Abstract
BackgroundOur 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.ResultsTo 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.ConclusionsContrary 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0359-4) contains supplementary material, which is available to authorized users.
Highlights
Our aim is to understand the evolution of species-rich plant groups that shifted from tropical into cold/ temperate biomes
Ten major clades consistent with current taxonomy are present within Hypericaceae (Figure 2 and Additional file 1: Figure S1), allowing us to assign species richness to each clade for comparative analyses (Figure 3)
For the diversification rate analysis, detected shifts are marked by their probability
Summary
Our aim is to understand the evolution of species-rich plant groups that shifted from tropical into cold/ temperate biomes. 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. Large-scale global climate change dramatically alters the distribution of major biomes [7], and the ecological niches available to entire taxonomic groups [8,9]. The flowering plant families Araceae [13], Chloranthaceae [14], Nürk et al BMC Evolutionary Biology (2015) 15:80 and Malpighiaceae [15] are well-studied examples of formerly more widely distributed lineages that are currently mostly restricted to the tropics
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