Contrasting phylogeographic patterns in Sphagnum fimbriatum and Sphagnum squarrosum (Bryophyta, Sphagnopsida) in Europe

The chloroplast phylogeography of two peat mosses (Sphagnum fimbriatum and Sphagnum squarrosum) with similar distributions but different life history characteristics was investigated in Europe. Our main aim was to test whether similar distributions reflect similar phylogeographic and phylodemographic processes. Accessions covering the European distributions of the species were collected and approx. 2000 bp of the chloroplast genome of each species was sequenced. Maximum parsimony, statistical parsimony and phylodemographic analyses were used to address the question of whether these species with similar distributions show evidence of similar phylogeographic and phylodemographic processes. The chloroplast haplotypes of the currently spreading species S. fimbriatum showed strong geographic structure, whereas those of S. squarrosum, which has stable historical population sizes, showed only very weak geographic affinity and were widely distributed. We hypothesize that S. fimbriatum survived the last glaciations along the Atlantic coast of Europe, whereas S. squarrosum had numerous, scattered refugia in Europe. The dominance of one haplotype of S. fimbriatum across almost all of Europe suggests rapid colonization after the last glacial maximum. We hypothesize that high colonizing ability is an inherent characteristic of the species and its recent expansion in Europe is a response to climate change.     

Genetic structure and genealogy in the Sphagnum subsecundum complex (Sphagnaceae: Bryophyta)

Allopolyploidy is probably the most extensively studied mode of plant speciation and allopolyploid species appear to be common in the mosses (Bryophyta). The Sphagnum subsecundum complex includes species known to be gametophytically haploid or diploid, and it has been proposed that the diploids (i.e., with tetraploid sporophytes) are allopolyploids. Nucleotide sequence and microsatellite variation among haploids and diploids from Newfoundland and Scandinavia indicate that (1) the diploids exhibit fixed or nearly fixed heterozygosity at the majority of loci sampled, and are clearly allopolyploids, (2) diploids originated independently in North America and Europe, (3) the European diploids appear to have the haploid species, S. subsecundum, as the maternal parent based on shared chloroplast DNA haplotypes, (4) the North American diploids do not have the chloroplast DNA of any sampled haploid, (5) both North American and European diploids share nucleotide and microsatellite similarities with S. subsecundum, (6) the diploids harbor more nucleotide and microsatellite diversity than the haploids, and (7) diploids exhibit higher levels of linkage disequilibrium among microsatellite loci. An experiment demonstrates significant artifactual recombination between interspecific DNAs coamplified by PCR, which may be a complicating factor in the interpretation of sequence-based analyses of allopolyploids.     

Several Pleistocene refugia detected in the high alpine plant Phyteuma globulariifolium sternb & hoppe (Campanulaceae) in the European Alps

Phyteuma globulariifolium is a high alpine plant species growing in the European Alps and the Pyrenees. In order to elucidate its glacial history, 325 individuals from 69 populations were analysed using the amplified fragment length polymorphism (AFLP) technique. A strongly hierarchical phylogeographical pattern was detected: Two major east-west vicariant groups can be separated along a gap in the distributional area. A further subdivision into at least four populational groups is in congruence with presumed peripheral glacial refugia. There is no indication for survival on unglaciated mountain tops (nunataks) in the interior of the Pleistocene ice shield covering the Alps. Our results favour glacial survival in peripheral, unglaciated or not fully glaciated areas. Populations of P. globulariifolium in the Pyrenees are the result of relatively recent long-distance dispersal. Within the Alps, there is strong differentiation among groups of populations, whereas within them the differentiation is weak. This suggests high levels of gene-flow over short to middle distances.     

Crossing the uncrossable: novel trans‐valley biogeographic patterns revealed in the genetic history of low‐dispersal mygalomorph spiders (Antrodiaetidae,Antrodiaetus) from California

Antrodiaetus riversi is a dispersal‐limited, habitat‐specialized mygalomorph spider species endemic to mesic woodlands of northern and central California. Here, we build upon prior phylogeographic research using a much larger geographic sample and include additional nuclear genes, providing more detailed biogeographic insights throughout the range of this complex. Of particular interest is the uncovering of unexpected and replicated trans‐valley biogeographic patterns, where in two separate genetic clades western haplotypes in the California south Coast Ranges are phylogenetically closely related to eastern haplotypes from central and northern Sierran foothills. In both instances, these trans‐valley phylogenetic patterns are strongly supported by multiple genes. These western and eastern populations are currently separated by the Central Valley, a well‐recognized modern‐day and historical biogeographic barrier in California. For one clade, the directionality is clearly northeast to southwest, and all available evidence is consistent with a jump dispersal event estimated at 1.2–1.3 Ma. During this time period, paleogeographic data indicate that northern Sierran rivers emptied to the ocean in the south Coast Ranges, rather than at the San Francisco Bay. For the other trans‐valley clade genetic evidence is less conclusive regarding the mechanism and directionality of biogeographic exchange, although the estimated timeframe is similar (approximately 1.8 Ma). Despite the large number of biogeographic studies previously conducted in central California, to the best of our knowledge no prior studies have discussed or revealed a northern Sierran to south Coast Range biogeographic connection. This uniqueness may reflect the low‐dispersal biology of mygalomorph spiders, where ‘post‐event’ gene exchange rarely erases historical biogeographic signal.     

Allopolyploidy and homoploid hybridization in the Sphagnum subsecundum complex (Sphagnaceae: Bryophyta)

Several complexes of species in Sphagnum (peat mosses) originated through hybridization and allopolyploidy, suggesting that these processes have played a major evolutionary role in this genus. The Sphagnum subsecundum complex includes gametophytically haploid and diploid species in North America. Analyses of 12 microsatellite loci and sequences from two plastid DNA markers show that the evolutionary history of this group is substantially more complex than previously thought. Two taxonomic species, Sphagnum lescurii and Sphagnum inundatum, include both haploid and diploid populations. Within each ploidal level, S. lescurii and S. inundatum are not genetically differentiated. The diploid taxa show patterns of fixed heterozygosity for the microsatellite markers, consistent with an allopolyploid origin. Diploid S. lescurii is an allopolyploid between haploid S. lescurii and (haploid) S. subsecundum. Sphagnum carolinianum is an allopolyploid between haploid S. lescurii and an unknown parent. We detected homoploid hybridization between the haploids Sphagnum contortum and S. subsecundum. Finally, we report three samples of diploid Sphagnum platyphyllum (otherwise haploid) that have an allopolyploid origin involving north‐eastern haploid S. platyphyllum and an unidentified taxon. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 135–151.     

Trans‐Atlantic,trans‐Pacific and trans‐Indian Ocean dispersal in the small Gondwanan Laurales family Hernandiaceae

Aim To investigate the historical biogeography of the pantropical flowering plant family Hernandiaceae (Laurales), which today comprises 62 species in five genera. Location Hernandiaceae occur in Africa (9 species), Madagascar (4), the Neotropics (25), Australia (3), southern China, Indochina, Malesia, and on numerous Pacific Islands (32). These numbers include two widespread species, Hernandia nymphaeifolia, which ranges from East Africa to the Ogasawara Islands and New Caledonia, and Gyrocarpus americanus, thought to have a pantropical range. Methods We sampled 37 species from all genera, the widespread ones with multiple accessions, for a chloroplast DNA matrix of 2210 aligned nucleotides, and used maximum likelihood to infer species relationships. Divergence time estimation relied on an uncorrelated‐rates relaxed molecular clock calibrated with outgroup fossils of Lauraceae and Monimiaceae. Results The deepest split in the family is between a predominantly African–Madagascan–Malesian lineage comprising Hazomalania, Hernandia and Illigera, and an African–Neotropical lineage comprising Gyrocarpus and Sparattanthelium; this split may be 122 (110–134) Myr old. The stem lineages of the five genera date back at least to the Palaeocene, but six splits associated with transoceanic range disjunctions date only to the Oligocene and Miocene, implying long‐distance dispersal. It is inferred that Hernandia beninensis reached the West African islands of São Tomé and Bioko from the West Indies or the Guianas; Hernandia dispersed across the Pacific; and Illigera madagascariensis reached Madagascar from across the Indian Ocean. Main conclusions The disjunct ranges and divergence times of sister clades in the Hernandiaceae are partly congruent with the break‐up of West Gondwana, but mostly with later transoceanic dispersal. An exceptional ability to establish following prolonged oceanic dispersal may be largely responsible for the evolutionary persistence of this small clade.     

Ancient vicariance and climate‐driven extinction explain continental‐wide disjunctions in Africa: the case of the Rand Flora genus Canarina (Campanulaceae)

Transoceanic distributions have attracted the interest of scientists for centuries. Less attention has been paid to the evolutionary origins of ‘continent‐wide’ disjunctions, in which related taxa are distributed across isolated regions within the same continent. A prime example is the ‘Rand Flora’ pattern, which shows sister taxa disjunctly distributed in the continental margins of Africa. Here, we explore the evolutionary origins of this pattern using the genus Canarina, with three species: C. canariensis, associated with the Canarian laurisilva, and C. eminii and C. abyssinica, endemic to the Afromontane region in East Africa, as case study. We infer phylogenetic relationships, divergence times and the history of migration events within Canarina using Bayesian inference on a large sample of chloroplast and nuclear sequences. Ecological niche modelling was employed to infer the climatic niche of Canarina through time. Dating was performed with a novel nested approach to solve the problem of using deep time calibration points within a molecular dataset comprising both above‐species and population‐level sampling. Results show C. abyssinica as sister to a clade formed by disjunct C. eminii and C. canariensis. Miocene divergences were inferred among species, whereas infraspecific divergences fell within the Pleistocene–Holocene periods. Although C. eminii and C. canariensis showed a strong genetic geographic structure, among‐population divergences were older in the former than in the latter. Our results suggest that Canarina originated in East Africa and later migrated across North Africa, with vicariance and aridification‐driven extinction explaining the 7000 km/7 million year divergence between the Canarian and East African endemics.     

Recent divergence,intercontinental dispersal and shared polymorphism are shaping the genetic structure of amphi‐Atlantic peatmoss populations

Several lines of evidence suggest that recent long‐distance dispersal may have been important in the evolution of intercontinental distribution ranges of bryophytes. However, the absolute rate of intercontinental migration and its relative role in the development of certain distribution ranges is still poorly understood. To this end, the genetic structure of intercontinental populations of six peatmoss species showing an amphi‐Atlantic distribution was investigated using microsatellite markers. Methods relying on the coalescent were applied (im and migrate ) to understand the evolution of this distribution pattern in peatmosses. Intercontinental populations of the six peatmoss species were weakly albeit significantly differentiated (average F_ST = 0.104). This suggests that the North Atlantic Ocean is acting as a barrier to gene flow even in bryophytes adapted to long‐range dispersal. The im analysis suggested a relatively recent split of intercontinental populations dating back to the last two glacial periods (9000–289 000 years ago). In contrast to previous hypotheses, analyses indicated that both ongoing migration and ancestral polymorphism are important in explaining the intercontinental genetic similarity of peatmoss populations, but their relative contribution varies with species. Migration rates were significantly asymmetric towards America suggesting differential extinction of genotypes on the two continents or invasion of the American continent by European lineages. These results indicate that low genetic divergence of amphi‐Atlantic populations is a general pattern across numerous flowering plants and bryophytes. However, in bryophytes, ongoing intercontinental gene flow and retained shared ancestral polymorphism must both be considered to explain the genetic similarity of intercontinental populations.     

The extreme Beringian/Atlantic disjunction in Saxifraga rivularis (Saxifragaceae) has formed at least twice

Aim The oceanic Saxifraga rivularis L. presents one of the most extreme disjunctions known in the arctic flora: it has a small amphi‐Beringian range and a larger amphi‐Atlantic one. It was recently suggested to have had a single allopolyploid origin in Beringia at least one glacial cycle ago, followed by gradual expansion in a more humid period and differentiation into two allopatric subspecies (the Atlantic ssp. rivularis and the Beringian ssp. arctolitoralis). Here we explore the history of its extreme disjunction. Location The amphi‐Beringian and northern amphi‐Atlantic regions. Methods We obtained amplified fragment length polymorphisms (AFLPs) and chloroplast DNA sequences from 36 populations (287 individuals) and 13 populations (15 individuals), respectively. The data were analysed using principal coordinates analyses, Bayesian clustering methods, and analyses of molecular variance. Results Two distinctly divergent AFLP groups were observed, corresponding to the two described subspecies, but, surprisingly, four of the West Atlantic populations belonged to the supposedly Beringian endemic ssp. arctolitoralis. This was confirmed by re‐examination of their morphological characteristics. The overall AFLP diversity in the species was low (26.4% polymorphic markers), and there was no variation in the five investigated chloroplast DNA (cpDNA) regions. There was little geographic structuring of the AFLP diversity within each subspecies, even across the extreme disjunction in ssp. arctolitoralis, across the Bering Sea, and across the Atlantic Ocean, except that most plants from the arctic Svalbard archipelago formed a separate genetic group with relatively high diversity. Main conclusions The extreme disjunction in S. rivularis has evidently formed at least twice. The first expansion from Beringia was followed by allopatric differentiation into one Beringian and one Atlantic subspecies, which are distinctly divergent at AFLP loci but still harbour identical cpDNA haplotypes, suggesting that the expansion was quite recent but before the last glaciation. The next expansion from Beringia probably occurred by means of several long‐distance dispersals in the current interglacial, resulting in the colonization of the western Atlantic region by ssp. arctolitoralis. The poor geographic structuring within each subspecies suggests frequent long‐distance dispersals from two main Weichselian refugia, one Beringian and one western‐central European, but it is possible that the genetic group in Svalbard originates from an additional refugium.     

The presence of a cryptic barrier in the West Pacific Ocean suggests the effect of glacial climate changes on a widespread sea‐dispersed plant,Vigna marina (Fabaceae)

Ocean currents are an important driver of evolution for sea‐dispersed plants, enabling them to maintain reciprocal gene flow via sea‐dispersed diaspores and obtain wide distribution ranges. Although geographic barriers are known to be the primary factors shaping present genetic structure of sea‐dispersed plants, cryptic barriers which form clear genetic structure within oceanic regions are poorly understood. To test the presence of a cryptic barrier, we conducted a phylogeographic study together with past demographic inference for a widespread sea‐dispersed plant, Vigna marina, using 308 individuals collected from the entire Indo‐West Pacific (IWP) region. Chloroplast DNA variation showed strong genetic structure that separated populations into three groups: North Pacific (NP), South Pacific (SP) and Indian Ocean (IN) (F′_CT among groups = 0.954–1.000). According to the Approximate Bayesian computation inference, splitting time between NP and SP was approximately 20,200 years (95%HPD, 4,530–95,400) before present. Moreover, a signal of recent population expansion was detected in the NP group. This study clearly showed the presence of a cryptic barrier in the West Pacific region of the distributional range of V. marina. The locations of the cryptic barrier observed in V. marina corresponded to the genetic breaks found in other plants, suggesting the presence of a common cryptic barrier for sea‐dispersed plants. Demographic inference suggested that genetic structure related to this cryptic barrier has been present since the last glacial maximum and may reflect patterns of past population expansion from refugia.     

Genetic analysis of the peatmoss Sphagnum cribrosum (Sphagnaceae) indicates independent origins of an extreme infra‐specific morphology shift

Within Sphagnum cribrosum, a dioicous aquatic peatmoss, a unique morphological variant (the ‘waveform’), found at only two lakes in North Carolina, has a branching architecture that is extremely differentiated from anything otherwise known in Sphagnum, although the plants are microscopically indistinguishable from S. cribrosum. At one site where the two morphologies co‐occur, 60 years of field observations demonstrate the persistence of each morphology, even where the two forms grow intermixed. We conducted a reciprocal transplant experiment in which waveform and normal plants maintained their divergent morphologies for 8 months. We sampled populations throughout the range and conducted genetic and phylogenetic analyses with microsatellite markers and DNA sequences to investigate the genetic context of the waveform morphology within S. cribrosum. Haplotype networks from DNA sequences showed the two waveform populations are separated by 11 substitutions across three loci. Microsatellite analyses using nonparametric clustering and admixture models also indicated genetic dissimilarity between genotypes with waveform morphology at the two lakes. Both molecular datasets suggest that the waveform morphology had at least two independent origins, despite the proximity of the two lakes where it occurs uniquely. Given the clonal nature of the waveform, it is unlikely to form a cohesive evolutionary lineage deserving of taxonomic status. The analysis also revealed a genetically diverse population in Georgia as the potential source of variation found in all other populations of S. cribrosum. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 137–153.