Density-dependent mortality of eastern newts exposed to Batrachochytrium salamandrivorans
Tompros, A., E. D. Carter, A. Fenton, M. Wilber, M. Bohanon, P. Watcharaanantapong, K. Ash, D. L. Miller, and M. J. Gray.  2020.  Annual Meeting of the Southeast Partners in Amphibian and Reptile Conservation, Nauvoo, AL.  (invited)

Batrachochytrium salamandrivorans (Bsal) is an emerging chytrid fungus that is spreading across Europe, causing rapid declines in salamander populations. Bsal has yet to be confirmed in North America; however, it is likely only a matter of time before it arrives. A first step to understanding the possible epidemiology of Bsal is investigating whether pathogen transmission and subsequent disease-induced mortality is density-dependent. We performed our experiment in a controlled research facility with eastern newts (Notophthalamus viridescens) housed in 20 1-m2 tanks at 14oC with three initial Bsal infection prevalence (12.5, 25, 50%) and 11 host density (2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 32) treatments. Infected individuals were exposed to a high dose of zoospores (2.56x106) for 24 hours to guarantee infection then placed into tanks with uninfected susceptible individuals. Newts were uniquely marked and swabbed every three days for 60 days to determine infection status. All susceptible individuals eventually became infected with Bsal, indicating transmission was 100% among all treatments. However, tanks with higher initial infection prevalence reached 100% infection faster than those with lower initial infection prevalence. Within a density, tanks with higher infection prevalence also experienced more rapid mortality than lower infection prevalence. Disease-induced mortality was strongly densitydependent at lower host densities (2 – 8 newts / m2) and reached asymptotic maximum at higher densities, suggesting a Holling’s Type II functional response. Densities up to 8 newts / m2 are common in the eastern United States. Although reducing newt density might not affect transmission of Bsal, it reduced overall mortality, hence be a viable disease management strategy.