Ranavirus could facilitate local extinction of rare amphibian species

Abstract

There is growing evidence that pathogens play a role in population declines and species extinctions. For small populations, disease-induced extinction may be especially probable. We estimated the susceptibility of two amphibian species of conservation concern (the dusky gopher frog [Lithobates sevosus] and boreal toad [Anaxyrus boreas boreas]) to an emerging pathogen (ranavirus) using laboratory challenge experiments, and combined these data with published demographic parameter estimates to simulate the potential effects of ranavirus exposure on extinction risk. We included effects of life stage during pathogen exposure, pathogen exposure interval, hydroperiod of breeding habitat, population carrying capacity, and immigration in simulations. We found that both species were highly susceptible to ranavirus when exposed to the pathogen in water at environmentally relevant concentrations. Dusky gopher frogs experienced 100 % mortality in four of six life stages tested. Boreal toads experienced 100 % mortality when exposed as tadpoles or metamorphs, which were the only life stages tested. Simulations showed population declines, greater extinction probability, and faster times to extinction with ranavirus exposure. These effects were more evident with more frequent pathogen exposure intervals and lower carrying capacity. Immigration at natural rates did little to mitigate effects of ranavirus exposure unless immigration occurred every 2 years. Our results demonstrate that disease-induced extinction by emerging pathogens, such as ranavirus, is possible, and that threat may be especially high for species with small population sizes. For the species in this study, conservation organizations should incorporate ranavirus surveillance into monitoring programs and devise intervention strategies in the event that disease outbreaks occur.

Frog Virus 3 Genomes Reveal Prevalent Recombination between Ranavirus Lineages and Their Origins in Canada

“…The acquisition of CMTV-like genes by a FV3-like virus is hypothesized to have increased its virulence (11). Therefore, the potential spread of recombinant strains originating from the commercial pet trade and frog production facilities into wild amphibians is especially concerning, since common and endangered amphibian species are highly susceptible to this recombinant lineage and, thus, are at risk of local extinctions (16).…”

Pathogen Risk Analysis for Wild Amphibian Populations Following the First Report of a Ranavirus Outbreak in Farmed American Bullfrogs (Lithobates catesbeianus) from Northern Mexico

“…Ranavirus has been able to establish itself among populations of other amphibian species from the genus Lithobates , like the Northern leopard frog ( Lithobates pipiens ) [42] and the Dusky gopher frog ( Lithobates sevosus ), in which it has caused 100% mortality under experimental settings [43]. Regarding the family Hylidae, and in contrast to all other endemic amphibian species in Guasave, the Mexican leaf frog ( A. dacnicolor ) has actually shown evidence of population declines throughout Mexico [1].…”

Acute mortality in California tiger salamander (Ambystoma californiense) and Santa Cruz long-toed salamander (Ambystoma macrodactylum croceum) caused by Ribeiroia ondatrae (Class: Trematoda)

“…Most suspected disease agents credited with extirpations or extinctions in amphibians have been fungal ( Longcore et al, 1999 ; Fisher et al, 2012 ; Scheele et al, 2019 ) or viral ( Jancovich et al, 1997 ; Earl et al, 2016 ). The role of helminth parasites in amphibian mortality events or population declines is not as well studied or understood ( Tinsley, 1995 ; Fernández-Loras et al, 2011 ).…”