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DNA helps map skinks' travels

Wed, 22 Sep 2004

DNA helps map skinks' travels

An endangered skink's DNA has given researchers vital clues to its dispersal patterns and a shortcut to finding how best to manage its habitat. Like many native animals, the grand skink (Oligosoma grande) persists in small groups in a highly modified landscape.

Clusters of up to 20 skinks live on rocky outcrops, separated from similar groups by 50*150 metres of either native tussock grass or pasture, depending on land use. Their long-term survival depends in part on their ability to disperse between patches of habitat. Maximising connections between these patches requires an understanding of animal dispersal behaviour. Unfortunately, dispersal is difficult and time-consuming to measure by traditional methods, which usually involve ongoing observation.

Genetic approaches to measuring dispersal are emerging as potentially less expensive and time-consuming. Landcare Research scientist Dr Dianne Gleeson and PhD student Oliver Berry studied grand skinks at Macraes Flat, inland from Palmerston in North Otago. In a project requiring "rock-climbing skills and cunning", they caught the skinks and collected skin samples from their tails. Mr Berry then used the DNA to identify the skinks that were dispersers or non-dispersers. Dr Gleeson says although skinks are long-lived, results showed that most individuals dispersed less than a few hundred metres in their lifetime.

"This means they often lived on the same rock outcrop as close relatives, and, as our previous research shows, sometimes bred with them.

"Immigrant individuals can be identified by their distinctive genetic fingerprint. We used a database containing genetic information from all the candidate groups that a skink might have originated from, to match skinks to their group. If a skink was more typical of a group it was not captured in, then it was probably a disperser. "In other words, we could show whether Skink A came from Rock A, B or C.

Using traditional field methods, we would normally try to catch the skinks as they run between rocks, which is fairly 'hit and miss'." To test the reliability of this genetic approach, the researchers compared their results with known records of dispersal from a Department of Conservation field study, based at the same site.

"Once we were satisfied with the accuracy of the method, we compared rates of dispersal between skink groups in native tussock grassland and in pasture. "Dispersal rates of skinks separated by pasture are roughly half of those separated by tussock, and skinks in pasture were less genetically varied. Previous studies have shown that populations in pasture are less abundant and more extinction-prone than populations in tussock, possibly because pasture inhibits dispersal and recolonisation of rocks. "However, this is the first time we have been able to see the actual patterns of dispersal."

Dr Gleeson says it is clear that the type of agricultural land use surrounding the skinks does influence dispersal. "This knowledge will help land managers to minimise impacts on skinks without necessarily excluding agricultural development." Another key outcome from the research was the fact that the genetic approach to measuring dispersal produced similar data to the more time-consuming and potentially more expensive observation approaches traditionally used.

"The fieldwork for the genetic project took three months, while the traditional fieldwork (using marking and recapturing methods) took more than seven years to collect equivalent data."

"This has implications for how ecological questions are addressed by scientists in future. Genetic approaches to measuring dispersal are a major area of ecological research internationally." University of Canberra senior lecturer in ecology Dr Stephen Sarre co-supervised Mr Berry's project, and provided expert advice. Future research will include examining the degree of inbreeding among grand skinks, and the dispersal patterns of other endangered skinks.

ENDS

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