Alexandra N. Muellner

Bio: Alexandra N. Muellner is an academic researcher from Royal Botanic Gardens. The author has contributed to research in topics: Monophyly & Molecular phylogenetics. The author has an hindex of 9, co-authored 9 publications receiving 538 citations. Previous affiliations of Alexandra N. Muellner include University of Vienna.

Molecular phylogenetics of Meliaceae (Sapindales) based on nuclear and plastid DNA sequences.

Abstract: Phylogenetic analyses of Meliaceae, including representatives of all four currently recognized subfamilies and all but two tribes (32 genera and 35 species, respectively), were carried out using DNA sequence data from three regions: plastid genes rbcL, matK (partial), and nuclear 26S rDNA (partial). Individual and combined phylogenetic analyses were performed for the rbcL, matK, and 26S rDNA data sets. Although the percentage of informative characters is highest in the segment of matK sequenced, rbcL provides the greatest number of informative characters of the three regions, resulting in the best resolved trees. Results of parsimony analyses support the recognition of only two subfamilies (Melioideae and Swietenioideae), which are sister groups. Melieae are the only tribe recognized previously that are strongly supported as monophyletic. The members of the two small monogeneric subfamilies, Quivisianthe and Capuronianthus, fall within Melioideae and Swietenioideae, respectively, supporting their taxonomic inclusion in these groups. Furthermore, the data indicate a close relationship between Aglaieae and Guareeae and a possible monophyletic origin of Cedreleae of Swietenioideae. For Trichilieae (Melioideae) and Swietenieae (Swietenioideae) lack of monophyly is indicated.

The origin and evolution of Indomalesian, Australasian and Pacific island biotas: insights from Aglaieae (Meliaceae, Sapindales)

Abstract: Aim The role of long-distance dispersal in the Indomalesian, Australasian and Pacific flora is currently hotly debated. The lack of well-resolved phylogenetic trees for Pacific plants has been a major limitation for biogeographical analysis. Here, we present a well-resolved phylogenetic tree for the tribe Aglaieae in the mahogany family, Meliaceae, and use it to investigate the origin, evolution and dispersal history of biotas in this area. The subfamily Melioideae, including the tribe Aglaieae (Meliaceae, Sapindales), is a plant group with good representation in the region in terms of biomass and species numbers, wide ecological attributes and known animal vectors. The family has a good fossil record (especially from North America and Europe). Genera and species in the tribe Aglaieae therefore provide an excellent model group for addressing this debate. Location Indomalesia, Australasia, Pacific islands. Methods Results from nuclear internal transcribed spacer ribosomal DNA analyses of 82 taxa, based on sequence alignment guided by secondary structure models, were combined with evidence from fossils and distribution data. We used strict and relaxed molecular clock approaches to estimate divergence times within Aglaieae. Putative ancestral areas were investigated through area-based and event-based biogeographical approaches. Information on dispersal routes and their direction was inferred from the investigation of dispersal asymmetries between areas. Results Our study indicates that the crown group of Aglaieae dates back at least to the Late Eocene, with major divergence events occurring during the Oligocene and Miocene. It also suggests that dispersal routes existed during Miocene–Pliocene times from the area including Peninsular Malaysia, Sumatra and Borneo to Wallacea, India and Indochina, and from the area including New Guinea, New Ireland and New Britain further east to the Pacific islands at the peripheries of the distribution range. The origin of the Fijian species dates back to the Pliocene. Main conclusions Dispersal over oceanic water barriers has occurred during geological time and seems to have been a major driving force for divergence events in Aglaieae, with some old Gondwanan land masses (e.g. Australia) colonized only during recent times. Movement from the ancestral area was predominantly towards the east. Extant Fijian species of Aglaia are monophyletic and share morphological features rarely found in species of other areas, suggesting speciation within an endemic clade. Divergence of living taxa from their closest living relatives took place during both the Miocene and the Pliocene, and peaked in the Pliocene. The present-day distribution of many species in the tribe must therefore have arisen as a result of dispersal rather than vicariance events. Furthermore, colonization from Indomalesia to Australasia and the Pacific has frequently been followed by speciation.

Placing Biebersteiniaceae, a herbaceous clade of Sapindales, in a temporal and geographic context

Abstract: Biebersteiniaceae comprise a single genus with four species of perennial herbs occurring from central Asia to Greece. A previous molecular phylogenetic study placed one of the species in an isolated position in Sapindales, while morphological studies had placed Biebersteinia in or near Geraniaceae, albeit doubtfully. We tested the monophyly and placement of the family with data from the chloroplast genes rbcL and atpB obtained for all four species, other major clades of Sapindales and outgroups for a total of up to 114 taxa. Parsimony, Bayesian, and likelihood analyses place Biebersteinia in Sapindales, possibly as sister to the other eight families. Strict and relaxed molecular clocks constrained with fossils of Biebersteinia and up to eight other Sapindales suggest that the Biebersteinia crown group diversified in the Oligocene and Miocene, while the stem lineage dates back to the Late Paleocene. Ages for other sapindalean families are earlier than those obtained in more sparsely sampled analyses, although estimates for Burseraceae agree surprisingly well. Ancestral area analyses suggest that Biebersteinia expanded from the eastern part of its range (i.e. Tibet and Inner Mongolia) to the west, although analyses are hampered by the unclear sister group relationships.

Aglaia (Meliaceae): an evaluation of taxonomic concepts based on DNA data and secondary metabolites.

Abstract: We performed maximum parsimony and Bayesian analyses (nuclear ITS rDNA, plastid rps16 intron) to estimate phylogenetic relationships within Aglaia (over 100 species in Southeast Asia, the Pacific, and Australia) and its relations among Aglaieae (Meliaceae). Based on 67 accessions of Aglaieae, three taxa of Guareae, and two taxa of Melieae (outgroup), this study provides the first assessment of the current circumscription of Aglaieae, Aglaia, and its sections and to a more limited extent of species concepts in Aglaia. DNA data are compared to recently collected data on chemical profiles. Our analyses indicate (1) the monophyly of Aglaieae; (2) the polyphyly of Aphanamixis; (3) the paraphyly of Aglaia; (4) the existence of at least three entities with respect to Aglaia: (a) the core group of Aglaia section Amoora (dehiscent fruits) with close relationships to Lansium and Reinwardtiodendron, (b) a group comprising morphological intermediates between the two sections, and (c) the core group of Aglaia section Aglaia (indehiscent fruits). Macro- and micromolecular data indicate that complex species are more heterogeneous, i.e., probably containing more than one taxon each, than taxonomically isolated species. A third section in Aglaia is recognized to accommodate A. lawii, A. teysmanniana, and A. beccarii.

The tortoise and the hare II: relative utility of 21 noncoding chloroplast DNA sequences for phylogenetic analysis

Abstract: Chloroplast DNA sequences are a primary source of data for plant molecular systematic studies. A few key papers have provided the molecular systematics community with universal primer pairs for noncoding regions that have dominated the field, namely trnL-trnF and trnK/matK. These two regions have provided adequate information to resolve species relationships in some taxa, but often provide little resolution at low taxonomic levels. To obtain better phylogenetic resolution, sequence data from these regions are often coupled with other sequence data. Choosing an appropriate cpDNA region for phylogenetic investigation is difficult because of the scarcity of information about the tempo of evolutionary rates among different noncoding cpDNA regions. The focus of this investigation was to determine whether there is any predictable rate heterogeneity among 21 noncoding cpDNA regions identified as phylogenetically useful at low levels. To test for rate heterogeneity among the different cpDNA regions, we used three species from each of 10 groups representing eight major phylogenetic lineages of phanerogams. The results of this study clearly show that a survey using as few as three representative taxa can be predictive of the amount of phylogenetic information offered by a cpDNA region and that rate heterogeneity exists among noncoding cpDNA regions.

Angiosperm phylogeny: 17 genes, 640 taxa

Abstract: PREMISE OF THE STUDY Recent analyses employing up to five genes have provided numerous insights into angiosperm phylogeny, but many relationships have remained unresolved or poorly supported. In the hope of improving our understanding of angiosperm phylogeny, we expanded sampling of taxa and genes beyond previous analyses. METHODS We conducted two primary analyses based on 640 species representing 330 families. The first included 25260 aligned base pairs (bp) from 17 genes (representing all three plant genomes, i.e., nucleus, plastid, and mitochondrion). The second included 19846 aligned bp from 13 genes (representing only the nucleus and plastid). KEY RESULTS Many important questions of deep-level relationships in the nonmonocot angiosperms have now been resolved with strong support. Amborellaceae, Nymphaeales, and Austrobaileyales are successive sisters to the remaining angiosperms (Mesangiospermae), which are resolved into Chloranthales + Magnoliidae as sister to Monocotyledoneae + [Ceratophyllaceae + Eudicotyledoneae]. Eudicotyledoneae contains a basal grade subtending Gunneridae. Within Gunneridae, Gunnerales are sister to the remainder (Pentapetalae), which comprises (1) Superrosidae, consisting of Rosidae (including Vitaceae) and Saxifragales; and (2) Superasteridae, comprising Berberidopsidales, Santalales, Caryophyllales, Asteridae, and, based on this study, Dilleniaceae (although other recent analyses disagree with this placement). Within the major subclades of Pentapetalae, most deep-level relationships are resolved with strong support. CONCLUSIONS Our analyses confirm that with large amounts of sequence data, most deep-level relationships within the angiosperms can be resolved. We anticipate that this well-resolved angiosperm tree will be of broad utility for many areas of biology, including physiology, ecology, paleobiology, and genomics.

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

Abstract: 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.

Biological evidence supports an early and complex emergence of the Isthmus of Panama

Abstract: The linking of North and South America by the Isthmus of Panama had major impacts on global climate, oceanic and atmospheric currents, and biodiversity, yet the timing of this critical event remains contentious. The Isthmus is traditionally understood to have fully closed by ca. 3.5 million years ago (Ma), and this date has been used as a benchmark for oceanographic, climatic, and evolutionary research, but recent evidence suggests a more complex geological formation. Here, we analyze both molecular and fossil data to evaluate the tempo of biotic exchange across the Americas in light of geological evidence. We demonstrate significant waves of dispersal of terrestrial organisms at approximately ca. 20 and 6 Ma and corresponding events separating marine organisms in the Atlantic and Pacific oceans at ca. 23 and 7 Ma. The direction of dispersal and their rates were symmetrical until the last ca. 6 Ma, when northern migration of South American lineages increased significantly. Variability among taxa in their timing of dispersal or vicariance across the Isthmus is not explained by the ecological factors tested in these analyses, including biome type, dispersal ability, and elevation preference. Migration was therefore not generally regulated by intrinsic traits but more likely reflects the presence of emergent terrain several millions of years earlier than commonly assumed. These results indicate that the dramatic biotic turnover associated with the Great American Biotic Interchange was a long and complex process that began as early as the Oligocene–Miocene transition.

Biogeography of the Indo-Australian Archipelago

Abstract: The extraordinary species richness and endemism of the Indo-Australian Archipelago (IAA) exists in one of the most geologically dynamic regions of the planet. The provenance of its biota has been debated, particularly in the area known as Wallacea. Application of molecular genetic approaches and a better understanding of the region’s complex geology have stimulated much recent biogeographic work in the IAA. We review molecular phylogenetic and phylogeographic studies in light of current geological evidence. Present distribution patterns of species have been shaped largely by pre-Pleistocene dispersal and vicariance events, whereas more recent changes in the connectivity of islands within the Archipelago have influenced the partitioning of intraspecific variation. Many genetic studies have uncovered cryptic species with restricted distributions. We discuss the conservation significance of the region and highlight the need for cross-taxon comparative studies using newly developed analytical approaches well suited to the challenges of historical inference in this region.