Explosive radiation in high Andean Hypericum—rates of diversification among New World lineages

Abstract

The páramos, high-elevation Andean grasslands ranging from ca. 2800 m to the snow line, harbor one of the fastest evolving biomes worldwide since their appearance in the northern Andes 3–5 million years (Ma) ago. Hypericum (St. John's wort), with over 65% of its Neotropical species, has a center of diversity in these high Mountain ecosystems. Using nuclear rDNA internal transcribed spacer (ITS) sequences of a broad sample of New World Hypericum species we investigate phylogenetic patterns, estimate divergence times, and provide the first insights into diversification rates within the genus in the Neotropics. Two lineages appear to have independently dispersed into South America around 3.5 Ma ago, one of which has radiated in the páramos (Brathys). We find strong support for the polyphyly of section Trigynobrathys, several species of which group within Brathys, while others are found in temperate lowland South America (Trigynobrathys s.str.). All páramo species of Hypericum group in one clade. Within these páramo Hypericum species enormous phenotypic evolution has taken place (life forms from arborescent to prostrate shrubs) evidently in a short time frame. We hypothesize multiple mechanisms to be responsible for the low differentiation in the ITS region contrary to the high morphological diversity found in Hypericum in the páramos. Amongst these may be ongoing hybridization and incomplete lineage sorting, as well as the putative adaptive radiation, which can explain the contrast between phenotypic diversity and the close phylogenetic relationships.

Phylogenetic insights into Andean plant diversification

“…Similar crown node ages have been reported for the Páramo clade of the genus Hypericum (Hypericaceae), with diversification rates that are greater than in any other clade in Hypericum (Nürk et al, 2013). High diversification rates in the Páramos have also been suggested for the Andean genus Diplostephium (Asteraceae; Vargas and Madriñán, 2012).…”

Frequent colonization and little in situ speciation in Senecio in the tropical alpine‐like islands of eastern Africa

“…Altogether, in situ speciation is likely to be higher in the Páramo than in EA for Senecio species because although both alpine-like fl oras are of similar age, species richness in general and within particular clades is higher in the Páramo ( Sklenář et al, 2014 ). High speciation rates were reported for, e.g., Andean Gentianella Moench, Halenia Borkh., Hypericum L., and Lupinus L. ( Kadereit and von Hagen, 2003 ;Drummond et al, 2012b ;Nürk et al, 2013 ). However, it has to be considered that diff erent studies of Páramo lineages use a different lower bound of the Páramo and do not diff erentiate between montane and alpine-like habitats and/or combine tropical alpinelike and temperate alpine-like regions.…”

Flora do Espírito Santo: Hypericaceae

“…As informações sobre habitat, hábito, períodos de floração e frutificação foram obtidas das etiquetas das exsicatas. Hypericum está distribuído em quase todos os continentes, exceto na Antártida, e embora seja encontrado nos mais diversos ecossistemas, concentra em regiões temperadas sua maior riqueza (Meseguer et al 2013;Nürk et al 2013a). Nos trópicos, a distribuição de Hypericum costuma estar confinada a áreas de altitude elevada (Robson 2003), o que pode ser evidenciado pela sua ampla diversidade em ecossistemas tropicais montanos da América do Sul e África (Meseguer et al 2013;Nürk et al 2013a).…”

“…Hypericum está distribuído em quase todos os continentes, exceto na Antártida, e embora seja encontrado nos mais diversos ecossistemas, concentra em regiões temperadas sua maior riqueza (Meseguer et al 2013;Nürk et al 2013a). Nos trópicos, a distribuição de Hypericum costuma estar confinada a áreas de altitude elevada (Robson 2003), o que pode ser evidenciado pela sua ampla diversidade em ecossistemas tropicais montanos da América do Sul e África (Meseguer et al 2013;Nürk et al 2013a). Hypericum concentra mais de 80% das espécies descritas na família, o que corresponde a cerca de 500 espécies (Robson 2012;Nürk et al 2013b).…”