The evolution of the Aristolochia pallida complex (Aristolochiaceae) challenges traditional taxonomy and reflects large-scale glacial refugia in the Mediterranean.

The taxonomy of the Mediterranean Aristolochia pallida complex has been under debate since several decades with the following species currently recognized: A. pallida, A. lutea, A. nardiana, A. microstoma, A. merxmuelleri, A. croatica, and A. castellana. These taxa are distributed from Iberia to Turkey. To reconstruct phylogenetic and biogeographic patterns, we employed cpDNA sequence variation using both noncoding (intron and spacer) and protein-coding regions (i.e., trnK intron, matK gene, and trnK-psbA spacer). Our results show that the morphology-based traditional taxonomy was not corroborated by our phylogenetic analyses. Aristolochia pallida, A. lutea, A. nardiana, and A. microstoma were not monophyletic. Instead, strong geographic signals were detected. Two major clades, one exclusively occurring in Greece and a second one of pan-Mediterranean distribution, were found. Several subclades distributed in Greece, NW Turkey, Italy, as well as amphi-Adriatic subclades, and a subgroup of southern France and Spain, were revealed. The distribution areas of these groups are in close vicinity to hypothesized glacial refugia areas in the Mediterranean. According to molecular clock analyses the diversification of this complex started around 3-3.3 my, before the onset of glaciation cycles, and the further evolution of and within major lineages falls into the Pleistocene. Based on these data, we conclude that the Aristolochia pallida alliance survived in different Mediterranean refugia rarely with low, but often with a high potential for range extension, and a high degree of morphological diversity.

No obvious genetic erosion, but evident relict status at the westernmost range edge of the Pontic-Pannonian steppe plant Linum flavum L. (Linaceae) in Central Europe.

We investigate patterns of genetic variation along an east-west transect of Central European populations of Linum flavum and interpret the Quaternary history of its peripheral populations, especially those at the westernmost isolated range edge, discussing their migrations and possible relict status. We defined our peripheral transect across three study regions from Central Hungary, eastern Austria to southwestern Germany. Using AFLP fingerprinting and cpDNA sequence variation (rpL16 intron, atpI-H), we analyzed 267 and 95 individuals, respectively, representing each study region by four populations. Hierarchical AMOVA (AFLPs) indicated significant variation among study regions (12% of total variance) and moderate differentiation between populations (10%). Population differentiation was high at the westernmost range edge (11.5%, Germany), but also in the east (13.4%, Hungary), compared to the Austrian study region (8.6%). Correspondingly, AFLP diversity was highest in the center of the study transect in eastern Austria. CpDNA haplotypes support a pattern of regional structuring with the strongest separation of the westernmost range edge, and some haplotype sharing among Austrian and Hungarian individuals. Equilibrating nucleotide versus haplotype diversity patterns, the highly diverse populations at the Pannonian range edge (Austria) indicate long-term persistence, while Central Pannonian populations are obviously effected by recent bottlenecks. Intermediate nucleotide, but high haplotype diversity within the westernmost exclave (Swabian Alb), is indicative of a founder bottleneck during its pre-LGM or early postglacial migration history, followed by sufficient time to accumulate cpDNA variation. The not obviously reduced genetic diversity and distinctiveness of L. flavum at the westernmost range edge suggest a long-term persistence (relict status) of populations in this region, where the species has survived probably even the Würm glaciation in extra-Mediterranean refugia. This genetic relict variation represents an important part of the overall genetic diversity found in the western periphery of this steppe plant and highlights the high conservation priority of respective gene pools.

Diversity hotspots of the laurel forest on Tenerife, Canary Islands: a phylogeographic study of Laurus and Ixanthus.

BACKGROUND AND AIMS: Macaronesian laurel forest is among the worldwide hotspots of threatened biodiversity. With increasing evidence that woodland composition on the Canary Islands changed dramatically during the last few thousand years, the aim of this study was to find evidence for substantial recent population dynamics of two representative species from laurel forest. METHODS: Amplified fragment length polymorphism (AFLP) was used to evaluate fine-scaled genetic variation of the paradigmatic tree Laurus novocanariensis (Lauraceae) and a long-lived herbaceous gentian from core laurel forest, Ixanthus viscosus (Gentianaceae), on Tenerife. Bioclimatic variables were analysed to study the respective climate niches. A chloroplast DNA screening was performed to evaluate additional genetic variation. KEY RESULTS: Genetic diversity of the laurel tree showed severe geographic partitioning. On Tenerife, fine-scaled Bayesian clustering of genetic variation revealed a western and an eastern gene pool, separated by a zone of high admixture and with a third major gene pool. Compared with genetic clusters found on the other Canary Islands, the East-West differentiation on Tenerife seems to be more recent than differentiation between islands. This is substantiated by the finding of extremly low levels of chloroplast DNA-based polymorphisms. Ixanthus showed no geographic structuring of genetic variation. CONCLUSIONS: Genetic data from Tenerife indicate contemporary gene flow and dispersal on a micro/local scale rather than reflecting an old and relic woodland history. In particular for Laurus, it is shown that this species occupies a broad bioclimatic niche. This is not correlated with its respective distribution of genetic variation, therefore indicating its large potential for contemporary rapid and effective colonization. Ixanthus is more specialized to humid conditions and is mostly found in the natural Monteverde húmedo vegetation types, but even for this species indications for long-term persistence in the respective bioclimatically differentiated regions was not find.

Spatial and ecological population genetic structures within two island-endemic Aeonium species of different niche width.

The Crassulacean genus Aeonium is a well-known example for plant species radiation on oceanic archipelagos. However, while allopatric speciation among islands is documented for this genus, the role of intra-island speciation due to population divergence by topographical isolation or ecological heterogeneity has not yet been addressed. The aim of this study was to investigate intraspecific genetic structures and to identify spatial and ecological drivers of genetic population differentiation on the island scale. We analyzed inter simple sequence repeat variation within two island-endemic Aeonium species of La Palma: one widespread generalist that covers a large variety of different habitat types (Ae. davidbramwellii) and one narrow ecological specialist (Ae. nobile), in order to assess evolutionary potentials on this island. Gene pool differentiation and genetic diversity patterns were associated with major landscape structures in both species, with phylogeographic implications. However, overall levels of genetic differentiation were low. For the generalist species, outlier loci detection and loci-environment correlation approaches indicated moderate signatures of divergent selection pressures linked to temperature and precipitation variables, while the specialist species missed such patterns. Our data point to incipient differentiation among populations, emphasizing that ecological heterogeneity and topographical structuring within the small scales of an island can foster evolutionary processes. Very likely, such processes have contributed to the radiation of Aeonium on the Canary Islands. There is also support for different evolutionary mechanisms between generalist and specialist species.

Biogeography of Mediterranean Hotspot Biodiversity: Re-Evaluating the 'Tertiary Relict' Hypothesis of Macaronesian Laurel Forests.

The Macaronesian laurel forests (MLF) are dominated by trees with a laurophyll habit comparable to evergreen humid forests which were scattered across Europe and the Mediterranean in the Paleogene and Neogene. Therefore, MLF are traditionally regarded as an old, 'Tertiary relict' vegetation type. Here we address the question if key taxa of the MLF are relictual. We evaluated the relict hypothesis consulting fossil data and analyses based on molecular phylogenies of 18 representative species. For molecular dating we used the program BEAST, for ancestral trait reconstructions BayesTraits and Lagrange to infer ancestral areas. Our molecular dating showed that the origins of four species date back to the Upper Miocene while 14 originated in the Plio-Pleistocene. This coincides with the decline of fossil laurophyllous elements in Europe since the middle Miocene. Ancestral trait and area reconstructions indicate that MLF evolved partly from pre-adapted taxa from the Mediterranean, Macaronesia and the tropics. According to the fossil record laurophyllous taxa existed in Macaronesia since the Plio- and Pleistocene. MLF are composed of species with a heterogeneous origin. The taxa dated to the Pleistocene are likely not 'Tertiary relicts'. Some species may be interpreted as relictual. In this case, the establishment of most species in the Plio-Pleistocene suggests that there was a massive species turnover before this time. Alternatively, MLF were largely newly assembled through global recruitment rather than surviving as relicts of a once more widespread vegetation. This process may have possibly been triggered by the intensification of the trade winds at the end of the Pliocene as indicated by proxy data.

Molecular phylogenetic analyses identify Alpine differentiation and dysploid chromosome number changes as major forces for the evolution of the European endemic Phyteuma (Campanulaceae).

Phyteuma is a chromosomally and ecologically diverse vascular plant genus and constitutes an excellent system for studying both the role of chromosomal change for species diversification and the evolution of high-mountain biota. This kind of research is, however, hampered by the lack of a sound phylogenetic framework exacerbated by the notoriously low predictive power of traditional taxonomy with respect to phylogenetic relationships in Campanulaceae. Based on a comprehensive taxon sampling and analyses of nuclear and plastid sequence and AFLP fingerprint data, Phyteuma is confirmed as a monophyletic group sister to the monotypic Physoplexis, which is in line with their peculiar flower morphologies. Within Phyteuma two clades, largely corresponding to previously recognized sections, are consistently found. The traditional circumscription of taxonomic series is largely rejected. Whereas distinctness of the currently recognized species is mostly corroborated, some interspecific relationships remain ambiguous due to incongruences between nuclear and plastid data. Major forces for diversification and evolution of Phyteuma are descending dysploidy (i.e., a decrease in chromosome base number) as well as allopatric and ecological differentiation within the Alps, the genus' center of species diversity.

Old-New World and trans-African disjunctions of Thamnosma (Rutaceae): intercontinental long-distance dispersal and local differentiation in the succulent biome.

PREMISE OF THE STUDY: The succulent biome is highly fragmented throughout the Old and New World. The resulting disjunctions on global and regional scales have been explained by various hypotheses. To evaluate these, we used Thamnosma, which is restricted to the succulent biome and has trans-Atlantic and trans-African disjunctions. Its three main distribution centers are in southern North America, southern and eastern Africa including Socotra. METHODS: We conducted parsimony, maximum likelihood, and Bayesian phylogenetic analyses based on chloroplast and nuclear sequence data. We applied molecular clock calculations using the programs BEAST and MULTIDIVTIME and biogeographic reconstructions using S-DIVA and Lagrange. KEY RESULTS: Our data indicate a weakly supported paraphyly of the New World species with respect to a palaeotropical lineage, which is further subdivided into a southern African and a Horn of Africa group. The disjunctions in Thamnosma are mostly dated to the Miocene. CONCLUSIONS: We conclude that the Old-New World disjunction of Thamnosma is likely the result of long-distance dispersal. The Miocene closure of the arid corridor between southern and eastern Africa may have caused the split within the Old World lineage, thus making a vicariance explanation feasible. The colonization of Socotra is also due to long-distance dispersal. All recent Thamnosma species are part of the succulent biome, and the North American species may have been members of the arid Neogene Madro-Tertiary Geoflora. Phylogenetic niche conservatism, rare long-distance dispersal, and local differentiation account for the diversity among species of Thamnosma.

Evidence for a vicariant origin of Macaronesian-Eritreo/Arabian disjunctions in Campylanthus Roth (Plantaginaceae).

The numerous disjunct plant distributions between Macaronesia and eastern Africa-Arabia suggest that these could be the relicts of a once continuous vegetation belt along the southern Tethys, which has been fragmented by Upper Miocene-Pliocene aridification. We tested this vicariance hypothesis with a phylogenetic analysis of Campylanthus (Plantaginaceae), based on nuclear and plastid DNA sequence data. Our results indicate a basal split within Campylanthus giving rise to Macaronesian and Eritreo-Arabian lineages in the Pliocene/Upper Miocene. This is consistent with the vicariance hypothesis, thus obviating the need to postulate trans-Saharan long-distance dispersal. The biogeography of Campylanthus may parallel patterns in other plant groups and the implications for our understanding of the biogeography of northern and eastern Africa, and Arabia are discussed.