the genomics of desert tortoises

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 tortoisehad 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.

Murphy’s lab had been involved in molecular investigations of desert tortoises for several years. This work was initiated in association with the late Prof. David J. Morafka, and involved allozyme (protein electrophoresis) assays as well as sequencing mitochondrial DNA.

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:

  1. Defining the desert tortoise
    1. Sonoran vs. Mojave Desert
    2. Sinaloan thornscrub
  2. Genographic Assessment of the Recovery Units in the Mojave Desert population
  3. Ecological genetics of a hybrid zone(s)
  4. Multiple paternities, a.k.a. "Who's Your Daddy"
  5. Behavioral genetics
  6. 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.

The initial projects are well under way, some nearing completion. You can follow the links to the Desert Tortoise Council to read abstracts from this work. A photo essay on recent fieldwork in Sonora, Mexico can be seen here. And the complexities of the project can be gleaned from the acknowledgments for this aspect of the work.

Of course, as the project develops, new avenues of investigation develop. We discovered additional microsatellite loci in order to investigate the association between relatedness and social interactions. Beyond the desert tortoise, we are assessing relatedness and genetic diversity in the endangered bolson tortoise of Mexico (Gopherus flavomarginatus).

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