Abstract: Climate change is rapidly shifting the geographic range of thousands of species, but empirical research has not fully addressed the complexities of this global ecological trend. While many theoretical studies have shown that post-expansion populations experience decreased genetic variation, few studies have considered how the landscape mediates the spatial structure of genetic variation aside from distance alone.
The goals of this study were to 1.) understand broad genetic outcomes of expansion for the individuals in the newly colonized areas, 2.) determine which individuals’ genes contribute to future populations, and 3.) investigate how the landscape structures geneflow during expansion.
We use the range expansion of green jay (Cyanocorax yncas) in South Texas as a model system to explore the relationship between an expanding population and the landscape. Historically, green jay were found within about 50 miles of the Rio Grande in South Texas (current U.S. – Mexico Border), since about 1980 the species has steadily expanded its northern range limit to about 250 miles north of the Rio Grande. Using whole genome sequencing data from green jay (n=65) captured throughout 22 sites in Texas covering the range expansion area, we compared measures of genetic variation and heterozygosity with regional landscape and climatic variables. We then compared trends of genetic variation with simple null models of expansion across the same landscape to understand the causes of our measured differences in genetic variation. We also sampled 9 sites throughout Mexico to act as an outgroup for genetic analysis.
At a coarse spatial scale, our findings follow the expected trend of genetic variation decreasing as distance from the source population increases. This trend is most significant when comparing samples from Texas and Northern Mexico with samples from Southern Mexico. At a fine spatial scale, our findings indicate that range expansion may follow predictable pathways linked to the resource usage of the expanding species, in the case of green jay, riparian corridors. Preliminary results also indicate some climate gene associations, but further sampling will be necessary to determine if these associations are caused by selection or spatial autocorrelation. Our findings show that future studies of range expansion and species invasion dynamics should consider the role of resources and the landscape in mediating the pathway of expansion.
