Title

High prevalence and seasonal persistence of amphibian chytrid fungus infections in the desert-dwelling Amargosa toad, Anaxyrus nelsoni

Document Type

Article

Abstract

Hot summer conditions in the Mojave Desert of southern Nevada, USA, would not appear to favor the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd), which has a thermal limit around 28° C. Within this region, however, we detected Bd in an amphibian of conservation concern, the Amargosa Toad (Anaxyrus nelsoni). We assessed Bd prevalence and infection intensity (Bd load) across spring and summer in A. nelsoni at two sites over two years, and in the sympatric American Bullfrog, Lithobates catesbeianus, at one site during one year. We observed high overall Bd prevalence in both A. nelsoni (48%) and L. catesbeianus (74%), with Bd loads in A. nelsoni reaching 404,000 copies of ribosomal RNA internal transcribed spacer 1 (ITS 1 copy number; CN). Prevalence remained high in midsummer when air temperatures during sampling were 23.7–32.5° C and daily highs reached 36.1–37.8° C. We observed trends toward lower Bd prevalence in A. nelsoni during late summer, but even then infection prevalence was at least 26%, with Bd loads reaching 69,100 CN. The high levels of infection during summer months may be explained by the actual conditions experienced by these amphibians. Water temperatures associated with captures (13.2–27.8° C) and body temperatures of A. nelsoni (11.1–26.6° C) remained predominately favorable to Bd throughout summer sampling periods. The mostly nocturnal behavior of A. nelsoni also likely limited temperature extremes. Recapture data showed that A. nelsoni can clear Bd infection, and we observed no individuals with obvious symptoms of disease, indicating potential resistance to, or tolerance of, the pathogen in this species.