Revisited - Failure of tetrodotoxin to protect red-spotted newts, Notophthalmus viridescens, from endoparasites.

Red-spotted newts, Notophthalmus viridescens, contain tetrodotoxin (TTX) and its analogue 6-epiTTX in variable concentrations. In a follow-up study, newts were sampled from a pond in Pennsylvania, USA, in 2010, 2014, and 2018. Their toxin levels were assayed by liquid-chromatography-fluorescence detection (LC-FLD), and assessment of their infection with endoparasites such as nematodes and helminths was performed by histological examination of internal organs. In the 2010 and 2014 samples, average prevalence of parasite infection was 53 and 60%, respectively, but reached 100% in the 2018 sample, where metacercaria stages of the digenean trematode genus Australapatemon/Apatemon (family: Strigeidae) were predominant causing severe tissue damage in liver and kidney. Mean values of TTX and 6-epiTTX were not significantly different in parasitized or parasite-free newts over the study period, confirming previous findings that host toxicity and parasite load are not negatively correlated. Whereas the role of TTX in defence against predators is undisputed, its efficacy to prevent parasitic infections is less obvious. Toxin-resistance of various metazoan parasites may promote their widespread occurrence in poisonous newts.

Parasite age-intensity relationships in red-spotted newts: does immune memory influence salamander disease dynamics?

Acquired immune memory in vertebrates influences transmission and persistence of infections, with consequences for parasite dynamics at both the individual and population levels. The potential impact of acquired immunity is of particular interest for salamanders, whose acquired immune systems are thought to be less effective than those of frogs and other tetrapods. One way to examine the importance of acquired immunity to parasite dynamics at the population level is by examining the relationship between host age and parasite infection intensity. Acquired immunity reduces infection rates in older animals, causing decreased parasite intensity in older age classes and leading to curvilinear age-intensity relationships for persistent parasites and convex age-intensity relationships for transient parasites. We used age-intensity relationships to look for the signature of acquired immunity for 12 parasite taxa of red-spotted newts (Notophthalmus viridescens), using data from a 2-year parasitological survey of six newt populations. We estimated ages from snout-vent length (SVL) based on the relationship between SVL and skeletochronologically-derived ages in a subset of newts. We found evidence of acquired immunity to two parasite taxa, bacterial pathogens and the protist Amphibiocystidium viridescens, whose convex age-intensity relationships could not be easily explained by alternative mechanisms. Our results suggest that the acquired immune response of newts is sufficient to influence the dynamics of at least some parasites.

Widespread infection of the Eastern red-spotted newt (Notophthalmus viridescens) by a new species of Amphibiocystidium, a genus of fungus-like mesomycetozoan parasites not previously reported in North America.

Given the worldwide decline of amphibian populations due to emerging infectious diseases, it is imperative that we identify and address the causative agents. Many of the pathogens recently implicated in amphibian mortality and morbidity have been fungal or members of a poorly understood group of fungus-like protists, the mesomycetozoans. One mesomycetozoan, Amphibiocystidium ranae, is known to infect several European amphibian species and was associated with a recent decline of frogs in Italy. Here we present the first report of an Amphibiocystidium sp. in a North American amphibian, the Eastern red-spotted newt (Notophthalmus viridescens), and characterize it as the new species A. viridescens in the order Dermocystida based on morphological, geographical and phylogenetic evidence. We also describe the widespread and seasonal distribution of this parasite in red-spotted newt populations and provide evidence of mortality due to infection.

Helminth communities in five species of sympatric amphibians from three adjacent ephemeral ponds in southeastern Wisconsin.

Representatives of 5 amphibian species (313 individuals), including eastern American toads (Bufo americanus), wood frogs (Rana sylvatica), spring peepers (Pseudacris crucifer), blue-spotted salamanders (Ambystoma laterale), and central newts (Notophthalmus viridescens louisianensis), were collected from 3 ephemeral ponds during spring 1994, and they were inspected for helminth parasites. The component communities of anurans were more diverse than those of caudates. Infracommunities of all host species were isolationist and depauperate, due mostly to host ectothermy and low vagility. Toad infracommunities were dominated by skin-penetrating nematodes, and they had the highest values of mean total parasite abundance, mean species richness, and overall prevalence. This was likely due to their greater vagility compared with other host species. Infracommunities of wood frogs and blue-spotted salamanders had intermediate values for these measures of parasitism, whereas spring peeper and newt infracommunities had the lowest values. In addition to relative vagility, feeding habits and habitat preference were likely important in helminth community structure. Body size also seemed to play a role because mean wet weight of host species followed the same general trend as values of parasitism. However, effects of size were variable within host species and difficult to separate from other aspects of host ecology.

Field evidence for leech-borne transmission of amphibian Ichthyophonus sp.

Parasites have been implicated in mass mortality events and population declines of amphibians around the world. One pathogen associated with mortality events in North America is an Ichthyophonus sp.-like organism that affects red-spotted newts (Notophthalmus viridescens) and several frog species, yet little is known about the distribution of this pathogen in wild populations or the mechanism of transmission. In an effort to identify factors influencing the distribution and abundance of this pathogen, we measured Ichthyophonus sp. prevalence and a series of factors that could contribute to transmission in 16 newt populations during spring 2004. In contrast to our initial hypotheses of trophic transmission, several lines of evidence suggested a role for the amphibian leech (Placobdella picta) in Ichthyophonus sp. transmission. We propose the mechanistic hypothesis that a leech acquires Ichthyophonus sp. infection when inserting its proboscis into the muscles beneath the skin of infected newts and transmits the infection to other newts in subsequent feeding bouts. We also found effects of host sex, body mass, and breeding condition on Ichthyophonus sp. prevalence and the number of attached leeches. The number of leeches attached to newts was strongly related to the proportion of newt habitat containing emergent vegetation, suggesting that anthropogenic eutrophication might lead to more frequent or severe outbreaks of Ichthyophonus sp. infection in amphibians.

Longitudinal patterns of trypanosome infections in red-spotted newts.

Longitudinal data on Trypanosoma diemyctyli infections in individual red-spotted newts, Notophthalmus viridescens, were collected over a 5-yr period. Many newts (37%) retained infections throughout their adult lives and only 4.5% appeared to lose infections following their initial autumn sample. Individual infection levels were higher at their first sample as compared to their second sample. Newts of known age were transplanted between leech-free and leech-infested ponds. The time course of infection between previously exposed and unexposed individuals was similar when both were caged in a leech-infested pond. Previously infected individuals maintained stationary chronic levels for 3 mo in both leech-infected and leech-free ponds. The trends observed in these longitudinal data suggested that transmission by leeches is necessary for infection, that continued transmission does not significantly alter the dynamics of infrapopulation growth and stasis, and that constraints on trypanosome population growth occurred at the host individual level.