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- High prevalence and seasonal persistence of amphibian Chytrid fungus infections in the desert-dwelling amargosa toad, Anaxyrus nelsoni
- 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 mid-summer 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.
- Forrest, Edwards, Rivera, SJÖBERG, JAEGER
- Nearshore Pelagic Microbial Community Abundance Affects Recruitment Success of Giant Kelp, Macrocystis pyrifera
- Marine microbes mediate key ecological processes in kelp forest ecosystems and interact with the macroalgae. Pelagic and biofilm-associated microbes interact with macroalgal propagules at multiple stages of recruitment, yet these interactions have not been described for M. pyrifera. Here we investigate the influence of microbes from coastal environments on recruitment of giant kelp, Macrocystis pyrifera. Through repeated laboratory experiments we tested the effects of altered pelagic microbial abundance on the settlement and development of the microscopic propagules of M. pyrifera during recruitment. M. pyrifera zoospores were reared in laboratory microcosms exposed to environmental microbial community seawater source, throughout the complete haploid stages of the recruitment cycle, including zoospore release, followed by zoospore settlement, to gametophyte germination and development. We altered the microbial abundance states differentially in three independent experiments with repeated trials, where microbes were a) present or absent in seawater, b) altered in community composition, and c) altered in abundance. Within the third experiment, we also tested the effect of nearshore versus offshore microbial communities on the macroalgal propagules. Distinct pelagic microbial communities were collected from two southern California temperate environments reflecting contrasting intensity of human influence, the nearshore Point Loma kelp forest and the offshore Santa Catalina Island kelp forest. The Point Loma kelp forest is a high impacted coastal region adjacent to the populous San Diego Bay; whereas the kelp forest at Catalina Island is a low impacted region of the Channel Islands, 40 kilometers offshore the southern California coast, and is adjacent to a marine protected area. Kelp gametophytes reared with nearshore Point Loma microbes showed lower survival, growth, and deteriorated morphology compared to gametophytes with the offshore Catalina Island microbial community, and these effects were magnified under high microbial abundances. Reducing abundance of Point Loma microbes restored M. pyrifera propagule success. Yet an intermediate microbial abundance was optimal for kelp propagules reared with Catalina Island microbes, suggesting that microbes also have a beneficial influence on kelp. Our study shows that pelagic microbes from nearshore and offshore environments are differentially influencing kelp propagule success, which has significant implications for kelp recruitment and kelp forest ecosystem health.
- Morris, Haggerty, Papudeshi, Vega, Edwards, Dinsdale