Abstract
Many salmonid species exist in highly structured and isolated
populations, and are susceptible to habitat fragmentation and
disturbances. Gila Trout (Oncorhynchus gilae) is a threatened
species found in the Southwestern United States. Gila trout is managed
to preserve remnant populations (i.e. lineages) distributed across a
fragmented landscape. We evaluated genomic variation within and among
remaining lineages of Gila Trout using RADseq to assess how drift and
selection have structured populations using neutral and outlier loci. We
also examined whether a signature of hybridization was evident in relict
populations. Despite Gila Trout lineages being significantly
differentiated and highly structured with low effective population
sizes, we found that most lineages maintained genomic diversity and were
potentially locally adapted. Hybridization with non-native Rainbow Trout
(O. mykiss) was not detected in any lineage. Some lineages may
have experienced recent population bottlenecks perhaps associated with
mortality from drought and severe wildfires. Current management
strategies should be reevaluated and adapted to better account for
long-term effects of climate change. Specifically, we suggest
reconnecting some populations via dendritic stream networks to
facilitate natural dispersal in a metapopulation context. This would
allow natural genetic mixing on the landscape and potentially increase
adaptive potential. Furthermore, genetic rescue should be implemented to
preserve integrity of the unique Spruce Creek lineage that is currently
compromised by extremely low diversity.