New Insights Into the Cause of Recent Amphibian Declines

During the last decade, Karen Lips and colleagues have documented the spread of the amphibian chytrid fungus (Batrachochytrium dendrobatidis: "Bd") southward through Costa Rica and Panama, and its devastating impacts on amphibian populations. However, it has remained unclear whether Bd was also the cause of declines in areas north of the region studied by Lips et al., including Mexico, Guatemala, and the Monteverde region of Costa Rica. Throughout this region, a host of amphibian species either disappeared or markedly declined in the 1970s and 1980s, and the cause of these declines and extinctions has until now been largely speculative. 

In a new study published this week in the Proceedings of the National Academy of Sciences, Cheng and colleagues used museum specimens collected in Mexico and Central America during the period 1967-1987 to test for the presence or absence of Bd. Their results provide compelling evidence that since the 1970s Bd has been spreading south through southern Mexico and Central America (red dots with stars in figure). This timeline dovetails nicely with that for Costa Rica and Panama posited by Lips et al. (red dots in figure). Across their study sites, Cheng et al. also show a repeated pattern of Bd being absent from amphibians collected in the early years of their analyses followed by initial detections of Bd and the coincident decline of multiple amphibian species. 

So, it is now quite clear that Bd was a major cause of enigmatic amphibian declines that occurred in this region during past decades. The molecular technique developed by Cheng et al. to detect Bd on preserved museum specimens should open the door to a host of future Bd-related studies that take advantage of additional preserved amphibian specimens stored in museums around the world. I suspect that these specimens have many a tale to tell regarding the global spread of Bd and its impacts on amphibians. 

Further reading:
Lips, K. R. 1998. Decline of a tropical montane amphibian fauna. Conservation Biology 12:106-117.

Lips, K. R. 1999. Mass mortality and population declines of anurans at an upland site in western Panama. Conservation Biology 13:117-125.

Lips, K. R., F. Brem, R. Brenes, J. D. Reeve, R. A. Alford, J. Voyles, C. Carey, L. Livo, A. P. Pessier, and J. P. Collins. 2006. Emerging infectious disease and the loss of biodiversity in a Neotropical amphibian community. Proceedings of the National Academy of Sciences, USA 103:3165-3170.

Lips, K. R., J. R. Mendelson III, A. Munoz-Alonso, L. Canseco-Marquez, and D. G. Mulcahy. 2004. Amphibian population declines in montane southern Mexico: resurveys of historical localities. Biological Conservation 119:555-564.

Rovito, S. M., G. Parra-Olea, C. R. Vásquez-Almazán, T. J. Papenfuss, and D. B. Wake. 2009. Dramatic declines in neotropical salamander populations are an important part of the global amphibian crisis. Proceedings of the National Academy of Sciences 106 3231-3236.

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