The sweet tabaiba or there and back again: phylogeographic history of the Macaronesian Euphorbia balsamifera.

BACKGROUND AND AIMS: Biogeographic relationships between the Canary Islands and northwest Africa are often explained by oceanic dispersal and geographic proximity. Sister-group relationships between Canarian and eastern African/Arabian taxa, the "Rand Flora" pattern, are rare among plants, and have been attributed to the extinction of northwestern African populations. Euphorbia balsamifera is the only representative species of this pattern that is distributed in the Canary Islands and northwest Africa; it is also one of few species present in all seven islands. Previous studies placed E. balsamifera African populations as sister to the Canarian populations, but they were based on herbarium samples with highly degraded DNA. Here, we test the extinction hypothesis by sampling new continental populations; we also expand the Canarian sampling to examine the dynamics of island colonization and diversification. METHODS: Using target enrichment with genome skimming, we reconstructed phylogenetic relationships within E. balsamifera, and between this species and its disjunct relatives. A SNP dataset obtained from the target sequences was used to infer population-genetic diversity patterns. We employed convolutional neural networks (CNNs) to discriminate among alternative Canary Islands colonization scenarios. KEY RESULTS: Results confirm the Rand Flora sister-group relationship between western E. balsamifera and E. adenensis in the Eritreo-Arabian region, and recover an eastern-western geographic structure among E. balsamifera Canarian populations. CNNs supported a scenario of east-to-west island colonization, followed by population extinctions in Lanzarote and Fuerteventura and recolonization from Tenerife and Gran Canaria; a signal of admixture between the eastern island and northwest African populations was recovered. CONCLUSIONS: Populations of E. balsamifera from northwest Africa are not the remnants of an ancestral stock, but originated from migration events from Lanzarote and Fuerteventura. These results support the Surfing Syngameon Hypothesis for the colonization of the Canary Islands by E. balsamifera, but also a recent back-colonization to the continent.

Phylogenomics sheds new light on the drivers behind a long-lasting systematic riddle: the figwort family Scrophulariaceae.

The figwort family, Scrophulariaceae, comprises c. 2000 species whose evolutionary relationships at the tribal level have proven difficult to resolve, hindering our ability to understand their origin and diversification. We designed a specific probe kit for Scrophulariaceae, targeting 849 nuclear loci and obtaining plastid regions as by-products. We sampled c. 87% of the genera described in the family and use the nuclear dataset to estimate evolutionary relationships, timing of diversification, and biogeographic patterns. Ten tribes, including two new tribes, Androyeae and Camptolomeae, are supported, and the phylogenetic positions of Androya, Camptoloma, and Phygelius are unveiled. Our study reveals a major diversification at c. 60 million yr ago in some Gondwanan landmasses, where two different lineages diversified, one of which gave rise to nearly 81% of extant species. A Southern African origin is estimated for most modern-day tribes, with two exceptions, the American Leucophylleae, and the mainly Australian Myoporeae. The rapid mid-Eocene diversification is aligned with geographic expansion within southern Africa in most tribes, followed by range expansion to tropical Africa and multiple dispersals out of Africa. Our robust phylogeny provides a framework for future studies aimed at understanding the role of macroevolutionary patterns and processes that generated Scrophulariaceae diversity.

A road map for phylogenetic models of species trees.

The field of phylogenetics has burgeoned into a great diversity of statistical models, providing researchers with a vast amount of analytical tools for investigating the evolutionary theory. This abundance of theoretical work has the merit that many different aspects of evolution can be investigated using various types of data. However, empiricists may sometimes struggle to find the right model for their needs amid such variety. In particular, some computer programs gather the theory of many different models, published in hundreds of different papers, within the same operational framework. This makes it particularly difficult for users to obtain comprehensive information about the assumptions and structure of various models. Yet, a large part of phylogenetic models are structured in individual modules that can be linked together in the same conceptual framework, akin to some sort of phylogenetic supermodel. In this paper, we propose to browse through the network of phylogenetic models, emphasizing their modular structure, with the purpose to outline the commonalities and differences of individual models. Focusing on probabilistic models, we describe how to go from the model assumptions to the corresponding probability distributions as pedagogically as possible. To achieve this task, we resort heavily on graph theory to represent the probabilistic relationships among parameters and data, and present the models in their most elementary form (i.e. including parameters that are generally marginalized out), which simplifies the mathematics considerably. We concentrate on models designed for species trees, but evoke the link with other types of trees (e.g. gene trees).

Congruent evolutionary responses of European steppe biota to late Quaternary climate change.

Quaternary climatic oscillations had a large impact on European biogeography. Alternation of cold and warm stages caused recurrent glaciations, massive vegetation shifts, and large-scale range alterations in many species. The Eurasian steppe biome and its grasslands are a noteworthy example; they underwent climate-driven, large-scale contractions during warm stages and expansions during cold stages. Here, we evaluate the impact of these range alterations on the late Quaternary demography of several phylogenetically distant plant and insect species, typical of the Eurasian steppes. We compare three explicit demographic hypotheses by applying an approach combining convolutional neural networks with approximate Bayesian computation. We identified congruent demographic responses of cold stage expansion and warm stage contraction across all species, but also species-specific effects. The demographic history of the Eurasian steppe biota reflects major paleoecological turning points in the late Quaternary and emphasizes the role of climate as a driving force underlying patterns of genetic variance on the biome level.

Macroevolutionary dynamics in the transition of angiosperms to aquatic environments.

Angiosperm lineages in aquatic environments are characterized by high structural and functional diversity, and wide distributions. A long-standing evolutionary riddle is what processes have caused the relatively low diversity of aquatic angiosperms compared to their terrestrial relatives. We use diversification and ancestral reconstruction models with a comprehensive > 10 000 genus angiosperm phylogeny to elucidate the macroevolutionary dynamics associated with transitions of terrestrial plants to water. Our study reveals that net diversification rates are significantly lower in aquatic than in terrestrial angiosperms due to lower speciation and higher extinction. Shifts from land to water started early in angiosperm evolution, but most events were concentrated during the last c. 25 million years. Reversals to a terrestrial habitat started only 40 million years ago, but occurred at much higher rates. Within aquatic angiosperms, the estimated pattern is one of gradual accumulation of lineages, and relatively low and constant diversification rates throughout the Cenozoic. Low diversification rates, together with infrequent water transitions, account for the low diversity of aquatic angiosperms today. The stressful conditions and small global surface of the aquatic habitat available for angiosperms are hypothesized to explain this pattern.

Cyphoderia ampulla (Cyphoderiidae: Rhizaria), a tale of freshwater sailors: The causes and consequences of ecological transitions through the salinity barrier in a family of benthic protists.

The salinity barrier that separates marine and freshwater biomes is probably the most important division in biodiversity on Earth. Those organisms that successfully performed this transition had access to new ecosystems while undergoing changes in selective pressure, which often led to major shifts in diversification rates. While these transitions have been extensively investigated in animals, the tempo, mode, and outcome of crossing the salinity barrier have been scarcely studied in other eukaryotes. Here, we reconstructed the evolutionary history of the species complex Cyphoderia ampulla (Euglyphida: Cercozoa: Rhizaria) based on DNA sequences from the nuclear SSU rRNA gene and the mitochondrial cytochrome oxidase subunit I gene, obtained from publicly available environmental DNA data (GeneBank, EukBank) and isolated organisms. A tree calibrated with euglyphid fossils showed that four independent transitions towards freshwater systems occurred from the mid-Miocene onwards, coincident with important fluctuations in sea level. Ancestral trait reconstructions indicated that the whole family Cyphoderiidae had a marine origin and suggest that ancestors of the freshwater forms were euryhaline and lived in environments with fluctuating salinity. Diversification rates did not show any obvious increase concomitant with ecological transitions, but morphometric analyses indicated that species increased in size and homogenized their morphology after colonizing the new environments. This suggests adaptation to changes in selective pressure exerted by life in freshwater sediments.

Mitogenomics and hidden-trait models reveal the role of phoresy and host shifts in the diversification of parasitoid blister beetles (Coleoptera: Meloidae).

Changes in life history traits are often considered speciation triggers and can have dramatic effects on the evolutionary history of a lineage. Here, we examine the consequences of changes in two life history traits, host-type and phoresy, in the hypermetamorphic blister beetles, Meloidae. Subfamilies Nemognathinae and Meloinae exhibit a complex life cycle involving multiple metamorphoses and parasitoidism. Most genera and tribes are bee-parasitoids, and include phoretic or nonphoretic species, while two tribes feed on grasshopper eggs. These different life strategies are coupled with striking differences in species richness among clades. We generated a mitogenomic phylogeny for Nemognathinae and Meloinae, confirming the monophyly of these two clades, and used the dated phylogeny to explore the association between diversification rates and changes in host specificity and phoresy, using state-dependent speciation and extinction (SSE) models that include the effect of hidden traits. To account for the low taxon sampling, we implemented a phylogenetic-taxonomic approach based on birth-death simulations, and used a Bayesian framework to integrate parameter and phylogenetic uncertainty. Results show that the ancestral hypermetamorphic Meloidae was a nonphoretic bee-parasitoid, and that transitions towards a phoretic bee-parasitoid and grasshopper parasitoidism occurred multiple times. Nonphoretic bee-parasitoid lineages exhibit significantly higher relative extinction and lower diversification rates than phoretic bee-and grasshopper-parasitoids, but no significant differences were found between the latter two strategies. This suggests that Orthopteran host shifts and phoresy contributed jointly to the evolutionary success of the parasitoid meloidae. We also demonstrate that SSE models can be used to identify hidden traits coevolving with the focal trait in driving a lineage's diversification dynamics.

Menores y consumo de cannabis: un análisis por género y edad / Minors and cannabis use: an analysis by gender and age

El consumo de cannabis sigue constituyendo a día de hoy uno de los principales problemas de salud pública en la población juvenil tanto española como europea. A las elevadas prevalencias de consumo actuales se unen nuevos formatos y nuevos rituales de consumo, niveles de THC significativamente mayores y edades de inicio especialmente tempranas, lo cual suscita una creciente preocupación social, especialmente cuando nos referimos a adolescentes. El presente trabajo, llevado a cabo con una muestra de casi 4.000 estudiantes de 12 a 17 años de la comunidad gallega, no sólo permite constatar los elevados niveles de consumo existentes a edades tempranas y tasas de consumo problemático alarmantes, sino que evidencia la interesante interacción entre las variables género y edad, que se da en las fases iniciales del consumo. Asumir que en términos generales puede haber o no diferencias de género en el consumo de cannabis implica ignorar el papel de las normas y roles de género en los procesos de socialización de las y los adolescentes. De forma más concreta, se ha constatado niveles de consumo y consumo problemático (evaluado a través del CAST) significativamente mayores entre las chicas a los 14-15 años, produciéndose una progresiva masculinización del consumo de cannabis a partir de dicha edad. Estos resultados poseen interesantes implicaciones a la hora de diseñar nuevas estrategias y políticas de prevención. (AU)

Cannabis use continues to be one of the main public health problems in the Spanish and European youth population. The current high prevalence of consumption is compounded by new formats and new consumption rituals, significantly higher THC levels and particularly early age of onset, which is of growing social concern, especially when referring to adolescents. The present study, carried out with a sample of almost 4,000 students aged 12 to 17 years in the Galician community, not only allows us to confirm the high levels of consumption at early ages and alarming rates of problematic consumption, but also shows the interesting interaction between gender and age variables, which occurs in the initial phases of consumption. Assuming that in general terms there may or may not be gender differences in cannabis use implies ignoring the role of gender norms and roles in the socialization processes of adolescents. More specifically, significantly higher levels of consumption and problematic use (assessed through the CAST) have been found among girls at 14-15 years of age, with a progressive masculinization of cannabis use from that age onwards. These results have interesting implications for the design of new prevention strategies and policies. (AU)

Rare and widespread: integrating Bayesian MCMC approaches, Sanger sequencing and Hyb-Seq phylogenomics to reconstruct the origin of the enigmatic Rand Flora genus Camptoloma.

PREMISE: Genera that are widespread, with geographically discontinuous distributions and represented by few species, are intriguing. Is their achieved disjunct distribution recent or ancient in origin? Why are they species-poor? The Rand Flora is a continental-scale pattern in which closely related species appear codistributed in isolated regions over the continental margins of Africa. Genus Camptoloma (Scrophulariaceae) is the most notable example, comprising three species isolated from each other on the northwest, eastern, and southwest Africa. METHODS: We employed Sanger sequencing of nuclear and plastid markers, together with genomic target sequencing of 2190 low-copy nuclear genes, to infer interspecies relationships and the position of Camptoloma within Scrophulariaceae by using supermatrix and multispecies-coalescent approaches. Lineage divergence times and ancestral ranges were inferred with Bayesian Markov chain Monte Carlo (MCMC) approaches. The population history was estimated with phylogeographic coalescent methods. RESULTS: Camptoloma rotundifolium, restricted to Southern Africa, was shown to be a sister species to the disjunct clade formed by C. canariense, endemic to the Canary Islands, and C. lyperiiflorum, distributed in the Horn of Africa-Southern Arabia. Camptoloma was inferred to be sister to the mostly South African tribes Teedieae and Buddlejeae. Stem divergence was dated in the Late Miocene, while the origin of the extant disjunction was inferred as Early Pliocene. CONCLUSIONS: The current disjunct distribution of Camptoloma across Africa was likely the result of fragmentation and extinction and/or population bottlenecking events associated with historical aridification cycles during the Neogene; the pattern of species divergence, from south to north, is consistent with the "climatic refugia" Rand Flora hypothesis.

Modelling the tempo and mode of lineage dispersal.

Lineage dispersal is a basic macroevolutionary process shaping the distribution of biodiversity. Probabilistic approaches in biogeography, epidemiology, and macroecology often model dispersal as a background process to explain extant or infer past distributions. We propose framing questions around the mode, timing, rate, and direction of lineage dispersal itself, from a lineage- or geography-centric perspective. We review available methods for modelling lineage dispersal. Likelihood- and simulation-based approaches to modelling dispersal have made progress in accounting for the variation of lineage dispersal over space, time, and branches of a phylogeny and its interaction with diversification. Methodological improvements, guided by a focus on model adequacy, will lead to more realistic models that can answer fundamental questions about the tempo and mode of lineage dispersal.

Long-term isolation of European steppe outposts boosts the biome's conservation value.

The European steppes and their biota have been hypothesized to be either young remnants of the Pleistocene steppe belt or, alternatively, to represent relicts of long-term persisting populations; both scenarios directly bear on nature conservation priorities. Here, we evaluate the conservation value of threatened disjunct steppic grassland habitats in Europe in the context of the Eurasian steppe biome. We use genomic data and ecological niche modelling to assess pre-defined, biome-specific criteria for three plant and three arthropod species. We show that the evolutionary history of Eurasian steppe biota is strikingly congruent across species. The biota of European steppe outposts were long-term isolated from the Asian steppes, and European steppes emerged as disproportionally conservation relevant, harbouring regionally endemic genetic lineages, large genetic diversity, and a mosaic of stable refugia. We emphasize that conserving what is left of Europe's steppes is crucial for conserving the biological diversity of the entire Eurasian steppe biome.

Exploring the power of Bayesian birth-death skyline models to detect mass extinction events from phylogenies with only extant taxa.

Mass extinction events (MEEs), defined as significant losses of species diversity in significantly short time periods, have attracted the attention of biologists because of their link to major environmental change. MEEs have traditionally been studied through the fossil record, but the development of birth-death models has made it possible to detect their signature based on extant-taxa phylogenies. Most birth-death models consider MEEs as instantaneous events where a high proportion of species are simultaneously removed from the tree ("single pulse" approach), in contrast to the paleontological record, where MEEs have a time duration. Here, we explore the power of a Bayesian Birth-Death Skyline (BDSKY) model to detect the signature of MEEs through changes in extinction rates under a "time-slice" approach. In this approach, MEEs are time intervals where the extinction rate is greater than the speciation rate. Results showed BDSKY can detect and locate MEEs but that precision and accuracy depend on the phylogeny's size and MEE intensity. Comparisons of BDSKY with the single-pulse Bayesian model, CoMET, showed a similar frequency of Type II error and neither model exhibited Type I error. However, while CoMET performed better in detecting and locating MEEs for smaller phylogenies, BDSKY showed higher accuracy in estimating extinction and speciation rates.

Contrasting patterns of diversification between Amazonian and Atlantic forest clades of Neotropical lianas (Amphilophium, Bignonieae) inferred from plastid genomic data.

The mechanisms and processes underlying patterns of species distributions have intrigued ecologists and biogeographers for a long time. The Neotropics is the most species-rich region in the World, representing an excellent model for studying the drivers of diversification. In this study, we used a phylogenomic approach to infer relationships and examine the role of major geological and climatic events in shaping biogeographic patterns within Amphilophium (Bignonieae, Bignoniaceae), a genus of Neotropical lianas. Even though Amphilophium is broadly distributed across the Neotropics, it is centered in Amazonia and the Atlantic rainforest. We generated nearly-complete plastome sequences for 32 species of Amphilophium, representing 70% of the species diversity in the genus. The final dataset included 78 plastid-coding regions and was analyzed under Maximum Likelihood and Bayesian approaches to reconstruct the phylogeny of Amphilophium. We also used this dataset to estimate divergence times using a Bayesian relaxed-clock approach. We further inferred ancestral ranges, migration events, and shifts in diversification rates using a branch-specific diversification model and the Dispersal-Extinction-Cladogenesis (DEC) model implemented in a Bayesian phylogenetic framework. Overall, we obtained a well-resolved and strongly supported phylogeny for Amphilophium, with five main clades that are well characterized by morphological features. Amphilophium originated in the Early Oligocene, and started to diversify in the Late Oligocene. The first diversification event involved a split between Amazonian and Atlantic forest clades. These two clades showed very different diversification scenarios. Divergence within the Atlantic forest clade began in the Mid-Oligocene, while the Amazonian clade underwent rapid diversification starting in the Late Miocene. In-situ speciation characterized the Amazonian clade, whereas allopatric speciation driven by migration events into other Neotropical biomes were mostly inferred within the Atlantic forest clade. The diversification of Amphilophium in the Neotropics was triggered by major geological events and changes in landscape that occurred during the Late Paleogene and Neogene, with little influence of the climatic changes of the Pleistocene ice ages. The divergence times and range inferences support the role of the Western Amazonian "megawetlands" and the formation of the South American "dry diagonal" as key climatic and geological barriers that separated the Atlantic forest from the Amazonian lowlands. Timing of migration events agrees with a Mid-Miocene closure of the Central American Seaway.

High extinction rates and non-adaptive radiation explains patterns of low diversity and extreme morphological disparity in North American blister beetles (Coleoptera, Meloidae).

Untangling the relationship between morphological evolution and lineage diversification is key to explain global patterns of phenotypic disparity across the Tree of Life. Few studies have examined the relationship between high morphological disparity and extinction. In this study, we infer phylogenetic relationships and lineage divergence times within Eupomphini (Meloidae), a tribe of blister beetles endemic to the arid zone of North America, which exhibits a puzzling pattern of very low species richness but wild variation in morphological diversity across extant taxa. Using Bayesian and maximum likelihood inference, we estimate diversification and phenotypic evolutionary rates and infer the time and magnitude of extinction rate shifts and mass extinction events. Our results suggest that Eupomphini underwent an event of ancient radiation coupled with rapid morphological change, possibly linked to the loss of the evolutionary constraint in the elytral shape. A high extinction background associated to the Miocene-Pliocene transition decimated the diversity within each major clade, resulting in the species-poor genera observed today. Our study supports a connection between high extinction rates and patterns of decoupled phenotypic evolution and lineage diversification, and the possibility of a radiation in the absence of ecological release.

Conceptual and empirical advances in Neotropical biodiversity research.

The unparalleled biodiversity found in the American tropics (the Neotropics) has attracted the attention of naturalists for centuries. Despite major advances in recent years in our understanding of the origin and diversification of many Neotropical taxa and biotic regions, many questions remain to be answered. Additional biological and geological data are still needed, as well as methodological advances that are capable of bridging these research fields. In this review, aimed primarily at advanced students and early-career scientists, we introduce the concept of "trans-disciplinary biogeography," which refers to the integration of data from multiple areas of research in biology (e.g., community ecology, phylogeography, systematics, historical biogeography) and Earth and the physical sciences (e.g., geology, climatology, palaeontology), as a means to reconstruct the giant puzzle of Neotropical biodiversity and evolution in space and time. We caution against extrapolating results derived from the study of one or a few taxa to convey general scenarios of Neotropical evolution and landscape formation. We urge more coordination and integration of data and ideas among disciplines, transcending their traditional boundaries, as a basis for advancing tomorrow's ground-breaking research. Our review highlights the great opportunities for studying the Neotropical biota to understand the evolution of life.

Bridging the micro- and macroevolutionary levels in phylogenomics: Hyb-Seq solves relationships from populations to species and above.

Reconstructing phylogenetic relationships at the micro- and macroevoutionary levels within the same tree is problematic because of the need to use different data types and analytical frameworks. We test the power of target enrichment to provide phylogenetic resolution based on DNA sequences from above species to within populations, using a large herbarium sampling and Euphorbia balsamifera (Euphorbiaceae) as a case study. Target enrichment with custom probes was combined with genome skimming (Hyb-Seq) to sequence 431 low-copy nuclear genes and partial plastome DNA. We used supermatrix, multispecies-coalescent approaches, and Bayesian dating to estimate phylogenetic relationships and divergence times. Euphorbia balsamifera, with a disjunct Rand Flora-type distribution at opposite sides of Africa, comprises three well-supported subspecies: western Sahelian sepium is sister to eastern African-southern Arabian adenensis and Macaronesian-southwest Moroccan balsamifera. Lineage divergence times support Late Miocene to Pleistocene diversification and climate-driven vicariance to explain the Rand Flora pattern. We show that probes designed using genomic resources from taxa not directly related to the focal group are effective in providing phylogenetic resolution at deep and shallow evolutionary levels. Low capture efficiency in herbarium samples increased the proportion of missing data but did not bias estimation of phylogenetic relationships or branch lengths.

A tale of two forests: ongoing aridification drives population decline and genetic diversity loss at continental scale in Afro-Macaronesian evergreen-forest archipelago endemics.

Background and Aims: Various studies and conservationist reports have warned about the contraction of the last subtropical Afro-Macaronesian forests. These relict vegetation zones have been restricted to a few oceanic and continental islands around the edges of Africa, due to aridification. Previous studies on relict species have generally focused on glacial effects on narrow endemics; however, little is known about the effects of aridification on the fates of previously widespread subtropical lineages. Methods: Nuclear microsatellites and ecological niche modelling were used to understand observed patterns of genetic diversity in two emblematic species, widely distributed in these ecosystems: Canarina eminii (a palaeoendemic of the eastern Afromontane forests) and Canarina canariensis (a palaeoendemic of the Canarian laurel forests). The software DIYABC was used to test alternative demographic scenarios and an ensemble method was employed to model potential distributions of the selected plants from the end of the deglaciation to the present. Key Results: All the populations assessed experienced a strong and recent population decline, revealing that locally widespread endemisms may also be alarmingly threatened. Conclusions: The detected extinction debt, as well as the extinction spiral to which these populations are subjected, demands urgent conservation measures for the unique, biodiversity-rich ecosystems that they inhabit.

Testing the Role of the Red Queen and Court Jester as Drivers of the Macroevolution of Apollo Butterflies.

In macroevolution, the Red Queen (RQ) model posits that biodiversity dynamics depend mainly on species-intrinsic biotic factors such as interactions among species or life-history traits, while the Court Jester (CJ) model states that extrinsic environmental abiotic factors have a stronger role. Until recently, a lack of relevant methodological approaches has prevented the unraveling of contributions from these 2 types of factors to the evolutionary history of a lineage. Herein, we take advantage of the rapid development of new macroevolution models that tie diversification rates to changes in paleoenvironmental (extrinsic) and/or biotic (intrinsic) factors. We inferred a robust and fully-sampled species-level phylogeny, as well as divergence times and ancestral geographic ranges, and related these to the radiation of Apollo butterflies (Parnassiinae) using both extant (molecular) and extinct (fossil/morphological) evidence. We tested whether their diversification dynamics are better explained by an RQ or CJ hypothesis, by assessing whether speciation and extinction were mediated by diversity-dependence (niche filling) and clade-dependent host-plant association (RQ) or by large-scale continuous changes in extrinsic factors such as climate or geology (CJ). For the RQ hypothesis, we found significant differences in speciation rates associated with different host-plants but detected no sign of diversity-dependence. For CJ, the role of Himalayan-Tibetan building was substantial for biogeography but not a driver of high speciation, while positive dependence between warm climate and speciation/extinction was supported by continuously varying maximum-likelihood models. We find that rather than a single factor, the joint effect of multiple factors (biogeography, species traits, environmental drivers, and mass extinction) is responsible for current diversity patterns and that the same factor might act differently across clades, emphasizing the notion of opportunity. This study confirms the importance of the confluence of several factors rather than single explanations in modeling diversification within lineages.

Morphological Innovations and Vast Extensions of Mountain Habitats Triggered Rapid Diversification Within the Species-Rich Irano-Turanian Genus Acantholimon (Plumbaginaceae).

The Irano-Turanian floristic region spans a topographically complex and climatically continental territory, which has served as a source of xerophytic taxa for neighboring regions and is represented by a high percent of endemics. Yet, a comprehensive picture of the abiotic and biotic factors that have driven diversification within this biota remains to be established due to the scarcity of phylogenetic studies. Acantholimon is an important component of the subalpine steppe flora of the Irano-Turanian region, containing c. 200 cushion-forming sub-shrubby pungent-leaved species. Our recent molecular phylogenetic study has led to enlarging the circumscription of this genus to include eight mono- or oligospecific genera lacking the characteristic life-form and leaves. Using the same molecular phylogeny, here we investigate the tempo and mode of diversification as well as the biogeographic patterns in this genus, to test the hypothesis that a combination of key morphological innovations and abiotic factors is behind Acantholimon high species diversity. Molecular dating analysis indicates that Acantholimon s.l. started to diversify between the Late Miocene and the Pliocene and the biogeographic analysis points to an Eastern Iran-Afghanistan origin. Macroevolutionary models support the hypothesis that the high diversity of the genus is explained by accelerated diversification rates in two clades associated with the appearance of morphological key innovations such as a cushion life-form and pungent leaves; this would have favored the colonization of water-stressed, substrate-poor mountainous habitats along the newly uplifted IT mountains during the Mio-Pliocene. Given the apparent similarity of mountain habitats for most species of Acantholimon, we hypothesize that its current high species diversity responds to a scenario of non-adaptive radiation fueled by allopatric speciation rather than evolutionary radiation driven by ecological opportunity. Similar scenarios might underlie the high diversity of other speciose genera in the topographically complex Irano-Turanian landscape, though this remains to be tested with fine-grained distribution and climatic data.

Bipolar distributions in vascular plants: A review.

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-to-south 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.