Development of a new biosensor based on behavioural responses of (Ord. Isopoda) as a screening tool for detecting the quality of soil ecosystems

The loss of soil ecosystem functions and services represents a major threat to environmental sustainability and human well-being, particularly in the context of increasing anthropogenic pressures and large-scale soil degradation. Traditional approaches to soil quality assessment, largely based on physical and chemical parameters, are often insufficient to capture the biological complexity and ecological functioning of soils. Consequently, there is an urgent need for innovative, ecologically relevant, rapid, and cost-effective indicators capable of detecting early signs of soil degradation and supporting risk assessment and management strategies. This PhD thesis addresses these challenges by developing and validating a novel behavioural ecotoxicological endpoint based on the combined assessment of avoidance and population disaggregation responses in gregarious soil invertebrates, with a particular focus on the terrestrial isopod Porcellionides pruinosus. By integrating behavioural ecology into soil ecotoxicology, the proposed approach aims to capture not only individual stress responses but also alterations in population structure and adaptive capacity. The thesis explores the sensitivity and versatility of this endpoint under a wide range of conditions, including exposure to physical and chemical contaminants, abiotic and biotic stressors, real urban soils, and soils amended with biochar. Experimental results demonstrate that disaggregation responses occur at different levels of soil contamination than avoidance, revealing sublethal effects that may compromise population cohesion and soil habitat function even when organisms are able to migrate, reinforcing the need to use the two endpoints jointly. We demonstrated that disaggregation effects may affect even by abioic and biotic factors, suggesting the versatility of the bioassay even for other soil stressors. Furthermore, specific physicochemical properties of contaminants, such as Henry law constant of chemicals, were identified as a potential key descriptor of behavioural disruption, suggesting a potential role of volatility in the insurgence of social alterations. Behavioural outcomes were also shown a great versatility as rapid screening test for assessing reductions in invertebrate biodiversity in real soils, highlighting the ecological relevance of the proposed endpoint. Overall, this thesis demonstrates that behavioural bioassays integrating avoidance and disaggregation responses provide a sensitive and realistic early-warning system for assessing soil health, supporting their application in soil monitoring, biodiversity conservation, and sustainable land management.