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Anthropogenic dispersion of selected germplasm creates a geographic mosaic of contrasting maternal lineages in Crescentia cujete from Mesoamerica

Aguirre-Dugua, Xitlali, Llanderal-Mendoza, Jesús, González-Rodríguez, Antonio, Eguiarte, LuisE., Casas, Alejandro
Tree genetics & genomes 2018 v.14 no.2 pp. 18
Crescentia alata, Crescentia cujete, artificial selection, chloroplasts, domestication, farmers, geographical distribution, germplasm, haplotypes, home gardens, humans, interviews, microsatellite repeats, phenotype, seed dispersal, seeds, trees, Central America
The modification of the genetic/phenotypic composition of plant populations through artificial selection occurs both through time and space. We analyzed the role of human dispersal on the geographic distribution of maternal lineages of Crescentia cujete in Mesoamerica. We sampled 28 homegarden (224 individuals) and 12 wild populations (159 individuals). Semi-structured interviews provided information on the origin of cultivated trees. Six chloroplast microsatellites allowed for the identification of 21 haplotypes, four of them exclusively in 83% of homegarden trees. Wild haplotypes from local C. cujete and Crescentia alata were found at low frequencies (17%) under cultivation. Cultivated and wild haplotypes constituted two different haplogroups. Accordingly, barriers to seed dispersal were detected among neighboring cultivated and wild populations. Recorded events of human dispersal of cuttings and seeds attaining up to > 200 km agreed with homegardens’ lower diversity (Nei’s h = 0.55, dropping to 0.32 when excluding wild haplotypes). Wild populations displayed high diversity (h = 0.71) and isolation by distance, in agreement with physiographic provinces. Our results support the native status of wild C. cujete and a Pre-Columbian introduction of cultivated lineages that generated a novel genetic mosaic superimposed on native maternal lineages. The results reveal the active role of farmers in maintaining the identity of cultivated lineages through time, while chloroplast capture from local congeners has increased the diversity of maternal lineages under cultivation. Additional data are needed on the origins of cultivated lineages, but our results contribute new insights into tree domestication in this center of crop diversity.