Late Cretaceous origins for major nightshade lineages from total evidence timetree analysis
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Background and Aims
The timing of the radiation of nightshades (Solanaceae) has been contentious in the literature, with estimates of the crown age ranging from ca. 30 to 70 Mya (mid-Oligocene to late Cretaceous). The tempo of diversification of major lineages within the family (e.g., berries, tobaccos) has been equally challenging to resolve, in large part because of the paucity of fossil information. Recently described fossils present an opportunity to revisit the timing of nightshade diversification using more powerful model-based methods. Here, we simultaneously infer divergence times within Solanaceae and the placement of a select set of well-preserved and morphologically diverse fruit and seed fossils.
Methods
We assembled a family-wide morphological dataset, including 17 categorical and eight continuous characters, for 134 living and 14 fossil Solanaceae taxa, as well as sequence data for the extant taxa. We implemented a Bayesian total evidence dating analysis in RevBayes using (a time continuous and a time heterogeneous) fossilized birth-death model and models of character evolution for each type of data.
Key Results
The origin of Solanaceae was ∼98 Mya, and the major splits were roughly three-fold older than previously estimated. Although the 14 fossil taxa were phylogenetically placed with different degrees of confidence, we identified a fruit fossil and a seed fossil whose affinities were strongly supported. Moreover, most of the fossils lacking a precise placement were nevertheless confidently inferred to belong to the large berry clade.
Conclusions
Our study provides an example of how a sophisticated model used on a carefully assembled dataset can shed light on the timing of the evolution of a group, while accounting for phylogenetic uncertainty. The timetree we present here provides a temporal framework for further research, from comparative genomics and patterns of diversification to trait evolution and biogeography.
