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.

Spotlight on invertebrate phylum: Dicyemida

I’ve had a new gig for a couple of months now, lecturing in invertebrate biology and ecology at the University of the Sunshine Coast. As such, I’m rediscovering all kinds of information that I first learned many years ago, including lots of stuff about the ‘small’ invertebrate phyla. These are groups that are small in number not in body size, represented by relatively few taxa, and often overlooked because of the sheer magnitude of taxa in the other, ‘bigger’ phyla.

Everyone knows insects and their relatives – spiders, crabs, millipedes etc. Everyone knows snails, octopuses, sea stars, jellyfish, and, thanks to Finding Nemo, anemones. But what about the little groups? Who knows about the gastrotrichs, the bryophytes and the chaetognaths? Therefore, over the coming weeks I’m going to celebrate some of the smaller groups. I thought I’d start with one of the weirdest.

Phylum Dicyemida

Dicyemids are small, worm-like metazoans. Approximately 112 species of dicyemids have been described, and they live as parasites in renal sacs of cephalopods (Catalano 2012). The body plan of the Dicyemida is quite simple, with a total number of cells ranging from 8-40 (depending on the species), with the ciliated peripheral cells arranged in a kind of spiral formation around a central elongated axial cell (Catalano 2012, Suzuki et al. 2010). In essence, they wear their peripheral cells like a jacket around their axial cell. Their ‘head’ is a calotte, where they use the slightly differently-shaped cells at the anterior end to attach to the renal lining of their host (Suzuki et al. 2010). Dicyemids have no differentiated organs, nor any body cavities.

While the body plan of dicyemids is extremely simple, their reproductive biology is, by contrast, fairly mind-boggling. Dicyemids have a complicated sexual/asexual reproductive cycle, involving two kinds of morphotypes as represented in the following diagram (from Furuya and Tsuneki 2003):

dicyemid reprod

Life cycle of dicyemids. Abbreviations: A apical cell, AG agamete, An axial cell nucleus, AX axial cell, C calotte, DI developing infusiform embryo, DP dipolar cell, DV developing vermiform embryo, IN infusorigen, MP metapolar cell, PA parapolar cell, PP propolar cell, UP uropolar cell.

All of the reproductive activity of dicyemids occurs in the ctyoplasm of the axial cell. Essentially, what happens is this:

  • The nematogen is produced asexually, from vermiform embryos. Nematogens can continue to produce vermiform embryos and cycle along like this.
  • However, vermiform embryos can also form hermaphrodite rhombogens (instead of nematogens), which produce haploid gametes that are fertilised internally.
  • Sexually-produced embryos arising from this are called ‘infusiform’ and they leave their parent and are free-living in the sea until such time as they find an octopus kidney to settle down in. Whereupon they produce gametes asexually and vermiform embryos are formed. Precisely how they do that, however, is not known.

The reason for the asexual/sexual switch is not known. It is speculated, however, since host opportunities are relatively rare, that asexual reproduction in the same host site will enable the dicyemid population to survive. The trigger for sexual reproduction to take over as the dominant mechanism is not known, but may be linked to density of dicyemids in the host tissue (Furuya and Tsuneki 2003).

Dicyemids are frequently host-specific, and most likely evolved from free-living ancestors. Hence, their asexual reproductive cycle is probably an adaptation to living as a parasite (Furuya and Tsuneki 2003). In terms of phylogeny, dicyemids have been assumed previously to related to platyhelminths, presumably because of their worm-like morphology and parasitic ecology. However,more recently, dicyemids have been found to be more closely related to annelids (Suzuki et al. 2010).

References

Catalano (2012) A review of the families, genera and species of Dicyemida Van Bereden 1876. Zootaxa 3479, 1-32.

Furuya and Tsuneki (2003) Biology of dicyemid mesozoans. Zoological Science 20, 591-532.

Suzuki et al. (2010) Phylogenetic analysis of dicyemid mesozoans (Phylum Dicyemida) from innexin amino acid sequences: Dicyemids are not related to Platyhelminthes. Journal of Parasitology 96, 614-625.

Monday Awesome: Total solar eclipse in Queensland

OK, so it happened last Wednesday, but it was amazing. I didn’t get to see the whole thing as it was rather cloudy, but the clouds parted during totality and I got a glimpse of the completely covered sun.

Here’s one of the best photos I have seen of it, taken by CairnsDiveAdventures (@cairnsdiver) from Twitter:

Solar eclipse, Cairns. Photo via CairnsDiveAdventures.

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.

Monday awesome: tassie devil

I’m at a parasitologist conference with limited Internet. It’s in Launceston, Tasmania – not far from the place where devil facial tumour disease was discovered. I’ll write a piece on this disease later (when I have more time!) but for now, here’s a pic of a healthy devil spotted at the conference.

20120702-234440.jpg

Monday Awesome: Walking the ducks.

screenshot of the video

This was spotted over my morning coffee today and I knew it had to got straight to the Awesome post. It is a video (linky below, I can’t embed the whole thing) of a duck farmer.

A farmer in China, Hong Mingshun, takes his ducks for a walk to a new area to feed and swim. It’s sort of like a field trip I think, they do this a few times a year. He says that the ducks like to hang out somewhere new. The awesome thing about this is that he has 5000 ducks! I thought it would be like herding cats, but as you’ll see in the video, everyone’s very orderly.

http://media.theage.com.au/selections/farmer-takes-his-5000-ducks-for-a-walk-3401978.html