Search

Scheele et al (Reports, 29 March 2019, p. 1459) bring needed attention to the effects of amphibian infectious disease. However, the data and methods implicating the disease chytridiomycosis in 501 amphibian species declines are deficient. Which species are affected, and how many, remains a critical unanswered question. Amphibians are imperiled; protective actions require public support and robust science., (Copyright © 2020, American Association for the Advancement of Science.)

Amphibians, the most threatened group of vertebrates, are seen as indicators of the sixth mass extinction on earth. Thousands of species are threatened with extinction and many have been affected by an emerging infectious disease, chytridiomycosis, caused by the fungal pathogen, Batrachochytrium dendrobatidis (Bd). However, amphibians exhibit different responses to the pathogen, such as survival and population persistence with infection, or mortality of individuals and complete population collapse after pathogen invasion. Multiple factors can affect host pathogen dynamics, yet few studies have provided a temporal view that encompasses both the epizootic phase (i.e. pathogen invasion and host collapse), and the transition to a more stable co-existence (i.e. recovery of infected host populations). In the Sierra Nevada mountains of California, USA, conspecific populations of frogs currently exhibit dramatically different host/ Bd-pathogen dynamics. To provide a temporal context by which present day dynamics may be better understood, we use a Bd qPCR assay to test 1165 amphibian specimens collected between 1900 and 2005. Our historical analyses reveal a pattern of pathogen invasion and eventual spread across the Sierra Nevada over the last century. Although we found a small number of Bd-infections prior to 1970, these showed no sign of spread or increase in infection prevalence over multiple decades. After the late 1970s, when mass die offs were first noted, our data show Bd as much more prevalent and more spatially spread out, suggesting epizootic spread. However, across the ~400km2 area, we found no evidence of a wave-like pattern, but instead discovered multiple, nearly-simultaneous invasions within regions. We found that Bd invaded and spread in the central Sierra Nevada (Yosemite National Park area) about four decades before it invaded and spread in the southern Sierra Nevada (Sequoia and Kings Canyon National Parks area), and suggest that the temporal pattern of pathogen invasion may help explain divergent contemporary host pathogen dynamics., Competing Interests: The authors have declared that no competing interests exist.

Since the dawn of history, amphibians have been a part of human culture. Western Europeans built fires for cooking and warmth, adding large logs as needed. What occasionally emerged was astounding: large black animals (which had found shelter in the logs) with four legs and a tail, jet black with striking bright yellow spots. These fire salamanders were variously thought to be the product of the fire itself, or, as Aristotle reported, capable of extinguishing fire. Pliny the Elder is said to have tested this idea by throwing a salamander into flames - the salamander died! - nevertheless the association with fire persisted. Pliny perpetuated other fantastical claims, which spread; even Leonardo da Vinci contributed to the legend, and myths from different regions merged - at one point, asbestos was claimed to be salamander wool. Salamanders were attributed great powers; a single salamander upstream was thought to be sufficient to kill an army. King Francis I. of France chose a salamander as his emblem - a powerful symbol, born of fire, filled with poison, immune from burning, and even able to douse flames. Before the emergence of great cities and conurbations, people grew up surrounded by nature. Salamanders and newts, toads and frogs were all part of normal human experience. Myths such as those surrounding the fire salamanders were commonplace. Shakespeare's witches brewed with an eye of newt and tail of frog. As a child, we raised tadpoles and were taught to shudder at the appearance of a tiger salamander in a root cellar. In general, amphibians are seen as benign and harmless, even helpful as creatures that devour harmful insects and serve as an alternative food source. Thus, it came as a shock to most biologists and to the public at large in the 1980s that amphibians around the world were in decline and that they were at greater risk of extinction as a taxon than any other vertebrate group. A study of every amphibian species known in 2004 showed that on the order of 40% were at high risk of extinction, and by 2008, the decline of amphibians was seen as evidence of an impending sixth mass extinction., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Batrachochytrium dendrobatidis (Bd), an amphibian fungal pathogen, has infected >500 species and caused extinctions or declines in >200 species worldwide. Despite over a decade of research, little is known about its invasion biology. To better understand this, we conducted a museum specimen survey (1910-1997) of Bd in amphibians on 11 California islands and found a pattern consistent with the emergence of Bd epizootics on the mainland, suggesting that geographic isolation did not prevent Bd invasion. We propose that suitable habitat, host diversity, and human visitation overcome isolation from the mainland and play a role in Bd invasion.

A newly described pathogen poses a major threat to salamanders via trade