Population genetics, trait mapping and fungal pathogen surveillance using untargeted sequencing in timber rattlesnakes ( <i>Crotalus horridus)</i>

Abstract Timber rattlesnakes ( Crotalus horridus ) face escalating threats in the Northeastern Appalachians, including habitat fragmentation, human encroachment, and the fungal pathogen Ophidiomyces ophiodiicola . Using untargeted sequencing of DNA extracted from scale clips, we generated both host whole-genome and metagenomic data for 97 snakes from eight populations. Analysis of the snake genomes shows the populations surveyed exhibit relatively low levels of inbreeding and are genetically distinct, but that the degree of separation correlates only weakly with geographic distance. A genome-wide association analysis identified a locus associated with black-to-yellow color variation that contains an aldehyde dehydrogenase gene ( ALDH4A1 ) related to genes involved in hair color differences in humans. Metagenomic analysis showed that O. ophiodiicola read counts were generally higher in snakes exhibiting clinical signs of Snake Fungal Disease, but some visually asymptomatic snakes had high pathogen loads. Together, these findings highlight the dual utility of untargeted sequencing for population genetics and pathogen surveillance, providing a foundation for future studies of adaptation, disease dynamics, and conservation in this declining species.