EVOLUTION OF DOMESTICATION

CAIMITO: THE ORIGINS AND HISTORY OF A TROPICAL FRUIT TREE

droppedImage_3-1The caimito tree, Chrysophyllum cainito (Sapotaceae), is prized for its golden foliage and large, edible fruits. It has been widely planted throughout Central and South America and has often become naturalized. The origin of caimito is debated. Various authors argue that it is native only to the Greater Antilles and was planted across Central and South America only after the Spanish Conquest, others claim it originated in Mexico, while others believe that it is a native to Central America. In fact, in Panama it is being promoted as a native reforestation  species by a local NGO. The origin of caimito is also a key question because, outside of islands, mature tropical forests are very rarely invaded by exotic species, and caimito has been cited as an exceptional counterexample. With collaborators Dan Potter and Jennifer Petersen of UC Davis, we are testing hypotheses of the origin of this species and its center of domestication using phylogeographic approaches.
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Our results suggest that Chrysophyllum cainito evolved and was domesticated in southern Mesoamerica or northern South America, not in Mexico or the Antilles (Petersen et al. in review). An important implication of these results is that caimito is a native part of the Panamanian landscape, and Panama holds a large proportion of the genetic diversity of this species.

 

HUMAN SELECTION VS. NATURAL SELECTION ON FRUIT, SEED, AND SEEDLING CHARACTERISTICS IN A TROPICAL SEMI-DOMESTICATE

droppedImage-2A fundamental assumption of ethnobotany and the study of plant domestication is that natural selection in the wild necessarily acts in opposition to human selection. That is, that domesticated genotypes are less fit in natural environments than their wild progenitors. I am testing this idea using a semi-domesticated tree species, Chrysophyllum cainito (caimito or star apple), in Panama, where both natural selection and anthropogenic selection are currently at work. My studies focus on 1) quantifying variation in fruit and seed traits, 2) understanding how these traits are influenced by domestication, and 3) understanding how these traits affect survival and success in the wild.

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University of Panama student, Isis López

We have found that cultivated genotypes of caimito have larger and sweeter fruits, larger and more seeds, less acid, and less phenolics than wild-type fruits (Parker et al. 2010). The seeds from cultivated trees also germinate faster, have higher moisture content, and are more sensitive to desiccation. In field transplant experiments, we are investigating the relative performance of wild-type vs. cultivated individuals in the ancestral habitat, the understory of tropical forest.

I do my research in Panama with the support of the Smithsonian Tropical Research Institute, where I am a Research Associate. For an article about my work on caimito at the Smithsonian, click here. For a news essay on this work written by Kate Galloway, click here.

CONSERVING THE DIVERSITY OF TROPICAL FRUITS

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Prof. Josué Ortiz and Lic. Francisco Abre, Collaborators at Ciudad del Arbol

Planting caimito at Ciudad del Arbol

We collaborate with the University of Panama Extension and with Panamanian NGO/community organizers at “Proyecto Ciudad Del Arbol,” a reforestation site where we have established a common garden plantation of over 100 C. cainito genotypes that we collected from throughout Panama.

In addition to providing a common garden where we can study genetic variation in a common environment, our caimito plantation represents an important repository for genetic diversity for this semi-domesticate. The globalization of food production and distribution has had a negative impact on the local knowledge and utilization of local plant products. We hope to contribute to reversing the loss of this species from Panama’s cultural and culinary heritage.

 

 

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