Pervasive Introgression During Rapid Diversification of the European Mountain Genus Soldanella (L.) (Primulaceae).

Hybridization is a key mechanism involved in lineage diversification and speciation, especially in ecosystems that experienced repeated environmental oscillations. Recently radiated plant groups, which have evolved in mountain ecosystems impacted by historical climate change provide an excellent model system for studying the impact of gene flow on speciation. We combined organellar (whole-plastome) and nuclear genomic data (RAD-seq) with a cytogenetic approach (rDNA FISH) to investigate the effects of hybridization and introgression on evolution and speciation in the genus Soldanella (snowbells, Primulaceae). Pervasive introgression has already occurred among ancestral lineages of snowbells and has persisted throughout the entire evolutionary history of the genus, regardless of the ecology, cytotype, or distribution range size of the affected species. The highest extent of introgression has been detected in the Carpathian species, which is also reflected in their extensive karyotype variation. Introgression occurred even between species with dysploid and euploid cytotypes, which were considered to be reproductively isolated. The magnitude of introgression detected in snowbells is unprecedented in other mountain genera of the European Alpine System investigated hitherto. Our study stresses the prominent evolutionary role of hybridization in facilitating speciation and diversification on the one hand, but also enriching previously isolated genetic pools. [chloroplast capture; diversification; dysploidy; European Alpine system; introgression; nuclear-cytoplasmic discordance; ribosomal DNA.].

Mutualistic interactions shape global spatial congruence and climatic niche evolution in Neotropical mimetic butterflies.

Understanding the mechanisms underlying species distributions and coexistence is both a priority and a challenge for biodiversity hotspots such as the Neotropics. Here, we highlight that Müllerian mimicry, where defended prey species display similar warning signals, is key to the maintenance of biodiversity in the c. 400 species of the Neotropical butterfly tribe Ithomiini (Nymphalidae: Danainae). We show that mimicry drives large-scale spatial association among phenotypically similar species, providing new empirical evidence for the validity of Müller's model at a macroecological scale. Additionally, we show that mimetic interactions drive the evolutionary convergence of species climatic niche, thereby strengthening the co-occurrence of co-mimetic species. This study provides new insights into the importance of mutualistic interactions in shaping both niche evolution and species assemblages at large spatial scales. Critically, in the context of climate change, our results highlight the vulnerability to extinction cascades of such adaptively assembled communities tied by positive interactions.

Strong conservatism of floral morphology during the rapid diversification of the genus Helianthemum.

PREMISE: Divergence of floral morphology and breeding systems are often expected to be linked to angiosperm diversification and environmental niche divergence. However, available evidence for such relationships is not generalizable due to different taxonomic, geographical and time scales. The Palearctic genus Helianthemum shows the highest diversity of the family Cistaceae in terms of breeding systems, floral traits, and environmental conditions as a result of three recent evolutionary radiations since the Late Miocene. Here, we investigated the tempo and mode of evolution of floral morphology in the genus and its link with species diversification and environmental niche divergence. METHODS: We quantified 18 floral traits from 83 taxa and applied phylogenetic comparative methods using a robust phylogenetic framework based on genotyping-by-sequencing data. RESULTS: We found three different floral morphologies, putatively related to three different breeding systems: type I, characterized by small flowers without herkogamy and low pollen to ovule ratio; type II, represented by large flowers with approach herkogamy and intermediate pollen to ovule ratio; and type III, featured by small flowers with reverse herkogamy and the highest pollen to ovule ratio. Each morphology has been highly conserved across each radiation and has evolved independently of species diversification and ecological niche divergence. CONCLUSIONS: The combined results of trait, niche, and species diversification ultimately recovered a pattern of potentially non-adaptive radiations in Helianthemum and highlight the idea that evolutionary radiations can be decoupled from floral morphology evolution even in lineages that diversified in heterogeneous environments as the Mediterranean Basin.

Biogeographic history and environmental niche evolution in the palearctic genus Helianthemum (Cistaceae).

The biogeographic history and the degree of environmental niche conservatism provide essential clues to decipher the underlying macroevolutionary processes of species diversification and to understand contemporary patterns of biodiversity. The genus Helianthemum constitutes an excellent case study to investigate the impact of the geo-climatic changes and the environmental niche shifts on the origins of plant species diversity in the Mediterranean hotspot. It is a palearctic species-rich lineage with c. 140 species and subspecies mostly belonging to three distinct evolutionary radiations, almost confined to the Mediterranean region and occurring across varied environmental conditions. In this work, we studied the ample and rapid diversification of the genus Helianthemum across its whole distribution range by performing phylogenetic reconstructions of ancestral ranges and environmental niche evolution. We observed a striking synchrony of biogeographic movements with niche shifts between the three major clades of the genus Helianthemum, likely related to the geo-climatic events occurred in the Mediterranean Basin since the Upper Miocene. In particular, Late Miocene and Early Pliocene were dominated by episodes of range expansions, the Late Pliocene by range contraction and vicariance events, and Pleistocene by most intense environmental niche shifts and in-situ diversification. Our study also provides evidence for four main environmental niches in Helianthemum (i.e., Mediterranean, subdesert, humid-montane and subtropical-insular) and a tendency toward environmental niche conservatism within different subclades, with few niche shifts mostly occurring from Mediterranean ancestors. The relative longer time spent in Mediterranean areas by the ancestors of Helianthemum suggests that the larger species diversity observed in the Mediterranean (i.e. Northern Africa and Southern Europe) may have been generated by a time-for-speciation effect reinforced by environmental niche conservatism. Overall, our work highlights the role of the Mediterranean Basin as a 'cradle of diversity' and an 'evolutionary hub', facilitating the environmental transitions and determining the building up of a global plant biodiversity hotspot.

Continued Adaptation of C4 Photosynthesis After an Initial Burst of Changes in the Andropogoneae Grasses.

C$_{4}$ photosynthesis is a complex trait that sustains fast growth and high productivity in tropical and subtropical conditions and evolved repeatedly in flowering plants. One of the major C$_{4}$ lineages is Andropogoneae, a group of $\sim $1200 grass species that includes some of the world's most important crops and species dominating tropical and some temperate grasslands. Previous efforts to understand C$_{4}$ evolution in the group have compared a few model C$_{4}$ plants to distantly related C$_{3}$ species so that changes directly responsible for the transition to C$_{4}$ could not be distinguished from those that preceded or followed it. In this study, we analyze the genomes of 66 grass species, capturing the earliest diversification within Andropogoneae as well as their C$_{3}$ relatives. Phylogenomics combined with molecular dating and analyses of protein evolution show that many changes linked to the evolution of C$_{4}$ photosynthesis in Andropogoneae happened in the Early Miocene, between 21 and 18 Ma, after the split from its C$_{3}$ sister lineage, and before the diversification of the group. This initial burst of changes was followed by an extended period of modifications to leaf anatomy and biochemistry during the diversification of Andropogoneae, so that a single C$_{4}$ origin gave birth to a diversity of C$_{4}$ phenotypes during 18 million years of speciation events and migration across geographic and ecological spaces. Our comprehensive approach and broad sampling of the diversity in the group reveals that one key transition can lead to a plethora of phenotypes following sustained adaptation of the ancestral state. [Adaptive evolution; complex traits; herbarium genomics; Jansenelleae; leaf anatomy; Poaceae; phylogenomics.].

Phylogenetic signatures of ecological divergence and leapfrog adaptive radiation in Espeletia.

PREMISE: Events of accelerated species diversification represent one of Earth's most celebrated evolutionary outcomes. Northern Andean high-elevation ecosystems, or páramos, host some plant lineages that have experienced the fastest diversification rates, likely triggered by ecological opportunities created by mountain uplifts, local climate shifts, and key trait innovations. However, the mechanisms behind rapid speciation into the new adaptive zone provided by these opportunities have long remained unclear. METHODS: We address this issue by studying the Venezuelan clade of Espeletia, a species-rich group of páramo-endemics showing a dazzling ecological and morphological diversity. We performed several comparative analyses to study both lineage and trait diversification, using an updated molecular phylogeny of this plant group. RESULTS: We showed that sets of either vegetative or reproductive traits have conjointly diversified in Espeletia along different vegetation belts, leading to adaptive syndromes. Diversification in vegetative traits occurred earlier than in reproductive ones. The rate of species and morphological diversification showed a tendency to slow down over time, probably due to diversity dependence. We also found that closely related species exhibit significantly more overlap in their geographic distributions than distantly related taxa, suggesting that most events of ecological divergence occurred at close geographic proximity within páramos. CONCLUSIONS: These results provide compelling support for a scenario of small-scale ecological divergence along multiple ecological niche dimensions, possibly driven by competitive interactions between species, and acting sequentially over time in a leapfrog pattern.

Changing Ecological Opportunities Facilitated the Explosive Diversification of New Caledonian Oxera (Lamiaceae).

Phylogenies recurrently demonstrate that oceanic island systems have been home to rapid clade diversification and adaptive radiations. The existence of adaptive radiations posits a central role of natural selection causing ecological divergence and speciation, and some plant radiations have been highlighted as paradigmatic examples of such radiations. However, neutral processes may also drive speciation during clade radiations, with ecological divergence occurring following speciation. Here, we document an exceptionally rapid and unique radiation of Lamiaceae within the New Caledonian biodiversity hotspot. Specifically, we investigated various biological, ecological, and geographical drivers of species diversification within the genus Oxera. We found that Oxera underwent an initial process of rapid cladogenesis likely triggered by a dramatic period of aridity during the early Pliocene. This early diversification of Oxera was associated with an important phase of ecological diversification triggered by significant shifts of pollination syndromes, dispersal modes, and life forms. Finally, recent diversification of Oxera appears to have been further driven by the interplay of allopatry and habitat shifts likely related to climatic oscillations. This suggests that Oxera could be regarded as an adaptive radiation at an early evolutionary stage that has been obscured by more recent joint habitat diversification and neutral geographical processes. Diversification within Oxera has perhaps been triggered by varied ecological and biological drivers acting in a leapfrog pattern, but geographic processes may have been an equally important driver. We suspect that strictly adaptive radiations may be rare in plants and that most events of rapid clade diversification may have involved a mixture of geographical and ecological divergence.

Diverging phenological responses of Arctic seabirds to an earlier spring.

The timing of annual events such as reproduction is a critical component of how free-living organisms respond to ongoing climate change. This may be especially true in the Arctic, which is disproportionally impacted by climate warming. Here, we show that Arctic seabirds responded to climate change by moving the start of their reproduction earlier, coincident with an advancing onset of spring and that their response is phylogenetically and spatially structured. The phylogenetic signal is likely driven by seabird foraging behavior. Surface-feeding species advanced their reproduction in the last 35 years while diving species showed remarkably stable breeding timing. The earlier reproduction for Arctic surface-feeding birds was significant in the Pacific only, where spring advancement was most pronounced. In both the Atlantic and Pacific, seabirds with a long breeding season showed a greater response to the advancement of spring than seabirds with a short breeding season. Our results emphasize that spatial variation, phylogeny, and life history are important considerations in seabird phenological response to climate change and highlight the key role played by the species' foraging behavior.

Phylogenomic Analysis of the Explosive Adaptive Radiation of the Espeletia Complex (Asteraceae) in the Tropical Andes.

The subtribe Espeletiinae (Asteraceae), endemic to the high-elevations in the Northern Andes, exhibits an exceptional diversity of species, growth-forms, and reproductive strategies. This complex of 140 species includes large trees, dichotomous trees, shrubs and the extraordinary giant caulescent rosettes, considered as a classic example of adaptation in tropical high-elevation ecosystems. The subtribe has also long been recognized as a prominent case of adaptive radiation, but the understanding of its evolution has been hampered by a lack of phylogenetic resolution. Herein, we produce the first fully resolved phylogeny of all morphological groups of Espeletiinae, using whole plastomes and about a million nuclear nucleotides obtained with an original de novo assembly procedure without reference genome, and analyzed with traditional and coalescent-based approaches that consider the possible impact of incomplete lineage sorting and hybridization on phylogenetic inference. We show that the diversification of Espeletiinae started from a rosette ancestor about 2.3 Ma, after the final uplift of the Northern Andes. This was followed by two independent radiations in the Colombian and Venezuelan Andes, with a few trans-cordilleran dispersal events among low-elevation tree lineages but none among high-elevation rosettes. We demonstrate complex scenarios of morphological change in Espeletiinae, usually implying the convergent evolution of growth-forms with frequent loss/gains of various traits. For instance, caulescent rosettes evolved independently in both countries, likely as convergent adaptations to life in tropical high-elevation habitats. Tree growth-forms evolved independently three times from the repeated colonization of lower elevations by high-elevation rosette ancestors. The rate of morphological diversification increased during the early phase of the radiation, after which it decreased steadily towards the present. On the other hand, the rate of species diversification in the best-sampled Venezuelan radiation was on average very high (3.1 spp/My), with significant rate variation among growth-forms (much higher in polycarpic caulescent rosettes). Our results point out a scenario where both adaptive morphological evolution and geographical isolation due to Pleistocene climatic oscillations triggered an exceptionally rapid radiation for a continental plant group.

Climatic and topographical correlates of plant palaeo- and neoendemism in a Mediterranean biodiversity hotspot.

BACKGROUND AND AIMS: Understanding the evolutionary and ecological forces contributing to the emergence of biodiversity hotspots is of outstanding importance to elucidate how they may withstand current climate changes. Here we explored patterns of phylogenetic and non-phylogenetic plant endemism in a Mediterranean biodiversity hotspot. We hypothesized that areas with wet and equable climatic conditions would be prone to long-term persistence of endemic lineages (palaeoendemism), whilst areas of recent local speciation (neoendemism) would be more related to harsher environmental conditions and to high topographical relief promoting speciation. METHODS: We focused on the Baetic-Rifan biodiversity hotspot (southern Iberian Peninsula and northern Morocco) in combination with molecular phylogenetic information and relative phylogenetic endemism (RPE), a recent phylogenetic measure of endemism, allowing us to discern centres of palaeo- from those of neoendemism. Using eco-geographical regions as study units, we explored correlations between both RPE and endemic species richness with precipitation- and temperature-related variables and with elevation range. KEY RESULTS: Centres of neoendemism were concentrated towards the easternmost part of the hotspot, while centres of palaeoendemism were clustered in the vicinity of the Strait of Gibraltar. The RPE index, indicating more palaeoendemism, was positively correlated with total annual precipitation, while endemic species richness showed a poor correlation. In contrast, elevation range and mean annual temperature were poor predictors of RPE, despite elevation range showing a strong correlation with endemic species richness. CONCLUSIONS: The Baetic-Rifan biodiversity hotspot shows clearly differentiated centres of neo- and palaeoendemism. Topographical relief may have driven evolutionary diversification of newly evolved species, while water availability seems more critical for the long-term persistence of ancient lineages in refuge areas of smoother topography. Given climatic trends towards increasing aridification, conservation planners should pay particular attention to preserve areas retaining older phylogenetic lineages, as these areas act as 'natural museums' of biodiversity within the Baetic-Rifan biodiversity hotspot.

Consequences of climate change on the tree of life in Europe.

Many species are projected to become vulnerable to twenty-first-century climate changes, with consequent effects on the tree of life. If losses were not randomly distributed across the tree of life, climate change could lead to a disproportionate loss of evolutionary history. Here we estimate the consequences of climate change on the phylogenetic diversities of plant, bird and mammal assemblages across Europe. Using a consensus across ensembles of forecasts for 2020, 2050 and 2080 and high-resolution phylogenetic trees, we show that species vulnerability to climate change clusters weakly across phylogenies. Such phylogenetic signal in species vulnerabilities does not lead to higher loss of evolutionary history than expected with a model of random extinctions. This is because vulnerable species have neither fewer nor closer relatives than the remaining clades. Reductions in phylogenetic diversity will be greater in southern Europe, and gains are expected in regions of high latitude or altitude. However, losses will not be offset by gains and the tree of life faces a trend towards homogenization across the continent.

What it takes to invade grassland ecosystems: traits, introduction history and filtering processes.

Whether the success of alien species can be explained by their functional or phylogenetic characteristics remains unresolved because of data limitations, scale issues and weak quantifications of success. Using permanent grasslands across France (50 000 vegetation plots, 2000 species, 130 aliens) and building on the Rabinowitz's classification to quantify spread, we showed that phylogenetic and functional similarities to natives were the most important correlates of invasion success compared to intrinsic functional characteristics and introduction history. Results contrasted between spatial scales and components of invasion success. Widespread and common aliens were similar to co-occurring natives at coarse scales (indicating environmental filtering), but dissimilar at finer scales (indicating local competition). In contrast, regionally widespread but locally rare aliens showed patterns of competitive exclusion already at coarse scale. Quantifying trait differences between aliens and natives and distinguishing the components of invasion success improved our ability to understand and potentially predict alien spread at multiple scales.

From barcodes to genomes: extending the concept of DNA barcoding.

DNA barcoding has had a major impact on biodiversity science. The elegant simplicity of establishing massive scale databases for a few barcode loci is continuing to change our understanding of species diversity patterns, and continues to enhance human abilities to distinguish among species. Capitalizing on the developments of next generation sequencing technologies and decreasing costs of genome sequencing, there is now the opportunity for the DNA barcoding concept to be extended to new kinds of genomic data. We illustrate the benefits and capacity to do this, and also note the constraints and barriers to overcome before it is truly scalable. We advocate a twin track approach: (i) continuation and acceleration of global efforts to build the DNA barcode reference library of life on earth using standard DNA barcodes and (ii) active development and application of extended DNA barcodes using genome skimming to augment the standard barcoding approach.

Improving phylogenetic regression under complex evolutionary models.

Phylogenetic Generalized Least Square (PGLS) is the tool of choice among phylogenetic comparative methods to measure the correlation between species features such as morphological and life-history traits or niche characteristics. In its usual form, it assumes that the residual variation follows a homogenous model of evolution across the branches of the phylogenetic tree. Since a homogenous model of evolution is unlikely to be realistic in nature, we explored the robustness of the phylogenetic regression when this assumption is violated. We did so by simulating a set of traits under various heterogeneous models of evolution, and evaluating the statistical performance (type I error [the percentage of tests based on samples that incorrectly rejected a true null hypothesis] and power [the percentage of tests that correctly rejected a false null hypothesis]) of classical phylogenetic regression. We found that PGLS has good power but unacceptable type I error rates. This finding is important since this method has been increasingly used in comparative analyses over the last decade. To address this issue, we propose a simple solution based on transforming the underlying variance-covariance matrix to adjust for model heterogeneity within PGLS. We suggest that heterogeneous rates of evolution might be particularly prevalent in large phylogenetic trees, while most current approaches assume a homogenous rate of evolution. Our analysis demonstrates that overlooking rate heterogeneity can result in inflated type I errors, thus misleading comparative analyses. We show that it is possible to correct for this bias even when the underlying model of evolution is not known a priori.

Rare species support vulnerable functions in high-diversity ecosystems.

Around the world, the human-induced collapses of populations and species have triggered a sixth mass extinction crisis, with rare species often being the first to disappear. Although the role of species diversity in the maintenance of ecosystem processes has been widely investigated, the role of rare species remains controversial. A critical issue is whether common species insure against the loss of functions supported by rare species. This issue is even more critical in species-rich ecosystems where high functional redundancy among species is likely and where it is thus often assumed that ecosystem functioning is buffered against species loss. Here, using extensive datasets of species occurrences and functional traits from three highly diverse ecosystems (846 coral reef fishes, 2,979 alpine plants, and 662 tropical trees), we demonstrate that the most distinct combinations of traits are supported predominantly by rare species both in terms of local abundance and regional occupancy. Moreover, species that have low functional redundancy and are likely to support the most vulnerable functions, with no other species carrying similar combinations of traits, are rarer than expected by chance in all three ecosystems. For instance, 63% and 98% of fish species that are likely to support highly vulnerable functions in coral reef ecosystems are locally and regionally rare, respectively. For alpine plants, 32% and 89% of such species are locally and regionally rare, respectively. Remarkably, 47% of fish species and 55% of tropical tree species that are likely to support highly vulnerable functions have only one individual per sample on average. Our results emphasize the importance of rare species conservation, even in highly diverse ecosystems, which are thought to exhibit high functional redundancy. Rare species offer more than aesthetic, cultural, or taxonomic diversity value; they disproportionately increase the potential breadth of functions provided by ecosystems across spatial scales. As such, they are likely to insure against future uncertainty arising from climate change and the ever-increasing anthropogenic pressures on ecosystems. Our results call for a more detailed understanding of the role of rarity and functional vulnerability in ecosystem functioning.

Understanding the evolution of holoparasitic plants: the complete plastid genome of the holoparasite Cytinus hypocistis (Cytinaceae).

Background and Aims Plant plastid genomes are highly conserved in size, gene content and structure; however, parasitic plants are a noticeable exception to this evolutionary stability. Although the evolution of parasites could help to better understand plastome evolution in general, complete plastomes of parasites have been sequenced only for some lineages so far. Here we contribute to filling this gap by providing and analysing the complete plastome sequence of Cytinus hypocistis, the first parasite sequenced for Malvales and a species suspected to have an extremely small genome. Methods We sequenced and assembled de novo the plastid genome of Cytinus hypocistis using a shotgun approach on genomic DNA. Phylogenomic analyses based on coding regions were performed on Malvidae. For each coding region present in Cytinus, we tested for relaxation or intensification of selective pressures in the Cytinus lineage compared with autotrophic Malvales. Key Results Cytinus hypocistis has an extremely divergent genome that is among the smallest sequenced to date (19·4 kb), with only 23 genes and no inverted repeat regions. Phylogenomic analysis confirmed the position of Cytinus within Malvales. All coding regions of Cytinus plastome presented very high substitution rates compared with non-parasitic Malvales. Conclusions Some regions were inferred to be under relaxed negative selection in Cytinus, suggesting that further plastome reduction is occurring due to relaxed purifying selection associated with the loss of photosynthetic activity. On the other hand, increased selection intensity and strong positive selection were detected for rpl22 in the Cytinus lineage, which might indicate an evolutionary role in the host-parasite arms race, a point that needs further research.

Unraveling the biogeographical history of Chrysobalanaceae from plastid genomes.

PREMISE OF THE STUDY: The complex geological and climatic history of the Neotropics has had major implications on the diversification of plant lineages. Chrysobalanaceae is a pantropical family of trees and shrubs with 75% of its 531 species found in the Neotropics, and a time-calibrated phylogeny of this family should shed light on the tempo of diversification in the Neotropical flora. Previously published phylogenetic hypotheses of this family were poorly supported, and its biogeography remains unclear. METHODS: We assembled the complete plastid genome of 51 Chrysobalanaceae species, and increased taxon sampling by Sanger-sequencing of five plastid regions for an additional 88 species. We generated a time-calibrated tree including all 139 Chrsyobalanaceae species and 23 outgroups. We then conducted an ancestral area reconstruction analysis and estimated diversification rates in the family. KEY RESULTS: The tree generated with the plastid genome alignment was almost fully resolved. It supports the polyphyly of Licania and Hirtella. The family has diversified starting around the Eocene-Oligocene transition. An ancestral area reconstruction confirms a Paleotropical origin for Chrysobalanaceae with several transoceanic dispersal events. The main Neotropical clade likely resulted from a single migration event from Africa around 28 mya ago, which subsequently underwent rapid diversification. CONCLUSIONS: Given the diverse ecologies exhibited by extant species, we hypothesize that the rapid diversification of Chrysobalanaceae following the colonization of the Neotropics was triggered by habitat specialization during the complex geological and paleoclimatic history of the Neotropics.

How phylogeny shapes the taxonomic and functional structure of plant-insect networks.

Phylogenetically related species share a common evolutionary history and may therefore have similar traits. In terms of interaction networks, where traits are a major determinant, related species should therefore interact with other species which are also related. However, this prediction is challenged by current evidence that there is a weak, albeit significant, phylogenetic signal in species' taxonomic niche, i.e., the identity of interacting species. We studied mutualistic and antagonistic plant-insect interaction networks in species-rich alpine meadows and show that there is instead a very strong phylogenetic signal in species' functional niches-i.e., the mean functional traits of their interactors. This pattern emerges because related species tend to interact with species bearing certain traits that allow biotic interactions (pollination, herbivory) but not necessarily with species from all the same evolutionary lineages. Those traits define a set of potential interactors and show clear patterns of phylogenetic clustering on several portions of plants and insect phylogenies. Thus, this emerging pattern of low phylogenetic signal in taxonomic niches but high phylogenetic signal in functional niches may be driven by the interplay between functional trait convergence across plants' and insects' phylogenies and random sampling of the potential interactors.

The building of a biodiversity hotspot across a land-bridge in the Mediterranean.

Many of the macroevolutionary processes that have shaped present-day phylogenetic patterns were caused by geological events such as plate tectonics and temporary land-bridges. The study of spatial patterns of phylogenetic diversity can provide insights into these past events. Here we focus on a western Mediterranean biodiversity hotspot located in the southern Iberian Peninsula and northwest Africa, two regions that are separated by the Strait of Gibraltar. We explore the spatial structure of the phylogenetic relationships within and across large-scale plant assemblages. Significant turnover in terminal lineages tends to occur between landmasses, whereas turnover in deep lineages tends to occur within landmasses. Plant assemblages in the western ecoregions of this hotspot tend to be phylogenetically overdispersed but are phylogenetically clustered on its eastern margins. We discuss our results in the light of potential scenarios of niche evolution (or conservatism) and lineage diversification. The significant turnover between landmasses suggests a common scenario of allopatric speciation that could have been facilitated by the intermittent joining of the two continents. This may have constituted an important stimulus for diversification and the emergence of this western Mediterranean biodiversity hotspot.

Insights on the evolution of plant succulence from a remarkable radiation in Madagascar (Euphorbia).

Patterns of adaptation in response to environmental variation are central to our understanding of biodiversity, but predictions of how and when broad-scale environmental conditions such as climate affect organismal form and function remain incomplete. Succulent plants have evolved in response to arid conditions repeatedly, with various plant organs such as leaves, stems, and roots physically modified to increase water storage. Here, we investigate the role played by climate conditions in shaping the evolution of succulent forms in a plant clade endemic to Madagascar and the surrounding islands, part of the hyper-diverse genus Euphorbia (Euphorbiaceae). We used multivariate ordination of 19 climate variables to identify links between particular climate variables and three major forms of succulence-succulent leaves, cactiform stem succulence, and tubers. We then tested the relationship between climatic conditions and succulence, using comparative methods that account for shared evolutionary history. We confirm that plant water storage is associated with the two components of aridity, temperature, and precipitation. Cactiform stem succulence, however, is not prevalent in the driest environments, countering the widely held view of cactiforms as desert icons. Instead, leaf succulence and tubers are significantly associated with the lowest levels of precipitation. Our findings provide a clear link between broad-scale climatic conditions and adaptation in land plants, and new insights into the climatic conditions favoring different forms of succulence. This evidence for adaptation to climate raises concern over the evolutionary future of succulent plants as they, along with other organisms, face anthropogenic climate change.