title: Oligocene niche shift, Miocene diversification - cold tolerance and accelerated speciation rates in the St. John's Worts (Hypericum, Hypericaceae).
abstract: BACKGROUND
  Our aim is to understand the evolution of species-rich plant groups that shifted from tropical into cold/temperate biomes. It is well known that climate affects evolutionary processes, such as how fast species diversify, species range shifts, and species distributions. Many plant lineages may have gone extinct in the Northern Hemisphere due to Late Eocene climate cooling, while some tropical lineages may have adapted to temperate conditions and radiated; the hyper-diverse and geographically widespread genus Hypericum is one of these.
  
  
  RESULTS
  To investigate the effect of macroecological niche shifts on evolutionary success we combine historical biogeography with analyses of diversification dynamics and climatic niche shifts in a phylogenetic framework. Hypericum evolved cold tolerance c. 30 million years ago, and successfully colonized all ice-free continents, where today ~500 species exist. The other members of Hypericaceae stayed in their tropical habitats and evolved into ~120 species. We identified a 15-20 million year lag between the initial change in temperature preference in Hypericum and subsequent diversification rate shifts in the Miocene.
  
  
  CONCLUSIONS
  Contrary to the dramatic niche shift early in the evolution of Hypericum most extant species occur in temperate climates including high elevations in the tropics. These cold/temperate niches are a distinctive characteristic of Hypericum. We conclude that the initial release from an evolutionary constraint (from tropical to temperate climates) is an important novelty in Hypericum. However, the initial shift in the adaptive landscape into colder climates appears to be a precondition, and may not be directly related to increased diversification rates. Instead, subsequent events of mountain formation and further climate cooling may better explain distribution patterns and species-richness in Hypericum. These findings exemplify important macroevolutionary patterns of plant diversification during large-scale global climate change.
authors.affiliation: Centre for Organismal Studies Heidelberg, University of Heidelberg, Im Neuenheimer Feld 345, 69120, Heidelberg, Germany. n.nuerk@cos.uni-heidelberg.de.
authors.forename: Nicolai M
authors.initials: NM
authors.lastname: Nürk
authors.affiliation: Department of Biological Sciences, Institute for Bioinformatics & Evolutionary Studies, University of Idaho, 875 Perimeter MS 3051, Moscow, ID, 83844-3051, USA. uribe.convers@gmail.com.
authors.forename: Simon
authors.initials: S
authors.lastname: Uribe-Convers
authors.affiliation: Institute of Special Botany, Johannes Gutenberg University, Anselm-Franz-von-Bentzelweg 9a, 55099, Mainz, Germany. gehrke@uni-mainz.de.
authors.forename: Berit
authors.initials: B
authors.lastname: Gehrke
authors.affiliation: Department of Biological Sciences, Institute for Bioinformatics & Evolutionary Studies, University of Idaho, 875 Perimeter MS 3051, Moscow, ID, 83844-3051, USA. dtank@uidaho.edu.
authors.forename: David C
authors.initials: DC
authors.lastname: Tank
authors.affiliation: Institute of Plant Genetics and Crop Research (IPK), Correnzstrasse 3, 06466, Gatersleben, Germany. blattner@ipk-gatersleben.de.|German Centre of Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Deutscher Platz 5e, 04103, Leipzig, Germany. blattner@ipk-gatersleben.de.
authors.forename: Frank R
authors.initials: FR
authors.lastname: Blattner
mesh_terms: D005075:Biological Evolution; D057231:Climate Change; D003080:Cold Temperature; D005580:Fossils; D020902:Hypericum / Q000145:classification* / Q000235:genetics* / Q000502:physiology; D010802:Phylogeny