Anthropogenic environmental changes expose wildlife to numerous stressors, including pollution and diseases. Over the past 70 years, plastic production has increased exponentially, leading to significant plastic waste accumulation in terrestrial and marine environments. This waste can persists for centuries and poses growing concerns for wildlife. Microplastics (MP), defined as plastic particles between 1 mm and 1 μm in diameter, accumulate in freshwater primarily through direct deposition and agricultural runoff, negatively impacting aquatic food webs. Amphibians have experienced dramatic global declines due to the complex interaction of human-induced factors such as environmental pollution and infectious diseases. Amphibians are particularly susceptible to invasive pathogens like Ranaviruses (Rv), which can cause mass mortality events and local extinctions. Rv can be transmitted through direct contact or waterborne exposure to virions. The inconsistent outcomes of Rv epidemics, ranging from no apparent mortality to mass die-offs, suggest that environmental variation may influence disease outbreaks. Recent evidence indicates that MP accumulated in the aquatic environment can absorb heavy metals, antibiotics, persistent organic contaminants, and even pathogens like viruses. Amphibian larvae, exposed to MP primarily through ingestion with food or respiration, suffer from reduced growth, development, immune defence, reproductive output, and survival. Consequently, MP particles may adsorb deadly Rv, potentially increasing disease risk and exacerbating disease outcomes where Rv and MP co-occur in amphibian breeding waters. This raises the question of how the permanent presence of an emerging anthropogenic stressor (MP) in amphibian breeding ponds influences susceptibility to an invasive pathogen (Rv), and how these two stressors interact with each other and the amphibian host in the aquatic environment. To address this knowledge gap, I plan to investigate this issue on three different levels: (1) surveying the co-occurrence of the two stressors in situ, (2) conducting manipulative experiments on agile frog (Rana dalmatina) tadpoles in vivo, and (3) performing transmission studies in vitro. Specifically, with an extensive field survey (1.1), we will examine the environmental presence of the two stressors in breeding ponds along an urbanisation gradient using filtering and eDNA analysis. We will also assess their prevalence in amphibians at different life stages, combining non-invasive and invasive detection methods. Through manipulative experiments (2.1), I will study the developmental toxicity effects of natural and artificial microparticles during larval development using an MP-naïve population and examine (2.2) phenotypic divergence via local adaptations and phenotypic plasticity of amphibians using stressor-naïve and stressor-adapted populations. Additionally, with a manipulative experiment (2.3), the cumulative effects of MP and Rv will be assessed on survival, life-history, and plastic morphological and behavioural anti-predatory responses of tadpoles. Finally, we will experimentally investigate that (3.1) how different polymer types, sizes, and concentrations of MP, following an accumulation period in Rv liquid cultures, affect the potential vector role in transmission. Additionally, we will quantify (2.4) the Rv-exposed MPs transmission success between tadpoles and their effect on disease progression. This complex approach will yield exceptionally detailed insights into the interactive and cumulative effects of stressors on amphibian populations and can significantly contribute to more effective conservation implications.
New STARTING grant of Dávid Herczeg
