Development and Laboratory Validation of a Field-Deployable CRISPR-Cas12a eDNA Assay for Phylogeographic Lineage...

Environmental DNA (eDNA) tools are increasingly used for biodiversity monitoring, with most existing assays targeting species-level identification. However, the use of eDNA to resolve intraspecific genetic variation remains rare and methodologically underdeveloped. This study presents the development and laboratory validation of a novel molecular assay capable of detecting specific phylogeographic lineages, advancing eDNA applications by enabling resolution below the species level. The assay combines Recombinase Polymerase Amplification (RPA) and CRISPR-Cas12a technologies with a lateral flow platform for field-ready, on-site detection. Irish Arctic char (Salvelinus alpinus) was selected as the model due to its conservation relevance and post-glacial lineage diversity in Ireland. Mitochondrial genome sequencing of known Irish lineages identified a Protospacer Adjacent Motif (PAM) site unique to the Atlantic Subclade 1 lineage, allowing clear discrimination from co-occurring lineages. Two assays were optimised: a species-specific assay detecting all Arctic char lineages and a lineage-specific assay targeting Lineage 1. Both showed high sensitivity and specificity under laboratory conditions, with LbCas12a outperforming AsCas12a at optimised buffer concentrations. The lateral flow adaptation, utilising a dual-labelled FAM-Biotin probe, enabled portable and rapid detection with minimal equipment. Field validation using eDNA from Irish lakes highlighted the need for improved sampling protocols, as lake-edge surface samples failed to yield detections. This assay represents the first reported example of a CRISPR-based eDNA tool for phylogeographic lineage detection in the field. It offers a novel, non-invasive, and scalable approach to fine-scale ecological monitoring and establishes a foundation for future conservation tools targeting intraspecific diversity.