BioMaAS biologists participate in Western Spadefoot Research

Western Spadefoot (Spea hammondii)

It’s an unseasonably warm night for March. Five cars, all Toyotas and Subarus (and one out-of-place Mercedes Benz) are lingering after hours at Carnegie State Vehicular Recreation Area – a state park set aside for off-road vehicles. It’s dry as a bone out, and the heat, coupled with the buzz and whir of wheels tearing up the landscape, makes you wonder what brought a group of biologists to seek out an amphibian.

“I’ve never seen a western spadefoot” is the most common statement when you bring up the so-goblin-like-it’s-cute anuran. Like many anurans, western spadefoots (Spea hammondii) are picky about where they live. There may be thousands of them in a single puddle in the middle of Bakersfield and yet thousands of square miles of native grassland and vernal pools are simply bereft of them. These little creatures are also nocturnal – being most common an hour or two after sunset, and they are cryptic, with a habit of looking like and sitting still as a stone – even in the middle of the road. The keratinized protrusion on their foot, aka the namesake “spade” is used for digging into sand. While they may take refuge in mammal burrows, spadefoots can virtually vanish without a trace, scooching their butts backwards into sand and gravel within about 30 seconds.

Another feature that makes the western spadefoot elusive is pure misinformation. As a biologist, I have heard all my life that the only time you will see a spadefoot is during light rain. Even old, seasoned biologists will argue that winter’s first drizzle is the only time to observe the creature. But since 2022, BioMaAS biologists have been visiting this stretch of road, sometimes as late as July, and seeing little spadefoot metamorphs hopping across the dry road at night.

Finally, like so many amphibians in the state, the western spadefoot is rare because it’s threatened. While only considered a species of special concern by California Department of Fish & Wildlife, the western spadefoot is now up for listing at the federal level. Habitat loss, invasive species, and drought are all contributing factors to declines in the western spadefoot. But the point of tonight’s foray is to detect the grand villain of all amphibian threats: the fungus Batrachochytrium dendrobatidis (Bd).

Bd is perhaps the primary cause for amphibian declines globally (Skerratt et al. 2007). This is the fungus famously responsible for mass die-offs in Sierra Nevada Mountain yellow-legged frogs (Rana sierrae), Southern Mountain yellow-legged frogs (Rana muscosa) (Smith et al. 2016), Cascades frog (Rana cascadae) (DeLeon et al. 2017), California red-legged frogs (Adams et al. 2020), and a host of other species.

What is the prevalence of Bd in our friend, the western spadefoot? That’s San Francisco State Master’s Student Jakob Woodall’s research project. Under the tutelage of famed amphibian disease ecologist Vance Vredenburg, Jakob has been coming out to Carnegie, swabbing spadefoots, preserving the swabs, and sending them off to a lab to detect Bd. So far, they have been coming back positive for the fungus. He plans to compare the results of these ongoing surveys to Bd detected in museum specimens to make inferences on current infection rates with historical ones; and to see if there are differences in infection intensity between sex and age within this population.

Michael Voeltz, Lora Roame, and Shay Duffy watch researcher Jakob Woodall demonstrate how to swab a spadefoot for Bd

Jakob, a scrappy, curly-haired 28-year-old is full of energy and information. The grim topic of his work does not make anyone less excited to be in a wheelie-ravaged, disease-infected, ruderal desertscape. For, it’s not despite, but also because of the offroad vehicles that spadefoots persist here. ATV’s and off-road trucks create ruts large enough for spadefoots to breed, and all they need is a few couple weeks to metamorphize (Denver et al. 1998). Meanwhile, the crushed and barren landscape makes it possible for the spadefoots to cross into appropriate upland habitat without the resistance of dense invasive plant matter.

Jakob is already holding up an immature spadefoot he found at the gate. The animal’s googly catlike eyes perceive his flashlight with an unblinking look of vacant acceptance. Jakob demonstrates the proper way to hold the creature: with its front and back legs pinned between your fingers to prevent them from breaking a limb, then puts it into a container for later processing.

After a couple hours of wandering through dry arroyos, the group has found 46 spadefoots and placed them in their own containers. The animals are brought to a table in the campground, where Jakob swabs the skin on their little round tummies, between the webbing of their toes, and their armpits. The swabs go into alcohol preservative and the spadefoot is set free back into its habitat. With over 60 spadefoots observed in a 3-acre parcel over the course of two hours, you wouldn’t think that they were under threat at all.

“Why are there so many here if they all have Bd?” someone asks. Jakob leans his head to one side and shrugs. “One theory I have is that it’s so dry out here, and, you know, the frogs really spend the vast majority of their time in uplands, where it’s dry. I think that the Bd load actually subsides due to the dryness and that gives the frog a fighting chance.” Curiously, as another participant suggests, mortality in captive spadefoots cultured with Bd is higher than in the wild. This may, in fact, be because husbandry experts are prone to (and even required to by permits issued by State and Federal Governments) always provide their study animals unlimited access to water. If Jakob’s theory is correct, Bd would only continue to grow within a captive setting.

Jakob’s study is set to go on for several more seasons, and BioMaAS Biologists will be eagerly volunteering whenever he needs a hand grabbing these unique and weirdo “little buddies”. A few nights later, Biologist Shay Duffy gets the honor of releasing a big female spadefoot. We all crouch beside it as she places it on the dry arroyo pebbles. The spadefoot spins, disoriented, using one foot to rub a bulging eye and barely remembering to close her nictating glands. Then the chubby mother hops once, twice, and vanishes into the pebbles, her sage-green marbled body indiscernible from the stones and moss. A small, boxy male spadefoot is placed on a gravel bar and without thinking twice, makes a sassy wiggle of his butt and descends into the earth like Homer Simpson vanishing into a hedge. Upon close inspection, one can barely see one golden Eye of Sauron peeking out from between the granules of dirt. A squeal of laughter and excitement from the assembly – Shay, Michael, Lora, and Ivan.

“Is there anything in this world cuter than a spadefoot?” asks Michael. 

References

Adams AJ, Pessier A, Cranston P, Grasso RL. Chytridiomycosis-induced mortality in a threatened anuran. PLoS One. 2020 Nov 6;15(11):e0241119. doi: 10.1371/journal.pone.0241119. PMID: 33156870; PMCID: PMC7647137.

De León, M.E., Vredenburg, V.T. & Piovia-Scott, J. Recent Emergence of a Chytrid Fungal Pathogen in California Cascades Frogs (Rana cascadae). EcoHealth 14, 155–161 (2017). https://doi.org/10.1007/s10393-016-1201-1

Denver, R.J., N. Mirhadi, M. Phillips. Adaptive Plasticity in Amphibian Metamorphosis: Response of Scaphiophus hammindii Tadpoles to Habitat Desiccation. Ecology, 79(6), 1998, pp. 1859–1872 q 1998 by the Ecological Society of America

Skerratt LF, Berger L, Speare R, Cashins S, McDonald KR, Phillott AD, et al. Spread of chytridiomycosis has caused the rapid global decline and extinction of frogs. EcoHealth. 2007;4(2):125–34. 10.1007/s10393-007-0093-5

Smith, TC., A. M. Picco, R. Knapp. Ranaviruses Infect Mountain Yellow-Legged Frogs (Rana muscosa and Rana sierrae) Threatened by Batrachochytrium dendrobatidis. Herpetological Conservation and Biology 12:149–159. Submitted: 3 April 2016; Accepted: 20 December 2016; Published: 30 April 2017