Invasive crayfish in a desert spring system: Using landscape genetics to inform ecological restoration

Background/Question/Methods

The delimitation of dispersal routes utilized by invasive species has the potential to direct management efforts in invaded systems, and may be used to prevent the invasion of native communities. Landscape genetics provides a powerful tool to determine post-invasion movement corridors by integrating inferences of gene flow between populations with landscape connectivity metrics. This technique was used to describe dispersal patterns of invasive red swamp crayfish (Procambarus clarkii) through Ash Meadows, a spring system and endemic hotspot in the Mojave Desert. A combination of anthropogenic habitat degradation and the establishment of invasive species like P. clarkii has caused the extinction of an endemic poolfish, and extirpations and severe population declines of endangered pupfish in Ash Meadows. Although many Ash Meadows springs are hydrologically isolated, intermittent connectivity occurs during heavy precipitation events – allowing for dispersal of native and invasive species. We used a landscape genetics approach in combination with Geographic Information System (GIS) mapping of drainages to test alternative hypotheses of P. clarkii invasion routes and colonization events throughout Ash Meadows. Mitochondrial DNA (COI) and microsatellite markers were used to infer colonization events and gene flow for 15 sampled populations. 

Results/Conclusions

Modeled historic outflows, in conjunction with waterway mapping based on aerial imagery and LiDAR data, reveal highly variable drainage routes across the flat topography of Ash Meadows. These GIS maps and models explain how flooding events have caused the outflows of normally isolated springs to connect to a variety of other outflows, providing multiple corridors for movement of aquatic species between springs. Estimates of gene flow between P. clarkii populations (F_ST and assignment tests) highlight the drainages utilized by crayfish to reach distal springs. Additionally, analyses of mtDNA haplotype diversity and distribution suggests both single and multiple colonization events in isolated springs. These results will inform ecological restoration in Ash Meadows by directing the placement of barriers to prevent reinvasion of distal springs after eradication of P. clarkii populations.