Leaping into the future
In 2005, amphibian experts from around the world convened to discuss the global loss of amphibian biodiversity. More than 30% of known amphibian species were threatened with extinction and more were at risk, proportionately, than birds, mammals, or reptiles. The crisis was first noted in the late 20th century and the rate of decline was, and remains, alarming. More worrisome, losses were occurring in areas that were previously considered safe havens: preserved habitats. Among other problems, a fungal disease, chytridiomycosis, had invaded relatively pristine environments and caused a rate of decline that was historically unprecedented. To further confound the problem, the biology and habitat requirements of most of these species remained largely unknown.
At the Amphibian Conservation Summit of 2005, a plan, the Amphibian Conservation Action Plan (ACAP), was formulated by consensus of experts across multiple disciplines, including Dr. Oliver Ryder. One of the key long-term goals of this ambitious plan is to create an amphibian biobank to preserve frozen cells from every threatened and endangered amphibian species. The five-year plan included representation from every taxa. These cell lines would be a repository of genetic diversity that could be useful for a multitude of conservation and management needs, including studying health and disease, informing breeding decisions (for example, by characterizing cryptic species, those that appear to be the same species, but are genetically distinct), and rescuing genetic variation that might otherwise be lost.
Enter the cytogenetics team of San Diego Zoo Global’s Institute for Conservation Research. In 1975, Dr. Kurt Benirschke founded the Frozen Zoo®, and by 2006, it had expanded to include over 7,000 cell lines from nearly 40 vertebrate orders, but few reptiles and only one amphibian, an African clawed frog (Xenopus laevis). Efforts to establish amphibian cell lines began in earnest. A search of reported scientific literature and communications with colleagues revealed that cells from very few amphibian species had ever been cultured, let alone frozen, and most of the studies had used common laboratory specimens. The cytogenetics staff had expertise in pioneering and adapting culturing techniques, however, and hoped to expand the Frozen Zoo® to include many more amphibians and reptiles.
Fast forward a decade to 2016. Our adaptations proved successful for reptiles: over 200 snake, lizard, and turtle cell lines were accessioned into the Frozen Zoo®; eleven new species were grown and frozen in the last year alone. The amphibian cells, on the other hand, have been notoriously difficult. This has been due in part to the nature of amphibian skin, fewer sampling opportunities, and the very slow growth rate of the cells. It may take a year or more to painstakingly grow a cell line from a small biopsy! Furthermore, amphibians, as a group, have been particularly resistant to our attempts to generalize across this phylogenetic order.
To date, we have just over 80 cell lines, representing 21 species, including two severely endangered-- the largest collection in the world! While these numbers are impressive, amphibian cell lines still represent less than 1% of the Frozen Zoo® and are a far cry from the ACAP goal of an estimated 3000 at-risk amphibian species. We urgently need to advance our technology in amphibian cell culture. Follow along as we leap into 2017 and I chronicle how our team of four dedicated cytogeneticists endeavors to achieve this lofty goal, a race against extinction.