Joint effects of habitat, zooplankton, host stage structure and diversity on amphibian chytrid

Abstract

Why does the severity of parasite infection differ dramatically across habitats? This question remains challenging to answer because multiple correlated pathways drive disease. Here, we examined habitat-disease links through direct effects on parasites and indirect effects on parasite predators (zooplankton), host diversity and key life stages of hosts. We used a case study of amphibian hosts and the chytrid fungus, Batrachochytrium dendrobatidis, in a set of permanent and ephemeral alpine ponds. A field experiment showed that ultraviolet radiation (UVR) killed the free-living infectious stage of the parasite. Yet, permanent ponds with more UVR exposure had higher infection prevalence. Two habitat-related indirect effects worked together to counteract parasite losses from UVR: (i) UVR reduced the density of parasite predators and (ii) permanent sites fostered multi-season host larvae that fuelled parasite production. Host diversity was unlinked to hydroperiod or UVR but counteracted parasite gains; sites with higher diversity of host species had lower prevalence of infection. Thus, while habitat structure explained considerable variation in infection prevalence through two indirect pathways, it could not account for everything. This study demonstrates the importance of creating mechanistic, food web-based links between multiple habitat dimensions and disease.

Observations on the intensity and prevalence of <em>Batrachochytridium dendrobatidis</em> in sympatric and allopatric <em>Epidalea calamita</em> (native) and <em>Discoglossus pictus</em> (invasive) populations

“…Up to date, no symptomatology or mortality due to Bd infection has been detected in the surveyed area. However, parasite infection differs dramatically across years and habitats, and severe epidemics occur infrequently and unpredictably in a relatively small subset of habitats (Hite et al, 2016). The study conducted by Hite et al (2016) found that the structure of habitat and the existence of permanent waterbodies were linked to the density of Bd.…”

“…However, parasite infection differs dramatically across years and habitats, and severe epidemics occur infrequently and unpredictably in a relatively small subset of habitats (Hite et al, 2016). The study conducted by Hite et al (2016) found that the structure of habitat and the existence of permanent waterbodies were linked to the density of Bd. Our results show great differences among populations, possibly caused by important differences in structure among ephemeral or temporary ponds.…”

Invasive African clawed frogs in California: A reservoir for or predator against the chytrid fungus?

“…The zooplankton are also more appropriate regulators of Bd abundance than is X . laevis larvae because they are native to most aquatic systems and have been shown to potentially reduce Bd abundance through predation [ 13 ].…”

“…Bd transmission occurs through a motile zoospore stage that swims through the water to infect a new host or re-infect the current host. Zooplankton, such as Daphnia [ 6 , 7 , 12 , 13 ] and ciliates [ 14 ], consume the motile zoospore stage of Bd from the water column. The reduction of Bd zoospores may lead to reduced transmission rates to amphibians in the water [ 7 , 13 , 14 ].…”

Increased tropospheric ozone levels enhance pathogen infection levels of amphibians

“…Chytridiomycosis in the Spanish Central Range negatively affects the population-level dynamics of several amphibian species. The variability of its effects has been associated with water temperature variability (Fernandez-Beaskoetxea et al, 2015) and UV-B exposure (Ortíz-Santaliestra et al, 2011;Hite et al, 2016). However, the relationship between the presence of Bd and abiotic factors is not always clear, and the relationship between environmental variables and the prevalence of the infections is weak (Walker et al, 2010).…”