfree was born in 1947 in Brisbane, Queensland. She received a BSc in 1968 a PhD in 1972 and a DSc in 1988 all from the Australian National University. It was here that her interest in marsupial reproductive biology started.
In 1972-73 Renfree was a Fulbright Postdoctoral Fellow in the Department of Zoology at the University of Tennessee, where she investigated human uterine proteins and the factors affecting them. In 1973-74 she was a Ford Foundation Research Fellow at the Institute of Animal Genetics, University of Edinburgh, where she worked on mouse fetal development.
Returning to Australia, Renfree became a foundation staff member at Murdoch University in Western Australia, holding the positions of lecturer (1974-78), senior lecturer (1978-80) and associate professor of animal biology in reproductive physiology (1980-82). While at Murdoch, she studied a number of marsupials including grey kangaroos, quokkas, honey possums and tammar and agile wallabies.
Renfree moved to Monash University in 1982. She was a senior fellow from 1982-83 and a National Health and Medical Research Council principal research fellow in anatomy from 1984-1991.
In 1991 Renfree was appointed to her current position, Ian Potter Chair of Zoology and Head of Department, University of Melbourne. Her central research focus is to understand the control of reproduction and development in mammals.
In 1997 Renfree was elected to the Fellowship of the Australian Academy of Science. The following year she was elected to the Fellowship of the Australian Institute of Biology. She was awarded the Mueller Medal (ANZAAS) in 1997, the Gottschalk Medal (Australian Academy of Science) in 1980 and the Gold Conservation Medal (Zoological Society of San Diego) in 2000. In 1987, with Hugh Tyndale-Biscoe, she received the Whitley Book Award (Royal Zoological Society of New South Wales) for the textbook Reproductive Physiology of Marsupials.
Tell us about the other marsupial you worked on in Western Australia.
Not long after I arrived in Western Australia, Pat Woolley came to visit me. Pat was then a senior lecturer at La Trobe University, but had been a demonstrator to me when I was a student at ANU. She has always worked predominantly on dasyurid marsupials, the small mouse-like marsupials, and she had come over to the west to catch the dibbler. That had been rediscovered on one of the state reserves down in the south-west corner, after being thought to be extinct. Pat had confirmed that there were about 20 in this particular location, and she used to come over fairly regularly on fieldwork. She knew that area very well, having grown up at Denmark, in Western Australia.
So with Ross Young, my first PhD student, I went to help Pat in the field down near Mount Manypeaks, east of Albany, and I met my first dibbler. It was all very exciting – and there was beautiful countryside and spectacularly coloured water, and coastal heathlands full of wildflowers. It was very hot, of course, and full of bush flies and what have you. I was always in enormous admiration of Pat: no matter what the temperature and what the conditions, she always looked immaculate in the field. I've never looked immaculate in the field, I'm afraid.
I got chatting to one of the farmers on the property where we were catching dibblers, and he said, 'What about these honey possums, or honey mice?' Well, I had heard a little about them as being very interesting and very rare, and I remembered stories that 'Naughty Troughty' – Ellis Troughton, a famous biologist – used to tell. The farmer said, 'Yeah, whenever we're putting in a new fence, we push down the bush and we put our posthole digger through, and it puts a posthole in the sand plain every 20 metres or whatever. We come along the next morning and we have to take all these honey possums out of the holes. They fall in holes.' This was the most remarkable thing. What's a mammal doing, falling in a hole?
I just filed that piece of information away and Pat went back to Melbourne, but when I got talking to the people in the museum it turned out that there were hardly any specimens of honey possums in the museum. I started looking up the literature and decided, 'I think I can catch these.' So I bought myself a posthole digger, one of those hand augers. (I always tease people by saying my arms are different lengths because I dug so many holes, and you'd be surprised how many people believe that.)
I teamed up with Ron Wooller, one of the other young lecturers in the department, who was a bird person. He was working on honeyeaters, also in the same area. I said, 'Hey Ron, I need an ecologist. I've discovered how I can catch honey possums, and you might be interested because I could do the reproduction and you could do the ecology.' So for five days a month, every month for the next five years, we went down to Mount Manypeaks and trapped honey possums. We would put in grids consisting of postholes dug in the sand plain – we're talking about very thick scrub here, with roots and things like that, so it wasn't all that easy to do. At first I would buy number 10 tins, the very big tins for fruit or soup, take out the bottoms and put the tins in the top of the hole, because it had to be slippery enough that the honey possums didn't climb out. The Rolls Royce version of those was PVC pipes. We got several hundred metres of PVC piping, cut up into lengths.
I don't suppose you've ever tried to carry 300 pieces of slippery PVC pipe. Just to get them on the road down to Albany we had to devise a special way of carrying them – they were so slippery they kept falling off the truck. Anyway, we carried them through the scrub, put them in the holes in the ground, and then left them in permanently, covering the holes with a square piece of galvanised iron. Every month we'd open up all the traps, just by taking the piece of galvanised iron off the top, and then the next morning when we came along we would find that, sure enough, honey possums had fallen in. There's the sniffle, sniffle, oops! theory and there's the zoom, zoom, plop! theory for why they go in the holes, but to this day I have no idea why they do it.
What were they doing on the ground?
Well, we have observed them a fair bit in the banksia scrub, and they do jump across at tree level but they also come down and run across to a flowering tree and then run up to the next one. They like to nest in quite nice little hollows in the tops of the blackboys, the Xanthorrhoeceae plants, which don't usually join on by an aerial route to anything else. Plus there's a lot of ground-dwelling banksias. Banksia nutans is one species which isn't a bright coloured, bird attracting banksia; it's a cryptic brown but beautifully smelly banksia – it smells like coffee – with its flowers pointing downwards. It's clear it is mammal pollinated. I think they're using all of those flowers, because they live on nectar and pollen.
I had the idea that honey possums might have embryonic diapause, mainly because in the reproductive tract of kangaroos and wallabies, the birth canal is open after the first baby is born. In all other marsupials, connective tissue grows across that median vagina and it closes. Honey possums are like kangaroos and wallabies in having an open birth canal. Now, there is no scientific reason in the world why having that character should go with having embryonic diapause. Call it intuition, but I thought, 'There probably is something in this.' There were other observations which were consistent with diapause, and Bowley's paper from Western Australia in 1939 had concerned diapause in pygmy possums. So I went looking, once I learned how to catch them, and sure enough they had embryonic diapause. We now know very well that not only the honey possum has diapause but so do most of the other pygmy possum species, as you had suggested some time ago.
The honey possum was really a very exciting study. They're beautiful little animals, with three GT stripes down their backs. They're a matriarchal society, females are dominant – very good animals for a female scientist to work on! The females weigh 10 grams and the males are about seven to eight grams. But the most amazing thing of all was that they give birth to the smallest young of any mammal ever described. You were there when we found the first litter of neonates – one of the very few we ever found, in fact – less than five milligrams in weight. And yet they have the biggest sperm of any mammal, 360 microns, and five per cent of a male's body weight is testes. They're a remarkable species. We have published several papers on them but there's still much more to do and I'd love to get some more honey possums.
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