Behind the paper: using DNA to define conservation units for endangered dragons

This week, we have a new paper published online in the journal Conservation Genetics, with former Honours student Emma Carlson as lead author. The paper is titled “How many conservation units are there for the endangered grassland earless dragons?

Yes, that’s right, dragons! But not the fire-breathing sort. The grassland earless dragon (Tympanocyrptis pinguicolla) is a feisty, but tiny, agamid lizard from south-eastern Australia. As you can see from the pictures below, they can also be incredibly cute!

Once upon a time, there were likely many more earless dragons, making their homes in spider burrows and rock crevices throughout the region’s native temperate grasslands. Now, the species is restricted to just two areas: one in and around Canberra, Australia’s bush capital, the other in the Monaro region around the town of Cooma. Unfortunately it is not just the dragons who like the temperate grasslands, people do too. Much (possibly as much as 99%) of this ecosystem has been lost to agricultural and urban development, and grassland specialists like the earless dragons have suffered large declines in both range and population sizes, likely because of habitat loss and fragmentation, and the effects of severe droughts.

Fortunately, it is not too late to save the earless dragon. If we can protect more of their remaining habitat from development, and ensure that the remaining populations are large enough to be sustainable, this fairy tale may one day have a happy ending. You can read more in the National Recovery Plan. But we still have a lot to learn about the earless dragon and what it needs to survive. Have other factors apart from habitat loss contributed to recent population declines? How might climate change and severe droughts affect earless dragon foraging and reproductive behaviours? Can we establish insurance captive breeding populations [edit – this is already happening and captive breeding seems to be very successful – thanks to Lisa Doucette for updating me on this]?

One extremely important thing to know is just how many dragon populations – or even species – we are actually dealing with.

You see, above, I used the word “species” and I called all of these earless dragons by the same name, Tympanocyrptis pinguicolla. This is how they are currently “officially” recognised taxonomically, but there is compelling evidence that we may not actually be dealing with a single species at all, and definitely not a single population. For example, phylogenetic studies by Scott and Keogh (2000) and Melville et al (2007) identified significant mitochondrial genetic divergence between the Canberra and Cooma dragons, suggesting it has been at least 1.8 million years since these lineages shared a common ancestor.

I’ve written before about cryptic species and how being able to delineate closely related species pairs is important for conservation management. This is because we aim to protect all independent evolutionary lineages. The trouble is, there are many different species concepts out there that could be used to define species. We also know very little about geographic distributions, reproductive behaviours and hybridisation for many rare and threatened taxa, like the earless dragons, which makes it rather difficult to apply these species concepts in practice. So, how can we decide which populations constitute “valid” taxonomic species so we can implement appropriate conservation plans before they go extinct?

Well, I never thought I’d say this, but herein lies the beauty of the current Australian legislation. You see, the Australian EPBC Act (1999) allows a biological entity (e.g. a population, sub-species or putative new species) to be classed as a “species” for the purposes of conservation, just as long as there is sufficient evidence that it constitutes a distinct population of individuals that can produce fertile offspring or that are derived from a common gene pool. So, never mind waiting for the biologists to sort out all the minute taxonomic details, the Minister can choose to designate conservation units based on the best available evidence!

Which means… you guessed it… to work out how to save the earless dragon, we need the best available evidence… which is where our latest paper comes in.

A couple of years ago, Honours student Emma Carlson conducted the first comprehensive population genetic study of the extant grassland earless dragon populations, using microsatellite markers to genotype animals from both Canberra and the Monaro. Previous studies used markers from the maternally-inherited mitochondrial genome. To complement this work, we used markers from the nuclear genome, which is inherited from both parents and so provides a broader perspective of a population’s evolutionary history. So what did we find?

Well, the main result arising from Emma’s work is evidence for three distinct genetic clusters, or lineages, of grassland earless dragons. One of these lineages includes all animals sampled from the Monaro region, and none of the Canberra animals. The other two lineages represent sites from the north and south of Canberra respectively, which are separated by the Molonglo River, a natural barrier to dispersal.

In conjunction with the earlier phylogenetic studies described above, this provides very strong evidence that the Canberra and Monaro grassland earless dragons constitute two geographically and genetically isolated populations. For these reasons, we suggest that these groups should be recognised as two Evolutionarily Significant Units (ESUs) as defined by Moritz (1994). We cannot make the same definitive statement that the northern and southern Canberra lineages should also be classed as ESUs, because we only have evidence of genetic distinction between these groups at nuclear markers, and not from the mitochondrial genome. However, given that we were unable to detect gene flow between the northern and southern Canberra populations, we go further to suggest that all three lineages identified should be treated as distinct conservation management units.

Our results have a number of implications for management of the grassland earless dragon. First, and perhaps most importantly, the majority of sites from which they are known lie outside of nature reserves and protected lands. If all grassland earless dragons were representatives of the same lineage, then this might not be a problem, as long as sufficient animals were protected in the existing reserves. But now we have three distinct lineages to protect…

In the Monaro region, grassland earless dragons have a widespread but fragmented distribution, predominantly in agricultural land but with large areas of native vegetation that may still enable some connectivity among sites. Historically, dragons seem to have survived quite well in this area despite extensive livestock grazing, but things may be changing. Only one known grassland earless dragon site in this region is in a protected reserve, and recent surveys at that site were not able to detect the species (McGrath et al 2015). It will be important to ensure better protection for native grassland habitats in the Monaro, and to encourage movement of the dragons through this landscape to facilitate gene flow.

In Canberra, both the northern and southern dragon lineages are more seriously affected by habitat fragmentation. Sites where dragons occur are separated by high densities of roads and buildings, and include land occupied by an airport, a military training facility, agricultural grazing leases, a prison, and other commercial properties. While most sites in southern Canberra are now protected in nature reserves, none of the northern Canberra sites are similarly protected. This means that better habitat protection for the northern Canberra dragon lineage is a priority, especially as this region is under pressure from urban development. In addition, recent dramatic population collapses at some Canberra sites suggest that much of the suitable habitat is now too fragmented to allow animals to disperse between sites. This means that if a stochastic event, like a severe drought, were to wipe out most of the dragons from one location, it may be very difficult for individuals from elsewhere to recolonise those areas. Gradually, one by one, these little pockets of dragons might disappear. For this reason, within southern Canberra, maintenance of connectivity between nature reserves may be the key to the long-term survival of the grassland earless dragon.

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