Of poisons and parasites—the defensive role of tetrodotoxin against infections in newts

• Published in: The Journal of animal ecology 2018-07, Vol.87 (4), p.1192-1204
• Main Authors: Johnson, Pieter T. J., Calhoun, Dana M., Stokes, Amber N., Susbilla, Calvin B., McDevitt-Galles, Travis, Briggs, Cheryl J., Hoverman, Jason T., Tkach, Vasyl V., de Roode, Jacobus C.
• Format: Article
• Language: English
• Subjects: amphibian decline; Amphibians; animal toxicity; aposematism; Batrachochytrium; Body size; disease ecology; Females; Fungi; host–parasite interactions; immunity; Immunology; Infections; Infectious diseases; Leukocytes; Males; natural enemy ecology; Organic chemistry; Parasite and disease ecology; Parasites; Parasitic diseases; Poisons; Populations; Predation; Predators; Skin; Snakes; Sympatric populations; Taricha granulosa; Taricha torosa; Tetrodotoxin; Toxicity; Toxins; Viruses
• ISSN: 0021-8790; 1365-2656
• DOI: 10.1111/1365-2656.12816

1. Classical research on animal toxicity has focused on the role of toxins in protection against predators, but recent studies suggest these same compounds can offer a powerful defense against parasites and infectious diseases. 2. Newts in the genus Taricha are brightly colored and contain the potent neurotoxin, tetrodotoxin (TTX), which is hypothesized to have evolved as a defense against vertebrate predators such as garter snakes. However, newt populations often vary dramatically in toxicity, which is only partially explained by predation pressure. 3. The primary aim of this study was to evaluate the relationships between TTX concentration and infection by parasites. By systematically assessing micro- and macroparasite infection among 345 adult newts (sympatric populations of Taricha granulosa and T. torosa), we detected 18 unique taxa of helminths, fungi, viruses and protozoans. 4. For both newt species, per-host concentrations of TTX, which varied from undetectable to >60 µg/cm² skin, negatively predicted overall parasite richness as well as the likelihood of infection by the chytrid fungus, Batrachochytrium dendrobatidis, and ranavirus. No such effect was found on infection load among infected hosts. Despite commonly occuring at the same wetlands, T. torosa supported higher parasite richness and average infection load than T. granulosa. Host body size and sex (females > males) tended to positively predict infection levels in both species. For hosts in which we quantified leucocyte profiles, total white blood cell count correlated positively with both parasite richness and total infection load. 5. By coupling data on host toxicity and infection by a broad range of micro- and macroparasites, these results suggest that-alongside its effects on predators—tetrodotoxin may help protect newts against parasitic infections, highlighting the importance of integrative research on animal chemistry, immunological defenses and natural enemy ecology.