Invasive North American bullfrogs transmit lethal fungus Batrachochytrium dendrobatidis infections to native amphibian host species

Abstract

Invasive species can be a threat to native species in several ways, including 8 transmitting lethal infections caused by the parasites they carry. However, invasive species 9 may also be plagued by novel and lethal infections they acquire when invading, making 10 inferences regarding the ability of an invasive host to vector disease difficult from field 11 observations of infection and disease. This is the case for the pathogenic fungus 12 Batrachochytrium dendrobatidis (Bd) in Europe and one invasive host species, the North 13 American bullfrog Lithobates catesbeianus, hypothesized to be responsible for vectoring 14 lethal infection to European native amphibians. We tested this hypothesis experimentally 15 using the alpine newt Ichthyosaura alpestris as our model native host. Our results show that 16 infected bullfrog tadpoles are effective vectors of Bd. Native adult newts co-housed with 17 experimentally infected bullfrog tadpoles became Bd infected (molecular and histological 18 tests). Moreover, the exposed adult newts suffered mortality while the majority of infected 19 Bullfrog tadpoles survived until metamorphosis. These results cannot resolve the historical 20 role of alien species in establishing the distribution of Bd across Europe or other regions in 21 the world where this species was introduced, but they show its potential role as a Bd reservoir 22 capable of transmitting lethal infections to native amphibians. Finally, our results also suggest 23 that the removal of infected bullfrogs from aquatic environments may serve to reduce the 24 availability of Bd in European amphibian communities, offering another justification for 25 bullfrog eradication programmes that are currently underway or may be considered.

Routine habitat switching alters the likelihood and persistence of infection with a pathogenic parasite

“…Thus, infection risk for newts is not only a function of total zoospores to which newts are exposed (Experiment 2) but also how frequently newts are exposed to zoospores over time (Experiment 1). By extension, continuous and prolonged exposure would be most likely to manifest as increased mortality, and in support of this, a recent study showed how exposing newts constantly to an infected reservoir generated significant mortality (Miaud et al., ).…”

Rapid extirpation of a North American frog coincides with an increase in fungal pathogen prevalence: Historical analysis and implications for reintroduction

“…boylii indicates that Bd prevalence and loads are highest in R. catesbeiana (American bullfrog) and H. regilla (Figure ). Both R. catesbeiana and H. regilla are considered to be vectors of Bd in California (Adams et al., ; Padgett‐Flohr & Hopkins, ; Reeder et al., ), and as an often‐tolerant Bd reservoir host, bullfrogs have been implicated in declines of amphibians in places throughout the world where they are not native, including California (Daszak et al., ; Jennings & Hayes, ; Miaud et al., ). H. regilla and R. catesbeiana may have provided sufficient reservoir hosts to allow for Bd persistence in the system, facilitating chytridiomycosis‐induced extinction of R .…”

“…Data were arranged prior to mapping so that Bd-positive samples would be superimposed on Bd-negative samples when they overlapped. Data include sampled specimens collected from Ventura, Santa Barbara, Los Angeles, and San Luis Obispo counties including California(Daszak et al, 2004;Jennings & Hayes, 1994a;Miaud et al, 2016). H. regilla and R. catesbeiana may have provided sufficient reservoir hosts to allow for Bd persistence in the system, facilitating chytridiomycosis-induced extinction of R. boylii.…”

Genetic reconstruction of a bullfrog invasion to elucidate vectors of introduction and secondary spread

“…Bullfrogs are native to eastern North America (Bury and Whelan 1984), but now occur in nearly all lower 48 states and in over 40 countries. Their large size, high mobility, generalist eating habits, high fecundity, and function as a disease vector to other amphibians make the bullfrog an extremely successful invader and a major threat to biodiversity (Adams and Pearl 2007;Miaud et al 2016). For these reasons, evaluating sources, genetic properties and historical invasion pathways are key to the development of effective policy and management strategies needed to minimize their ecological impacts.…”