Research

photo of the habitat of the Hairy-nosed wombat

The southern hairy-nosed wombat, Lasiorhinus latifrons, is a large, burrowing marsupial of South Australia (map). Despite this species' prominence in terms of burrow excavations (which have even been detected from space!) and body size, much of its social and population biology remain unknown because it is elusive and primarily nocturnal. Recent advances in molecular techniques accompanied by a battery of powerful analytical tools means that many questions about population processes and responses to perturbation are now approachable, even for cryptic species.

I used highly-resolving genetic markers called microsatellites to investigate three timescales of molecular change, which provide information about three corresponding levels of population biology. Social organization, relatedness, and dispersal of individuals - within-population processes that operate on the shortest of timescales (genotypic) - were examined in continuous and fragmented habitats. The distribution of alleles among populations - intermediate in timescale (genic) - enabled inference of between-population processes such as gene flow and elucidation of short-term population history. The degree to which southern hairy-nosed wombat populations were subdivided prior to European colonization - information at the longest timescale (genealogical) - is being determined by examining allele phylogenies.

This project, under the guidance of Drs. Andrea Taylor and Paul Sunnucks, is among the first studies to examine all three levels with a single molecular marker, as well as to be entirely based upon DNA procured from non-invasively collected hair.

Hairy-nosed wombats

The southern hairy-nosed wombat, Lasiorhinus latifrons, exists in five regions in South Australia, although fossil evidence suggests that its distribution was once more continuous. Agricultural practices and competition with rabbits likely precipitated its decline. Although it is not endangered, there is reason for concern since many of the ingredients are present that led to the near-extinction of its congener, the northern hairy-nosed wombat, L. krefftii. That species is Australia's most endangered marsupial, existing in a single colony in Queensland. Andrea Taylor found that it has a relatedness structure highly unusual for mammals, in that same-sex but not opposite-sex relatives shared burrows more than expected. This may be a response to isolation, or may reflect normal population processes, something I hope to elucidate in the southern species.

Hairy-nosed wombats are arid-adapted and live in interconnected burrow systems called warrens. Wombats are by far the largest herbivorous burrowers.

Non-invasive Sampling

I collected hair by suspending double-sided sticky-tape between two stakes placed on either side of burrow entrances. As wombats entered or exited their burrows they kindly made hair donations, from which I extracted DNA from individual follicles. This method is particularly effective because it does not disrupt animal movements, and also because hairy-nosed wombats are notoriously difficult to trap. It required about a week of collecting and replacing tapes from 250 or so burrows to ensure that I detected every wombat that used an area, and to secure good burrow-use information. I also placed individuals into age-classes by measuring footprints left in flour at the base of tapes.

DNA extractions, from single hairs, were performed in the field while hair was fresh off the wombat. In the lab I then used 15 of an available 28 hairy-nosed wombat loci to generate DNA profiles for each individual. Gender was determined via a sex-linked marker.

Social Organization and Dispersal

I defined social organization and dispersal in large, contiguous populations, and then investigated how these are altered by long-term isolation. The former is unknown for this species, and the latter is a query into the determinants of population declines, also having conservation implications for its endangered relative (the northern hairy-nosed wombat). These population processes, very difficult to study using traditional means, are relatively straightforward to quantify with molecular markers since they are reflected in relatedness and genetic structure. Being measurable, they enable examination of the proximate mechanisms of extinction, something that has received very little attention in any animal group.

Continuous Habitat

Non-fragmented environment

To characterize population processes in non-fragmented environments, I sampled biannually (in and out of the mating season) for three years at Brookfield Conservation Park in the Murraylands of South Australia. I also sampled a population on the Nullarbor Plain, a very remote area at the far western extent of their range. The hard limestone shelf that covers much of the Murraylands, and which may restrict burrowing sites, is further below the soil surface on the Nullarbor. This may influence group size and social organization - something I hope to determine.

Fragmented Habitat

To examine the effects of habitat fragmentation on population processes it was first necessary to identify isolated populations, a species-specific parameter that is not obvious simply on the basis of geographic proximity. To do this I used historical records and constructed GIS maps to locate candidates across the species' range, and then sampled them non-intensively. Genotypic data from the 14 candidate populations were analysed with a powerful combination of genetic methods to identify those that are effectively demographically isolated.

Two populations exhibited genetic signatures of isolation, one likely due to geography and the other agriculture, and both of these populations were extensively resampled. This work illustrates that a molecular approach can be employed to screen populations for evidence of isolation resulting from habitat fragmentation, even when little information is available about what might constitute fragmentation for the study species.

Isolated population at the head of a canyon

Isolated population surrounded by cropland

Map of species distribution and study sites

FOR RESEARCH RESULTS, SEE RESULTS PAGE

Relevant papers

Beheregaray, L.B., Sunnucks, P., Alpers, D.A. & Taylor A.C. (2000) A set of microsatellite loci for the Hairy-nosed wombats (Lasiorhinus krefftii and L. latifrons). Conservation Genetics 1, 89-92.

Sloane, M., Sunnucks, P., Beheregaray, L.B., Alpers, D.L. & Taylor A.C. (2000) Highly reliable genetic identification of individual northern hairy-nosed wombats from remotely collected hairs: a feasible censusing method. Molecular Ecology 9, 1233-1240.

Sunnucks, P. (2000) Efficient genetic markers for population biology. Trends in Ecology & Evolution 15, 199-203.

Taylor, A.C., Horsup, A., Johnson, C.N., Sunnucks, P. & Sherwin, W. (1997) Unusual relatedness structure detected by microsatellite analysis, and parentage analysis in an endangered marsupial, the Northern Hairy-nosed wombat, Lasiorhinus krefftii. Molecular Ecology 6: 9-20.

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