Recent oceanic long-distance dispersal and divergence in the amphi-Atlantic rain forest genus Renealmia L.f. (Zingiberaceae)

Renealmia L.f. (Zingiberaceae) is one of the few tropical plant genera with numerous species in both Africa and South America but not in Asia. Based on phylogenetic analysis of nuclear ribosomal internal transcribed spacer (ITS) and chloroplast trnL-F DNA, Renealmia is shown to be monophyletic with high branch support. Low sequence divergence found in the two genome regions (ITS: 0-2.4%; trnL-F: 0-1.9%) suggests recent diversification within the genus. Molecular divergence age estimates give further support to the recent origin of the genus and show that Renealmia has attained its amphi-Atlantic distribution by an oceanic long-distance dispersal event from Africa to South America during the Miocene or Pliocene (15.8-2.7 My ago). Some support is found for the hypothesis that speciation in neotropical Renealmia was influenced by the Andean orogeny. Speciation has been approximately simultaneous on both sides of the Atlantic, but increased taxon sampling is required to compare the speciation rates between the New World and Old World tropics.     

Nuclear ribosomal DNA and karyotypes indicate a NW African origin of South American Hypochaeris (Asteraceae, Cichorieae)

Hypochaeris has a disjunct distribution, with more than 15 species in the Mediterranean region, the Canary Islands, Europe, and Asia, and more than 40 species in South America. Previous studies have suggested that the New World taxa have evolved from ancestors similar to the central European H. maculata. Based on internal transcribed spacer (ITS) sequences and fluorescence in situ hybridization (FISH) with 5S and 18S-25S rDNA of the previously overlooked Hypochaeris angustifolia from Moyen Atlas, Morocco, we show that it is sister to the entire South American group. A biogeographic analysis supports the hypothesis of long-distance dispersal from NW Africa across the Atlantic Ocean for the origin of the South American taxa rather than migration from North America, through the Panamian land bridge, followed by subsequent extinction in North America. With the assumption of a molecular clock, the trans-Atlantic dispersal from NW Africa to South America is roughly estimated to have taken place during Pliocene or Pleistocene.     

Phylogeny, divergence times, and historical biogeography of New World Dryopteris (Dryopteridaceae)

? Premise of the study: Dryopteris is a large, cosmopolitan fern genus ideal for addressing questions about diversification, biogeography, hybridization, and polyploidy, which have historically been understudied in ferns. We constructed a highly resolved, well-supported phylogeny for New World Dryopteris and used it to investigate biogeographic patterns and divergence times. ? Methods: We analyzed relationships among 97 species of Dryopteris, including taxa from all major biogeographic regions, with analyses based on 5699 aligned nucleotides from seven plastid loci. Phylogenetic analyses used maximum parsimony, maximum likelihood, and Bayesian inference. We conducted divergence time analyses using BEAST and biogeographic analyses using maximum parsimony, maximum likelihood, Bayesian, and S-DIVA approaches. We explored the monophyly of subgenera and sections in the most recent generic classification and of geographic groups of taxa using Templeton tests. ? Key results: The genus Dryopteris arose ca. 42 million years ago (Ma). Most of the Central and South American species form a well-supported clade which arose 32 Ma, but the remaining New World species are the result of multiple, independent dispersal and vicariance events involving Asia, Europe, and Africa over the last 15 Myr. We identified six long-distance dispersal events and three vicariance events in the immediate ancestry of New World species; reconstructions for another four lineages were ambiguous. ? Conclusions: New World Dryopteris are not monophyletic; vicariance has dominated the history of the North American species, while long-distance dispersal prevails in the Central and South American species, a pattern not previously seen in plants.     

Ancient trans-Atlantic flight explains locust biogeography: molecular phylogenetics of Schistocerca

The desert locust (Schistocerca gregaria) has been an important agricultural pest at least since biblical times. Although the ecology, physiology and behaviour of this insect species have been well characterized, its biogeographical origins and evolutionary history are more obscure. Schistocerca gregaria occurs throughout Africa, the Middle East and Western Asia, but all other species in the genus Schistocerca are found in the New World. Because S. gregaria has the capacity for extreme long-distance movement associated with swarming behaviour, dispersal may have played an important role in determining current distribution patterns. Some authors have argued that S. gregaria is the product of an eastward trans-Atlantic dispersal from North America to Africa; others consider it more likely that the New World taxa are the product of westward dispersal from Africa. Here, we present a mitochondrial DNA phylogeny of Schistocerca species that supports the monophyly of New World species (including the Galapagos endemic Halmenus) relative to S. gregaria. In concert with observed patterns of molecular divergence, and in contrast to previous morphological studies, our analysis indicates a single trans-Atlantic flight from Africa to South America, followed by extensive speciation and ecological divergence in the New World.     

Phylogenetic relationships and evolution in Chrysosplenium (Saxifragaceae) based on matK sequence data

Chrysosplenium (Saxifragaceae) consists of 57 species widely distributed in temperate and arctic regions of the Northern Hemisphere, with two species restricted to the southern part of South America. Species relationships within the genus are highly problematic. The genus has traditionally been divided into two groups, sometimes recognized as sections (Oppositifolia and Alternifolia), based on leaf arrangement, or, alternatively, into 17 series. Based on morphological features, Hara suggested that the genus originated in South America and then subsequently migrated to the Northern Hemisphere. We conducted phylogenetic analyses of DNA sequences of the chloroplast gene matK for species of Chrysosplenium to elucidate relationships, test Hara's biogeographic hypothesis for the genus, and examine chromosomal and gynoecial diversification. These analyses revealed that both sections Oppositifolia and Alternifolia are monophyletic and form two large sister clades. Hence, leaf arrangement is a good indicator of relationships within this genus. Hara's series Pilosa and Macrostemon are each also monophyletic; however, series Oppositifolia, Alternifolia, and Nepalensia are clearly not monophyletic. MacClade reconstructions suggest that the genus arose in Eastern Asia, rather than in South America, with several independent migration events from Asia to the New World. In one well-defined subclade, species from eastern and western North America form a discrete clade, with Old World species as their sister group, suggesting that the eastern and western North American taxa diverged following migration to that continent. The South American species forms a clade with species from eastern Asia; this disjunction may be the result of ancient long-distance dispersal. Character mapping demonstrated that gynoecial diversification is dynamic, with reversals from inferior to half-inferior ovaries, as well as to ovaries that appear superior. Chromosomal evolution also appears to be labile with several independent origins of n = 12 (from an original number of n = 11) and multiple episodes of aneuploidy.     

Phylogeny, biogeography, and host-plant association in the subfamily Apaturinae (Insecta: Lepidoptera: Nymphalidae) inferred from eight nuclear and seven mitochondrial genes

The subfamily Apaturinae consists of 20 genera and shows disjunct distributions and unique host-plant associations. Most genera of this subfamily are distributed in Eurasia South-East Asia and Africa, whereas the genera Doxocopa and Asterocampa are distributed mainly in South America and North America, respectively. Although the Apaturinae larvae mainly feed on the Cannabaceae, those of the genus Apatura are associated with Salix and Populus (Salicaceae), which are distantly related to the Cannabaceae. Here, we infer the phylogeny of Apaturinae and reconstruct the history of host shifting and of colonization in the New World. We analyzed 9761 bp of nuclear and mitochondrial DNA sequence data, including the genes encoding EF1a, Wg, ArgK, CAD, GAPDH, IDH, MDH, RpS5, COI, COII, ATPase8, ATPase6, COIII, ND3, and ND5 for 12 apaturine genera. We also inferred the phylogeny with six additional genera using mitochondrial sequence data alone. Within the Apaturinae, two major clades are recovered in all the datasets. These clades separate the New World genera, Doxocopa and Asterocampa, indicating that dispersal to the New World occurred at least twice. According to our divergence time estimates, these genera originated during the Early Oligocene to the Early Miocene, implying that they migrated across the Bering Land Bridge rather than the Atlantic Land Bridge. The temporal estimates also show that host shifting to Salix or Populus in Apatura occurred more than 15 million years after the divergence of their host plants. Our phylogenetic results are inconsistent with the previously accepted apaturine genus groups and indicate that their higher classification should be reconsidered.     

Phylogenetic biogeography of the leafy liverwort Herbertus (Jungermanniales, Herbertaceae) based on nuclear and chloroplast DNA sequence data: correlation between genetic variation and geographical distribution

Aim The cosmopolitan genus Herbertus is notorious for having a difficult taxonomy and for the fact that there is limited knowledge of species ranges and relationships. Topologies generated from variable molecular markers are used to discuss biogeographical patterns in Herbertus and to compare them with the geological history of continents and outcomes reported for other land plants. Location Africa, Asia, Azores, Europe, southern South America, northern South America, North America, New Zealand. Methods Phylogenetic analyses of nuclear ribosomal internal transcribed spacer and chloroplast (cp) trnL–trnF sequences of 66 accessions of Herbertus and the outgroup species Triandrophyllum subtrifidum and Mastigophora diclados were used to investigate biogeographical patterns in Herbertus. Areas of putative endemism were defined based on the distribution of species included in the analyses. Maximum parsimony analyses were undertaken to reconstruct ancestral areas and intraspecies migration routes. Results The analyses reveal species‐level cladograms with a correlation between genetic variation and the geographical distribution of the related accessions. The southern South American Herbertus runcinatus is sister to the remainder of the genus, which is split into two main clades. One contains the Neotropical–African Herbertus juniperoideus and the New Zealand/Tasmanian Herbertus oldfieldianus. An African accession of H. juniperoideus is nested within Neotropical accessions. The second main clade includes species that inhabit Asia, the Holarctic, Africa, and northern South America. Maximum parsimony analyses indicate that this clade arose in Asia. Herbertus sendtneri originated in Asia and subsequently colonized the Holarctic and northern South America. An Asian origin and colonization into Africa is indicated for H. dicranus. Main conclusions The current distribution of Herbertus cannot be explained by Gondwanan vicariance. A more feasible explanation of the range is a combination of short‐distance dispersal, rare long‐distance dispersal events (especially into regions that faced floral displacements as a result of climatic changes) extinction, recolonization, and diversification. The African Herbertus flora is a mixture of Asian and Neotropical elements. Southern South America harbours an isolated species. The molecular data indicate partial decoupling of molecular and morphological variation in Herbertus. Biogeographical patterns in Herbertus are not dissimilar to those of other groups of bryophytes, but elucidation of the geographical ranges requires a molecular approach. Some patterns could be the result of maintenance of Herbertus in the inner Tropics during glacial maxima, and dispersal into temperate regions in warm phases.     

Melastomeae come full circle: biogeographic reconstruction and molecular clock dating

Rhexia, with 11 species in the Coastal Plain province of North America, is the only temperate zone endemic of the tropical eudicot family Melastomataceae. It is a member of the only pantropical tribe of that family, Melastomeae. Based on the chloroplast gene ndhF, we use a fossil-calibrated molecular clock to address the question of the geographic origin and age of Rhexia. Sequences from 37 species in 21 genera representing the tribe's geographical range were analyzed together with five outgroups. To obtain better clade support, another chloroplast region, the rpl16 intron, was added for 24 of the species. Parsimony analysis of the combined data and maximum-likelihood analysis of ndhF alone indicate that the deepest split is between Rhexia plus its sister group, a small Central American genus, and all other Melastomeae. Old World Melastomeae are monophyletic and nested within New World Melastomeae. Although likelihood-ratio tests of clock and nonclock substitution models for the full or moderately pruned datasets rejected the clock, these models yielded identical topologies (for 30 taxa) with few significantly different branch lengths as assessed by a Student's t-test. Age estimates obtained were 22 million years ago (Mya) for the divergence of Rhexia from its sister group, 12 Mya for the dispersal of Melastomeae from the New World to West Africa, and 1 Mya for the diversification of Melastoma in Southeast Asia. The only other genus of Melastomeae to have reached Southeast Asia from Africa or Madagascar is Osbeckia. The age and geographic distribution of fossils, which come from Miocene sites throughout Eurasia, suggest that Melastomeae once ranged from Eurasia across Beringia to North America from whence they reached South America and subsequently Africa and Southeast Asia. Climate deterioration led to their extinction in the Northern Hemisphere, with Rhexia possibly surviving in Coastal Plain refugia.     

Biogeography of ‘tropical Anagallis’ (Myrsinaceae) inferred from nuclear and plastid DNA sequence data

Aim ‘Tropical Anagallis’ corresponds to one of two evolutionary lineages within the genus Anagallis L. Generally, species within this lineage have a limited distribution in (sub‐)tropical regions in Africa or Madagascar. Two species, however, are endemic to South America, and exhibit a trans‐Atlantic disjunction with the rest of the species within the lineage. To investigate this disjunct distribution, as well as other dispersal events, the distribution of extant taxa was used to hypothesize the ancestral area(s) of distribution. Location Africa, Madagascar, Europe and South America. Methods Dispersal–vicariance analysis (DIVA) was used to optimize distribution areas onto parsimony and Bayesian phylogenies based on sequence data from four chloroplast loci and the nuclear internal transcribed spacers (ITS). Results Parsimony analysis gave one most parsimonious tree while Bayesian analysis resulted in a collapsed node due to alternative placements of Anagallis nummularifolia Baker, endemic to Madagascar. Optimization of the present distribution using DIVA, and the most parsimonious tree and six alternative topologies of the Bayesian analysis, show an origin of the lineage in Europe as most likely, although one topology indicates a broader ancestral distribution area. Dispersal to Africa appears to have been a single event, while two parallel dispersal events seem to have resulted in the American as well as Madagascan distributions. Main conclusions The lineage ‘tropical Anagallis’ evolved in Europe and may have been present in the Eocene boreotropical forests, although scarcity of fossils makes assessment of age difficult. Dispersal to South America is proposed to have been via the North Atlantic land bridge, or, more likely, through transport by the North Equatorial Current. Dispersal from Europe to Africa represents a single event, while dispersal to Madagascar from mainland Africa has occurred twice.     

Canary Grasses (Phalaris,Poaceae): biogeography,molecular dating and the role of floret structure in dispersal

Canary grasses (Phalaris, Poaceae) include 21 species, widely spread throughout the temperate and subtropical regions of the world with two centres of diversity: the Mediterranean Basin and western North America. The genus contains annual and perennial, endemic, cosmopolitan, wild, and invasive species with diploid, tetraploid and hexaploid cytotypes. As such, Phalaris presents an ideal platform to study diversification via historic hybridization and polyploidy events, and geographical dispersal in grasses. We present the first empirical phylogeographic study for Phalaris testing current, intuitive hypotheses on the centres of origin, historic dispersal events and diversification within a geological timeframe. Bayesian methods (beast , version 1.6.2) were used to establish divergence dates, and dispersal–vicariance analyses (rasp , version 2.1b) were implemented for ancestral node reconstructions. Our phylogeographic results indicate that the genus emerged during the Miocene epoch [20.6–8.4 Ma (million years ago)] in the Mediterranean basin followed by dispersal and vicariance events to Africa, Asia and the Americas. We propose that a diploid ancestor of P. arundinacea migrated to western North America via the Bering Strait, where further diversification emerged in the New World. It appears that polyploidy played a major role in the evolution of the genus in the Old World, while diversification in the New World followed a primarily diploid pathway. Dispersal to various parts of the Americas followed different routes. Fertile florets with hairy protruding sterile lemmas showed significant correlation with wider geographical distribution.     

A phylogeny of Anisophylleaceae based on six nuclear and plastid loci: ancient disjunctions and recent dispersal between South America, Africa, and Asia

The Anisophylleaceae comprise 29-34 species of shrubs and trees occurring in lowland forests and swamps in tropical Africa, Asia, and South America. These species are placed in four genera with disjunct geographic distributions; Anisophyllea has 25-30 species in South America, Africa, and Malesia; Combretocarpus has one species in Sumatra and Borneo; Poga one species in equatorial Africa; and Polygonanthus two in the Amazon Basin. Here we use a phylogeny based on six nuclear and plastid loci sequenced for 15 species representing the four genera to infer their relationships and the relative and absolute ages of the range disjunctions. Combretocarpus is sister to the other three genera, and Polygonanthus then sister to Poga and Anisophyllea. Ansiophyllea, represented by 12 species from all three continents, is monophyletic. A relaxed Bayesian clock calibrated with the oldest fossils from a relevant outgroup, Tetramelaceae, suggests that the disjunctions between Combretocarpus, Poga, and Polygonanthus date back to the Cretaceous, Mid-, and Upper Eocene, whereas the intercontinental disjunctions within Anisophyllea appear to date back only some 22-23 million years and thus probably result from long-distance dispersal.     

Molecular phylogenetic analysis of Leibnitzia Cass. (Asteraceae: Mutisieae: Gerbera-complex), an Asian-North American disjunct genus

Leibnitzia comprises six species of perennial herbs that are adapted to high elevation conditions and is one of only two Asteraceae genera known to have an exclusively disjunct distribution spanning central to eastern Asia and North America. Molecular phylogenetic analysis of Leibnitzia and other Gerbera-complex members indicates that Leibnitzia is monophyletic, which is in contrast with our expectation that the American Leibnitzia species L. Lyrata and L. Occimadremis would be more closely related to another American member of the Gerbera-complex, namely Chaptalia. Ancestral area reconstructions show that the historical biogeography of the Gerbera-complex mirrors that of the entire Asteraceae, with early diverging lineages located in South America that were followed by transfers to Africa and Eurasia and, most recently, to North America. Intercontinental transfer of Leibnitzia appears to have been directed from Asia to North America. Independent calibrations of nuclear (ribosomal DNA internal transcribed spacer region) and chloroplast (trnL-rpl32 intron) DNA sequence data using relaxed clock methods and either mean rate or fossil-based priors unanimously support Miocene and younger divergence times for Gerbera-complex taxa. The ages are not consistent with most Gondwanan vicariance episodes and, thus, the global distribution of Gerbera-complex members must be explained in large part by long-distance dispersal. American species of Leibnitzia are estimated to have diverged from then- Asian ancestor during the Quaternary (ca. 2 mya) and either migrated overland to North America via Beringia and retreated southwards along high elevation corridors to their- present location in southwestern North America or were dispersed long distance.     

Genetic relationships among American species of the genus Prosopis (Mimosoideae, Leguminosae) inferred from ITS sequences: evidence for long-distance dispersal

Aim  The genus Prosopis includes 44 species and has a pseudoamphitropical, disjunct distribution. We aimed to determine whether American Prosopis sections arose in North or South America, and to explain the current distribution of their species on the basis of their genetic relationships.
Location  South-western USA, Mexico, Caribbean Antilles, Peru–Ecuador, central and northern Argentina, south-western Argentina (Patagonia) and Cuyo, south-western Asia and northern Africa.
Methods  Internal transcribed spacer fragments from 21 species of Prosopis were sequenced and the data were used to analyse the phylogenetic relationships using Microlobius and Mimosa as outgroups. Genetic distances were calculated to estimate the degree of divergence. Dispersal–vicariance (DIVA) analysis was conducted to help understand the biogeographical history of the genus.
Main conclusions  The sections Strombocarpa and Algarobia are not monophyletic. Prosopis argentina (section Monilicarpa ) and the species of Algarobia are included in single clade. The phylogeny, DIVA analysis, and the pattern of genetic distances indicate that the ancestral area for the American species was wide, from south-western USA to Central and northern Argentina. Successive vicariance events split this area, and long-distance dispersal episodes (perhaps mediated by birds) led to recolonizations from North to South America, and vice versa .     

DISPERSAL,VICARIANCE, AND CLOCKS: HISTORICAL BIOGEOGRAPHY AND SPECIATION IN A COSMOPOLITAN PASSERINE GENUS (ANTHUS: MOTACILLIDAE)

Dispersal and vicariant hypotheses have for decades been at odds with each other, notwithstanding the fact that both are well-established natural processes with important histories in biogeographic analyses. Despite their importance, neither dispersal nor vicariant methodologies are problem-free. The now widely used molecular techniques for generating phylogenies have provided a mechanism by which both dispersal- and vicariance-driven speciation can be better tested via the application of molecular clocks; unfortunately, substantial problems can also exist in the employment of those clocks. To begin to assess the relative roles of dispersal and vicariance in the establishment of avifaunas, especially intercontinental avifaunas, I applied a test for clocklike behavior in molecular data, as well as a program that infers ancestral areas and dispersal events, to a phylogeny of a speciose, cosmopolitan avian genus (Anthus; Motacillidae). Daughter-lineages above just 25 of 40 nodes in the Anthus phylogeny are evolving in a clocklike manner and are thus dateable by a molecular clock. Dating the applicable nodes suggests that Anthus arose nearly 7 million yr ago, probably in eastern Asia, and that between 6 and 5 million yr ago, Anthus species were present in Africa, the Palearctic, and North and South America. Speciation rates have been high throughout the Pliocene and quite low during the Pleistocene; further evidence that the Pleistocene may have had little effect in generating modern species. Intercontinental movements since 5 million yr ago have been few and largely restricted to interchange between Eurasia and Africa. Species swarms on North America, Africa, and Eurasia (but not South America or Australia) are the product of multiple invasions, rather than being solely the result of within-continent speciation. Dispersal has clearly played an important role in the distribution of this group.     

Monophyly of Kelloggia Torrey ex Benth. (Rubiaceae) and evolution of its intercontinental disjunction between western North America and eastern Asia

Kelloggia Torrey ex Bentham (Rubiaceae) consists of two species disjunctly distributed in western North America (K. galioides Torrey) and the western part of eastern Asia (K. chinensis Franch.). The two species exhibit a high level of morphological divergence. To test its monophyly and to infer its biogeographic history, we estimated the phylogeny of Kelloggia and its relatives from sequences of three chloroplast DNA regions (rbcL gene, atpB-rbcL spacer, and rps16 intron). The monophyly of Kelloggia was strongly supported, and it forms a sister relationship with the tribe Rubieae. The divergence time between the two disjunct species of Kelloggia was estimated to be 5.42 ± 2.32 million years ago (mya) using the penalized likelihood method based on rbcL sequence data with fossil calibration. Our result does not support the Madrean-Tethyan hypothesis, which assumes an earlier divergence time of 20-25 mya. Ancestral area analysis, as well as dispersal-vicariance (DIVA) analysis, suggests the Asian origin of Kelloggia and the importance of Eurasia in the diversification of its close relatives in the Rubieae-Theligoneae-Paederieae group. The intercontinental disjunction in Kelloggia is suggested to have evolved via long-distance dispersal from Asia into western North America.     

Historical biogeography of Heteropterinae skippers via Beringian and post‐Tethyan corridors

Skippers are a species rich and widespread group of butterflies with evolutionary patterns and processes largely unstudied despite some recent efforts. Among Hesperiidae, the subfamily Heteropterinae is a moderately diverse clade comprising ca. 200 species distributed from North to South America and from Africa to the Palearctic region. While some regions are species rich, others are far less diverse. Using anchored phylogenomics, we infer a robust timetree and estimate ancestral ranges to understand the biogeographic history of these skippers. Inferences based on up to 383 exons recover a robust backbone for the subfamily along with the monophyly of all genera. Bayesian divergence time estimates suggest an origin of Heteropterinae in the late Eocene, ca. 40 million years ago. Maximum likelihood ancestral range estimates indicate an origin of the group in the New World. The eastern Palearctic was likely colonized via a Beringian route and a reverse colonization event resulted in two independent and extant American clades. We estimate a vicariant event between Central and South America that significantly predates estimates of the proto‐Caribbean seaway closure, indicating active overwater dispersal in the Oligocene. The colonization of Africa from the east Palearctic is synchronous with the closure of the Tethys Ocean, while the colonization of Madagascar appears to be comparatively recent. Our results shed light on the systematics and biogeography of Heteropterinae skippers and unveil the evolutionary history of a new leaf in the skipper tree‐of‐life.     

Intercontinental Mediterranean disjunct mosses: morphological and molecular patterns

This study focused on three species that occur disjunctly between western North America and the Mediterranean region of southern Europe, northern Africa, and western Asia, forming the so-called Madrean-Tethyan distribution pattern. Quantitative morphological characters were measured in New and Old World plants to find any subtle phenotypic differentiation between the disjunct populations. Sequences from the nuclear ribosomal internal transcribed spacer region were obtained from the same populations to assess differentiation at the molecular level and to compare molecular diversity with patterns of morphological similarity among plants. Little or no morphological differentiation existed between New and Old World plants in any of the species, but internal transcribed spacer (ITS) sequences revealed some phylogeographic structure. Patterns of morphological similarity in all three species were incongruent with phylogeographic structure revealed by sequence data. New World populations were more variable than Old World populations at the molecular level in the three species. Despite some evidence for differentiation between disjunct plants, no plausible mutation rate would date the divergence at ≥20 million years ago (MYA), as implied by the Madrean-Tethyan hypothesis. Recent long-distance dispersal is a more likely explanation for intercontinental disjunctions in these species.     

The diversification of Halenia (Gentianaceae): ecological opportunity versus key innovation

The plant genus Halenia (Gentianaceae) consists of herbs growing in temperate and tropical alpine habitats and most species possess flowers in which nectar is produced in spurs. This probably helps reward only specialized long-tongued pollinators, and a narrow pollinator/flower relationship is thought to accelerate diversification rates (a key innovation). To test the pattern of diversification of Halenia against the unspurred sister group we reconstructed phylogenetic relationships among 22 species plus outgroups using nuclear ITS and chloroplast rpl16 intron sequence data. We show that Halenia originated in East Asia and migrated via North America into Central America. From there, it colonized South America three times independently, probably within the last million years. Significant changes in diversification rates were found during the evolution of Halenia using a sister group method, a likelihood method, and a diversity-through-time plot. In contrast to other studies, we could not observe a direct speciation rate effect of the evolution of nectar spurs in comparison with the unspurred sister group of Halenia. Rather, increases in diversification occurred following the colonization of Central and South America by spurred progenitor taxa. This later switch in diversification may have resulted from the availability of new geographical and ecological opportunities, or from the availability of more and different pollinators in these regions. Following the latter hypothesis, the nectar spurs were a preadaption and functioned as a key innovation only in this new biotic environment. After an initial rapid increase, a reduction in diversification rate was observed in Central America, probably illustrating density dependence of speciation rates. Finally, we found preliminary evidence for the key innovation hypothesis in geologically young spurred and unspurred lineages of Halenia in South America.     

Inferring long-distance dispersal and topographic barriers during post-glacial colonization from the genetic structure of red maple (Acer rubrum L.) in New England

Aim  This study aims to assess the role of long-distance seed dispersal and topographic barriers in the post-glacial colonization of red maple ( Acer rubrum L.) using chloroplast DNA (cpDNA) variation, and to understand whether this explains the relatively higher northern diversity found in eastern North American tree species compared with that in Europe.
Location  North-eastern United States.
Methods  The distribution of intraspecific cpDNA variation in temperate tree populations has been used to identify aspects of post-glacial population spread, including topographic barriers to population expansion and spread by long-distance seed dispersal. We sequenced c.  370 cpDNA base pairs from 221 individuals in 100 populations throughout the north-eastern United States, and analysed spatial patterns of diversity and differentiation.
Results  Red maple has high genetic diversity near its northern range limit, but this diversity is not partitioned by topographic barriers, suggesting that the northern Appalachian Mountains were not a barrier to the colonization of red maple. We also found no evidence of the patchy genetic structure that has been associated with spread by rare long-distance seed dispersal in previous studies.
Main conclusions  Constraints on post-glacial colonization in eastern North America seem to have been less stringent than those in northern Europe, where bottlenecks arising from long-distance colonization and topographic barriers appear to have strongly reduced genetic diversity. In eastern North America, high northern genetic diversity may have been maintained by a combination of frequent long-distance dispersal, minor topographic obstacles and diffuse northern refugia near the ice sheet.