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.
Highlights
In his revision of Theobroma, Cuatrecasas (1964) recognized 22 species of understory trees all found in Neotropical lowland rainforests from the Amazon basin to Southern Mexico
The distribution of Theobroma cacao in the Neotropics is plotted separately, together with another widespread species, and this may contain some cultivated individuals. These figures show that Northwestern South America, Colombia, is the most species-rich region for Theobroma, Herrania, and all Theobromeae based on herbarium collections (26 species of Theobromeae can be found in Colombia)
The diversification of Theobroma and Herrania coincide with periods of uplift in the Northwestern Andes
Summary
In his revision of Theobroma, Cuatrecasas (1964) recognized 22 species of understory trees all found in Neotropical lowland rainforests from the Amazon basin to Southern Mexico. The distribution of Theobroma cacao in the Neotropics is plotted separately, together with another widespread species, and this may contain some cultivated individuals These figures show that Northwestern South America, Colombia, is the most species-rich region for Theobroma, Herrania, and all Theobromeae based on herbarium collections (26 species of Theobromeae can be found in Colombia). Theobroma is of great interest from a biogeographic viewpoint as it is distributed in an area that has been subject to much relatively recent geological activity It is of interest because it includes the economically important species Theobroma cacao, the source of chocolate, predicted to be a $100 billion dollar industry by 2016 with worldwide demand increasing by 2.5% a year largely driven by newly emerging markets (Markets and Markets, 2011). Information on the origin and evolutionary history of Theobroma cacao and its relatives will assist with planning crop improvement strategies
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