Alexandra N. Muellner-Riehl

The role of the uplift of the Qinghai-Tibetan Plateau for the evolution of Tibetan biotas

Biodiversity is unevenly distributed on Earth and hotspots of biodiversity are often associated with areas that have undergone orogenic activity during recent geological history (i.e. tens of millions of years). Understanding the underlying processes that have driven the accumulation of species in some areas and not in others may help guide prioritization in conservation and may facilitate forecasts on ecosystem services under future climate conditions. Consequently, the study of the origin and evolution of biodiversity in mountain systems has motivated growing scientific interest. Despite an increasing number of studies, the origin and evolution of diversity hotspots associated with the Qinghai‐Tibetan Plateau (QTP) remains poorly understood. We review literature related to the diversification of organisms linked to the uplift of the QTP. To promote hypothesis‐based research, we provide a geological and palaeoclimatic scenario for the region of the QTP and argue that further studies would benefit from providing a complete set of complementary analyses (molecular dating, biogeographic, and diversification rates analyses) to test for a link between organismic diversification and past geological and climatic changes in this region. In general, we found that the contribution of biological interchange between the QTP and other hotspots of biodiversity has not been sufficiently studied to date. Finally, we suggest that the biological consequences of the uplift of the QTP would be best understood using a meta‐analysis approach, encompassing studies on a variety of organisms (plants and animals) from diverse habitats (forests, meadows, rivers), and thermal belts (montane, subalpine, alpine, nival). Since the species diversity in the QTP region is better documented for some organismic groups than for others, we suggest that baseline taxonomic work should be promoted.

Niche evolution through time and across continents: The story of Neotropical Cedrela (Meliaceae)

UNLABELLED PREMISE OF THE STUDY Climatic and geological changes have been considered as major drivers of biological diversification. However, it has been generally assumed that lineages retain common environmental affinities, suggesting a limited capacity to switch their climatic niche. We tested this assumption with a study of the evolution of climatic niches in the Neotropical tree genus Cedrela (Meliaceae). • METHODS We combined distribution models of extant Cedrela with a dated molecular phylogeny based on one nuclear (ITS) and three plastid markers (psbA-trnH, trnS-G and psbB-T-N) to reconstruct the evolutionary dynamics of climatic niches. We calculated relative disparity of climatic tolerances over time to test for niche evolution within subclades or divergence between subclades and conservatism among closely related groups. Published fossil records and studies on paleosols were evaluated for the distribution and climatic conditions of extinct Cedrela. • KEY RESULTS The fossil record of Cedrela suggested a major biome shift from paratropical conditions into warm-temperate seasonal climates in the Early Oligocene of western North America. In the Miocene, Cedrela extended from North America (John Day Formation, Oregon, USA) to southern Central America (Gatún, Panama). Diversification in the early evolutionary history was mainly driven by changes in precipitation. Temperature had an increasing impact on ecological diversification of the genus from the Miocene onwards. Sister-species comparisons revealed that recent speciation events may be related to divergence of climatic tolerances. • CONCLUSIONS Our study highlights the complexity of climatic niche dynamics, and shows how conservatism and evolution have acted on different temporal scales and climatic parameters in Cedrela.

Molecular phylogenetics and molecular clock dating of Sapindales based on plastid rbcL, atpB and trnL-trnF DNA sequences

This study focuses on reconstructing the time-calibrated phylogeny of the nine families comprising the order Sapindales, representing a diverse and economically important group of eudicots including citrus, mahogany, tree-of-heaven, cashew, mango, pistachio, frankincense, myrrh, lychee, rambutan, maple, and buckeye. We sampled three molecular markers, plastid genes rbcL and atpB, and the trnL-trnLF spacer region, and covered one-third of the generic diversity of Sapindales. All three markers produced congruent phylogenies using maximum likelihood and Bayesian methods for a set of taxa that included outgroups, i.e., members of the closely related orders Brassicales and Malvales, and the more distantly related Crossosomatales, Ranunculales, and Ceratophyllales. All results confirmed the current delimitation of the families within Sapindales, and the monophyly of the order. Concerning inter-familial relationships, Biebersteiniaceae and Nitrariaceae formed a basal grade (or sister clade) to the rest of Sapindales with moderate support. The sister relationship of Kirkiaceae to Anacardiaceae and Burseraceae was strongly supported. The clade combining Anacardiaceae and Burseraceae as well as the clade combining Meliaceae, Simaroubaceae, and Rutaceae each received strong support. The sister relationship between Meliaceae and Simaroubaceae was moderately supported. The position of Sapindaceae could not be resolved with confidence. The Sapindales separated from their sister clade, comprising Brassicales and Malvales, in the Early Cretaceous at ca. 112 Ma, and diversified into the nine families from ca. 105 Ma until ca. 87 Ma during Early to Late Cretaceous times. Biebersteiniaceae and Nitrariaceae have the longest stem lineages observed in Sapindales, possibly indicating that extinction may have had a greater role in shaping their extant diversity than elsewhere within the order. Divergence within the larger families (Anacardiaceae, Burseraceae, Meliaceae, Rutaceae, Sapindaceae, Simaroubaceae) started during the Late Cretaceous, extending into the Paleogene and Neogene.

Two new genera of Gentianinae (Gentianaceae): Sinogentiana and Kuepferia supported by molecular phylogenetic evidence

Subtribe Gentianinae, encompassing Gentiana, Tripterospermum, Metagentiana and Crawfurdia, represents one of the most species-rich clades of Gentianaceae. Only a few taxonomic uncertainties have remained at generic level in subtribe Gentianinae: the inclusion of Gentiana sect. Otophora in Gentiana, and the polyphyletic nature of Metagentiana. In both cases, data were lacking in earlier studies to resolve ambiguities and provide the baseline for a solid taxonomic treatment of these lineages. For the present study, we increased the number of species sequenced for Gentiana sect. Otophora and Metagentiana, using a combination of nuclear (ITS) and plastid (trnL-F, atpB-rbcL) markers. We reconstructed phylogenetic relationships in Gentianinae conducting maximum likelihood and Bayesian analyses. Our results show that Gentiana sect. Otophora is monophyletic and more closely related to Metagentiana than to Gentiana. We suggest excluding Gentiana sect. Otophora from Gentiana and elevating this group to the rank of genus described here under the name Kuepferia. Metagentiana is monophyletic when excluding two species, M striata and M souliei, here described as the new genus Sinogentiana.

Spatio-temporal evolution of Allium L. in the Qinghai-Tibet-Plateau region:Immigration and in situ radiation

A plethora of studies investigating the origin and evolution of diverse mountain taxa has assumed a causal link between geological processes (orogenesis) and a biological response (diversification). Yet, a substantial delay (up to 30 Myr) between the start of orogenesis and diversification is often observed. Evolutionary biologists should therefore identify alternative drivers of diversification and maintenance of biodiversity in mountain systems. Using phylogenetic, biogeographic, and diversification rate analyses, we could identify two independent processes that most likely explain the diversity of the widespread genus Allium in the Qinghai–Tibet Plateau (QTP) region: (1) While the QTP-related taxa of the subgenus Melanocrommyum diversified in situ, (2) QTP-related taxa of other subgenera migrated into the QTP from multiple source areas. Furthermore, shifts in diversification rates within Allium could not be attributed spatially and temporally to the uplift history of the QTP region. Instead, global cooling and climate oscillations in the Quaternary were major contributors to increased speciation rates in three clades of Allium. Our study therefore adds to the growing evidence supporting the “mountain-geo-biodiversity hypothesis”, which highlights the role of climate oscillations for the diversification of mountain organisms.

Evolutionary radiations in the species-rich mountain genus Saxifraga L.

BackgroundA large number of taxa have undergone evolutionary radiations in mountainous areas, rendering alpine systems particularly suitable to study the extrinsic and intrinsic factors that have shaped diversification patterns in plants. The species-rich genus Saxifraga L. is widely distributed throughout the Northern Hemisphere, with high species numbers in the regions adjacent to the Qinghai-Tibet Plateau (QTP) in particular the Hengduan Mountains and the Himalayas. Using a dataset of 297 taxa (representing at least 60% of extant Saxifraga species), we explored the variation of infrageneric diversification rates. In addition, we used state-dependent speciation and extinction models to test the effects of geographic distribution in the Hengduan Mountains and the entire QTP region as well as of two morphological traits (cushion habit and specialized lime-secreting glands, so-called hydathodes) on the diversification of this genus.ResultsWe detected two to three rate shifts across the Saxifraga phylogeny and two of these shifts led to radiations within two large subclades of Saxifraga, sect. Ciliatae Haworth subsect. Hirculoideae Engl. & Irmsch. and sect. Porphyrion Tausch subsect. Kabschia Engl. GEOSSE analyses showed that presence in the Hengduan Mountains had a positive effect on diversification across Saxifraga. Influence of these mountains was strongest in Saxifraga sect. Ciliatae subsect. Hirculoideae given its pronounced distribution there, and thus the radiation in this group can be classified at least partially as geographic. In contrast, the evolution of the cushion life form and lime-secreting hydathodes had positive effects on diversification only in selected Saxifraga sections, including sect. Porphyrion subsect. Kabschia. We therefore argue that radiation in this group was likely adaptive.ConclusionsOur study underlines the complexity of processes and factors underpinning plant radiations: Even in closely related lineages occupying the same life zone, shifts in diversification are not necessarily governed by similar factors. In conclusion, alpine plant radiations result from a complex interaction among geographical settings and/or climatic modifications providing key opportunities for diversification as well as the evolution of key innovations.

Increasing phylogenetic support for explosively radiating taxa: The promise of high‐throughput sequencing for Oxytropis (Fabaceae)

The origin and evolution of alpine biota are not yet fully understood, particularly in the vast Asian mountain regions. In addition, in these regions, most studies have concentrated on taxa occurring in areas benefitting from relatively generous rainfall from the summer monsoon. In this study, we collected a large number of Oxytropis species throughout their distribution range, and investigated the taxonomy and evolution of this diverse legume genus, which also occurs in mountainous areas prone to drought. Using nuclear (ITS) and plastid (trnL‐F) markers, we reconstructed phylogenetic relationships within Oxytropis, conducting maximum parsimony, fasttree‐like, maximum likelihood, Bayesian, and BEAST analyses. We also used Anchored Hybrid Enrichment (AHE) to test the power of this method to resolve relationships among a small subset of Oxytropis species. For AHE, we sampled eight species and obtained 527 low‐copy and orthologous nuclear loci. We show that the taxonomy of this genus that radiated explosively in Asian mountains will remain recalcitrant based on conventional molecular methods. Because of a severe lack of resolution, none of the available taxonomic treatments for Oxytropis could either be confirmed or refuted based upon ITS and trnL‐F. Nevertheless, we confirm the status of several species, and identify morphological or genetic particularities for some groups of species. The AHE approach yielded a highly supported phylogenetic tree, suggesting that increased taxon sampling coupled with AHE methods promise advances in the study of the taxonomy and evolution of Oxytropis, thus providing further analytical opportunities, such as diversification rate and biogeographical analyses.

Two New Species of the Asian Genus Tripterospermum (Gentianaceae)

Abstract This paper presents descriptions and illustrations for two new species of Gentianaceae, Tripterospermum maculatum from Sichuan Province (China) and T. tanatorajanense from Sulawesi (Indonesia). Based on literature search, Tripterospermum maculatum is morphologically close to T. pingbianense and T. lanceolatum, and T. tanatorajanense resembles T. luzonense and T. alutaceifolium. To test if the new species differ from their morphologically most similar species, we measured various traits on herbarium specimens and performed a principal component analysis (PCA). This analysis showed that the new species differ from similar species in gross morphology for several diagnostic traits. Tripterospermum maculatum differs from T. pingbianense and T. lanceolatum by having calyx lobes longer than calyx tubes, a whitish-yellow corolla maculated with purple dots, and a gynophore shorter than the ovary. Tripterospermum tanatorajanense is distinct from T. luzonense by having a narrowly winged calyx. It differs from T. alutaceifolium and T. luzonense by having a shorter ovary and a slightly longer gynophore. A key including all species of Tripterospermum is provided.

Genetic diversity and distribution of Senegalia senegal (L.) Britton under climate change scenarios in West Africa

Climate change is predicted to impact species’ genetic diversity and distribution. We used Senegalia senegal (L.) Britton, an economically important species distributed in the Sudano-Sahelian savannah belt of West Africa, to investigate the impact of climate change on intraspecific genetic diversity and distribution. We used ten nuclear and two plastid microsatellite markers to assess genetic variation, population structure and differentiation across thirteen sites in West Africa. We projected suitable range, and potential impact of climate change on genetic diversity using a maximum entropy approach, under four different climate change scenarios. We found higher genetic and haplotype diversity at both nuclear and plastid markers than previously reported. Genetic differentiation was strong for chloroplast and moderate for the nuclear genome. Both genomes indicated three spatially structured genetic groups. The distribution of Senegalia senegal is strongly correlated with extractable nitrogen, coarse fragments, soil organic carbon stock, precipitation of warmest and coldest quarter and mean temperature of driest quarter. We predicted 40.96 to 6.34 per cent of the current distribution to favourably support the species’ ecological requirements under future climate scenarios. Our results suggest that climate change is going to affect the population genetic structure of Senegalia senegal, and that patterns of genetic diversity are going to influence the species’ adaptive response to climate change. Our study contributes to the growing evidence predicting the loss of economically relevant plants in West Africa in the next decades due to climate change.

Geological and climatic influences on mountain biodiversity

Mountains are key features of the Earth’s surface and host a substantial proportion of the world’s species. However, the links between the evolution and distribution of biodiversity and the formation of mountains remain poorly understood. Here, we integrate multiple datasets to assess the relationships between species richness in mountains, geology and climate at global and regional scales. Specifically, we analyse how erosion, relief, soil and climate relate to the geographical distribution of terrestrial tetrapods, which include amphibians, birds and mammals. We find that centres of species richness correlate with areas of high temperatures, annual rainfall and topographic relief, supporting previous studies. We unveil additional links between mountain-building processes and biodiversity: species richness correlates with erosion rates and heterogeneity of soil types, with a varying response across continents. These additional links are prominent but under-explored, and probably relate to the interplay between surface uplift, climate change and atmospheric circulation through time. They are also influenced by the location and orientation of mountain ranges in relation to air circulation patterns, and how species diversification, dispersal and refugia respond to climate change. A better understanding of biosphere–lithosphere interactions is needed to understand the patterns and evolution of mountain biodiversity across space and time.Species richness in mountain environments is linked to mountain-building and climatic processes, an integration of geological, climatic, and biological datasets reveals.