Explore the vast range of titles available.

Bipolar disjunct distributions are a fascinating biogeographic pattern exhibited by about 30 vascular plants, whose populations reach very high latitudes in the northern and southern hemispheres. In this review, we first propose a new framework for the definition of bipolar disjunctions and then reformulate a list of guiding principles to consider how to study bipolar species. Vicariance and convergent evolution hypotheses have been argued to explain the origin of this fragmented distribution pattern, but we show here that they can be rejected for all bipolar species, except for Carex microglochin. Instead, human introduction and dispersal (either direct or by mountain-hopping)—facilitated by standard and nonstandard vectors—are the most likely explanations for the origin of bipolar plant disjunctions. Successful establishment after dispersal is key for colonization of the disjunct areas and appear to be related to both intrinsic (e.g., self-compatibility) and extrinsic (mutualistic and antagonistic interactions) characteristics. Most studies on plant bipolar disjunctions have been conducted in Carex (Cyperaceae), the genus of vascular plants with the largest number of bipolar species. We found a predominant north-tosouth direction of dispersal, with an estimated time of diversification in agreement with major cooling events during the Pliocene and Pleistocene. Bipolar Carex species do not seem to depend on specialized traits for long-distance dispersal and could have dispersed through one or multiple stochastic events, with birds as the most likely dispersal vector.

Chromosome evolution has been demonstrated to have profound effects on diversification rates and speciation in angiosperms. While polyploidy has predated some major radiations in plants, it has also been related to decreased diversification rates. There has been comparatively little attention to the evolutionary role of gains and losses of single chromosomes, which may or not entail changes in the DNA content (then called aneuploidy or dysploidy, respectively). In this study we investigate the role of chromosome number transitions and of possible associated genome size changes in angiosperm evolution. We model the tempo and mode of chromosome number evolution and its possible correlation with patterns of cladogenesis in 15 angiosperm clades. Inferred polyploid transitions are distributed more frequently towards recent times than single chromosome gains and losses. This is likely because the latter events do not entail changes in DNA content and are probably due to fission or fusion events (dysploidy), as revealed by an analysis of the relationship between genome size and chromosome number. Our results support the general pattern that recently originated polyploids fail to persist, and suggest that dysploidy may have comparatively longer-term persistence than polyploidy. Changes in chromosome number associated with dysploidy were typically observed across the phylogenies based on a chi-square analysis, consistent with these changes being neutral with respect to diversification.

Aim: We set out to explain the bipolar distribution of Carex maritima, clarifying the direction and timing of dispersal. We also tested mountain-hopping and direct long-distance dispersal hypotheses, as well as the relationship of Ċ maritima with biotic and abiotic factors that could explain the bipolar distribution. Location: Arctic/boreal latitudes of both hemispheres. Methods: Molecular and bioclimatic data were obtained for C maritima and related species from section Foetidae. We sequenced two (rps16 and 5'trnK intron) plastid DNA regions (cpDNA) and the external and internal transcribed spacers (ETS and ITS) of the nuclear ribosomal gene region (nrDNA) and inferred phylogenetic relationships, divergence time estimates and biogeographical patterns using maximum likelihood, statistical parsimony, Bayesian inference and ecological niche modelling. Results: Carex maritima populations from the Southern Hemisphere were genetically and ecologically differentiated from their northern counterparts and formed a monophyletic group nested within a paraphyletic C. maritima. Divergence time analysis estimated a middle-late Pleistocene divergence of the southern lineage (0.23 Ma; 95% highest posterior density: 0.03-0.51 Ma). Southern Hemisphere populations are more stenotopic than the Northern Hemisphere ones, which tolerate harsher conditions. Main conclusions: Our results point to a middle-late Pleistocene migration of C. maritima by long-distance dispersal, either directly or via mountain-hopping, from the Northern Hemisphere to the Southern Hemisphere.

Aim To evaluate how Cenozoic climate changes shaped the evolution and distribution of Carex section Rhynchocystis. Location Western Palaearctic and Afrotropical regions (Rand Flora pattern). Methods DNA regions ITS, ETS (nuclear), matK and rpl32-trnLUAG (plastid) were amplified for 86 samples of species from section Rhynchocystis. Phylogenetic and phylogeographical relationships were inferred using maximum parsimony, Bayesian inference and coalescent-based species tree approaches. Divergence times and ancestral areas were also inferred. Results Carex section Rhynchocystis is a clade that diversified during the middle Miocene in Europe. Most cladogenesis events date to the middle and late Miocene. The Afrotropical group seems to have originated from a colonization event from Europe that occurred in the late Miocene. Main conclusions Species of the section Rhynchocystis in the Western Palaearctic are Miocene relicts. Late Miocene-Pliocene aridification of the Mediterranean rather than the more commonly reported Pleistocene glaciations seems to have shaped the phylogeography of the group. Putative Miocene-Pliocene refugia were probably located in the Mediterranean peninsulas and islands, as well as in the eastern shores of the ancient Paratethys Sea. The colonization of Africa could have been facilitated by Miocene-Pliocene global cooling.

PREMISE OF THE STUDY: Barleria is a large, pantropical genus of ca. 265 species mainly distributed in the Old World with only one species, B. oenotheroides, extending to the neotropics. This amphi-Atlantic disjunction, frequently displayed by pantropical taxa, has been traditionally explained with vicariance or geodispersal hypotheses and increasingly with long-distance dispersal. The native status of this species in the New World is controversial. METHODS: A molecular phylogeographic study based on the nuclear ribosomal ITS region and plastid trnL-F, rps16, and trn5-G sequences was done to clarify the origin of this tropical intercontinental disjunction. Divergence times were estimated with various analytical approaches, including different markers and primary calibration points. KEY RESULTS: Divergence ages estimated for Barleria lineages disagree with vicariance or geodispersal hypotheses. Genetic differentiation of American vs. African populations of B. oenotheroides does not support a recent anthropogenic introduction to the New World. Our data suggest ancient long-distance dispersal from the Old to the New World probably during the Pliocene or Upper Miocene. The number of dispersal events remains unclear. CONCLUSIONS: Our study demonstrates the native status of Barleria in the New World, resolving one of only three presumed natural Old World-New World disjunctions at the species level among Acanthaceae. This case constitutes a further documented example of the \"out-of-Africa\" pattern in the family, despite their lack of documented assisted-dispersal syndromes, and highlights the importance of long-distance dispersal to explain pantropical distributions in many families.

Carex subgenus Psyllophorae is an engaging study group due to its early diversification compared to most Carex lineages, and its remarkable disjunct distribution in four continents corresponding to three independent sections: sect. Psyllophorae in Western Palearctic, sect. Schoenoxiphium in Afrotropical region, and sect. Junciformes in South America (SA) and SW Pacific. The latter section is mainly distributed in Patagonia and the Andes, where it is one of the few Carex groups with a significant in situ diversification. We assess the role of historical geo-climatic events in the evolutionary history of the group, particularly intercontinental colonization events and diversification processes, with an emphasis on SA. We performed an integrative study using phylogenetic (four DNA regions), divergence times, diversification rates, biogeographic reconstruction, and bioclimatic niche evolution analyses. The crown age of subg. Psyllophorae (early Miocene) supports this lineage as one of the oldest within Carex . The diversification rate probably decreased over time in the whole subgenus. Geography seems to have played a primary role in the diversification of subg. Psyllophorae . Inferred divergence times imply a diversification scenario away from primary Gondwanan vicariance hypotheses and suggest long-distance dispersal-mediated allopatric diversification. Section Junciformes remained in Northern Patagonia since its divergence until Plio-Pleistocene glaciations. Andean orogeny appears to have acted as a northward corridor, which contrasts with the general pattern of North-to-South migration for temperate-adapted organisms. A striking niche conservatism characterizes the evolution of this section. Colonization of the SW Pacific took place on a single long-distance dispersal event from SA. The little ecological changes involved in the trans-Pacific disjunction imply the preadaptation of the group prior to the colonization of the SW Pacific. The high species number of the section results from simple accumulation of morphological changes (disparification), rather than shifts in ecological niche related to increased diversification rates (radiation).

Plants growing in high-mountain environments may share common morphological features through convergent evolution resulting from an adaptative response to similar ecological conditions. The Carex flava species complex (sect. Ceratocystis, Cyperaceae) includes four dwarf morphotypes from Circum-Mediterranean mountains whose taxonomic status has remained obscure due to their apparent morphological resemblance. In this study we investigate whether these dwarf mountain morphotypes result from convergent evolution or common ancestry, and whether there are ecological differences promoting differentiation between the dwarf morphotypes and their taxonomically related large, well-developed counterparts. We used phylogenetic analyses of nrDNA (ITS) and ptDNA (rps16 and 5'trnK) sequences, ancestral state reconstruction, multivariate analyses of macro- and micromorphological data, and species distribution modeling. Dwarf morphotype populations were found to belong to three different genetic lineages, and several morphotype shifts from well-developed to dwarf were suggested by ancestral state reconstructions. Distribution modeling supported differences in climatic niche at regional scale between the large forms, mainly from lowland, and the dwarf mountain morphotypes. Our results suggest that dwarf mountain morphotypes within this sedge group are small forms of different lineages that have recurrently adapted to mountain habitats through convergent evolution.

PREMISE OF THE STUDY: The sedge Carex macloviana d'Urv presents a bipolar distribution. To clarify the origin of its distribution, we consider the four main hypotheses: long‐distance dispersal (either by mountain hopping or by direct dispersal), vicariance, parallel evolution, and human introduction. METHODS: Phylogenetic, phylogeographic, and divergence time estimation analyses were carried out based on two nuclear ribosomal (ETS and ITS) regions, one nuclear single copy gene (CATP), and three plastid DNA regions (rps16 and 5′trnK introns, and psbA‐trnH spacer), using Bayesian inference, maximum likelihood, and statistical parsimony. Bioclimatic data were used to characterize the climatic niche of C. macloviana. KEY RESULTS: Carex macloviana constitutes a paraphyletic species, dating back to the Pleistocene (0.62 Mya, 95% highest posterior density: 0.29–1.00 Mya). This species displays strong genetic structure between hemispheres, with two different lineages in the Southern Hemisphere and limited genetic differentiation in Northern Hemisphere populations. Also, populations from the Southern Hemisphere show a narrower climatic niche with regards to the Northern Hemisphere populations. CONCLUSIONS: Carex macloviana reached its bipolar distribution by long‐distance dispersal, although it was not possible to determine whether it was caused by mountain hopping or by direct dispersal. While there is some support that Carex macloviana might have colonized the Northern Hemisphere by south‐to‐north transhemisphere dispersal during the Pleistocene, unlike the southwards dispersal pattern inferred for other bipolar Carex L. species, we cannot entirely rule out north‐to‐south dispersion.

Anticipating the evolutionary responses of species to ongoing climate change is essential to propose effective management and conservation measures. The Western Mediterranean Basin constitutes one of the hotspots of biodiversity where the effects of climate change are expected to be more dramatic. Plant species with ecological relevance constitute ideal models to evaluate and predict the impact of climate change on ecosystems. Here we investigate these impacts through the spatio-temporal comparison of genetic diversity/structure (AFLPs), potential distribution under different future scenarios of climate change, and ecological space in two Western Mediterranean sister species of genus Carex . Both species are ecologically key in their riparian habitats, but display contrasting distribution patterns, with one widespread in the Iberian Peninsula and North Africa ( C. reuteriana ), while the other ( C. panormitana ) is a restricted, probably endangered, Central Mediterranean endemic. At present, we found a strong genetic structure driven by geography in both species, and lower values of genetic diversity and a narrower ecological space in C. panormitana than in C. reuteriana , while the allelic rarity was higher in the former than in C. reuteriana subspecies. Future projections predict an overall dramatic reduction of suitable areas for both species under all climate change scenarios, which could be almost total for C. panormitana . In addition, gene diversity was inferred to decrease in all taxa, with genetic structure reinforcing in C. reuteriana by the loss of admixture among populations. Our findings stress the need for a reassessment of C. panormitana conservation status under IUCN Red List criteria and the implementation of conservation measures.

Aim: The bipolar disjunction, a biogeographical pattern defined by taxa with a distribution at very high latitudes in both hemispheres (> 55° N; > 52° S), is only known to occur in about 30 vascular plant species. Our aim was to use the bipolar species Carex arctogena to test the four classic hypotheses proposed to explain this exceptional disjunction: convergent evolution, vicariance, mountain-hopping and direct long-distance dispersal. Location: Arctic/boreal and temperate latitudes of both hemispheres. Methods: A combination of molecular and bioclimatic data was used to test phylogeographical hypotheses in C. arctogena. Three chloroplast markers (atpF–atpH, matK and rps16) and the nuclear ITS region were sequenced for all species in Carex sections Capituligerae and Longespicatae; Carex rupestris, C. obtusata and Uncinia triquetra were used as outrgroups. Phylogenetic relationships, divergence-time estimates and biogeographical patterns were inferred using maximum likelihood, statistical parsimony and Bayesian inference. Results: Carex sections Capituligerae and Longespicatae formed a monophyletic group that diverged during the late Miocene. Two main lineages of arctogena were inferred. Southern Hemisphere populations of C. arctogena shared the same haplotype as a widespread circumboreal lineage. Bioclimatic data show that Southern and Northern Hemisphere populations currently differ in their ecological regimes. Main conclusions: Two of the four hypotheses accounting for bipolar disjunctions may be rejected. Our results suggest that direct long-distance dispersal, probably southwards and mediated by birds, best explains the bipolar distribution of C. arctogena.