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In the beginning

What is its name?

This tiny marsupial lived alongside the Aboriginal Noongyar people in the south-west of Western Australia. For some thousands of years, they shared the sweet nectar produced from the ancient species of plants that predominated in the south-west of Western Australia. The Noongyar called it 'noolbenger' and, today, it is the totem animal for some of the Noongyar people.
When Europeans arrived in the early nineteenth century, they noticed the little animal curling the end of its tail around small twigs while it licked nectar from flowers and called it a 'honey possum' or a 'honey mouse'.
In February 1838, a French natural historian, who was an advisor to the faculty of zoology in the Muséum d'Histoire Naturelle in Paris, visited Western Australia collecting specimens. Jules Verreaux was also a taxidermist and he returned to France with a stuffed specimen, recognising it as unknown to the scientific world. A colleague at the Museum, Mr Gervais, notified the Zoological Society of London on the 11th January, 1842 of this new species from Western Australia, naming it Tarsipes rostratus, within a new Family name of Tarsipedidae. The news was published in Paris in L'Institut on 3rd March, 1842.
By coincidence, again in March, Captain George Grey, a keen naturalist and the Governor of South Australia, sent a skin of a honey possum, together with a description, also to the Zoological Society of London, suggesting that it be named Tarsipes spenserae, after his wife, Lady Spencer. These findings were published by the Society on 8th March, 1842. With typical British bias against the French, the scientific name for the honey possum was accepted as Tarsipes spenserae for nearly 150 years and it is only recently that the earlier claim by Gervais and Verraux (albeit by only 5 days) has been recognised (Mahoney, 1981).
The original type specimen of Tarsipes rostratus can be seen today in the vaults of the Natural History Museum in Paris (see Picture).

Where did the honey possum come from? Recent DNA studies suggest a close relationship with the monito del monte (Dromiciops gliroides) - a small possum-like marsupial from Chile in South America (Palma, 2003; Palma and Spotorno, 1999). The ancient ancestors of Dromiciops are the microbiotheriid fossils and these have been found in South America, Antarctica and South Australia; an indication that these early marsupials invaded Australia from South America and Antarctica when all were part of the great southern land mass called Gondwana. Australia drifted from Antarctica first, breaking the connection with South America about 45 to 40 million years ago, and the subsequent differentiation (or derivation) of these microbiotheriid ancestors into the present-day marsupials in Australia is being investigated by molecular analysis (Kavanagh, Burk-Herrick, Westerman and Springer, 2004). The honey possum shares characteristics with the wallabies, kangaroos and dasyurid marsupials but it may have been specialising, alone, as a nectar feeder for more than 40 million years (Nilsson, Arnason, Spencer and Janke, 2004), given that the West-Australian biota was rich in Proteaceae and Myrtaceae (the food plants of the honey possum today) as early as 57 million years ago (Hopper, Harvey, Chappill, Main and Main, 1996).

Is it a possum?
Although it is called a possum, perhaps because of its prehensile tail that clings to small branches for stability, it appears to be only very distantly related to them, being classified as a single species in a monotypic genus, either as the sole member of the super-family Tarsipedoididae (Kirsch, 1977) or of the family Tarsipedidae within the super-family Petauroidea (Kirsch, Lapointe and Springer, 1997).

Where does it live?
Only in the south west corner of Western Australia, from south of Geraldton across to Esperance.
Each dot on the distribution map indicates the location of a specimen in the collection of the WA Museum.
The lines are isoflors, joining points of equal plant species richness within the Family Proteaceae (after (Hopper, 1979)) the numbers of species being shown.

Can it travel far? There is very little difference either in the genetic structure or the external appearance between honey possums collected from the northern and southern parts of their range (Bryant, Spencer, Bradley and Wooller, 2000). As well, it has one of the highest levels of genetic variation found in vertebrates, indicating a significant level of out-breeding (Bryant, 2004). These studies indicate that honey possums in the recent past were able to move freely throughout this area and interchange their genes. Individual animals are also surprisingly mobile. Radio-tracking honey possums with radio-transmitters weighing 0.7g revealed one animal travelling 500m one day and pollen, identified on the snout of 3 honey possums, could only be traced to Banksia occidentalis, located several kilometres away (Bradshaw, Phillips, Tomlinson, Holley, Jennings and Bradshaw, 2007)

What does it eat? Field biology of the honey possum commenced in the 1980s with a long-term study of the feeding biology and population dynamics of animals in the Fitzgerald River National Park on the south coast by researchers from Murdoch University. These workers identified the food plants of the honey possum as belonging mainly to the plant Families of Proteaceae, Myrtaceae and Epacridaceae (Wooller, Russell and Renfree, 1984), although they have been recorded as eating from grass trees and kangaroo paws.

How does it eat? The honey possum has a very specialised upper and lower jaw, as well as an extraordinary dental system, described in detail by Gervais (Gervais and Verreaux, 1842). He notes that the lower jaw bones and the teeth are 'transparent'. The teeth are greatly reduced, except for the two front teeth in the lower jaw. These form a keel-like structure, supporting the tongue as it moves in and out of the mouth about 4 times a second. The adaptations of the mouth and digestive system to its specialised diet (Richardson, Wooller and Collins, 1986) include an elongated snout and a long tongue containing many surface projections (or papillae) that help to collect the pollen, which is then scraped off by a series of combs on the roof of the mouth. The contents of the pollen is digested during its 6-hour passage through the stomach and intestine, as practically all the pollen grains that are excreted in the faeces are empty.

How much does it eat? A study of the kidneys revealed that the honey possum is capable of drinking large amounts of fluid, up to twice its body weight per day (Slaven and Richardson, 1988) but studies in its natural environment by (Bradshaw and Bradshaw, 1999), using isotopic turnover techniques, determined the precise amounts of pollen and nectar and found that, on average, a 9g honey possum drinks 7ml of nectar and eats 1g of pollen each day.

Is this enough? The amount of energy in this quantity of nectar is enough to fuel the high metabolic rate of honey possums when they are active in their environment (Bradshaw and Bradshaw, 1999). Mammals also need nitrogen to make body protein. Once grown, these needs include the small amounts required for processes such as the repair of tissue and the synthesis of enzymes. For the honey possum, this minimum requirement is about 2.6 milligrams (mg) of nitrogen each day (Bradshaw and Bradshaw, 2001).
Honey possums have few young when compared with other marsupials of similar size (Russell, 1982). The production of young requires greater amounts of nitrogen, especially while the young are in the pouch as the mother needs to provide milk (rich in protein) for about 8 to 9 weeks (Russell, 1986). Practically all the nitrogen has to come from the pollen that she eats. Pollens vary in their nitrogen content, and can be as low as 1% (Faegri and van der Pijl, 1971). Banksia, however, has a high nitrogen content of 4.6% and the daily intake of 0.7-1g should provide the honey possum with 28 to 40 mg N per day. This is more than enough (Bradshaw and Bradshaw, 2009).

Do honey possums get stressed? Researchers who have kept honey possums in captivity have observed aberrant behaviour, which appears to have been the result of stress (Fairfax, 1979; Vose, 1972). A reliable indicator of stress is the increase of the steroid hormone, cortisol, secreted from the adrenal gland in marsupials (McDonald and Bradshaw, 1977). It is cortisol that stimulates the increase in energy required by an animal to escape from danger and honey possums have extremely large adrenal glands when compared to their body size. In addition, honey possums kept in small cages had higher levels of cortisol when they were taken from their cages and further confined for weighing, as well as having their pouches examined (Oates, Bradshaw, Bradshaw, Stead-Richardson and Philippe, 2007).

How do they breed? The female honey possum, like many mammals, regularly produces eggs in the ovary that ovulate and pass into the 2 uteri, where they will meet up with the spermatozoa from the males and develop into embryos. The interval between each production of eggs is an average of 23 days (Oates, et al., 2007).
The males are very interesting. They are smaller than the females and have extremely large testes (that produce the spermatozoa), representing about 4.2% of their body weight (Renfree, Russell and Wooller, 1984). As well, the spermatozoa are the largest of any known mammalian sperm (Woolley and Scarlett, 1984). Using genetic markers, scientists have shown that the embryos in the one female have been fertilized by sperm from different males (Bryant, 2004), a process known as sperm competition. In other words, the male that can produce the most spermatozoa that can move the fastest to reach the egg, succeeds in passing on his genes to the next generation of honey possums. Male honey possums seem very well equipped to do just that!

How do the young develop? The embryos of the honey possum are tiny when they are born, the size of a grain of rice (Renfree, et al., 1984), but still manage to climb across the mother's fur, find the pouch and attach themselves to a nipple. They do this in the short time before the next group of eggs ripen and ovulate from the ovary. While they are in the pouch, the mother mates again but these new embryos are prevented from developing beyond a round ball of cells (called a 'blastocyst') by the action of the young in the pouch (called 'joeys') suckling on the teat - a process that is common in kangaroos and wallabies (Renfree, 1979). When the joeys grow and finally leave the pouch, the blastocysts may resume their development and be born a few days later (Oates, et al., 2007). But, not always! The mother has the ability to keep the embryos for longer periods and may appear to wait for a signal, such as a decrease in the length of daylight when days shorten (Bradshaw, Everett and Bradshaw, 2000; Oates, Bradshaw and Bradshaw, 2004). Or, it may be when food supply is better, such as the spring season, when more flowers bloom.

How often? Research in two southern areas of their range has shown that honey possums breed 2 or 3 times a year, depending on the richness of their environment (Wooller, Renfree, Russell, Dunning, Green and Duncan, 1981). Their periods of reproduction occur during an increase in the number of flowers (Wooller, Richardson, Garavanta, Saffer and Bryant, 2000), which is possibly linked to an increased rainfall during the previous year (Wooller, Richardson, Garavanta, Saffer, Anthony and Wooller, 1998). In another region, of poorer flower production, the numbers of honey possums in the population were highest two years after higher rainfall (Bradshaw et al., 2007). Interestingly, in this later study, capture rates of honey possums were highest during the periods of low barometric pressure. What does this mean?
The production of 2 to 3 young each time during 2 to 3 breeding periods a year makes an easy calculation of 4 to 9 young a year. As females become sexually mature when they are 7 to 8 months old and only live for about 3 years, this allows them to produce about 20 young in a lifetime - not many for a mammal of this size.

Is it enough? It must be, because they have been living undisturbed for many millions of years, leaving enough offspring to maintain the populations. Few young can be interpreted as the sign of very successful breeding. Many factors have contributed to this, such as: - enough to eat, healthy young with genetic variability that help them adapt to a changing environment, the quality of the maternal care, weather conditions that maintain their environment.

Will it be enough for the future? In the long term, like all other animals, the main danger for the honey possum is the loss of their habitat. As more and more ground is cleared for agriculture and urban development, there is less habitat available for the animals that lived there. In the short-term, the destruction of their food supply by plant disease and bush-fire are catastrophic. They, and their food, are killed by fire. But fires have always occurred naturally during their long stay on Earth, and the populations have managed to survive them. Two studies have investigated the effect of bush-fire on 2 populations in the south-west of Western Australia. In both, the honey possums were able to re-invade the burnt territory from an unburnt refuge area after a few years, when some plant species were able to grow and produce flowers. But a viable population that depends on the full suite of mature flowering plants requires at least 20 to 30 years after a fire (Bradshaw, et al., 2007; Everaardt, 2008). The interval of natural fire (i.e. caused by lightning) in these southern regions has been 30 to 100 years (Hassell and Dodson, 2003).
The slow rate of reproduction of honey possums evolved in a benevolent environment of infrequent and irregular fire. It is likely that it will not be enough to sustain future populations exposed to fire at more frequent intervals.


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Honey Possum South West, Western Australia
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