Phytogeographic history of the Tea family inferred through high-resolution phylogeny and fossils

The tea family (Theaceae) has a highly unusual amphi-Pacific disjunct
distribution: most extant species in the family are restricted to
subtropical evergreen broadleaf forests in East Asia, while a handful of
species occur exclusively in the subtropical and tropical Americas. Here
we used an approach that integrates the rich fossil evidence of this group
with phylogenies in biogeographic analysis to study the processes behind
this distribution pattern. We first combined genome-skimming sequencing
with existing molecular data to build a robust species-level phylogeny for
c.140 Theaceae species, resolving most important unclarified
relationships. We then developed an empirical Bayesian method to
incorporate distribution evidence from fossil specimens into historical
biogeographic analyses and used this method to account for the
spatiotemporal history of Theaceae fossils. We compared our method with an
alternative Bayesian approach and show that it provides consistent results
while significantly reduces computational demands which allows analyses of
much larger datasets. Our analyses revealed a circumboreal distribution of
the family from the early Cenozoic to the Miocene and inferred repeated
expansions and retractions of the modelled distribution in the Northern
Hemisphere, suggesting that the current Theaceae distribution could be the
remnant of a larger continuous distribution associated with the
boreotropical forest that has been hypothesized to occupy most of the
northern latitudes in the early Cenozoic. These results contradict with
studies that only considered current species distributions and showcase
the necessity of integrating fossil and molecular data in phylogeny-based
parametric biogeographic models to improve the reliability of inferred
biogeographical events.