Defining the Desert Tortoise, Gopherus agassizii
HOGL has contributed to genetic research for the conservation of Desert Tortoises, Gopherus agassizii, since 1999. Taylor Edwards, along with collaborators Dr. Robert Murphy, Royal Onterio Museum and Dr. Kristin Berry, U.S. Geological Survey Western Ecological Research Center have embarked on a long-term investigation of Defining the Desert Tortoise:
 The study of Berry et al. (Defining the Desert Tortoise(s), 2002) established the necessity of a genogeographic investigation of the desert tortoise, Gopherus agassizii.
Shortly before the paper appeared, a group of researchers established a
team to investigate the genetics of the desert tortoise. All the pieces
fell into place. Dr. Kristin Berry had
been studying the rapid spread of disease in the tortoises using plasma
assays. She saved the red blood cells from more than 800 tortoises. The
blood contained DNA and there was no need for harassing tortoises to
obtain DNA samples.
Taylor Edwards
had developed a suite of microsatellite DNA markers for Sonoran desert
tortoises. He brought cutting-edge expertise to the team, and the
robotic capabilities of laboratory work at the University of Arizona's
Genomic Analysis and Technology Core.
The project advanced through the cooperation of many additional
colleagues and friends, and governmental agencies.
The project has involved key aspects as follows:
- Defining the desert tortoise
- Sonoran Desert vs. Mojave
- Sinaloan thornscrub
- Genographic Assessment of the Recovery Units in the Mojave Desert population
- Ecological genetics of a species friction zone
- Multiple paternities, a.k.a. "Who's Your Daddy"
- Behavioral genetics
- MHC variation and response to pathogens
Most
of the project uses two sources of molecular data. Nuclear
microsatellite DNA is used to assess gene flow and population
variability. Mitochondrial DNA sequences are used to track the history
of maternal dispersion and dispersal, including translocations by
humans. A major contribution to this effort has been fieldwork in Sonora, Mexico, which has involved a multi-faceted, multinational, and
cooperative effort (The Mexican Tortoise Project).
The initial projects are well under way, some nearing completion. Of
course, as the project develops, new avenues of investigation arise.
We are actively discovering additional microsatellite loci in order to
investigate the association between relatedness and social
interactions. We have even used our marker set and database in a Desert Tortoise forensic case! Beyond the desert tortoise, we are assessing relatedness
and genetic diversity in the endangered bolson tortoise of Mexico (Gopherus flavomarginatus), and plans are underway to perform parallel studies on the gopher tortoise (Gopherus polyphemus) in association with Prof. Mary Brown (University of Florida). images copyrighted by RW Murphy
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