New Research Describes Two Distinct Species of Desert Tortoise

It has been 150 years since scientists officially described the desert tortoise as a species.  However, new research published this month indicates that we have actually been sharing the desert with at least two genetically distinct species of the desert tortoise.  Historically, many biologists and wildlife officials assumed the desert tortoise constituted a single species spanning the Mojave and Sonoran deserts in the US and Mexico.  The new research describes genetic, behavioral and physical differences that distinguish the two species of desert tortoise.   According to the research by Robert W. Murphy and Kristin H. Berry, among other scientists, the population of desert tortoise east of the Colorado River (Gopherus morafkai) is genetically distinct from the population to the west (Gopherus agassizii). 

Distribution of the desert tortoises aligned with Gopherus agassizii. The light gray depicts the range of the "Sonoran" population of the tortoise (Gopherus morafkai). Map from the research article published on ZooKeys.

The recognition of the two distinct species means that the "Mojave" population (Gopherus agassizii) is actually much more imperiled and occupies a smaller range than previously thought.  This is due to the fact that the "Sonoran" species (morafkai) can no longer be considered a "genetic reservoir" for the Mojave species, and vice versa.  Wildlife officials will have a tougher job on their hands to ensure the recovery of both tortoise populations, and the habitat loss imposed by energy projects will be even more significant as we strive to maintain biodiversity across America's southwestern deserts.

This dude, Dr. James Graham Cooper, first officially "discovered" and described the desert tortoise in 1861 (obviously the tortoise was known to Native American's long before).  Nearly 150 years later, DNA sampling and study of physiological and behavioral differences across the tortoise population revealed that we have been living with at least two different species! Photo from the research article published in ZooKeys, courtesy of the Archives of the California Academy of Sciences.

The desert tortoise is a crucial species in the desert ecosystem, digging burrows that provide homes to other desert wildlife, including the Western burrowing owl, lizards, snakes, and small mammals. 

This desert tortoise (Gopherus agassizii) found in the western Mojave Desert is now officially different from its relatives across the Colorado River.