Short Term Minimum Water Temperatures Determine Levels of Infection by the Amphibian Chytrid Fungus in Alytes obstetricans Tadpoles

Abstract

Amphibians are one of the groups of wildlife most seriously threatened by emerging infectious disease. In particular, chytridiomycosis, caused by the aquatic fungus Batrachochytrium dendrobatidis, is responsible for amphibian species declines on a worldwide scale. Population-level outcomes following the introduction of the pathogen are context dependent and mediated by a large suite of abiotic and biotic variables. In particular, studies have shown that temperature has a key role in determining infection dynamics owing to the ectothermic nature of the amphibian host and temperature-dependency of pathogen growth rates. To assess the temperature-dependent seasonality of infectious burdens in a susceptible host species, we monitored lowland populations of larval midwife toads, Alytes obstetricians, in Central Spain throughout the year. We found that infections were highly seasonal, and inversely correlated against water temperature, with the highest burdens of infection seen during the colder months. Short-term impacts of water-temperature were found, with the minimum temperatures occurring before sampling being more highly predictive of infectious burdens than were longer-term spans of temperature. Our results will be useful for selecting the optimal time for disease surveys and, more broadly, for determining the key periods to undertake disease mitigation.

Early exposure to Batrachochytrium dendrobatidis causes profound immunosuppression in amphibians

“…The ratio of neutrophils/lymphocytes was not related to Bd infection load in tadpoles after controlling for mass and Gosner stage (F 3,29 =0.6427, p=0.5945). The infection intensity of tadpoles ranged between 270 and 8690 Bd genome equivalents, which is in accordance with values found in previous studies (Fernández-Beaskoetxea et al 2015).…”

“…Tadpoles were wild caught from infected and non-infected populations of the Provinces of Teruel and Zamora (north and central Spain). Alytes obstetricans is an amphibian species highly susceptible to Bd with an extremely long larval stage characterised by high prevalences and fungal loads upon metamorphic climax (Fernández-Beaskoetxea et al 2015). To determine the leukocyte profiles, tadpoles were raised in captivity until metamorphosis and blood samples were obtained by heart puncture from tadpoles and juveniles prior to terminal anaesthesia.…”

Reduced immune function predicts disease susceptibility in frogs infected with a deadly fungal pathogen

“…Interestingly, some natural populations of L. yavapaiensis maintain similarly high Bd loads [millions of genome equivalents (GE)] with no indication of morbidity or mortality from chytridiomycosis, whereas other populations exhibit chytridiomycosis die-offs at significantly lower infection intensities, and climatic factors predict these differences ( Savage et al ., 2015 ). This pattern holds across a range of amphibian species and geographical regions; temperature largely explains the variation in Bd infection intensity among individuals in a number of recent field- and laboratory-based studies ( Murray et al , 2013 ; Fernández-Beaskoetxea et al , 2015 ; Tinsley et al , 2015 ).…”

Infection with Batrachochytrium dendrobatidis lowers heat tolerance of tadpole hosts and cannot be cleared by brief exposure to CTmax

“…Environmental conditions can have a large influence on Bd host-parasite dynamics [5, 6], temperature being a major factor influencing its prevalence (i.e., the proportion of infected animals) and virulence [7]. Growth and reproductive characteristics of Bd are known to highly depend on temperature [8–10], and there is a negative correlation between temperature and Bd prevalence or pathogen load, chytrid infections often being more severe in winter or in colder areas [6, 11, 12].…”