California's only native species of freshwater turtle may actually be two species, according to herpeteologists who've just published new work on the animal's genetic makeup, with a possible third species south of the border.
The Western pond turtle, Actinemys marmorata or Emys marmorata depending on which biologist you're talking to, was formerly widespread in ponds, lakes, and steams from Baja California through British Columbia, and has declined precipitously since Europeans arrived on the Pacific Coast due to hunting, conversion of its habitat, and competition from introduced species such as the red-eared slider. (Which is why you should never release a red-eared slider, or any captive turtle really, into the wild.)
Scientists have long argued over whether the northeastern and southwestern California populations of the western pond turtle, which differ somewhat in anatomy, ought to be considered distinct subspecies. Now, the authors of a paper published this year in the journal Molecular Ecology say that deeper genetic differences between the populations merit a split into two full species, and they propose naming the more southerly species Emys pallida.
That more southerly species ranges along the California coast from the San Francisco Bay Area to Baja California, and the paper's authors, Phillip Spinks, Robert Thomson, and H. Bradley Shaffer, observe that the Baja population is genetically distinct enough from the rest of Emys pallida that it warrants examination as a potential third species of western pond turtle.
Interestingly enough, Spinks and Shaffer co-authored a paper in 2005 in the same journal that concluded there wasn't enough data to justify splitting western pond turtles into subspecies, and here nine years later they've now proposed making that split even wider, into full species. The earlier paper only examined DNA found in the the turtles' mitochondria, which is passed down along the maternal line. Mitochondrial didn't offer a clear enough delineation between regional populations to suggest a taxonomic split, hence the cocnlusions of the 2005 paper. Now Spinks, Shaffer and Thomson have examined the much wider portion of the turtles' genome, including DNA found in cell nuclei as well as in mitochondria, and that additional data draws a very different picture.
What does this split mean for conservation of western pond turtles of whatever species? Spinks et al observe that the new species happens to occupy part of the Pacific coast where pond turtles face some serious threats:
Pond turtles from southern California are in precipitous decline, with few stable, reproducing populations known between Los Angeles and the US/Mexico border. The recognition of E. pallida as a distinct species and the possibility that stable populations in Baja California represent a unique evolutionary lineage emphasize the critical need for immediate conservation in southern California and Baja California, Mexico.
Even before the larger species Emys marmorata was split and its more-threatened southern members given their own species, conservationists already regarded the pond turtle with concern. Emys marmorata isn't listed on either the state or federal endangered species lists, but California's Department of Fish and Wildlife does list the pre-split species as a "Species of Special Concern," and the International Union for the Conservation of Nature (IUCN) listed the turtle as Vulnerable in 1996.
Now, with a new species in Southern California -- including a remarkable relictual population in the Mojave River between Camp Cady and Afton Canyon -- it's likely that wildlife advocates will turn their attention to getting greater protection for Emys pallida.
That way, Emys pallida might have a better chance of escaping the fate of another freshwater turtle species, the Sonoran mud turtle, which once lived in a bit of the California desert but has probably been extinct in the state for half a century. Here's hoping.