Dirk C. Albach

Hybridization and speciation

Hybridization has many and varied impacts on the process of speciation. Hybridization may slow or reverse differentiation by allowing gene flow and recombination. It may accelerate speciation via adaptive introgression or cause near‐instantaneous speciation by allopolyploidization. It may have multiple effects at different stages and in different spatial contexts within a single speciation event. We offer a perspective on the context and evolutionary significance of hybridization during speciation, highlighting issues of current interest and debate. In secondary contact zones, it is uncertain if barriers to gene flow will be strengthened or broken down due to recombination and gene flow. Theory and empirical evidence suggest the latter is more likely, except within and around strongly selected genomic regions. Hybridization may contribute to speciation through the formation of new hybrid taxa, whereas introgression of a few loci may promote adaptive divergence and so facilitate speciation. Gene regulatory networks, epigenetic effects and the evolution of selfish genetic material in the genome suggest that the Dobzhansky–Muller model of hybrid incompatibilities requires a broader interpretation. Finally, although the incidence of reinforcement remains uncertain, this and other interactions in areas of sympatry may have knock‐on effects on speciation both within and outside regions of hybridization.

Phylogeny of the eudicots : a nearly complete familial analysis based on rbcL gene sequences

A phylogenetic analysis of 589 plastid rbcL gene sequences representing nearly all eudicot families (a total of 308 families; seven photosynthetic and four parasitic families are missing) was performed, and bootstrap re-sampling was used to assess support for clades. Based on these data, the ordinal classification of eudicots is revised following the previous classification of angiosperms by the Angiosperm Phylogeny Group (APG). Putative additional orders are discussed (e.g. Dilleniales, Escalloniales, Vitales), and several additional families are assigned to orders for future updates of the APG classification. The use of rbcL alone in such a large matrix was found to be practical in discovering and providing bootstrap support for most orders. Combination of these data with other matrices for the rest of the angiosperms should provide the framework for a complete phylogeny to be used in macro-evolutionary studies.

Piecing together the "new" Plantaginaceae.

Scrophulariaceae is one of the families that has been divided extensively due to the results of DNA sequence studies. One of its segregates is a vastly enlarged Plantaginaceae. In a phylogenetic study of 47 members of Plantaginaceae and seven outgroups based on 3561 aligned characters from four DNA regions (the nuclear ribosomal ITS region and the plastid trnL-F, rps16 intron, and matK-trnK intron regions), the relationships within this clade were analyzed. The results from parsimony and Bayesian analyses support the removal of the Lindernieae from Gratioleae to a position outside Plantaginaceae. A group of mainly New World genera is paraphyletic with respect to a clade of Old World genera. Among the New World taxa, those offering oil as a pollinator reward cluster together. Ourisia is sister to this clade. Gratioleae consist of Gratiola, Otacanthus, Bacopa, Stemodia, Scoparia, and Mecardonia. Cheloneae plus Russelia and Tetranema together constitute the sister group to a clade predominantly composed of Old World taxa. Among the Old World clade, Ellisiophyllum and Lafuentea have been analyzed for the first time in a molecular phylogenetic analysis. The former genus is sister to Sibthorpia and the latter is surprisingly the sister to Antirrhineae.

Classification, Origin, and Diversification of the New Zealand Hebes (Scrophulariaceae)

The New Zealand hebes (Scrophulariaceae) are members of a large Southern Hemisphere clade nested within Veronica. Analysis of ITS and rbcL sequences suggests that the New Zealand species are derived from a single common ancestor that arrived via long-distance dispersal. After the establishment of this initial founder population in New Zealand, the hebes have undergone at least two major episodes of diversification, giving rise to six clades. The great degree of morphological diversity in the New Zealand hebes contrasts with a corresponding low level of sequence divergence. New Zealand was a source of new emigrants to other regions in the South Pacific that were preadapted to high mountains or forest margins. Our results suggest that two instances of long-distance dispersal from New Zealand to South America, at least one instance from New Zealand to Australia, and one instance from New Zealand to New Guinea have occurred relatively recently. Shorter hops to the Chatham Islands and the subantarctic islands are also supported by the sequence data.

Towards resolving Lamiales relationships: insights from rapidly evolving chloroplast sequences

BackgroundIn the large angiosperm order Lamiales, a diverse array of highly specialized life strategies such as carnivory, parasitism, epiphytism, and desiccation tolerance occur, and some lineages possess drastically accelerated DNA substitutional rates or miniaturized genomes. However, understanding the evolution of these phenomena in the order, and clarifying borders of and relationships among lamialean families, has been hindered by largely unresolved trees in the past.ResultsOur analysis of the rapidly evolving trnK/matK, trnL-F and rps16 chloroplast regions enabled us to infer more precise phylogenetic hypotheses for the Lamiales. Relationships among the nine first-branching families in the Lamiales tree are now resolved with very strong support. Subsequent to Plocospermataceae, a clade consisting of Carlemanniaceae plus Oleaceae branches, followed by Tetrachondraceae and a newly inferred clade composed of Gesneriaceae plus Calceolariaceae, which is also supported by morphological characters. Plantaginaceae (incl. Gratioleae) and Scrophulariaceae are well separated in the backbone grade; Lamiaceae and Verbenaceae appear in distant clades, while the recently described Linderniaceae are confirmed to be monophyletic and in an isolated position.ConclusionsConfidence about deep nodes of the Lamiales tree is an important step towards understanding the evolutionary diversification of a major clade of flowering plants. The degree of resolution obtained here now provides a first opportunity to discuss the evolution of morphological and biochemical traits in Lamiales. The multiple independent evolution of the carnivorous syndrome, once in Lentibulariaceae and a second time in Byblidaceae, is strongly supported by all analyses and topological tests. The evolution of selected morphological characters such as flower symmetry is discussed. The addition of further sequence data from introns and spacers holds promise to eventually obtain a fully resolved plastid tree of Lamiales.

Comparative phylogeography of the Veronica alpina complex in Europe and North America

The Veronica alpina complex comprises eight species of alpine habitats over a wide range of mountain systems in the Northern Hemisphere. The occurrence of sympatric species in the European and North American mountain systems allowed us not only to investigate the effect of the ice ages on intraspecific phylogeographical patterns and genetic diversity in different continents of the Northern Hemisphere, but also to compare these patterns in closely related species. Plastid DNA trnL‐F sequences and AFLP (amplified fragment length polymorphism) fingerprints were used to infer the phylogenetic history of the group and phylogeographical patterns within species. Hybrid origin of tetraploid eastern North American V. wormskjoldii from western North American V. nutans (= V. wormskjoldii s.l.) and Eurasian V. alpina is suggested. A number of phylogeographical groups have been found both in V. alpina from Europe and in V. nutans from western North America. Phylogeographical substructuring in the Alps is inferred for V. alpina but not for V. bellidioides, which is moreover characterized by an overall very low genetic diversity. Western North American V. cusickii is much more genetically diverse than its sympatric relative, V. nutans, an effect that is likely due to differences in the breeding system. Populations of V. nutans are differentiated into three groups, those from the Cascades and from the southern and the northern Rocky Mountains. Genetic diversity seems to be higher in the North American V. nutans than in the morphologically and ecologically similar European V. alpina. A possible scenario to explain this pattern is suggested.

Paraphyly of Veronica (Veroniceae; Scrophulariaceae): Evidence from the Internal Transcribed Spacer (ITS) Sequences of Nuclear Ribosomal DNA

Veronica (Veroniceae; Scrophulariaceae) and segregated genera, such as Hebe from New Zealand has been debated intensively in the past. We conducted an analysis of sequence data from the internal transcribed spacer region of nuclear ribosomal DNA (ITS) to evaluate the validity of segregate genera and the monophyly of Veronica. According to the results presented here, Veronica is paraphyletic, with the Hebe complex, Synthyris, and Paederota nested within the larger Veronica clade. Pseudolysimachion is in a basal polytomy of the expanded Veronica clade in the strict consensus tree and might be nested within Veronica as well. Clades within Veronica do not correspond to sections traditionally recognized. This study provides a first estimation of the phylogeny of Veroniceae using molecular data and can serve as a starting point for future investigations of Veronica and relatives.

A new classification of the tribe Veroniceae: problems and a possible solution

Based on the most recent evidence from phylogenetic analyses of Veronica and its related genera, we propose a new infratribal and infrageneric rearrangement for Veroniceae and Veronica. These recent analyses have settled the long dispute about the relationship of the Northern Hemisphere Veronica and the Southern Hemisphere Hebe complex and have shown the derivation of the latter from within the former. Other currently recognized genera such as Synthyris and Pseudolysimachion are also derived from within Veronica. A classification based on monophyletic genera therefore needs to either lump some well recognized genera into a large genus Veronica or split Veronica into several genera that seem impossible to separate using morphological or structural characters. We discuss the advantages and disadvantages and conclude that it is best to recognize a large genus Veronica (including Hebe, Parahebe, Chionohebe, Heliohebe, Detzneria, Derwentia, Pseudolysimachion, Synthyris and Besseya) with 13 subgenera, along with 8 other genera, Scrofella, Veronicastrum (inclusive of Calorhabdos and Botryopleuron), Lagotis, Wulfenia, Kashmiria, Picrorhiza, Wulfeniopsis and Paederota, in Veroniceae.

Species Boundaries and Phylogeographic Patterns in Cryptic Taxa Inferred from AFLP Markers: Veronica subgen. Pentasepalae (Scrophulariaceae) in the Western Mediterranean

Abstract We show the power of detailed AFLP study to address questions of species delimitation and genetic diversity in morphologically-cryptic plants. We have combined this technique with karyological studies to explore species boundaries in the Western Mediterranean representatives of Veronica subgen. Pentasepalae. Several members of this subgenus are represented in the Iberian Peninsula and North Africa by morphologically similar populations, which lead to different taxonomic hypotheses. We have analyzed genetic variation with two different objectives: first, to provide a basis on which one taxonomic hypothesis is favored against its alternatives, and second, to obtain a satisfactory interpretation of phylogeographic patterns. The usefulness of several parameters and analyses is considered in order to help rank taxa and to reveal details of their speciation modes. Some of these parameters are presented with a geographical background to facilitate phylogeographic interpretations. The data support one of the previously proposed taxonomic hypotheses, which results in the recognition of eight taxa. An east-to-west migration route within the Iberian Peninsula is hypothesized, coinciding with the general pattern proposed for Veronica subgen. Pentasepalae. Further data on genetic variability and chromosome counts for 41 populations are provided.

Veronica: Parallel morphological evolution and phylogeography in the Mediterranean

Abstract.The genus Veronica s. lat. comprises about 450 species (including about 180 species from the southern hemisphere Hebe-complex), many of which grow in the Mediterranean area. Their extreme variability in morphology, life form and habitats has led to many suggestions regarding evolution and biogeography. Difficulties arise from parallel syndromes, widespread among alpine species and lowland perennials, and particularly among annual species of the genus. We have used sequences of the plastid trnL-F region and nuclear ribosomal ITS sequences to differentiate between different clades of Veronica and reveal cases of parallel evolution. Based on this data, cases of parallel evolution have been found in biogeographical patterns among the alpine species of Veroniceae, in which species from European mountains have affinities to those in the Central Asian/Himalayan region whereas alpine species from Turkey are probably more recently derived from lowland southwestern Asian taxa. Different subspecies of Veronica bombycina gained their characteristic morphology independently and parallel in adaptation to their alpine environment. Pinnatifid leaves have been gained parallel in perennial grassland species of Veronica. Finally, parallel evolutionary trends in many characters, not only morphological but also molecular characters, are common among annual species of Veronica.