Was die Diversifikation von Pflanzen in Gebirgsregionen antreibt: Der Fall Gentiana in der Qinghai-Tibet-Plateau Region
Zusammenfassung der Projektergebnisse
Biodiversity is unevenly distributed on Earth, some areas containing a remarkable species richness. Many of these so-called “biodiversity hotspots” are associated with mountain systems. Whereas the evolutionary history of some of these areas are rather well understood, it remains relatively poorly studied in the largest and highest geological feature on Earth: the Qinghai-Tibetan Plateau (QTP). Using complementary sequence-based methods (phylogenetic analyses, molecular dating, biogeographic analyses and diversification rates analyses) or occurrence-based methods (niche evolution), we investigated how the tremendous biodiversity of alpine plants came into existence in and around the QTP. To do so, we relied on state-of-the-art geological and climatic scenarios for this region. As a study model, we used Gentiana as well as the subtribe and tribe (respectively Gentianinae and Gentianeae) containing it, because these clades are notorious components of the alpine flora in the QTP and elsewhere. We resolved phylogenetic relationships between Gentiana and closely related clades, describing two new genera in the process: Kuepferia and Sinogentiana. We could then perform further analyses based upon a solid topological resolution. Among other exciting results, we found that Gentiana (as well as Gentianinae and Gentianeae) are very likely to have originated in the QTP during the Eocene, which corresponds to the early uplift of the plateau. From the QTP, other areas of the world were colonized: a single old migration from the QTP to Europe was recovered (Early Miocene), but almost always, migrations spanned from the end of the Miocene into the Pliocene. Our biogeographic reconstructions thus show that not only the QTP acted as source area for numerous Gentianeae genera, but also that the timing of these migrations coincided with the “out-of-Tibet” hypothesis: this hypothesis was developed based on fossils of cold adapted mammals (e.g. wholly rhino). In this matter, our project is to our knowledge the first to report such a timely parallel. Our results hence support the assumed importance of the QTP as an early evolutionary opportunity for organisms to adapt to cold and harsh climates (in an otherwise warm and humid global climate), giving the edge to Tibetan taxa to colonized cold habitats that became available only later, following the Miocene cooling (e.g. the Arctic). Furthermore, diversification rates analyses showed a minor, yet constant increase of speciation rates overtime, from mid-Eocene to present: this might indicate that as the QTP uplift progressed (and thus its sheer size increased), the entire region fostered diversification more and could host more and more species. Nevertheless, no explosive radiation was detected for alpine clades within Gentianinae. Only in two clades, shifts in diversification regimes were identified, namely in Gentiana section Cruciata and Tripterospermum. In both cases, diversification seems to have followed significant changes in their niche. For example, faster diversification rates are associated with a switch from niche conservatism (in related genera), to niche evolution in Tripterospermum (which displays the broadest climatic niche preferences). Also, we could show that Tripterospermum (understory plant) derived from lineages preferring open alpine habitats. This shift in diversification regime is attended by the production of berries, a trait only found in Tripterospermum, here depicted as a key innovation. Similarly, QTP species of Gentiana section Cruciata seem to occur at lower altitudes in comparison to QTP species from other sections. In both Gentiana section Cruciata and Tripterospermum, we could therefore show that drastic increase in diversification rates in QTP taxa are not necessary associated with any major geological or climatic events in and around the QTP, but rather to profound shifts in their climatic niche. Altogether, our study underlines the importance of the alpine/subalpine ecotone as an evolutionary opportunity for niche shifts, potentially resulting in the divergence of some lineages, and ultimately contributing to local species richness. The length of this ecotone, as well as its distribution, might nevertheless be climate-dependent: hence we suggest more studies on the role of ecotones in mountain systems should be encouraged.
Projektbezogene Publikationen (Auswahl)
- (2014) Two new genera of Gentianinae (Gentianaceae): Sinogentiana and Kuepferia supported by molecular phylogenetic evidence. TAXON, 63, 342–354
Favre, A., Matuszak, S., Sun, H., Liu, E., Yuan, Y.M. & Muellner-Riehl, A.N.
(Siehe online unter https://doi.org/10.12705/632.5) - Spatio-temporal evolution of Gentiana (Gentianaceae): the role of geological events, climate change, and migration in the establishment of mountainous hotspots of biodiversity. Botanikertagung 2015, “From Molecules to the Field”, 30.8. – 3.9.2015, Ludwig-Maximilians-Universität & Technische Universität München
Favre, A., Michalak, I., Chen, C.H., Wang, J.C., Pringle, J., Matuszak, S., Sun, H., Liu, E., Yuan, Y.M., Struwe, L. & Muellner-Riehl, A.N.
- Dispersal routes between biodiversity hotspots in Asia: the case of the mountain genus Tripterospermum (Gentianinae, Gentianaceae) and its close relatives. Journal of Biogeography 43,3, March 2016, Pages 580-590
Matuszak, S., Muellner-Riehl, A.N., Sun, H. & Favre, A.
(Siehe online unter https://doi.org/10.1111/jbi.12617) - Key innovations and climatic niche divergence as drivers of diversification in subtropical Gentianinae in southeastern and eastern Asia. American Journal of Botany 103,5, May 2016, Pages 899-911
Matuszak, S., Favre, A., Schnitzler, J. & Muellner-Riehl, A.N.
(Siehe online unter https://doi.org/10.3732/ajb.1500352)
