Domestication of a Mesoamerican cultivated fruit tree, Spondias purpurea
One of the most elusive questions regarding the evolution of cultivated plants is the number of times a species was taken into cultivation within a domestication center (5, 11). In the Near East center of domestication (the “Fertile Crescent”), the wild ancestors of the crops upon which agriculture was founded are known (e.g., wheats, barley, pea, lentil, and chickpea) (12). The geographic distributions of these wild ancestors, together with biochemical and genetic data, have been used to suggest that emmer wheat, einkorn wheat, peas, chickpeas, and lentils were domesticated from wild progenitors just once or a few times in a single geographic region (12–18)
In contrast to the Near East center, crops domesticated in the Mediterranean region and other parts of the world have been derived more than once from their wild progenitors [e.g., olives (19–21), rice (22, 23), and breadfruit (24)]. Within the Mesoamerican center of domestication (Central Mexico to north-western Costa Rica), at least 80 native species have been cultivated historically (2, 3 25–29). Some native crop species have complex evolutionary histories, and may have been domesticated multiple times within Mesoamerica [e.g., avocados (30) and one of the cultivated chili pepper species, Capsicum frutescens (25)]. Today, many of the native crop species of Mesoamerica are cultivated in traditional agricultural habitats, such as backyard gardens and living fences (1–3, 12, 31–33). They are grown and sold on a regional scale and have not yet undergone the intensive selection and large-scale cultivation characteristic of modern agriculture. Consequently, some Mesoamerican crop populations often resemble their wild relatives, with transitional, morphologically intermediate forms existing between cultivated populations and their progenitors (3). The native crop species of Mesoamerica provide a unique opportunity to document the domestication process in its incipient stages. In this paper, we report on the origins of one of the Mesoamerican cultivated fruit trees, Spondias purpurea L. (Anacardiaceae).