Abstract
Species in the early stages of domestication, in which wild and cultivated forms co-occur, provide important opportunities to develop and test hypotheses about the origins of crop species. Chrysophyllum cainito (Sapotaceae), the star apple or caimito, is a semidomesticated tree widely cultivated for its edible fruits; it is known to be native to the neotropics, but its precise geographic origins have not been firmly established. Here, we report results of microsatellite marker analyses supporting the hypothesis that the center of domestication for caimito was the Isthmus of Panama, a region in which few crop species are believed to have originated, despite its importance as a crossroads for the dispersal of domesticated plants between North and South America. Our data suggest that caimito was domesticated in a geographically restricted area while incorporating a diverse gene pool. These results refute the generally accepted Antillean origin of caimito, as well as alternative hypotheses that the species was domesticated independently in the two areas or over a broad geographic range including both. Human-mediated dispersal from Panama to the north and east was accompanied by strong reductions in both genotypic and phenotypic diversity. Within Panama, cultivated and wild trees show little neutral genetic divergence, in contrast to striking phenotypic differentiation in fruit and seed traits. In addition to providing a rare example of data that support the hypothesis of a narrow geographic origin on the Isthmus of Panama for a now widespread cultivated plant species, this study is one of the first investigations of the origins of an edible species of the large pantropical family Sapotaceae.
Highlights
Crop domestication is a long-term evolutionary process whereby wild plant populations become exploited via human management practices, leading to phenotypic and/ or genetic differences between domesticated forms and their wild progenitors
We sampled 206 individuals of Chrysophyllum cainito collected from localities in the Greater Antilles (Dominican Republic and Jamaica) and both northern (Mexico and Guatemala) and southern (Costa Rica and Panama) Mesoamerica, as well as a total of 26 individuals of the congeneric species C. argenteum, C. mexicanum, and C. oliviforme from areas where they were growing in proximity to C. cainito (Table 1)
Provenance of wild and domesticated Chrysophyllum cainito. Both Bayesian (Figs 2 and 3) and distance-based (Fig. 4) cluster analyses separated the sampled individuals of C. cainito into two major groups, one comprised primarily of wild and cultivated individuals sampled from Panama in southern Mesoamerica, the other comprised primarily of individuals from the Antilles and northern Mesoamerica
Summary
Crop domestication is a long-term evolutionary process whereby wild plant populations become exploited via human management practices, leading to phenotypic and/ or genetic differences between domesticated forms and their wild progenitors. The trajectory of domestication may occur at the intra- or interspecific level, and may result in changes in morphological traits and the genetic loci that control them (reviewed in Pickersgill 2007) and/or allele frequencies at neutral loci (see Casas et al 2007). The process by which human selection of natural variation over many generations may eventually result in the fixation of desired phenotypes has provided a cornerstone for expanding our understanding of evolution since Darwin’s On the Origin of Species (Darwin 1859).
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