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In some cases, admixture occurred upon secondary contact with other lineages. erminea experienced serial bouts of climate-mediated introgression, a repeated signature of introgressive hybridization should be evident in the genomes of refugial descendants now being explored on a genomic scale.We define introgressive hybridization as interbreeding and the movement of alleles between two genetically distinct lineages.Phylogeography of high-latitude Mustela erminea, the stoat or ermine (Family: Mustelidae) delineates four genetically distinct mitochondrial lineages geographically corresponding to these four refugia.Although glacial isolation appears to have impacted the long-term evolution of this mammalian meso-carnivore, the effects of glacial recession and subsequent secondary contact between refugial lineages remain unexplored.To understand how recurrent periods of isolation and contact may have impacted evolution at high latitudes, we investigated introgression dynamics in the stoat (Mustela erminea), a Holarctic mammalian carnivore, using whole-genome sequences.We identify two spatio-temporally distinct episodes of introgression coincident with large-scale climatic shifts: contemporary introgression in a mainland contact zone and ancient contact ~200 km south of the contemporary zone, in the archipelagos along North America’s North Pacific Coast.e PSMC plots for hybrid samples (YTAK, SYT, NPC) and their source populations (Beringia, East).
K = 6 has the lowest cross-validation score for our data and shows an identical pattern to K3 but with additional substructure within the East clade, indicative of microrefugial substructure near Appalachia and consistent with PCA results suggesting East expansion from a single refugium Phylogenetic placement of admixed samples and historical demography.
b PCA with the West population removed demonstrates additional structure within the East clade, centered on Vermont (VT).