By Dr Jennifer Pierson, Senior Ecologist; and Felicity L'Hotellier, Senior Field Ecologist
High in the hills on Australian Wildlife Conservancy (AWC)'s Mount Zero-Taravale Wildlife Sanctuary, the Sharman's Rock-wallaby lives among rocky outcrops and large granite boulders. At night, they venture out to feed on grass and shrubs in the surrounding woodlands.
This shy wallaby has the most restricted distribution of all the rock-wallaby species, with over half of the known subpopulations found on Mount Zero-Taravale. Our current estimates of the global population is likely less than 1,000 individuals making it one of the rarest rock-wallabies in Australia.
However, the shy nature of this wallaby has made estimating population, and monitoring any changes over time, extremely difficult.
Bread Leue/AWC Currently, AWC implements an extensive camera survey for Sharman's Rock-wallabies every year. Helicopters are used to access remote sites across the sanctuary, in addition to a set of road-based sites, to set cameras and baits in the landscape for four weeks. These camera surveys provide vital information on which sites are occupied by Sharman's Rock-wallabies and can confirm if females are breeding if we happen to capture images of females with pouch young or juvenile animals.
To ensure we are providing the best protection for this species, and our management actions (e.g., fire management program) are effective, we really need to be able to track trends in the subpopulation sizes. Tracking trends helps detect declines in subpopulations before any colonies blink out, as well as detect important increases in response to successful management actions we implement.
Blanche d'Anastasi/AWC AWC ecologists have been busy trialing a new technique to monitor Sharman's Rock-wallabies using DNA in their scat (i.e. scat DNA). We recently used this technique to estimate how many Banded Hare-wallabies were at Mt Gibson Wildlife Sanctuary and on Faure Island in WA. The method relies on a few things:
- Ability to find fresh scat in the landscape
- Background information of genetic diversity in the region (genomic data)
- Develop a targeted panel of informative genes
- Ability to obtain DNA and genotypes from scat
In winter 2024, the first steps were taken to test if this method will work to track subpopulations of Sharman's Rock-wallabies at Mount Zero-Taravale.
Felicity L'Hotellier/AWC Finding fresh scat in the landscape
It may seem like finding a needle in haystack, but sharp-eyed field ecologists are pretty good at finding signs of animals when they are around. During the camera surveys, ecologists tested a couple different approaches to finding fresh scat, and compared if we found more after having baited cameras in the area.
First, we trialed a method using a fixed area, that is defining an area of 20 m x 20 m and trying to do a comprehensive search of the plot. Next, we tried a more opportunistic approach where we looked across the site near the camera in all the places we could access that provide pathways for wallabies to travel. We did this when we first put cameras out and again when we collected them at a subset of our camera survey sites.
We found that opportunistic sampling resulted in higher rates of encountering scat, and surprisingly we found just as much before baits were out as after we baited the sites. This was encouraging that if Sharman's Rock-wallabies are using an area, we will be able to collect scat in the landscape.
Blanche d'Anastasi/AWC Background information of genetic diversity in the region (genomic data)
One of the more challenging aspects of developing the method is obtaining good background data on the genetic diversity of local populations. This data is needed to make sure we select genes that are present in frequencies that are informative.
We need quality tissue from about 20 individuals to get genomic background data. In August - September 2024, we spent two weeks conducting a targeted trapping survey for Sharman's Rock-wallabies in order to get both tissue and fresh scat that matched the tissue so we could test the method.
While we only caught two individuals during this effort, we collected plenty of fresh matching scat which we needed. One of the females had pouch young so we know they are breeding.
Luckily, we were able to collaborate with the Australian Museum, which has the remaining tissue samples we needed to get the background data.
Felicity L'Hotellier/AWC Develop a targeted panel informative genes
Once we know the background genetic diversity of the subpopulations, we can select a smaller number of genes to target for genotyping. By narrowing in on the informative genes that will allow us to identify individuals and what sex they are, we can use sequencing methods that perform better with the low-quality DNA that we can obtain from scat.
For example, using tissue, we might look at thousands of genes across the genome, but we might only need to evaluate ~ 100 informative ones to identify individuals.
Ability to obtain DNA from scat
The final step is to see if we can get DNA that will sequence in the smaller, targeted panel that we designed.
Initially, we will use fresh scat collected during our trapping session to test if we can use DNA from Sharman's Rock-wallabies scat. When we analyse scat we know matches tissue, we know what the correct genotype should be and can test the basic methodology.
If this is successful, we will start testing the scat collected during the camera surveys and try to get an understanding of our general success rate at genotyping scats and what characteristics (e.g. color, sheen, etc.) of the scat indicate success.
AWC If we can get genotypes from scats at a good rate (>50%) then we can design a sampling method to collect scats at Mount Zero-Taravale to start monitoring populations.
Genotypes can be used to identify individuals and their sex, and comparing genotypes can tell us how related individuals are. When we look at how related individuals are in relation to the landscape, we can also start learning about how Sharman's Rock-wallabies might be moving among the rocky outcrops.
This information will greatly improve our ability to make science-informed management decisions to help protect this incredibly rare rock-wallaby.
