Genetic structure and diversity identify incipient domestication of Piquiá [ Caryocar villosum (Aubl.) pers.] along the lower Tapajós River, Brazilian Amazonia

In Amazonia there are at least 85 arboreal species with domesticated populations, among which piquia [Caryocar villosum (Aubl.) Pers.] is widely distributed. In some regions, there is ethnobotanical evidence of domestication for its fruit. To understand more about piquia domestication, we evaluated genetic diversity and structure of two regions, sampling 130 trees in forests and homegardens (92 trees in the Tapajos National Forest and 38 in the Rio Ouro Preto Extractive Reserve), using seven microsatellite markers. In Tapajos, piquia trees form large aggregations near archaeological sites, while in Ouro Preto the aggregations are smaller. The Tapajos presented higher effective number of alleles, allelic richness and expected heterozygosity, with lower observed heterozygosity and, consequently, a higher fixation index and lower apparent outcrossing rate. Genetic structure exists between regions, forming four probable groups: one that corresponds mainly to Ouro Preto and the others in the Tapajos. When the Tapajos was analyzed separately, we found four genetic groups that do not correspond to homegarden and forest systems. In the homegardens we found lower number of effective alleles, allelic richness and observed heterozygosity. These subtle differences in genetic diversity between homegarden and forest trees identify piquia’s incipient domestication, agreeing with ethnobotanical evidence. The piquia stands near archaeological sites and the existence of four genetic groups suggest that piquia was introduced into the Tapajos during pre-Columbian times from at least three different sources. Trail registration numbers: SisBio—58609-1, from August 5, 2017; SisGen—A3D06AA, from March 26, 2020.