Asimina triloba genetic data

Dispersal and colonization are among the most important ecological processes for species persistence as they allow species to track changing environmental conditions. During the last glacial maximum (LGM), many cold-intolerant Northern Hemisphere plants retreated to southern glacial refugia. During subsequent warming periods, these species expanded their ranges northward. Interestingly, some tree species with limited seed dispersal migrated considerable distances after the LGM ~19,000 year before present (YBP). It has been hypothesized that indigenous peoples may have dispersed valued species, in some cases beyond the southern limits of the Laurentide Ice Sheet. To investigate this question we employed a molecular genetics approach on a widespread North American understory tree species whose fruit was valued by indigenous peoples. Twenty putative anthropogenic (near pre-Columbian habitations) and 62 wild populations of Asimina triloba (pawpaw), which produces the largest edible fruit of any North American tree, were genetically assayed with nine microsatellite loci.

Putative anthropogenic populations were characterized by reduced genetic diversity and greater excess heterozygosity relative to wild populations. Anthropogenic populations in regions that were glaciated during the LGM had profiles consistent with founder effects and reduced gene flow, and shared rare alleles with wild populations hundreds of kilometers away (mean = 723.1 km). Some of the most compelling evidence for human-mediated dispersal is that putative anthropogenic and wild populations sharing rare alleles were separated by significantly greater distances (mean = 695.3 km) than wild populations sharing rare alleles (mean = 607.1 km; p = 0.014). Collectively the genetic data suggest that long-distance dispersal played an important role in the distribution of pawpaw and is consistent with the hypothesized role of indigenous peoples.