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ARS Home » Southeast Area » Miami, Florida » Subtropical Horticulture Research » Research » Publications at this Location » Publication #323740

Research Project: Genetic Characterization, Genetic Improvement, and Best Horticultural Management Practices for Subtropical/Tropical Ornamental Germplasm

Location: Subtropical Horticulture Research

Title: The age of chocolate: a diversification history of Theobroma and Malvaceae

Author
item Richardson, James - Royal Botanical Gardens
item Whitlock, Barbera - University Of Miami
item Meerow, Alan

Submitted to: FRONTIERS IN ECOLOGY AND EVOLUTION
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2015
Publication Date: 11/10/2015
Citation: Richardson, J., Whitlock, B., Meerow, A.W. 2015. The age of chocolate: a diversification history of Theobroma and Malvaceae. FRONTIERS IN ECOLOGY AND EVOLUTION. Vol3: pg 15.

Interpretive Summary: Using DNA sequences from both chloroplast and nuclear genes, we developed a darted tree of life for the large mallow or hibiscus family Malvaceae and the chocolate tree genus Theobroma and its closest living relative, Herrania,in order to test the hypothesis that the greater biodiversity in the American tropics was due to the uplift of the Andes. We show that the diversification of the genera Theobroma and Herrania occurred from 12.7 million years ago and thus coincided with Andean uplift from the mid-Miocene and that this lineage had a faster diversification rate than other major groups in Malvaceae. We also determined that Theobroma cacao, the source of chocolate, diverged from its most recent common ancestor 9.9 million years ago in the mid-to late-Miocene, suggesting that this economically important species has had ample time to generate significant within-species genetic diversity useful for a developing chocolate industry. In addition, we show that a faster diversification rate is an explanation for the greater species diversity at lower latitudes. Alternatively, tropical conditions may have existed for longer and occupied greater areas than temperate ones meaning that tropical lineages have had more time and space in which to diversify. Our dated molecular phylogeny of Malvaceae demonstrated that at least one temperate lineage within the family diverged from tropical ancestors then diversified at a rate comparable with many tropical lineages in the family. These results are consistent with the hypothesis that the mallow family is more species rich in the tropics because the tropical lineages have existed for longer and occupied more space than temperate ones, and not because of differences in their rate of diversification. The information generated by this study on the origin and evolutionary history of Theobroma cacao and its relatives will assist with planning crop improvement, and assist in the process ensuring the long-term sustainability of the chocolate industry by protecting it from the risks posed by climate change.

Technical Abstract: Dated molecular phylogenies of broadly distributed lineages can help to compare patterns of diversification in different parts of the world. An explanation for greater Neotropical diversity compared to other parts of the tropics is that it was an accident of the Andean orogeny. Using dated phylogenies, of chloroplast ndhF and nuclear DNA WRKY sequence datasets, generated using BEAST we demonstrate that the diversification of the genera Theobroma and Herrania occurred from 12.7 (11.6-14.9 [95% HPD]) million years ago (Ma) and thus coincided with Andean uplift from the mid-Miocene and that this lineage had a faster diversification rate than other major clades in Malvaceae. We also demonstrate that Theobroma cacao, the source of chocolate, diverged from its most recent common ancestor 9.9 (7.7-12.9 95% HPD) Ma, in the mid-to late-Miocene, suggesting that this economically important species has had ample time to generate significant within-species genetic diversity that is useful information for a developing chocolate industry. In addition, we address questions related to the latitudinal gradient in species diversity within Malvaceae. A faster diversification rate is an explanation for the greater species diversity at lower latitudes. Alternatively, tropical conditions may have existed for longer and occupied greater areas than temperate ones meaning that tropical lineages have had more time and space in which to diversify. Our dated molecular phylogeny of Malvaceae demonstrated that at least one temperate lineage within the family diverged from tropical ancestors then diversified at a rate comparable with many tropical lineages in the family. These results are consistent with the hypothesis that Malvaceae are more species rich in the tropics because tropical lineages within the family have existed for longer and occupied more space than temperate ones, and not because of differences in diversification rate.