Tracing the impact of the Andean uplift - Evolution of St. John's wort (Hypericum L.) in South America: historical biogeography, character evolution, niche shifts and age estimations
Zusammenfassung der Projektergebnisse
In the South American mountain ranges, an extraordinarily species-rich flora has evolved since the northern Andes have acquired ca. 3 million years ago the adequate elevation for the development of the tropic-alpine páramo ecosystem. The medicinally striking genus Hypericum (St. John’s Wort, Hypericaceae) is an important and often abundant member of the páramo flora. More than 40% of ‘New World’ Hypericum species are native to these high-elevation habitats in the Andes. We studied the evolutionary history of páramo Hypericum species, ultimately aiming at understanding the impact of the Andean uplift on the evolution and accumulation of biological diversity. Herein and based on extensive collections compiled, a comprehensive phylogenetic framework, and ample of distributional data we demonstrate a single colonization of the páramo and rapid radiation with high rates of net diversification producing the species richness in Andean Hypericum. The final uplift of the Andes and the emergence of the high-elevation páramo ecosystem certainly triggered diversification in Hypericum. But the release from an ecologic constrain, rather than phenotypic key-innovations, was the evolutionary event that enabled Hypericum to diversify in the newly available ecosystem and to produce the unparalleled species richness in the northern Andes. The evolutionary history of New World Hypericum has been highlighted with special focus on Andean species. The results were unexpected in several parts, and they will have a major impact for any future research on ‘New World’ Hypericum. Most project aims as outlined in the original proposal have been successfully addressed, and the following conclusions could be drawn from our analyses: 1) Species richness in Andean Hypericum results from in-situ radiation. We demonstrated species in the Andes to be monophyletic and descendants of a single colonizing ancestral population. 2) New World Hypericum started to diversify ca. 20 Ma in North America. Out of this temperate region two independent dispersals into South America are evident in the data: the first dispersal established >5 Ma a (temperate) southeast South American lineage, the second around 3 Ma resulted in the Andean radiation. 3) Ancestral founder populations of both southeast South American and Andean clades were most likely distributed in North America. Additionally, we have shown that long-distance dispersal is repeatedly invoked in the biogeographic history of New World Hypericum. 4) The final uplift of the northern Andes coincides with a significant increase in net diversification rates in Hypericum indicating that the emergence of the tropic-alpine páramo ecosystem triggered radiation in this group. 5) Páramo Hypericum species cannot be identified by apomorphic morphological traits. High rates of phenotypic evolution are indicated for the Andean as well as North American species. We conclude that phenotypic evolution in the Andean lineage may promote, but is not sufficient to explain, increased diversification. 6) Dispersal and establishment in the northern Andes involved climatic niche shifts and the invasion of the antecedent not occupied tropic-alpine mountain biome. These results indicate that ecologic release and ecologic opportunity in the newly available environments is driving hyper-diversification in páramo Hypericum.
Projektbezogene Publikationen (Auswahl)
- (2013). Explosive radiation in high Andean Hypericum – Rates of diversification among New World lineages. Front. Genet. 4:175
Nürk NM, Scheriau C & Madriñán S
(Siehe online unter https://doi.org/10.3389/fgene.2013.00175) - (2013). Molecular phylogenetics and morphological evolution of St. John's Wort (Hypericum; Hypericaceae). Mol. Phylogen. Evol. 66(1): 1–16
Nürk NM, Madriñán S, Carine MA, Chase MW & Blattner FR
(Siehe online unter https://doi.org/10.1016/j.ympev.2012.08.022) - (2015). Oligocene niche shift, Miocene diversification – Cold tolerance and accelerated speciation rates in the St. John’s Worts (Hypericum). BMC Evol. Biol. 15:80
Nürk NM, Uribe-Convers S, Gehrke B, Tank DC & Blattner FR
(Siehe online unter https://doi.org/10.1186/s12862-015-0359-4)
