Rethink the Sink: Urban cores act as leaky sinks to maintain regional gene flow in coyotes

Urbanization is an accelerating evolutionary force, yet the patterns and drivers of urban gene flow remain largely obscured. This leaves a critical gap in testing the interplay between demographic and genetic models of urban connectivity. Specifically: the urban fragmentation model, where structural barriers restrict gene flow and drive genetic drift; the urban facilitation model, where permeable matrices enhance functional connectivity; and the urban sink hypothesis, a demographic model where high mortality creates unsustainable population sinks. We used high-resolution RAD-capture data to conduct landscape genomics and gene flow analyses to resolve these models and investigate contemporary evolution in urban coyotes (Canis latrans) across the greater Los Angeles, CA, USA metropolitan area. By incorporating fine-scale environmental, social-ecological, and historical variables of the built environment, we rigorously assessed how urban heterogeneity shapes intra-city evolutionary dynamics. We found weak population structure, heavily influenced by family groups. There was extensive landscape permeability and gene flow across the study area including across four major highways. We also identified heavily asymmetric gene flow from exurban source populations into the urban core, supporting the urban sink paradigm. However, rather than acting as a genetic dead-end, the urban matrix showed striking functional heterogeneity: one urban core functioned as a 'genetic sponge,' absorbing unique transient alleles from multiple surrounding sources, and both urban cores operated as permeable 'leaky sinks,' exporting critical gene flow to other populations. Consequently, urban demographic sinks can simultaneously act as vital genetic bridges. Our findings reject a pure urban fragmentation model while demonstrating that demographic sink dynamics and genetic facilitation are not mutually exclusive. This demonstrates that high-turnover urban sinks can buffer regional biodiversity against genetic erosion, highlighting the need to prioritize matrix permeability and inter-patch connectivity in urban conservation strategies.