View Program - 2022 Population, Evolutionary, and Quantitative Genetics Conference

Admixture is a phenomenon where divergent populations interbred, mixing their genomes, and it is increasingly appreciated as a central process in evolution. The biological phenomenon is thought to drive an array of evolutionary outcomes including shaping patterns of genetic variation, introducing novel adaptive variation, and introducing deleterious mutations. However, when this process is driven by human activity, threatening the genomic integrity of one or more parental species, it becomes a focus of conservation. Increased attention towards the Neotropical cats of the Leopardus genus was prompted after recent studies demonstrated extensive admixture among this species complex and the identification of a new species. In particular, interest in L. geoffroyi and L. guttulus was prompted after genetic studies identified extensive hybridization at their geographic contact zone in southern Brazil, both of which are threatened by human-mediated habitat fragmentation and destruction. This geographic contact zone is where two distinct biomes intersect, Pampas and Atlantic Forest, each of which is associated with one of the two hybridizing species. To understand the age and structure of this hybrid zone, we are using a low-coverage (~1x) whole-genome sequencing approach across ~200 individuals that span a ~2500 km range including the hybrid zone and both parental ranges. This data includes sequencing from 27 L. geoffroyi and 30 L. guttulus, with the remaining individuals representing a gradient of ancestry proportions. We have also sequenced the complete genomes from one pure individual per species at ~20x and ~40x depth. With this data we have identified introgression of genomic regions between species, and distinct signatures of admixture in the autosomes relative to the X chromosome. L. geoffroyi is the major ancestry in ~70% of the admixed individuals and expands southward from the hybrid zone towards the parental distribution of this species. The semi-arid Pampas ecoregion dominating this species range has experienced increased habitat alteration in recent decades. These results are indicative of human-mediated hybridization, and highlight the need for continued study of this complex hybrid zone.

Human-Mediated Admixture in South American Neotropical Cats