Environmental Drivers of Ranavirus in Free-Living Amphibians in Constructed Ponds

Abstract

Amphibian ranaviruses occur globally, but we are only beginning to understand mechanisms for emergence. Ranaviruses are aquatic pathogens which can cause > 90% mortality in larvae of many aquatic-breeding amphibians, making them important focal host taxa. Host susceptibilities and virulence of ranaviruses have been studied extensively in controlled laboratory settings, but research is needed to identify drivers of infection in natural environments. Constructed ponds, essential components of wetland restoration, have been associated with higher ranavirus prevalence than natural ponds, posing a conundrum for conservation efforts, and emphasizing the need to understand potential drivers. In this study, we analyzed 4 years of Frog virus 3 prevalence and associated environmental parameters in populations of wood frogs (Lithobates sylvaticus) and green frogs (Lithobates clamitans) in a constructed pond system. High prevalence was best predicted by low temperature, high host density, low zooplankton concentrations, and Gosner stages approaching metamorphosis. This study identified important variables to measure in assessments of ranaviral infection risk in newly constructed ponds, including effects of zooplankton, which have not been previously quantified in natural settings. Examining factors mediating diseases in natural environments, particularly in managed conservation settings, is important to both validate laboratory findings in situ, and to inform future conservation planning, particularly in the context of adaptive management.Electronic supplementary materialThe online version of this article (10.1007/s10393-018-1350-5) contains supplementary material, which is available to authorized users.

Ranavirus Amplification in Low-Diversity Amphibian Communities

“…Our data show that it is not uncommon for temperatures to fluctuate more than 12 • C at a single location in a single day. Given that amphibians explore their environment throughout the day in pursuit of food and thermal optima, and to evade predators, the effect of temperature on RV infections is difficult to assess accurately, particularly in small bodies of water (101). While amplification effects in other host-pathogen systems have been directly linked to the number of (susceptible) hosts in a specified area (102), ranavirus epidemics in amphibians are generally not following this pattern.…”

“…Our data show that it is not uncommon for temperatures to fluctuate more than 12°C at a single location in a single day. Given that amphibians explore their environment throughout the day in pursuit of food and thermal optima, and to evade predators, the effect of temperature on RV infections is difficult to assess accurately, particularly in small bodies of water ( 101 ).…”

Review: Examining the Natural Role of Amphibian Antimicrobial Peptide Magainin

“…The North American green frog is an amphibian species commonly found on the eastern coast of North America and is known to be susceptible to the amphibian pathogens Ranavirus and Bd [ 25 , 26 ]. Chytridiomycosis is widespread in frog species, with preserved green frog specimens showing a relatively high prevalence of the disease [ 27 ].…”

Prevalence of Ranavirus in Spotted Salamander (Ambystoma Maculatum) Larvae From Created Vernal Pools in West Virginia, Usa

“…We did not find any associations between ranavirus infection prevalence and habitat characteristics. The lack of association between water temperature and prevalence reflects the uncertainty around this relationship, which varies by species and viral strain (Brand et al 2016; Youker-Smith et al 2018). Moreover, temporal water temperature readings may provide more insight than our point measurement.…”

“…Conversely, prevalence of ranavirus in common frogs ( Rana temporaria ) increased with pond depth (North et al 2015). For wood frogs and green frogs in created vernal pools, models predicted that deeper water would increase infection prevalence, potentially due to decreased likelihood of pool sediment freezing, thereby allowing infection reservoir species to persist in the pool (Youker-Smith et al 2018). We also did not find an association between predator presence and ranavirus infection prevalence.…”