Articles > Domestication of a Mesoamerican cultivated fruit tree, Spondias purpurea

Domestication of a Mesoamerican cultivated fruit tree, Spondias purpurea

Posted on May 09, 2007

Evolution

 

Domestication of a Mesoamerican cultivated fruit tree, Spondias purpurea

 
Allison Miller†‡§ and Barbara Schaal†
 
†Department of Biology, Campus Box 1137, Washington University, 1 Brookings Drive, St. Louis, MO 63130; and ‡Missouri Botanical Gardens, 4500 Shaw Boulevard, St. Louis, MO 63110
§ To whom correspondence should be sent at the present address: University of Colorado Museum, UCB 265, University of Colorado, Boulder, CO 80309. E-mail: allison.j.miller@colorado.edu .
 
Contributed by Barbara Schaal, June 28, 2005
 
 
 

Abstract

 
Contemporary patterns of genetic variation in crops reflect historical processes associated with domestication, such as the geographic origin(s) of cultivated populations. Although significant progress has been made in identifying several global centers of domestication, few studies have addressed the issue of multiple origins of cultivated plant populations from different geographic regions within a domestication center. This study investigates the domestication history of jocote (Spondias purpurea), a Mesoamerican cultivated fruit tree. Sequences of the chloroplast spacer trnG–trnS were obtained for cultivated and wild S. purpurea trees, two sympatric taxa (Spondias mombin var. mombin and Spondias radlkoferi), and two outgroups (S. mombin var. globosa and Spondias testudinus). A phylogeographic approach was used and statistically significant associations of clades and geographical location were tested with a nested clade analysis. The sequences confirm that wild populations of S. purpurea are the likely progenitors of cultivated jocote trees. This study provides phylogeographic evidence of multiple domestications of this Mesoamerican cultivated fruit tree. Haplotypes detected in S. purpurea trees form two clusters, each of which includes alleles recovered in both cultivated and wild populations from distinct geographic regions. Cultivated S. purpurea populations have fewer unique trnG–trnS alleles than wild populations; however, five haplotypes were absent in the wild. The presence of unique alleles in cultivation may reflect contemporary extinction of the tropical dry forests of Mesoamerica. These data indicate that some agricultural habitats may be functioning as reservoirs of genetic variation in S. purpurea.

 
Keywords: crop origins, Mesoamerica, phylogeography, genetic variation

 
Proc Natl Acad Sci U S A. 2005 September 6; 102(36): 12801–12806.
 
 
 
 
 
The geographic origins of most cultivated plants can be traced to several global centers of domestication (e.g., Fertile Crescent Region of the Middle East, Mesoamerica, the Andes, eastern Asia, sub-Saharan Africa; refs. 1–5). In each center, humans selected and cultivated a suite of native plants. Over time, the cultivated populations became genetically distinct from their wild progenitors as the evolutionary process of domestication proceeded (6). Recently, much attention has focused on the centers of domestication and their associated crops and putative wild ancestors as concerns mount about the lack of genetic diversity in cultivated plants (7). It has been estimated that the diversity found in cultivated populations has declined by as much as 80% over the past 100 years (7–9). How this loss occurs, either all at once or gradually over generations, is not clear. Scientific investigations focusing on the genetic resources contained in cultivated plants and their wild ancestors have documented the historical processes associated with domestication, providing new perspectives on contemporary patterns of genetic variation in cultivated populations and their wild ancestors (e.g., ref. 10).

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).