As you visit Oakland Zoo this winter and spring you may notice that the animals and projects we are supporting at our Quarters for Conservation booth in Flamingo Plaza have changed. I would like you to pay special attention to the developing partnership with the San Francisco State University Mountain Yellow-Legged Frog project. This project teams up Oakland Zoo with San Francisco State University in bringing awareness to and supporting the recovery of this critically endangered species that is found right here in the mountains of California.
Once one of the most numerous species found in their alpine habitat in the Sierra Nevada, Transverse, and Peninsular ranges they are now one of the rarest despite this habitat being found in some of the most well-managed and inaccessible areas of the state. During some of the initial research looking into this decline the focus was on the impact and removal of game fish that were introduced to their alpine habitats, such as trout. The Mountain Yellow-Legged Frog evolved in a habitat where such efficient predators were not common and the eggs, tadpoles, and frogs themselves became easy prey. With the management and removal of these introduced fish species some areas showed rapid recovery of frogs. However, some did not, and in fact the overall population continued to decline. The emerging disease known as the chytrid fungus (Batrachochytrium dendrobatidis) was found to be the cause of this continued decline and was attacking the frogs during one of their most sensitive transitions in life, the one between tadpole and juvenile life stages. The chytrid fungus works by attacking the keratin in the skin of juvenile and adult frogs preventing them from being able to use their skin to respirate and exchange water leading to their deaths, wiping out whole populations. For some reason the disease does not affect the tadpoles of the Mountain Yellow-Legged Frog, but it will remain with them through the several years they spend as a tadpole. This makes the tadpoles, along with several other frog species that are not affected, a means to not only infect their own kind with this deadly fungus, but to make it almost impossible to eliminate from the environment.
With this revelation the focus to save the Mountain Yellow-Legged Frog changed to not only manage and remove non-native fish, but to support the frogs in gaining resistance to the chytrid fungus during this transition in their life. The support comes in the form of a bacterium called Janthinobacterium lividum. The bacteria was discovered on the skin of a fellow amphibian, the red-backed salamander, and later discovered to also be present on the skins of Mountain Yellow-Legged Frog in varying levels. This bacterium has the unique feature of having anti-fungal properties and when found in greater numbers on amphibian skin can help to increase resistance to the chytrid fungus. Now, in steps Dr. Vance Vredenburg and the San Francisco State University Mountain Yellow-Legged Frog Project. Dr. Vredenburg has been pioneering skin bio augmentation treatments using Janthinobacterium lividum to support juvenile frogs that are being rereleased or will be re-released into their habitats in both Northern and Southern California. Through a partnership with San Diego Zoo, San Francisco Zoo, and soon Oakland Zoo, San Francisco State University is hoping to tip the balance for these frogs by collecting them as eggs from their habitat, hatching them in captivity, raise them to juvenile frogs, treating them with this anti-chytrid bacterium, and release them back into their natal ponds and streams. It is hoped that not only will this prove to provide long term resistance to chytrid, but will be naturally passed between frogs as they naturally congregate together in the shallows off the banks of the rivers and lakes they live.
If you are interested in learning more about the plight of the Mountain Yellow-Legged Frog and supporting them as well during their most vulnerable transitions you can join us on Wednesday February 5th at 6:30 p.m. in the Marian Zimmer Auditorium at our Conservation Speaker Series event when Dr. Vance Vredenburg joins us to discuss his work with the Mountain Yellow-Legged Frog and the implications his research has to save this and potentially numerous other amphibian species worldwide.
by Victor Alm, Zoological Manager