Field evidence of enzootic chytrid infection in a Mediterranean mountain amphibian

Abstract

Emerging infectious diseases drive amphibian population declines worldwide. The chytrid fungus Batrachochytrium dendrobatidis ( Bd ) has caused severe losses, although impacts vary among species and environments. The Apennine yellow-bellied toad ( Bombina variegata pachypus ), endemic to Italy, has declined since the 1990s, yet Bd status in southern populations is poorly known. In 2024, we screened three populations within the Appennino Lucano, Val d Agri e Lagonegrese National Park (southern Italy). Fifty adults, representing nearly the entire local populations, were sampled from three artificial aquatic breeding sites (livestock drinking-troughs). Quantitative PCR detected Bd DNA in two asymptomatic individuals (4% prevalence; 10.05 and 18.99 GE µL⁻ 1 ). Low prevalence and absence of clinical signs are consistent with enzootic persistence rather than an epizootic outbreak. The species’ thermophilous breeding ecology, relying on shallow, sun-exposed water bodies, may contribute to environmental conditions less favourable to Bd growth. Genetic diversity and skin microbiome defences may further enhance resistance. However, habitat fragmentation could increase vulnerability by reducing connectivity and recolonization. Our results highlight the potential role of open, sunlit rural water bodies in supporting reproduction and potentially limiting disease impact.

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