Do Frogs Get Their Kicks on Route 66? Continental U.S. Transect Reveals Spatial and Temporal Patterns of Batrachochytrium dendrobatidis Infection

Abstract

The chytrid fungus Batrachochytrium dendrobatidis (Bd) has been devastating amphibians globally. Two general scenarios have been proposed for the nature and spread of this pathogen: Bd is an epidemic, spreading as a wave and wiping out individuals, populations, and species in its path; and Bd is endemic, widespread throughout many geographic regions on every continent except Antarctica. To explore these hypotheses, we conducted a transcontinental transect of United States Department of Defense (DoD) installations along U.S. Highway 66 from California to central Illinois, and continuing eastward to the Atlantic Seaboard along U.S. Interstate 64 (in sum from Marine Corps Base Camp Pendleton in California to Naval Air Station Oceana in Virginia). We addressed the following questions: 1) Does Bd occur in amphibian populations on protected DoD environments? 2) Is there a temporal pattern to the presence of Bd? 3) Is there a spatial pattern to the presence of Bd? and 4) In these limited human-traffic areas, is Bd acting as an epidemic (i.e., with evidence of recent introduction and/or die-offs due to chytridiomycosis), or as an endemic (present without clinical signs of disease)? Bd was detected on 13 of the 15 bases sampled. Samples from 30 amphibian species were collected (10% of known United States' species); half (15) tested Bd positive. There was a strong temporal (seasonal) component; in total, 78.5% of all positive samples came in the first (spring/early-summer) sampling period. There was also a strong spatial component—the eleven temperate DoD installations had higher prevalences of Bd infection (20.8%) than the four arid (<60 mm annual precipitation) bases (8.5%). These data support the conclusion that Bd is now widespread, and promote the idea that Bd can today be considered endemic across much of North America, extending from coast-to-coast, with the exception of remote pockets of naïve populations.

DROUGHT REDUCES CHYTRID FUNGUS (BATRACHOCHYTRIUM DENDROBATIDIS) INFECTION INTENSITY AND MORTALITY BUT NOT PREVALENCE IN ADULT CRAWFISH FROGS (LITHOBATES AREOLATUS)

“…Variations in natural history, life history, behavioral, and immunologic traits among species can strongly affect the development and outcome of Bd infection (Voyles et al 2011). In addition, intraspecific variation in ecology (e.g., Puschendorf et al 2009), geography (e.g., Kriger et al 2007), and season (e.g., Lannoo et al 2011) can also influence infection prevalence, infection intensity, and host mortality. Batrachochytrium dendrobatidis infections are generally thought to be most intense in cool, humid habitats (e.g., Woodhams et al 2005) and in species that aggregate when threatened by dehydration (Longo et al 2010).…”

Chytrid Infection Dynamics in Cricket Frogs on Military and Public Lands in the Midwestern United States

“…Numerous studies have shown higher Bd prevalence during cooler months (Woodhams and Alford 2005; Kriger and Hero 2007a;Lannoo et al 2011). In Virginia, Bd prevalence was significantly higher during the spring (45%) than during late summer (2%; Pullen et al 2010) and Rothermel et al (2008) identified a similar trend.…”

“…In Virginia, Bd prevalence was significantly higher during the spring (45%) than during late summer (2%; Pullen et al 2010) and Rothermel et al (2008) identified a similar trend. Further, Lannoo et al (2011) found the majority of positive tests resulted from the first sampling period and reported prevalence rates of 39.3% in the spring, 6.1% in the summer, and 4.5% in the autumn. We found similar results for prevalence rates in 2009 for all three periods, with 59.4% in the spring, 5.8% in the summer, and 2.8% in the autumn; Bd prevalence in Cricket Frogs was significantly higher during the spring sampling period when compared with summer and autumn samples in 2009.…”

“…We suspected occurrence and prevalence rates may be lower on sites such as military installations because of the potential of increased transmission rates at high-traffic sites. In a country-wide survey of U.S. military installations, Lannoo et al (2011) found that Bd was present at 86.7% (13/15) of bases sampled, although the authors noted the lack of detection at the two remaining sites could have been due to insufficient sampling. Across their three sampling periods (spring, summer, and autumn of 2009), they found an overall prevalence rate of 16.6%.…”

Canopy cover and drought influence the landscape epidemiology of an amphibian chytrid fungus

“…Bd is widespread among amphibian species in North America and is now found across much of the continent (Lannoo et al 2011). However, susceptibility to Bd infection varies among species and populations (Retallick et al 2004, Blaustein et al 2005, Woodhams and Alford 2005, and infection varies spatially across landscapes (Woodhams and Alford 2005, Muths et al 2008, Pearl et al 2009, Adams et al 2010, Phillott et al 2013.…”