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Identifying spatial patterns of gene flow in the Blainville's horned lizard (Phrynosoma blainvillii) in urban Southern California
Landscape genetics combines principles of landscape ecology and population genetics to determine the effect of landscape characteristics on the functional connectivity of populations. Functional connectivity, the degree to which organisms move across the landscape, provides a proxy for gene flow and is limited by characteristics of the species and the environment. Identifying the landscape variables that promote or impede functional connectivity can provide a comprehensive look at the fine-scale genetic effects of natural and anthropogenic fragmentation and landscape change. Here, I examine population genetic structure and functional connectivity among populations of an ecological specialist, the Blainville's horned lizard (Phrynosoma blainvillii), in a fragmented landscape in southern California. I studied horned lizards from Los Angeles and Ventura counties at the boundary between evolutionary lineages. Using RADseq SNP data, I assessed population genetic structure, as inferred from Bayesian assignment tests. I interpreted the results in the context of broad-scale phylogeography, as well as at a fine-scale among habitat fragments in the highly urbanized region. Based on the ecological requirements of P. blainvillii, I developed a suite of hypotheses to test the at-site landscape variables that promote production of horned lizards and the between-site landscape variables that impede gene flow. I used gravity models to test which of the hypotheses best explained the estimates of functional connectivity. My results show strong population genetic structure across small habitat fragments in the study area, indicating an effect of habitat fragmentation. Further, the gravity models show that elements of topography, microclimate, soil and vegetation types, fire history, and anthropogenic development are important components of functional connectivity in this part of the species' range. Together, my results highlight the importance of natural and anthropogenic landscape factors at- and between-sites, species-specific characteristics, and habitat fragmentation on the patterns of genetic structure and connectivity of P. blainvillii in Southern California.