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. 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.
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). 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.
Interviewed by Dr Hugh Tyndale-Biscoe in 2000.
Marilyn, could we start this interview by hearing a bit about your family background and the influences that set you on the path to marsupial biology?
I was born in Brisbane, where my parents had moved during the war years. My father was at that time a lawyer in the Department of Supply, but later he became the Commonwealth Crown Solicitor and so I grew up in Canberra. We moved there when Canberra was still a big country town, long before Lake Burley Griffin, and I went to school and university there. I still think of it very much as home.
I went to the Canberra Girls' Grammar School, not far from where we lived, and did a somewhat unusual set of subjects for someone who was to go on in science. For my Leaving Certificate I did French, German, English, geography, maths and biology, but I only took up biology after Intermediate, having done some physics and chemistry before that time. At that stage we didn't have a biology teacher at school and so they recruited a certain Mrs Nicholson to come and teach biology to the fourth- and fifth-year students. Mrs Nick, as she was fondly known, had the enormous challenge of teaching us the five-year syllabus in those last two years of high school, to get us ready for the Leaving Certificate. Every lesson, and often on Saturday mornings, she used to trot us off to the old Institute of Anatomy. Three things there have stuck in my mind: the platypus collection, including a model platypus burrow; the psychology chart, where you looked at different coloured numbers to see whether you were colour blind; and Phar Lap – not only his heart but the whole horse, stuffed.
Mrs Nick was a very important person for me – and she was absolutely deadeye with a piece of chalk. If you were chattering in class, she would pick up a small piece of chalk and throw it at you: pretty effective at shutting you up. She was a remarkable person, a Doctor of Science at a time when very few women in Australia had doctorates, let alone a higher doctorate. She was terribly enthusiastic about her science and biology, and she brought a lot of additional interest to it through her husband, A J Nicholson, the famous population biologist. (He was Chief of the CSIRO Division of Entomology, working mainly on blowflies.)
My big sister Bev provided me with another important link with science. She was Frank Fenner's technician when he was developing the myxomatosis program, and also a technician in the John Curtin School of Medical Research. While I was quite young I often used to visit her in the John Curtin School, and many years later, between school and university, I worked there myself for a short time.
The other important influence was my father, who loved the Australian bush and bushwalking. Having grown up in Melbourne, he told lots of stories of hiking all over Mount Donna Buang and the Dandenongs and elsewhere as a boy. He was a King's Scout and did lots of excursions – all by train and on foot, as there were no cars to go in. He always was very interested in birds and he had Cayley's big book, What Bird is That?, with the question mark over the bird on the front. I certainly love the bush, and always love being outside.
Perhaps that influence extended to your sporting activities, especially at university.
Well, I've scuba dived almost as long as I can remember, and I was lucky enough to win the Australian universities underwater championship. I was on the cross-country ski team – actually, I had been on the downhill ski team but I hurt my knee quite badly, upon which I was told, 'That's all right, we need someone on the cross-country team'! Also, I played basketball pretty regularly, and I've always done a lot of swimming. So sport has been pretty important.
Did you yourself choose biology as your preferred university subject?
Absolutely. I had no doubt that I wanted to do some sort of biology. But I hadn't done the normal science subjects, and people said I wouldn't be able to do science at university if I hadn't done chemistry. I said 'Why not?' and to ANU's credit they allowed students to enrol in chemistry at university, not having done it in their Leaving Certificate. And so I did first-year biology. I don't know if ANU still allow that, but it is something I'm trying to change here so that students who have a non-physical and chemical type background will be allowed to do science and at least have a chance of passing that chemistry. I don't think that at third-year or fourth-year high school you know what you want to do for the rest of your life.
Some other people in Mrs Nick's class came through with you, didn't they, and you all came out on that first trip to Booligal.
Yes. There were Robyn Henderson and probably two or three others, and Beth Crichton. She had been a year ahead of me but came into my class to repeat fifth year – because she was too young, I think. We all went on to ANU, and Beth and I remained in the same class through our entire undergraduate degree.
I had forgotten about that wonderful excursion – 'Hay, hell and Booligal'. Spending two weeks in the bush with all of these terrific, enthusiastic staff members was the highlight of our undergraduate degree. I remember Tim Marples saying, 'Call me Tim,' and Dick Barwick saying, 'Call me Dick,' and Hugh saying nothing. We discussed it amongst ourselves, and Robyn Henderson and I were delegated to go and ask, 'Dr Tyndale-Biscoe, what may we call you?' And you looked very stern and said, 'You may call me Dr Biscoe.'
You did the third year, and then there was a choice of Honours. Was that when you took the fateful step to work on marsupials?
Yes. The course at ANU was terrific – 100 per cent biology, effectively, once you got through first year. I had a number of favourite subjects. Biochemistry was certainly one of the areas that I really loved, and also the reproduction and development course. So when, at the end of third year, we had to talk to supervisors and decide what we wanted to do, I announced that I wanted to do biochemistry and fieldwork. Everybody laughed and said, 'No, that's impossible.' In the end we came to some arrangement with you and Chris Bryant, and in effect I did do biochemistry and fieldwork – and I'm still doing it. That approach was certainly not the traditional one; perhaps it was way ahead of its time.
It was a good mix. Unlike a number of your contemporaries whom I tried to persuade to do Honours, you didn't suffer from the idea that as a woman you should not go on to a higher degree, did you?
Well, I didn't suffer from it, but my father was somewhat traditional and didn't expect me to go to university. He expected my brother to go to university, but although my sister and I could if we wanted to, it was not really the done thing. When I said I'd like to do university science, he said, 'All right, you can have one year, and we'll see how you go.' At the end of that first year I picked up a scholarship and supported myself through the rest of university – he didn't have to pay after that. Once I showed him I could pass, and I picked up the scholarship and so on, he was very pleased and enthusiastic and supportive from then on.
In the climate of the time you didn't go around announcing to people outside your actual class that you were doing science, and you didn't admit that you were doing a higher degree. When I was a PhD student, I would never have dreamt of telling some boy that I'd met at a party that I was doing a PhD: I 'worked in the Zoology Department'. But within the department I don't think I ever suffered any form of discrimination at all.
For your PhD work, you picked the tammar.
The PhD project was an extension of my Honours project, which had been to look at the composition of the fetal fluids of the tammar. I wanted to go on and look at the maternal fetal influences. There were 12 tammars in your little colony of tammars at the time and you very generously said I could do this project, using half of the tammars: I could have six and you would have six. When I said that was not enough, you said, 'All right, off you go to Kangaroo Island and catch some.' So I gathered together three of my friends, Roland Scollay, Ross Davey and Peter Temple-Smith, and we went off to Kangaroo Island.
The only contact there that we had was Joy Davis, a lady who lived on a farm on Kangaroo Island and had been supplying you with small numbers of tammars. She took me under her wing and showed me how she snared them, a very good way of getting males, but I soon realised it just didn't work for females – and I needed females. Joy said there was no other way, that this was how they'd always been caught, so I came home and then returned with my three friends, netting and all sorts of other things. We sewed sinkers all around the edge of nets to make throwing nets, and we put netting along the fences and tried to chase the tammars into it, but we couldn't catch one. The days were going by, soon the Great Supervisor was coming to see how we'd got on, and we still didn't have any tammars.
We decided to try hand netting so Joy's son Peter Davis, who was about my age, said maybe he could help us. Using a broom handle and some fencing wire that Peter spot-welded for us into a hoop, we constructed a big butterfly net, and when we went out that night we were able to catch about 15 tammars. But only two of them were females. So Hugh arrives the next day: 'How have you got on?' 'Good. We know how to catch them now.' 'How many have you got?' 'Two.' 'What! What have you been doing all this time?'
After you'd assured yourself that there was no other way of catching them, though, I seem to remember we got 25 females when we went out that first night. That was the seed of the colony which eventually, years later, grew to be six or seven hundred in Canberra. It was 300 by the time I left.
And you're still taking your students back and doing the same sort of thing, but now you have a proper laboratory there.
A couple of years ago we built a caravan, which we call the Wallavan, to serve two purposes. We tow it into the middle of a paddock and set it up, and then we can go out and collect samples from the animals and process them in our mobile laboratory. We can run two or three microscopes in the van, we have fluorescent lights, a cold light source, we have liquid nitrogen cryoshippers – it's much better than sitting under a tree on a camp table and getting insects down the back of your neck.
Or having the whole thing blown away by a storm.
Yes, it's quite sophisticated now. The fact that we're actually doing molecular biology in the middle of a paddock at night is of great interest to our overseas colleagues.
So now we've got the background. What did you do for your PhD?
I was looking at every aspect of maternal-fetal interactions: what was coming from the mother to the fetus and what was passing from the fetus back to the mother. We made a beginning on the hormonal control of that and the role of the corpus luteum, which is the structure in the ovary that secretes progesterone, the hormone of pregnancy. Geoff Sharman had shown originally – and you, in subsequent work – how critical the corpus luteum in marsupials was in two ways: to hold the embryo in the state of suspended animation that we call embryonic diapause, and then, once it started going, for pregnancy. We were able to stimulate reactivation after diapause by giving progesterone injections as Sharman had done but carried that all the way through to full term – the first time that had been done.
I was also very interested in just how the placenta was functioning: whether it was an endocrine organ and an organ of physiological exchange. Every textbook you picked up till then talked about 'placental mammals', meaning eutherian mammals – you and me, and sheep, cows, goats and dogs. But marsupials, by inference, didn't have a functional placenta. I was able to show that marsupials have a fully functional placenta, which does produce hormones. Some of that work was followed up later, subsequent to my PhD.
The most interesting thing was the maternal recognition of pregnancy, the influence the placenta had on the mother. That too had been denied for marsupials; only important, advanced mammals like us could do that. I was able to show that the placenta, in the presence of the fetus, stimulated the uterus it was growing in to elaborate and proliferate.
Just a point there: the wallaby has two uteri, one of which is pregnant.
Yes. All marsupials have two separate uteri, but in kangaroos and wallabies there's only one baby. In any one pregnant cycle one of the uteri becomes gravid, and it is sitting right next to another uterus in the same hormonal environment that can act as a 'control'. This control system is a biologist's dream. I was able to show that the endometrium on the gravid uterus elaborated much more than on the contralateral side – it made different proteins, it was heavier, it produced all sorts of things. That resulted in a letter to Nature, so the first paper published from my PhD was a Nature publication.
There was still considerable disbelief, however, particularly by our colleague Geoff Sharman and by my husband-to-be, Roger Short. I remember giving a seminar at Edinburgh in the Institute of Animal Genetics, where I was working with Anne McLaren, when Geoff Sharman was visiting Roger Short. (Roger was the Director of the Medical Research Council Unit of Reproductive Biology in Edinburgh.) Geoff and Roger came and sat up the back, chatting to each other through the whole seminar, with little looks going backwards and forwards. As soon as I finished, it was clear from the questions that came that they didn't believe a word of it. But I had the last laugh.
What did you find that demonstrated the role of the placenta, the transport of the materials?
The placenta absolutely regulates what gets across it – no surprise now, but until that time no-one had demonstrated it in any marsupial. So the proteins, the amino acids, the glucose, waste products like urea, were all different in composition from the concentrations in the maternal serum, and they were different in each fetal compartment. The fetus itself is surrounded by an amnion, and the composition of that fluid is different from the composition of the yolk sac fluid which was right around it. And then there's another compartment that would be just as big, called the allantois. That is an extension of the embryonic bladder and acts as a place for storing the excretory products, so it's very high in urea. The fact that all of these three compartments – the amnion, the yolk sac and the allantois – are so different showed us quite dramatically that marsupials are just like any other mammal: they have a fully functional placenta and they are able to regulate precisely what goes from mother to fetus.
Not long after my PhD I was able to establish, in collaboration with Brian Heap (who was then at Cambridge, at Babraham), that the placenta synthesises progesterone in very small amounts, and it doesn't make any oestrogen that we know of. So it is similar to the placentas of other animals. Marsupial pregnancy is about the same length as the oestrous cycle, so in a sense there's never been selection for the placenta to continue producing hormones. That function is taken by the corpus luteum, which is so critical for marsupial pregnancy. In recent years, though, my colleague Geoff Shaw and I have shown unequivocally that the marsupial placenta synthesises a number of hormones – particularly, significant quantities of prostaglandin. That's critical for parturition, in fact, and we think we know now how that works. More recently, Laura Parry, a postdoctoral fellow in my group, has shown that the placenta also synthesises relaxin. So it is a placenta in every definition of the word; it's just that we didn't have the techniques to study it.
Although Geoff Sharman and Roger Short were sceptical of your results, you did have a champion at that time, Professor Amoroso, or 'Amo'.
Amo was just the loveliest person. He worked in Cambridge, but was from Trinidad and always called himself an 'Afro-Saxon'. Two weeks ago I visited Trinidad for the first time, and to have that link, to see where Amo grew up, was fantastic. He visited us in Australia in about 1970, before I finished my PhD, and then again for the International Conference of Comparative Reproduction in '72.
Because his interest was comparative placentation, he was fascinated by what I was doing with the tammar and in looking at these embryos. No-one else had previously done any physiological studies of marsupial embryos. He was very supportive, and I've always tried to remember just how valuable the interest of a very senior and important person is. I think a lot of important people don't understand what an influence it can have on your life if only they will say a nice thing to you – 'Gosh, that's exciting. Isn't that interesting.' I've always admired Amo for making time for students. He was almost like a grandfather figure in the background, and many years later when I went to Cambridge for a short sabbatical with Brian Heap I was fortunate enough to co-author (with Amo and Brian) Amo's paper on the evolution of viviparity. That turned out to be his last paper.
That was a nice echo of your PhD work. Would tell us some more about that work?
I was interested in embryonic diapause, in which the embryo is in 'suspended animation'. It grows to become a blastocyst of about 100 cells, which then stays completely unchanged for 11 months.
The tammar is an unusual species because it's a seasonally breeding marsupial. All of the females carry a blastocyst in their uterus while they have a young in the pouch. The pouch young weans in about October but the blastocyst stays quiescent, undividing, until just before Christmas – the longest day in the southern hemisphere which is about 22 December. Then nearly all of the female wallabies on Kangaroo Island reactivate and they give birth about a month later, on or about 22 January: within a week, between 22 January and 1 February, they go from having no new young in the pouch to having a young in the pouch. We showed during my PhD that about 85 per cent of females will give birth at that time of the year, about 10 per cent have unfertilised eggs and only the remaining five per cent haven't ovulated. It's a highly successful means of reproduction.
The only day of the year when they're not actually pregnant is the day they give birth. We used to think they all mated eight hours after giving birth, but one of my PhD students, Carl Rudd, subsequently showed that the majority of matings were about an hour after birth. Ovulation occurs 40 hours after birth, so it's only on the day that they give birth that they don't actually have a new conceptus in the uterus and so are not pregnant.
The new conceptus in the uterus, which is first a fertilised egg, cleaves into two cells, four cells and so on, and grows up to be about 100 cells. If the young in the pouch is still sucking, that 100-cell embryo stays completely quiescent. If you remove the sucking stimulus – if the pouch young is lost in the wild or if, for experimental purposes, you remove it – the embryo reactivates and starts growing again. So we can time all stages of pregnancy very precisely because we're starting at a blastocyst stage, the 100-cell stage, and going on from there. The hormonal and photoperiodic control of that diapause has been the subject of a great deal of work and several PhDs now, in both our laboratories, to understand how that works.
Let's go now to the end of 1972, when you took up a postdoctoral fellowship in the United States. Why did you make that choice?
Actually, I finished my PhD in March and worked in Zoology at ANU for six months as a research assistant, funded by a CSIRO grant. During that time I was able to write up all my papers, which was enormously valuable. It's very difficult to write up things when you go on somewhere else.
During my PhD I had been in contact with Joe Daniel at the University of Tennessee. He worked on both uterine secretions – the subject of my PhD – and embryonic diapause in seals, particularly on uterine proteins and their role in embryonic diapause. Marsupials aren't unique in having embryonic diapause – about 96 species of mammals, on last count, have diapause. About 33 of those are marsupials: almost all of the kangaroos and wallabies and one or two others that we will touch on later. Of the other mammals, there are seals, bears, badgers, skunks, polar bears, rodents – a large number of rats and mice – some bats, only one ungulate (the roe deer), and that's pretty much it. Joe Daniel was interested in having me go there for a postdoc, so I applied for a Fulbright Fellowship and was lucky enough to get one to go and work with him.
What project did you do?
The project that was paying me, supported partly by a grant from the National Institutes of Health (NIH), was to work on human uterine proteins and on the influence of melatonin on the uterine secretions. That's interesting because of what we subsequently did with melatonin and seasonal breeding, and because of Roger's work. We were also to look at human uterine flushings, so I did plenty of electrophoresis and learnt tissue culture. I did a lot of culturing work there. We had human cell lines, looking at whether there were growth promoting or growth inhibiting factors in the uterine secretions – in this case it was a model system, the tissue culture, but with a view to how that would stimulate early embryonic growth.
Probably the most valuable thing I did there was to learn how to write a grant application, because Joe had me helping him with his NIH applications. If I'd done nothing else for the rest of my stay there, that would be an enormously valuable experience, the thing that really made a difference to my career. But being a marsupial person at heart, I couldn't bear to be in a place where there were all those opossums – 'possums – skulking around, without doing something with them. With Joe's complete support I became 'the 'possum lady from Australia'. We advertised in the local newspaper and I got all these phone calls from Tennessee hillbillies, 'Are you the 'possum lady from Australia? I've got a 'possum in my henhouse.' I'd trot off in my car and knock on the door: 'Y-e-s?' I'd say, 'I've come to collect the 'possums,' and the door would open wider. There'd be a gun in one hand and a dog in the other! 'Sure.' Because I came from so far away, I was totally immune from danger. Had I come from the next valley, I would have been shot at – it's just amazing, exactly like the films. In fact, I've whitewater canoed on the river that the film Deliverance was filmed on.
So I'd go out to the henhouse or the garage or wherever it was, and there'd be a 'possum curled up. I'd pick it up, put it in my bag and take it back to the department. They had given me a cage on the roof of the Zoology building which had been an aviary, and I put my 'possums in there. So it was outside. Nobody in America ever keeps any animals outside, and they all said I'd never get them to breed. But they bred like steam, I had no trouble at all. The only thing I had to be really careful about was that I wasn't up there at dusk or at night when the campus police were driving by, with their pistols on their hips, because I would have been a silhouette on the roof of the building and they would definitely have shot first and asked questions later. It's a very different way of life in some parts of the US, for sure.
What I did in Tennessee was really to repeat and extend the work of Carl Hartmann, an eminent reproductive biologist. At the turn of the century we knew more about reproduction in marsupials than in eutherian mammals, and Hartmann was one of the people up to the 1930s that contributed to our understanding of ovarian function and endocrinology in primates and humans – but he set the scene for all of our work, however, in that all his early work was on marsupials, on Didelphis.
I wanted to solve a little conundrum in the literature. Hartmann had said that the corpus luteum was needed for pregnancy, because he'd taken it out early in gestation and showed, as you subsequently showed with the tammar and the quokka, that pregnancy fails if you take it out early. But I knew, from work by you and Geoff Sharman and some others, that it was likely to be needed only in the first couple of days – probably they could then go all the way through pregnancy. So I took the corpus luteum out at all different stages and showed, indeed, that they were just like all the other marsupials: they could go through pregnancy, once pregnancy had taken hold. It was nice to get that exception out of the literature.
I also tried with Joe to do some culture of the embryos. At that time Denis New, in Cambridge, had managed to culture Didelphis embryos from primitive streak stage through to beyond the head fold stage. We've subsequently done that here with wallabies: we can actually grow them through to a fairly well developed embryo, certainly a head fold stage, as Lynne Selwood has now done so successfully with Sminthopsis. I think it would be possible to culture a marsupial embryo entirely through pregnancy – and what a fantastic model system that would be for understanding embryonic development, teratogens and so on. But because we didn't have a hypothesis when we put that up to the National Health and Medical Research Council (NHMRC), we couldn't get funded to develop the techniques. We did do some culture and we tried to do some blastocyst culture, but nobody yet has cracked the system for getting a marsupial blastocyst to grow. We can get them to go from later stages, but we can't get the blastocyst to grow. And that was true of the opossum as well. If they were a bit later you could get them to go, but at that early stage you couldn't.
In all three projects there – the uterine proteins, the endocrinology of opossum, and the culture – I learnt techniques and approaches that complemented what I'd done in my PhD and provided me with a lot of tools to go on with.
You went from there to Edinburgh, didn't you?
Yes, on a Ford Foundation Fellowship. I went to work with Anne McLaren in the Institute of Animal Genetics, in the old King's Buildings at the University of Edinburgh. The department was led by the famous Waddington, who was very much in charge of a fine genetics group. That was where I started to learn a little bit about genetics. Of course, it was entirely a mouse lab – no opportunity in Edinburgh to work on marsupials. I did some work on mice and a little bit of work with John Hearn on the uterine proteins in marmosets. John had done his PhD at ANU just behind me, and then when he finished he went to work with Roger Short. So John was in Roger's labs in Edinburgh and I was in Anne McLaren's lab. That was a very nice time, because we were very good friends and it allowed me to get to know that unit as well as Anne McLaren's. In Anne's unit I worked on alphafetoprotein, a protein specific to fetuses that has a number of growth promoting activities. Amongst other things I repeated on the mouse what I'd done on the tammar, and that was the first time that anyone had looked at fetal fluids in any of the mouse compartments.
They're different in the mouse, though, aren't they?
Very different, but still quite tightly regulated, just as in the tammar. Of course, the mouse has a highly invasive placenta, like a human's. I did some more embryo culture work there with Hugh Hensleigh, an American postdoc. We got mouse blastocysts to develop outgrowth of the trophoblast. That was very interesting. I published a couple of papers from that time with Anne.
That was the start of a very long and fantastic friendship with Anne. By the time I finished my PhD I had two scientific heroes, Anne McLaren and Roger Short. Before that I didn't know Roger personally at all, except for the episode when he'd sat up the back of my seminar and 'cast nasturtiums' at what I was saying.
Having worked with Anne, whom you obviously admired, presumably you could have stayed in Britain as so many Australian scientists have done. Yet you chose to return to Australia.
Yes. In the same week that Anne moved her whole lab to London to establish the Medical Research Council Mammalian Development Unit, I left to take up a new lectureship at Murdoch University, in Perth.
I was always very keen to come back to Australia. I'm terribly nationalistic. I really love living in Australia: it's a fantastic country and there is nowhere else quite like it. I love visiting other countries, where I've learnt and benefited enormously, but Australia has a special way of life – quite apart from the fact that I happen to work on Australian animals. Also, one of the conditions of my Fulbright Fellowship required me to come back to Australia for at least as long as I'd had the Fulbright. So I would have had to come back for at least a year.
I have to say that Perth was about as far away as I could imagine being; it hadn't really come into my range of thinking. But a lectureship in invertebrate biology was advertised, and another in vertebrate biology. I applied (amongst 300 candidates), I was interviewed – in the staff club in Edinburgh, if I remember rightly – by Bob Dunlop, the Dean of the Vet School, and I got one of the two positions.
In Perth, presumably, you could have taken up any field of research you fancied. Yet you returned to marsupials. In America and Britain did you encounter any prejudice against marsupial research as being a sideline, not really central to research?
Certainly that attitude was held, and probably still is, in many places. In fact, that must have been the time when I got to know John Rasweiler, who is a bat researcher but in Obstetrics and Gynaecology at Cornell Medical School. He and I used to joke that we were going to set up 'The Institute for Funny Animal Research', and he was going to work on bats and I would work on marsupials – because that's how we felt people viewed anything that wasn't a mouse (or a rat) or a sheep or a primate. My field very much was reproduction, but in Australia you weren't anybody in that unless you worked on sheep. Australians have made a disproportionately important contribution to reproductive physiology because we grew up 'on the sheep's back'. Our world pre-eminence in reproduction comes from our ability to capitalise on the sheep industry and manipulate sheep reproduction. Working on something like marsupials was not viewed the same way.
At Murdoch I was in a school of Environmental and Life sciences and I did about half of my teaching in the newly established vet school there, so it certainly would have been possible to do almost anything, but especially sheep. But somehow I never considered it; I just assumed I would build up a colony of marsupials. Murdoch was a wonderful campus for that, because there were 600 acres of pine plantation.
When I arrived at Murdoch at the end of 1973 – we took in my first students in '74 – there was no campus, no university. We were put into the Noalimba migrant centre, where three blocks were still full of British migrants and three blocks belonged to Murdoch University. One was the rooms where those of us who had arrived from out of state or from out of country lived, and the other two were our offices. We didn't have labs, just all these converted bedrooms.
I can give two examples of the conditions we were working under. The photocopiers had been put in the men's toilet in one of these blocks. You could see the migrants looking at all these women walking in and out of the men's toilet with sheafs of paper, and wondering what the heck went on!
The other example arose from life at Murdoch being one long meeting. During my nine years there I would have been on 45 committees, and chairman of about 20 of those, so it was an enormous administrative load. I don't know how we did it. I'm glad I was young, because I didn't really think about it, but I would never do it twice. Right from the start we had innumerable meetings: How do you plan a university? How many subjects could a student fail before being asked to show cause as to why they should be allowed to continue? What regulations would we have for a PhD? How many courses would we have? How would we design the degree?
One night we went in to dinner at about 6.15, having had one of these enormous meetings. (Dinner was in the cafeteria for the migrant centre, and if you were going to have 'late' dinner – late being 6 o'clock instead of 5 – you had to write your name on a list.) We all trooped in and as everyone was served and it came to my turn, the lady with her big serving spoon said, 'You know, dearie, the late dinners are for the men who work.' She didn't realise what she'd bitten off when she said that!
Did women members of staff there have good support from their colleagues?
I was the only woman for a long time. I had variable support – very good at the most senior levels, but not at the middle levels. That was the first place where I met any discrimination. I really did meet a lot of discrimination at Murdoch: I had outside research grants, I had a lot of students, I was the wrong sex, the wrong age.
In returning to work on marsupials, what did you study?
The university gradually built on its 600 acres of pine plantation, but I got in pretty early. There were three 'chiefs' when I arrived there and I was the third 'Indian', so I was able to persuade them to give me about 20 acres of land at the bottom end of campus. In those days CSIRO still gave grants to university people, and with a grant which gave me a four-wheel drive vehicle and fences I put up a colony at Murdoch, which was fantastic. By the time I left, we had three or four hundred animals.
Because tammars are still classified as vermin on Kangaroo Island, they were the obvious choice. By then there was 15 years of work on tammars, making them the best understood of the macropods. Quokkas, which had been Geoff Sharman's original animal when he was in Western Australia and yours when you were there, don't breed as well as tammars. They are less amenable, and it's harder to get permits because the quokka is very highly protected – it's almost extinct on the mainland. So it was just easier to go to Kangaroo Island and collect animals. As well as the tammar colony at Murdoch, I had some grey kangaroos and I also got agile wallabies. I did also have quokkas later.
Tom Spence, the director of Perth Zoo, said the zoo had too many agile wallabies and would have to cull them, and he offered me some agile wallaby material. I didn't want any tissue, but I told him I'd love to have the animals. The zoo people said, 'You'll never be able to catch them and take them across because they suffer from capture myopathy, muscle wastage. If you catch them they get terribly stressed and they go into tetany. They lie down and die.' I thought we could probably catch them by using our techniques, so I said, 'What do we lose? If we try and we're successful, we'll know within the first animal or two. Can't we have a go, instead of you anaesthetising and killing them?' So Greg Wallace and Ross Young (my PhD students at the time) and I went over to the zoo with our nets and our bags, and we caught one animal at a time. We caught all 35 that they wanted to get rid of, transported them over to Murdoch and had them in our colony for the next five years. We simply handled them in the same way as tammars, and we never had a moment's trouble. The zoo people were just flabbergasted.
So did you use the agiles for your experiment on lactation because you had them?
Yes, and because they bred the whole year round and they had concurrent asynchronous lactation. The agile wallaby has the same type of reproductive pattern as the tammar, but it doesn't have a seasonal reactivation. The blastocyst reactivates when the young gets big enough to leave the pouch, becoming a young at foot. It then sucks less frequently than when it's in the pouch, and the sucking stimulus decreases over time as the baby gets bigger. When the sucking stimulus gets infrequent enough, the blastocyst reactivates and you get another one born. So in the agile wallaby and many of the kangaroos you can have a young at foot which will suck from one mammary gland; one in the pouch, which will be anything from bean size to hand size, sucking from another mammary gland; plus the blastocyst in the uterus waiting its turn. The remarkable thing is that the two adjacent lactating mammary glands are producing milk of totally different compositions and yet they're in the same hormonal environment. It's like your left breast and your right breast producing two milks of totally different compositions – different amounts of protein, of fat, of carbohydrate – and different in volume.
Understanding the control of lactation has been a continuing interest of mine. We have an awful lot still to learn about the control of lactation, which will apply to all mammals, and we've been doing quite a bit of that, both directly and indirectly, since the agile wallaby study. Dennis Lincoln, a neurophysiologist who took over as director of the Mammalian Reproductive Unit in Edinburgh when Roger left, came to Murdoch and worked on neuropeptides, particularly oxytocin. We were able to show that the two glands have differing sensitivities to mesotocin, the marsupial equivalent to oxytocin. If we stimulated electronically an electrode in the mesotocinergic neurons of the brain, we could get a milk ejection with exquisitely sensitive and small amounts of stimuli. So the two glands react differently to the hormone and to the sucking stimulus. We were able to show that the little one got its milk by sucking. The stimulus from its tiny, baby, pouch-young suck resulted in a milk ejection but it didn't cause the big gland to milk eject, because it needed a bigger stimulus. If the big baby put its head in the pouch to have a drink, the little one got a drink whether it wanted one or not. Yet the opposite didn't happen, because if the little one sucked, the big gland was insensitive. Had they had the same sensitivity, then the pouch would have filled up with milk and the little one would have drowned. It is a fantastic mechanism. And subsequently, here at Melbourne, we showed a few years ago that the oxytocin receptor concentration is quite different in the two sets of glands too. So that parallels the prolactin receptor story.
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.
After your nine years at Murdoch, you made the big life moves.
Yes, b-i-g life moves! I gave a paper at a conference – I suspect it was the International Endocrine Congress in Melbourne, in about 1980, for which my group had come over. And Roger Short had come from Edinburgh. I don't know quite how or why it happened, but over the next 18 months or so we conducted a courtship between Edinburgh and Perth, and we were married in Canberra in January 1982.
In association with that international congress, you and I ran a conference to which we brought all the embryonic diapause people from around the world. That was published in 1981. Do you remember?
That was only the second international conference on embryonic diapause, and Roger came to that. Maybe that was where it started. Geoff Shaw composed a limerick from that meeting:
Anyway, I then put my lab in Murdoch on hold and went to Edinburgh. I had got a Royal Society Fellowship to work there for a year, and I honestly didn't know whether I would come back to Australia or not. We had two amazing offers from Oregon – Roger was offered the directorship of the Primate Center there and they offered me a chair in physiology and a mythical amount of dollars. We turned it down because on the US west coast we would have been the maximum distance from both our families. So we went back to Edinburgh and wondered. Then David de Kretser and Geoff Thorburn created two positions for us, offering Roger a personal chair in physiology at Monash University.
In 1982 we came back to Monash. They created a research fellowship for me, which then allowed me to apply for an NHMRC Fellowship, so for almost 10 years after that I had an NHMRC Principal Research Fellowship at Monash. That was a wonderful time, because it was full-time research. And at Monash I set up another wallaby colony, my third. It was in a small area of land where we were only ever able to keep about 150 tammars.
Three important things happened at Monash. One was the birth of my two daughters, Tamsin and Kirsten, in 1983 and 1986. Had I not been in a full-time research position, it would have been really difficult juggling teaching with raising a young family.
Secondly, we began several studies. My NHMRC Fellowship paid me a grant to look, in collaboration with Roger, at the contraceptive effects of breastfeeding. We did a big study on breastfeeding women, in association with the Nursing Mothers' Association of Australia. That was a fantastic study; they were wonderful people.
We showed that if you breastfed actively and on demand, rather than for 10 minutes each side every four hours or every eight hours as the dogma was at the time, the contraceptive effects were very great – probably better than a condom. That has led on to all sorts of other things that Roger has subsequently followed up. I remember taking Tammy, who was at that time still very much a breastfed baby, into our NHMRC interview. I think she's their youngest interviewee ever! She was as good as gold (fortunately!).
You and I wrote our book between my daughter number one and daughter number two. It had a three-year gestation, I suppose. That was a really exciting time, and even though you were in Canberra and I was in Melbourne, it was just such fun exchanging those ideas. Each of us took responsibility for a different chapter and would send it off to the other. I'm still very proud of that book. My group call it 'The Bible', but it's now a bit out of date, of course. I need to do something about that in the near future.
The third thing at Monash, which led us into a whole new line of research, was that Dione Gilmour, of the ABC Natural History Unit, approached me and said, 'We want to get some footage of birth of a kangaroo or a wallaby. Can you help us?' We said it would be difficult but yes, we'd do it. David Parer and his wife, Liz Parer-Cook, who are the best wildlife photographers and sound people anywhere – even David Attenborough acknowledges the high standard of their work – spent sizeable parts of the next four breeding seasons filming the birth of the tammar. This was for The Nature of Australia, a series to celebrate Australia's bicentenary in 1988. It took us four years to get the 'film in the can', and then they used five minutes of the footage! That taught me an important lesson too, and I subsequently made, with David's help, a little 11-minute film that we use for research and teaching purposes on the birth of the tammar.
That ABC project was wonderful, because we were forced to set up a system and learn the signals from the animals that they were going to give birth. We discovered that when they were about to give birth, we could pick them up and hold them half in a sack, with just their heads covered, and the whole birth process would go on. So all of that footage was taken with me holding the wallaby and David filming.
In order to get something ourselves from that filming process, we decided to take blood samples. That opened the door to the technique that we now have used over and over again for getting blood samples right throughout the entire period of parturition, and in doing so we have discovered almost the entire hormonal sequence that controls birth. Prostaglandin goes up, mesotocin goes up, they trigger birth, and within an hour after birth they're both down again. Oestrogen goes up eight hours after birth – that wasn't so new, but we now know the precise relationship to the prostaglandin peak. Progesterone falls. And we have subsequently gone on to show that the signal for birth comes from the fetal adrenal, and that fetal cortisol is synthesised by the fetal adrenal. In a link that we're pretty sure of, but not yet 100 per cent sure, it acts via the PGHS system – the cyclo-oxygenases and prostaglandin synthase systems. The cortisol switches those enzymes on, which puts the prostaglandin peak up, the muscles contract and the baby is born. That is, the signal comes from the fetal adrenal, via the fetal circulation, to the placenta and to the endometrium. So both endometrial tissue and placental tissue make the prostaglandin.
That links in with your studies of marsupial maternal-fetal interactions. And then there is prostaglandin's effect on behaviour, which we discovered one evening.
That's right. When we thought that prostaglandin was the most important signal and you thought prolactin was, we said, 'Right, let's get together and do this experiment.' Geoff Shaw and Terry Fletcher went up to Canberra to work with you and Lyn Hinds. Geoff noticed that the animals that were given injections of prostaglandin all sat down on their tails, with their tails forward in what we now know is the birth posture.
They were like broody hens.
But the controls just stood there. Geoff followed that up, showing that there's a clear dose-response curve: if you give a lot of prostaglandin you get a long period when the animal sits in the birth posture with its tail between its legs and licks its pouch, getting ready for birth. The ultimate proof was giving it to males – the males sit down in the birth posture and busily lick their scrotums. We've now defined parturition in extraordinary detail for a marsupial, and it's very like the system we see in sheep.
That presents another interesting parallel. For 150 years people dismissed the marsupial young as being incapable of doing anything when it was born.
And even though the marsupial is only giving birth to a bean, a 400 milligram baby, that baby is still telling the mother, 'Hey, it's time for me to come out.' The fact that the baby can redirect the whole of maternal physiology shows again that they're perfectly good mammals in every sense of the word.
That takes us on to the other exciting work you've done with your colleagues, on sex determination and differentiation in marsupials.
It has been the most exciting and unique aspect of our work, and has attracted enormous international interest. It started in 1985-6 when I was trying to complete my embryology – which has got diverted and still isn't complete. I was doing a lot of scanning electron microscopy, and these tiny little fetuses have to be dissected very carefully to get them just right for good images in the scanning EM. One day I was sitting at the microscope preparing the specimen, for some reason targeting the gonads and the reproductive system, when I saw little lumps in the region where the scrotum would be. Well, the dogma had been that you couldn't tell the sex of a marsupial until 10 days after birth. I had believed that, I had taught my students that, I'm sure you had told me that, we put that in our book. It may have been Geoff Sharman who originated it, because you couldn't easily see a scrotum or a pouch until about eight to 10 days after birth.
When I told Roger I could see scrotal bulges in these embryos, he said, 'Rubbish, it can't possibly be.' I said to him, 'It is, it's a scrotum. I'll show you,' and that was the start of the sex differentiation work. Meanwhile, Geoff Shaw, who had done a PhD with me had gone to Queensland, but we recruited him back to my lab, and O Wai-Sum, who had done her PhD originally with Roger in Edinburgh, came as a visitor from Hong Kong. In 1988 we published four very important papers, one on the morphology of the scrotum and the mammary gland in the neonate, one on the hormone treatment of young, one on the mechanism that might control it and one on MIS, the Mullerian inhibitory substance.
We were able to show that in the fetus, males have two little scrotal bulges either side of the phallus and females have four little dots which are going to be the mammary glands. At this stage the gonad is undifferentiated, a gonadal ridge. On the day of birth it's still an undifferentiated gonad, with scrotal bulges in the male and four mammary glands in the female. No XX animal ever has a scrotum and no XY animal ever has a pouch; it's exclusive according to the sex.
That's not the way the scrotum develops in eutherian mammals, where it depends on the hormones. It requires testosterone to masculinise the labio-scrotal folds to form a scrotum in the male and the labia in the female. That's totally hormonal dependent, but we had no hormones in the fetus or the newborn, because the gonad wasn't formed at all. That observation completely overthrew the dogma which had existed for the previous 50 years, that all of sexual differentiation depends on having a testis: once you've got a testis everything else happens – you get a scrotum, you get a penis, you get a prostate.
By 10 days after birth, when the testis is producing lots of testosterone, it looks like the stage which we thought was when we could first tell the sex. The bulges have moved together into the midline for the scrotum, and the pouch can be seen. We then gave hormones to neonates, but we still couldn't get them to make a scrotum. The work has gone on from there, showing that the scrotum and pouch are controlled by a gene or genes on the X chromosome, and we're now on the search for the genes that do that. We actually have a PhD student looking at that project at the moment. Just in the last year we've discovered an androgen – a male hormone – which is a testosterone metabolite that is probably a key hormone in male differentiation in all mammals. That has not been recognised before. So marsupials are once again proving that they're magnificent animals as a biomedical model, and we're rewriting textbooks on this stuff. It's very exciting work.
It is a nice vindication of your decision at the beginning of your career to work on marsupials: you can elucidate fundamental principles in mammalian biology.
Absolutely. There's just so much to learn from these animals on our doorstep, and our North American colleagues are very envious that we have so many. Of course there are marsupials in South America, but very few people work on them because there is not the same variety and they are not such amenable animals for research.
So, where next?
There's mountains of work to be done on the sex differentiation story. We're taking very much a molecular approach combined with an endocrine approach, and that's not so common. Geneticists tend to work on just the genes and the sequence of the genes and their structure. I'm interested in what the genes are doing. We are interested in the differentiation events, not the sex determining events, and in combining the genes and hormones – which genes are switching on which hormones, how the hormones are working.
One little anecdote I can tell you concerns the study we have going with John Hutson at Royal Children's Hospital. In looking at all of this we were interested also in testicular descent. In the embryo the testes develop high up in the abdomen and, although there's differential growth, they end up by going down towards a gap in the body wall called the inguinal canal, passing through it into the scrotum and remaining in the scrotum for the rest of the mammal's life. We've worked with John Hutson on some aspects of this, and he was saying, 'I really need a model for closure of this inguinal canal. We think we know the hormone or the growth factor that closes it, but I can only test it in culture.' He could get inguinal canals from boys whose canals he closed at surgery – it's the most common developmental abnormality in man and if the testes don't descend, the testes can become necrotic and cancerous. Then not only is the boy infertile, but he has a potential cancer later. So it's very important that the inguinal canal closes, and inguinal hernia is very common.
I said to John that I thought tammars closed their inguinal canal, and he said, 'What! There is no mammal so far described, other than humans, that has a closed inguinal canal, not even other primates.' I said, 'Well, if it is so unusual, I'd better go and have a look.' We had a dead wallaby so we put a probe up the inguinal canal, trying first one way and then another, but we couldn't get it through. We now know that, effectively, the canal is closed, and I think it's closed because they have an upright posture and they hop. We know that it is not closed in other marsupials, such as brush-tail possums. We tested that straight away. We already know from the respiratory physiologists' work that a kangaroo disconnects its normal breathing control of the diaphragm and uses its guts as a piston to breathe when it's hopping, so it has a very efficient mechanism there. If you're getting a piston to work the diaphragm, imagine the pressure on the poor little inguinal canal if it were open-ended. The guts would go through there, they'd have hernias and they'd be dead. So I think what causes the difference is upright posture – bipedalism in humans and hopping in kangaroos.
An extensive review of the Zoology Department at the University of Melbourne, and recommendations that there should be greater emphasis on developmental biology in the school, led to your being appointed to the Chair.
That's right. The job was advertised in 1990, when I was still at Monash. My salary at that stage was coming from my ability to get grants, which depended entirely on whether I was lucky enough to get a committee which saw value in using marsupials as a biomedical model. I suppose about half of the people, about half of the time, couldn't see any reason why an Australian mammal might tell us anything about medical research. It was always very much on a knife edge as to whether we would get funded or not. Roger was going to be due for retirement within a few years of that time and I thought, 'Well, we've got two young children. If my grant doesn't get up and Roger is retired, it'll be awfully difficult educating them on one pension.' When I started my NHMRC Fellowship, there was no pension, no superannuation associated with it; that only came in during the last year. I'd lost my superannuation from Murdoch when I left there, because I was on a non-pensionable arrangement. So I thought I had better throw my hat in the ring at Melbourne University, and was lucky enough to be offered the job. I moved over here in 1991.
Then Roger, a week before he was due to retire in '95, resigned and took up a professorial fellowship at Royal Women's Hospital. So now we're both at Melbourne University, but we still live close to Monash. That gives me a long drive every day, which I don't enjoy much, but Zoology is a wonderful department and we've built it up to be one of the strongest departments on marsupial biology anywhere in Australia. And of course it still has its other strengths – marine biology, evolutionary and behavioural biology, and neuroscience, although that really is not so strong as it used to be. It was established by Burnstock when he was the head of department, and a number of those people have actually moved elsewhere in the university and elsewhere in Australia. We still have an active neuroscience research group, but largely funded by NHMRC, and the students aren't so interested in that as they are in conservation, reproduction and development, and behaviour.
So you find the students are still quite interested in studies on Australian fauna?
Yes, both the marine fauna and the terrestrial fauna, particularly marsupials. One of the things I've done is to encourage long field courses, much like our Booligal trip but different in some aspects. We run a week-long field course on marsupials and monotremes, and there are two summer week-long courses in marine biology, one on marine ecology and one on marine invertebrate biology. The students just love those three courses, which are the most popular ones and also very important for teaching biology.
There is a huge demand but you can only deal with small numbers. We have quotas of 35 for the marine courses and 40 for the marsupial one, because you can't transport larger numbers, you can't take them to the field sites, you can't sleep them, you can't do the field. If we could cope with 100 students, there would be more than 100 students who would want to do each of those. But even at the level we're able to run it at, it's one of the things that lead to graduate students and honours students, and it's a reason why this department has one of the best reputations for students, not only in the university but in Australia. We did very well on the course experience evaluation questionnaire, being one of very few departments singled out for Brownie points. It's been great fun building that up, and it's good to see that now we have also got a very large graduate school in the department.
Your career is still progressing in a splendid way and I hear that just this last week you've been awarded a medal in America. What is that?
It is the Gold Conservation Medal for 2000, awarded by the Zoological Society of San Diego. Such hugely eminent people as George Schaller, Jane Goodall, David Attenborough, the Duke of Edinburgh and E O Wilson have been awarded this, and I don't feel I belong in that category at all. But it was a great honour and a wonderful recognition, for me and my students and colleagues, of the value of marsupial research and that you can do it if you put your heart into it.
It's a great recognition, and you've been a tremendous advocate of marsupial studies. Thank you very much for talking to us today.
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