Aggregation behavior of Terrestrial Isopods as an Indicator to assess Biotic and Abiotic Stressors

Shifts in abiotic and biotic factors can alter the behavior of edaphic organisms and compromise the soil habitat function. This study explores the impact of temperature, soil moisture, salinity, pH, edaphic interference, oleic acid (necromone signals), and microbial community dilution on the aggregation behavior of Porcellionides pruinosus as a potential new indicator of population-level stress. Aggregation patterns were quantified using two novel ecological indices, the Disaggregation Index, which measures groups formed by a single individual or at most two individuals, and the Disaggregation in Group Index, which quantifies the total number of groups formed at the end of the experiments. The disaggregation indices range from 0 (highest level of aggregation) to 1 (highest level of disaggregation). A value of 0.5 has been set as the concern threshold, that is, the point at which more than 50% of the population is fragmented. Results reveal that most environmental factors modulate aggregation. A U-shaped disaggregation was observed for temperature and soil moisture, with population fragmentation occurring at both extremes. In contrast, salinity and biotic factors caused disaggregation following a sigmoidal curve. Only pH did not influence the aggregation behavior; on the contrary, an aggregation trend was observed at the lower and upper limits tested, showing a bimodal distribution. The cluster analysis revealed three primary trends in the disaggregation response curves as a function of stress level: Parabolic, sigmoidal and bimodal. Given the need for tools to assess soil health and monitor habitat function, these findings demonstrate that terrestrial isopods' aggregation behavior is a sensitive indicator of soil changes and can be used to detect and quantify environmental stress through measurable changes in degree of aggregation. Valuable insights on laboratory conditions are also produced to standardize this bioassay.