Wombats: furry, subterranean, and occasionally terrifying.

Common wombat (image from http://www.australianmuseum.net.au, © G A Hoye/Nature Focus)

Wombats: moving footstools.

The marsupial family Vombatidae comprises three species: the northern hairy nosed (NHN)(Lasiorhinus krefftii), the southern hairy nosed (SHN) (Lasiorhinus latifrons) and the common (Vombatus ursinus). Adult wombats are around 30cm tall, rectangular in shape (80-100cm long) and weigh between 20 – 35kg (Van Dyck & Strahan 2008). I’ve always thought they look more like footstools than most other animals. The shape is not for putting your feet up after a long day though. Wombats are burrowing machines, and their squat shape is good for moving through tunnels. They also have extra hard patches on the front of their head and on their rump, to compact earthen burrow walls. Common wombats can excavate living quarters in burrows up to 20m long, which can interconnect with other burrows and have several entry/exit points, AND they can have several of these long burrows throughout their home range (McIlroy 2008).

Although wombats have short legs, they can move at up to 40 km/h over short distances if necessary (ref: Australian Museum). Wombats can be aggressive amongst themselves and towards humans, particularly if startled by a person. See here for a story about a wombat attack in 2010.

The NHN wombat is highly endangered, with only a few still living in a moderately secret location near Clermont in central Queensland. The SHN wombat is doing comparatively better, spread across the southern coast of South Australia, and the common wombat is, well, common across Tasmania, ACT, and the eastern parts of Victoria, New South Wales and South Australia.

Why are wombats so cool?

Because they live underground and minimise their exposure to hot daytime temperatures by hanging around in their burrows. They emerge in the evenings to browse on grasses, and have an almost rodent-like dentition as a result of this dietary preference. This lifestyle also means that they have very low energy requirements for an animal of their size. Evans et al. (2003) describe wombats as having an “energetically frugal lifestyle”. The field metabolic rate of a SHN wombat (mean 3,141 kJ/day during the dry season) can be as low as 40% of that expected for a herbivore of wombat size (Evans et al. 2003). They also have very low turnover rates for water, and this combined with their underground lifestyle and slow metabolism means that they are excellent at conserving energy. Which is handy for an animal that, in the case of the SHN wombat, lives in an environment that can be extremely hot and/or dry; and feeds on (often dry) grass of poor nutrition content.

Wombat skull. Note rodent-y dentition. (image from http://www.wombania.com/wombat-pictures/wombat-skull.jpg)

What kinds of parasites do ‘energetically frugal footstools’ have?

Several.

Fasciola hepatica. (Image from:

Fasciola hepatica. (Image from:

Helminths:

Wombats are hosts to the agriculturally-important trematode Fasciola hepatica. Although not an important reservoir host, common wombats do seem to be adversely affected by pathology of F. hepatica infection (Spratt et al. 2008). Wombats are also host to eight species of cestodes (Spratt et al. 1991) including the anoplocephalid Progamotaenia vombati (formerly known P. festiva in wombats, but found to be a species complex across wombats, wallabies and kangaroos (see Beveridge & Shamsi 2009)). Common wombats are also known to host the taeniid Echinococcus granulosus (also known as hydatids), but not in high prevalence and only recorded from parts of Victoria, which indicates that they are not a major intermediate host (see Jenkins 2006).

Ectoparasites:

Wombats are host to 6 species of flea genus Echindophaga. Two species of Lycopsyllalasiorhini and nova, are known only from wombats (Dunnet & Mardon 1974, Gerhardt et al. 2000). Wombats also host ticks, including the widespread species Ixodes tasmani, I. cornuatus and Amblyomma triguttatum, and Bothriocroton auruginans and I. victoriensis (which are both known as ‘wombat ticks’) (Roberts 1970, Gerhardt et al. 2000).

But perhaps the most famous wombat ectoparasite is the astigmatan mite Sarcoptes scabei. Causing the medical (veterinary in this case) condition scabies, this tiny mite has jumped from people to domestic animals to wildlife, and can make life very difficult for affected wombats. Heavy mite infestations can cause hair loss and crusts on the skin of wombats, and can cause severe pathology at the site of infestation, and throughout the body of the affected animal (Skerratt et al. 1999). Wombats with severe infestations can die from a combination of the pathological effects, and from starvation caused by decreased ability to masticate their food, reduced ability to compete with healthy wombats for food, and possibly the increased energy demands caused by the severe infestation (Skerratt et al. 1999).

Final word:

Wombats are good as gingerbread biscuits too.

Homemade marsupial biscuits. L-R: bandicoots, wombats, Tas devils. (photo by me)

References

Beveridge I and Shamsi S (2009) Revision of the Progamotaenia festiva species complex (Cestoda: Anoplocephalidae) from Australasian marsupials, with the resurrection of P. fellicola (Nybelin, 1917) comb. nov. Zootaxa 1990, 1-29.

Dunnet GM and Mardon DK (1974) A monograph of Australian fleas. Aust J Zool Supp Ser 30. 1-273.

Jenkins DJ (2006) Echinococcus granulises in Australia: widespread and doing well. Parasitology International 55, S203-206.

McIlroy JC (2008) Common wombat, Vombatus ursinus. In: Mammals of Australia, eds Van Dyck S, Strahan, R. Reed Books, Sydney.

Skerratt LF, Middleton D, Beveridge I (1999) Distribution of life cycle stages of Sarcoptes scabei var wombat and effects of severe mange on common wombats in Victoria. J Wildl Dis 35, 633-646.

Spratt DM, Beveridge I, Walter EL (1991) A catalogue of Australasian montremes and marsupials and their recorded helminth parasites. Rec S Aust Mus Monogr Ser 1, 1-105.

Spratt DM et al. (2008) Guide to the identification of common parasites of Australian mammals. In: Medicine of Australian Mammals, eds Vogelnest L, Woods R. CSIRO Publishing, Melbourne.

Van Dyck S, and Strahan R (2008) Mammals of Australia. Reed Books, Sydney.

Scicomm win: explanatory videos for papers.

Some people I know at ANU have published a review called ‘Conceptual domain of the matrix in fragmented landscapes’ (Driscoll et al. TREE in press, look at it here). They sought to identify how the matrix works in terms of animals moving around in fragmented landscapes (i.e., between patches of remnant vegetation). The authors have also released a short animated video to describe the main findings from their work. This is the cool bit. They’ve managed to condense their research into 4 mins – which is a hard task in itself. Observe:

http://www.youtube.com/watch?v=JZwTZ-d1ZRE

Some journals now include a graphical abstract for works published (e.g., International Journal for Parasitology), where authors of papers provide a picture to represent their work. Making a video takes it a step further, and allows research to be more accessible, particularly for busy people, and interested people across all levels of scientific understanding. For example, reading the paper is probably beyond the comprehension of most school kids. But the video could make an important contribution to an environmental science class and help kids understand sophisticated concepts. Stop-motion animation may be beyond some people’s AV capabilities (me included!), but a video narrated in plain English is a brilliant way to communicate science, and to get your science to reach more people.

 

Science round-up: What morsels have I found this week?

Oh, I have been neglectful. I’ve started a new project and it is leaving little time to wander the interwebs, get distracted reading things and write blog posts.

I have some very mammal-related offerings this week. A new species of African monkey has been described, panic about hantavirus in Yosemite NP is escalating, and population crashes of arctic lemmings is a bad thing.

New monkey species.

Cercopithecus lomamiensis juveniles, image from Hart et al. 2012.

Published in PLoS One, Hart et al. describe the second new species of African primate in 28 years. They don’t say how long it had been beyond that other species 28 years ago. These monkeys are commonly known as guenons, and are semi-arboreal, with records of them using spaces all the way between the canopy and the forest floor. This paper is really neat because it presents a very thorough description, including morphology, molecular data, ecological information and vocalisation data. And, because PLoS journals are online, they included the necessary information pertaining to hard-copy availability of the description (as the manuscript would have pre-dated the changes to the Code of Zoological Nomenclature that I posted about last week). The highlight of the article for me was learning that males of this new monkey have a blue perineum.

Hantavirus in Yosemite.

Peromyscus maniculatus, from Nebraska (photo from IncreasingDisorder’s camera)

Hantavirus is not really a new thing, and but this is the first time that an outbreak on this scale has occured. The virus is rodent-borne, with deermice, Peromyscus spp., being the main culprits. The current outbreak at Yosemite National Park in California has killed 3 people out of the nine confirmed cases so far. But because of the popularity of the site as a tourist destination, officials have sent health advisory notices out to almost a quarter of a million people who have visited the park (info from BBC News). Hantavirus is potentially deadly, so it’s not such a bad thing that these precautions are being taken.

Lemming population crashes are bad….

Stoat with lemming (image via ScienceNOW)

…if you rely on them to eat. Research published in Proc R Soc B and reported by ScienceNOW indicate that recent population crashes of collared lemming populations has had implications for the survival of various carnivores who mainly eat lemmings. As keystone species, the lemmings essentially hold the arctic ecosystems they inhabit together. The natural cycles of population fluctuation observed in arctic lemmings was interrupted by a severe decrease in numbers over the years since 2000. This is thought to be a result of decreased snow cover, and by extension, climate change. Population sizes of lemming predators have also decreased as a result of the population decline.

Devil facial tumour disease (or: Sometimes not everything comes back to parasites)

Last week, I had the pleasure of meeting some Tasmanian devils (Sarcophilus harrisii). They are the largest (extant) carnivorous marsupial, and are quite lovely, with broad, almost dog-like faces, and an odd loping gait that was rather endearing. The devils I met were housed at a wildlife park near Launceston and they are part of a carefully managed breeding program, as an insurance population, for the species. Devils in the wild are currently under siege from a nasty disease, devil facial tumour disease (DFTD), which emerged in northeastern Tasmania in the mid 1990s. The disease was determined to be a kind of cancer, transmitted via biting (McCallum et al. 2007, Lachish et al. 2011). DFTD causes large tumours on the faces and necks of devils, and are very nasty to look at so I’m not going to post any pictures. Devils usually die within six months or so of the development of a cancerous lesion, either by starvation or by secondary infections or metastasis (Deakin et al. 2012). The emergence of DFTD has altered population age structures and caused rapid declines in populations of devils across most of Tasmania (Lachish et al. 2011).

Tassie devils (taken at Trowunna Wildlife Park).

Generally, cancers are not transmissible between hosts/victims, although a notable exception to this rule is canine transmissible venereal tumour (see Belov 2012 for example) which is a sexually-transmitted sarcoma in dogs, so the revelation that DFTD was transmitted between devils prompted a bit of a discussion about whether this new disease was perhaps parasitic. I don’t have a reference for that statement – I remember Hamish McCallum (Griffith University) presenting something about it at a conference a few years back, but could not find any references on this idea. It came up again at the conference I was at last week and was discussed by Greg Woods (immunologist, University of Tasmania). The discussion was subsequently reported in the Launceston Examiner newspaper (July 3) as Scientists have said strong evidence was emerging that the catastrophic Tasmanian devil facial tumour disease should be regarded as a parasite.”, which got me all riled up as it was not true at all. Perhaps they shouldn’t get the work experience kids to write articles for them, but bad journalism and poor communication of science is a whole other argument for another day. Let’s get back to the devils.

So what is it then?

DFTD, as mentioned above, is a transmissible cancer. It is thought that the cancer, which is highly metatstatic, originated from one female devil probably in the early 1990s (Deakin et al. 2012, Murchison et al. 2012). Devils are a fighty bunch. Many interactions, including feeding and reproducing, involve biting each other. Devils usually end up feeding communally on carcasses and biting is used as a communication mechanism in order for everyone to get in and have a snack. Here (below) is a photo I took of some captive devils feeding, and while I watched, a couple more came over for a snack and a bit of fighting was observed as the newcomers jostled for position. The cancer itself has its origins in mutant Schwann cells (which are associated with nerve fibres) and was passed from animal to animal, rather than being a cancer that spontaneously arose independently in animals (Belov 2012). We know this because many cancer samples have been examined, and they have been found to all be clones of each other and their genetic composition is remarkably stable (Deakin et al. 2012). Spontaneously arising cancers would display more genetic heterogeneity in the mutations observed, but this is not seen in DFTD cancer cell lines.

Devils feeding (taken at Trowunna Wildlife Park).

The mechanism by which the cancer arose is unknown, but is probably just a (really bad) random mutation. The reason why it is so dangerous to devils is that it metastasizes quickly (in about 65% of cases), and, somehow, evades the devil’s immune system (Belov 2012). Therefore, the devil does not fight the infection. Tasmanian devils have very low MHC diversity (Major HistoCompatability) (Belov 2012). This is a key aspect of mammalian immune system function, as MHC works towards recognizing ‘self’ from ‘non-self’ in the context of fighting infectious pathogens. Low genetic diversity of MHC would mean that devils may be increasingly susceptible to infection by some pathogens. The result of all this is that devils pass a new kind of cancer to each other, which is highly virulent, and in combination with the devils’ bitey behaviour and slightly wonky immune response that does not recognise the cells as pathogens, kills many devils. Rapid deaths cause population declines, and the threat of extinction (McCallum et al. 2007).

But does that make DFTD a parasite?

In a word, no. Just because this cancer behaves in a different way to which we are accustomed, does not make it parasitic. As we know, canine transmissible venereal cancer is also transmitted between hosts/victims, so DFTD is perhaps not as unusual as first thought. The virulence of DFTD is largely due to its ability to metastasise quickly (killing the host fast), aided by the devil immune system lacking the ability to recognise these cells as pathogens. Although parasites can occasionally cause nasty pathology and sometimes kill their host, it is not in their best interests to do so. DFTD, on the other hand, seems to have no such qualms and if left unchecked, would likely take down the entire species in the wild. While cancer tumours grow in such a way that they are able to acquire nutrients (through angiogenesis in cancerous cells, which is quite a nifty process in itself) from the host’s body, that is a feature of all cancer tumours – in humans and animals. Does that mean that all cancers are therefore parasitic? No. Parasites have a life cycle, for a start, and cancer cells divide by binary fission like other cells. These processes are not the same as each other. Further, parasites are separate, distinct, organisms to their hosts, whereas DFTD has more or less the same DNA as its devil hosts. DFTD cancer cells can be identified as devil DNA.

Final word

DFTD is a transmissible, highly virulent cancer affecting Tasmanian devils. The transmission method of the cancer means that young devils are affected and this causes populations to decline because many devils do not live long enough to reproduce. Thankfully, there is a real push for research into understanding the cancer in order to combat it. Whether that’s a vaccine or something different, I don’t know. It’s too soon to tell. But hopefully a solution will be found before the devils’ populations get to the point of no return.

References

Belov 2012 Bioessays 34: 285–292 DOI 10.1002/bies.201100161

Deakin 2012 PLoS Genetics 8(2): e1002483. doi:10.1371/journal.pgen.1002483

Lachish 2011 Heredity 106, 172–182 doi:10.1038/hdy.2010.17

McCallum 2007 EcoHealth 4, 318–325, DOI: 10.1007/s10393-007-0118-0

Murchison 2012 Cell 148, 780–791 DOI 10.1016/j.cell.2011.11.065