Field Scat Used as Non-Invasive Research Technique on Elusive Desert Tortoises

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Mojave Desert tortoises are elusive creatures that are often difficult to study in the field. Published in a new issue of Chelonian Conservation and Biology, researchers test a non-invasive research technique using field scat to collect DNA and positively identify individual tortoises.

Chelonian Conservation and Biology Volume 18 Issue 2

Chelonian Conservation and Biology Volume 18 Issue 2

“Sometimes even what might appear to be basic information (such as how many tortoises reside in an area, how they interact with each other and how far and how often they roam) can be difficult to determine because tortoises are elusive.

Chelonian Conservation and Biology—The Mojave Desert tortoise may be an icon of its ecoregion, but researchers struggle to gather even basic information about this shy, burrowing reptile. Its scat, however, is easy to find and collect. The stool can be used to identify individual animals, allowing agencies to monitor this threatened, federally protected species.

As reported in the current issue of Chelonian Conservation and Biology, researchers from the U.S. Geological Survey and University of Nevada, Reno, compared protocols for extracting DNA from scat samples to determine the genetic makeup of individual tortoises and identify the ideal method for desert tortoise studies. Such scat genotyping has been helpful in studying mammals, and the technique is touted as being non-invasive to animals and their habitats. Until now, relatively few studies have applied it to tortoises.

“Sometimes even what might appear to be basic information (such as how many tortoises reside in an area, how they interact with each other and how far and how often they roam) can be difficult to determine because tortoises are elusive,” said researcher Amy Vandergast. “Their sign, including scat, can be easier to find. Because all individuals shed epithelial cells in their stool, scat that is found during field surveys provides another means of identifying individuals using molecular markers.”

The researchers tested six DNA extraction protocols on scat samples collected from a threatened tortoise species, Gopherus agassizii, in the Mojave Desert area in southern Nevada and California. They aimed to find out whether they could accurately identify individual tortoises from stool samples and hoped to pinpoint the ideal tool for genotyping the samples and using the genetic markers to monitor tortoise populations.

The study found that sample quality was paramount; the caliber of the genotype depended more heavily on the quality of the DNA sample than the type of extraction method used. Despite a relatively small sample size, 30 percent of field-collected scat and 70 percent of fresh scat were genotyped accurately. The researchers decided that the Qiagen DNeasy Plant Mini extraction kit extracts DNA most efficiently from tortoise scat.

The results of the study indicate that collecting scat in the field and analyzing the DNA can supplement standard survey and monitoring techniques. With additional information from the DNA extracted from scat, researchers and management agencies could learn more about the population dynamics, relationships and movements of individuals throughout the tortoise species’ range.

Full text of the article “Development of a Genotyping Protocol for Mojave Desert Tortoise Scat,” Chelonian Conservation and Biology, Vol. 18, No. 2, 2019, is now available at https://www.chelonianjournals.org/doi/full/10.2744/CCB-1394.1.

About Chelonian Conservation and Biology

Chelonian Conservation and Biology is an international scientific journal of turtle and tortoise research. Its objective is to share any aspects of research on turtles and tortoises. Of special interest are articles dealing with conservation biology, systematic relationships, chelonian diversity, geographic distribution, natural history, ecology, reproduction, morphology and natural variation, population status, husbandry, community conservation initiatives and human exploitation or conservation management issues. For more information, please visit [http://www.chelonian.org/.

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Dominique Scanlan
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