Unmatched tempo of evolution in Southern African semi-desert ice plants

Do phylogenetic community metrics reveal the South African quartz fields as terrestrial-habitat islands?

BACKGROUND AND AIMS

The quartz fields of the Greater Cape Floristic Region (GCFR) are arid and island-like special habitats, hosting ~142 habitat-specialized plant species, of which 81 % are local endemics, characterized by a rapid turnover of species between and among sites. We use several phylogenetic community metrics: (1) to examine species diversity and phylogenetic structure within and among quartz fields; (2) to investigate whether quartz field specialists are evolutionarily drawn from local species pools, whereas the alternative hypothesis posits that there is no significant evolutionary connection between quartz field specialists and the local species pools; and (3) to determine whether there is an association between certain traits and the presence of species in quartz fields.

METHODS

We sampled and developed dated phylogenies for six species-rich angiosperm families (Aizoaceae, Asteraceae, Crassulaceae, Cyperaceae, Fabaceae and Santalaceae) represented in the quartz field floras of southern Africa. Specifically, we focused on the flora of three quartz field regions in South Africa (Knersvlakte, Little Karoo and Overberg) and their surrounding species pools to address our research questions by scoring traits associated with harsh environments.

KEY RESULTS

We found that the Overberg and Little Karoo had the highest level of species overlap for families Aizoaceae and Fabaceae, whereas the Knersvlakte and the Overberg had the highest species overlap for families Asteraceae, Crassulaceae and Santalaceae. Although our phylogenetic community structure and trait analyses showed no clear patterns, relatively low pairwise phylogenetic distances between specialists and their local species pools for Aizoaceae suggest that quartz species could be drawn evolutionarily from their surrounding areas. We also found that families Aizoaceae and Crassulaceae in Knersvlakte and Little Karoo were phylogenetically even.

CONCLUSIONS

Despite their proximity to one another within the GCFR, the studied areas differ in their species pools and the phylogenetic structure of their specialists. Our work provides further justification for increased conservation focus on these unique habitats under future scenarios of global change.

The CAM lineages of planet Earth

BACKGROUND AND SCOPE

The growth of experimental studies of crassulacean acid metabolism (CAM) in diverse plant clades, coupled with recent advances in molecular systematics, presents an opportunity to re-assess the phylogenetic distribution and diversity of species capable of CAM. It has been more than two decades since the last comprehensive lists of CAM taxa were published, and an updated survey of the occurrence and distribution of CAM taxa is needed to facilitate and guide future CAM research. We aimed to survey the phylogenetic distribution of these taxa, their diverse morphology, physiology and ecology, and the likely number of evolutionary origins of CAM based on currently known lineages.

RESULTS AND CONCLUSIONS

We found direct evidence (in the form of experimental or field observations of gas exchange, day-night fluctuations in organic acids, carbon isotope ratios and enzymatic activity) for CAM in 370 genera of vascular plants, representing 38 families. Further assumptions about the frequency of CAM species in CAM clades and the distribution of CAM in the Cactaceae and Crassulaceae bring the currently estimated number of CAM-capable species to nearly 7 % of all vascular plants. The phylogenetic distribution of these taxa suggests a minimum of 66 independent origins of CAM in vascular plants, possibly with dozens more. To achieve further insight into CAM origins, there is a need for more extensive and systematic surveys of previously unstudied lineages, particularly in living material to identify low-level CAM activity, and for denser sampling to increase phylogenetic resolution in CAM-evolving clades. This should allow further progress in understanding the functional significance of this pathway by integration with studies on the evolution and genomics of CAM in its many forms.

The diverse diaspora of CAM: a pole-to-pole sketch

BACKGROUND

Crassulacean acid metabolism (CAM) photosynthesis is a successful adaptation that has evolved often in angiosperms, gymnosperms, ferns and lycophytes. Present in ~5 % of vascular plants, the CAM diaspora includes all continents apart from Antarctica. Species with CAM inhabit most landscapes colonized by vascular plants, from the Arctic Circle to Tierra del Fuego, from below sea level to 4800 m a.s.l., from rainforests to deserts. They have colonized terrestrial, epiphytic, lithophytic, palustrine and aquatic systems, developing perennial, annual or geophyte strategies that can be structurally arborescent, shrub, forb, cladode, epiphyte, vine or leafless with photosynthetic roots. CAM can enhance survival by conserving water, trapping carbon, reducing carbon loss and/or via photoprotection.

SCOPE

This review assesses the phylogenetic diversity and historical biogeography of selected lineages with CAM, i.e. ferns, gymnosperms and eumagnoliids, Orchidaceae, Bromeliaceae, Crassulaceae, Euphorbiaceae, Aizoaceae, Portulacineae (Montiaceae, Basellaceae, Halophytaceae, Didiereaceae, Talinaceae, Portulacaceae, Anacampserotaceae and Cactaceae) and aquatics.

CONCLUSIONS

Most extant CAM lineages diversified after the Oligocene/Miocene, as the planet dried and CO2 concentrations dropped. Radiations exploited changing ecological landscapes, including Andean emergence, Panamanian Isthmus closure, Sundaland emergence and submergence, changing climates and desertification. Evidence remains sparse for or against theories that CAM biochemistry tends to evolve before pronounced changes in anatomy and that CAM tends to be a culminating xerophytic trait. In perennial taxa, any form of CAM can occur depending upon the lineage and the habitat, although facultative CAM appears uncommon in epiphytes. CAM annuals lack strong CAM. In CAM annuals, C3 + CAM predominates, and inducible or facultative CAM is common.

Atmospheric CO2 decline and the timing of CAM plant evolution

BACKGROUND AND AIMS

CAM photosynthesis is hypothesized to have evolved in atmospheres of low CO2 concentration in recent geological time because of its ability to concentrate CO2 around Rubisco and boost water use efficiency relative to C3 photosynthesis. We assess this hypothesis by compiling estimates of when CAM clades arose using phylogenetic chronograms for 73 CAM clades. We further consider evidence of how atmospheric CO2 affects CAM relative to C3 photosynthesis.

RESULTS

Where CAM origins can be inferred, strong CAM is estimated to have appeared in the past 30 million years in 46 of 48 examined clades, after atmospheric CO2 had declined from high (near 800 ppm) to lower (<450 ppm) values. In turn, 21 of 25 clades containing CAM species (but where CAM origins are less certain) also arose in the past 30 million years. In these clades, CAM is probably younger than the clade origin. We found evidence for repeated weak CAM evolution during the higher CO2 conditions before 30 million years ago, and possible strong CAM origins in the Crassulaceae during the Cretaceous period prior to atmospheric CO2 decline. Most CAM-specific clades arose in the past 15 million years, in a similar pattern observed for origins of C4 clades.

CONCLUSIONS

The evidence indicates strong CAM repeatedly evolved in reduced CO2 conditions of the past 30 million years. Weaker CAM can pre-date low CO2 and, in the Crassulaceae, strong CAM may also have arisen in water-limited microsites under relatively high CO2. Experimental evidence from extant CAM species demonstrates that elevated CO2 reduces the importance of nocturnal CO2 fixation by increasing the contribution of C3 photosynthesis to daily carbon gain. Thus, the advantage of strong CAM would be reduced in high CO2, such that its evolution appears less likely and restricted to more extreme environments than possible in low CO2.

Diversification of flowering plants in space and time

The rapid diversification and high species richness of flowering plants is regarded as 'Darwin's second abominable mystery'. Today the global spatiotemporal pattern of plant diversification remains elusive. Using a newly generated genus-level phylogeny and global distribution data for 14,244 flowering plant genera, we describe the diversification dynamics of angiosperms through space and time. Our analyses show that diversification rates increased throughout the early Cretaceous and then slightly decreased or remained mostly stable until the end of the Cretaceous-Paleogene mass extinction event 66 million years ago. After that, diversification rates increased again towards the present. Younger genera with high diversification rates dominate temperate and dryland regions, whereas old genera with low diversification dominate the tropics. This leads to a negative correlation between spatial patterns of diversification and genus diversity. Our findings suggest that global changes since the Cenozoic shaped the patterns of flowering plant diversity and support an emerging consensus that diversification rates are higher outside the tropics.

Tissue succulence in plants: Carrying water for climate change

Tissue succulence in plants involves the storage of water in one or more organs or tissues to assist in maintaining water potentials on daily or seasonal time scales. This drought-avoidance or drought-resistance strategy allows plants to occupy diverse environments including arid regions, regions with rocky soils, epiphytic habitats, and saline soils. Climate-resilient strategies are of increasing interest in the context of the global climate crisis, which is leading to hotter and drier conditions in many regions throughout the globe. Here, we describe a short history of succulent plants, the basic concepts of tissue succulence, the anatomical diversity of succulent morphologies and associated adaptive traits, the evolutionary, phylogenetic, and biogeographical diversity of succulent plants, extinction risks to succulents due to poaching from their natural environments, and the myriad uses and applications of economically important succulent species and the products derived from them. Lastly, we discuss current prospects for engineering tissue succulence to improve salinity and drought tolerance in crops.

The relationship between transposable elements and ecological niches in the Greater Cape Floristic Region: A study on the genus Pteronia (Asteraceae)

Non-coding repetitive DNA (repeatome) is an active part of the nuclear genome, involved in its structure, evolution and function. It is dominated by transposable elements (TEs) and satellite DNA and is prone to the most rapid changes over time. The TEs activity presumably causes the global genome reorganization and may play an adaptive or regulatory role in response to environmental challenges. This assumption is applied here for the first time to plants from the Cape Floristic hotspot to determine whether changes in repetitive DNA are related to responses to a harsh, but extremely species-rich environment. The genus Pteronia (Asteraceae) serves as a suitable model group because it shows considerable variation in genome size at the diploid level and has high and nearly equal levels of endemism in the two main Cape biomes, Fynbos and Succulent Karoo. First, we constructed a phylogeny based on multiple low-copy genes that served as a phylogenetic framework for detecting quantitative and qualitative changes in the repeatome. Second, we performed a comparative analysis of the environments of two groups of Pteronia differing in their TEs bursts. Our results suggest that the environmental transition from the Succulent Karoo to the Fynbos is accompanied by TEs burst, which is likely also driving phylogenetic divergence. We thus hypothesize that analysis of rapidly evolving repeatome could serve as an important proxy for determining the molecular basis of lineage divergence in rapidly radiating groups.

Adnate Leaf-Base and the Origin of Ribs in Succulent Stems of Euphorbia L

Stem succulence evolved independently in many plant lineages as an adaptation to arid environments. One of the most interesting cases is the convergence between Cactaceae and Euphorbia, which have anatomical adaptations mostly to increase photosynthetic capability and water storage. Our goal was to describe the shoot development in two succulent species of Euphorbia using light microscopy coupled with high-resolution X-ray-computed tomography. Collateral cortical bundles were observed associated with the stem ribs in both species. The analysis of vasculature demonstrated that these bundles are, in fact, leaf traces that run axially along a portion of the internode. That structural pattern is due to an ontogenetic alteration. During shoot development, the leaf-bases remain adnate to the stem near the SAM, forming an axial component. When the internode elongates, the leaf bundles stretch as cortical bundles. The meristematic activity associated with the bundles forms the stem ribs, as leaf veins near the node, and induce rib formation along the entire internode even in the portion where the leaf traces join the stele. In addition, heterochronic shifts are also involved in the evolution of the shoot system in these Euphorbia, being related to early deciduous reduced leaves and the transference of the main photosynthetic function to the stem. This study demonstrates for the first time the influence of leaf developmental shifts and stem rib formation in Euphorbia and sheds new light on the evolution of stem succulence.

Evidence linking life-form to a major shift in diversification rate in Crassula

PREMISE

Plants have evolved different ecological strategies in response to environmental challenges, and a higher lability of such strategies is more common in plant groups that adapt to various niches. Crassula (Crassulaceae), occurring in varied mesic to xeric habitats, exhibits a remarkable diversity of life-forms. However, whether any particular life-form trait has shaped species diversification in Crassula has remained unexplored. This study aims to investigate diversification patterns within Crassula and identify potential links to its life-form evolution.

METHODS

A phylogenetic tree of 140 Crassula taxa was reconstructed using plastid and nuclear loci and dated based on the nuclear DNA information only. We reconstructed ancestral life-form characters to estimate the evolutionary trends of ecophysiological change, and subsequently estimated net diversification rates. Multiple diversification models were applied to examine the association between certain life-forms and net diversification rates.

RESULTS

Our findings confirm a radiation within Crassula in the last 10 million years. A configuration of net diversification rate shifts was detected, which coincides with the emergence of a speciose lineage during the late Miocene. The results of ancestral state reconstruction demonstrate a high lability of life-forms in Crassula, and the trait-dependent diversification analyses revealed that the increased diversification is strongly associated with a compact growth form.

CONCLUSIONS

Transitions between life-forms in Crassula seem to have driven adaptation and shaped diversification of this genus across various habitats. The diversification patterns we inferred are similar to those observed in other major succulent lineages, with the most-speciose clades originating in the late Miocene.

Linking the evolution of development of stem vascular system in Nyctaginaceae and its correlation to habit and species diversification

BACKGROUND

Alternative patterns of secondary growth in stems of Nyctaginaceae is present in all growth habits of the family and have been known for a long time. However, the interpretation of types of cambial variants have been controversial, given that different authors have given them different developmental interpretations. The different growth habits coupled with an enormous stem anatomical diversity offers the unique opportunity to investigate the evolution of complex developments, to address how these anatomies shifted within habits, and how the acquisition of novel cambial variants and habit transitions impacted the diversification of the family.

METHODS

We integrated developmental data with a phylogenetic framework to investigate the diversity and evolution of stem anatomy in Nyctaginaceae using phylogenetic comparative methods, reconstructing ancestral states, and examining whether anatomical shifts correspond to species diversification rate shifts in the family.

RESULTS

Two types of cambial variants, interxylary phloem and successive cambia, were recorded in Nyctaginaceae, which result from four different ontogenies. These ontogenetic trajectories depart from two distinct primary vascular structures (regular or polycyclic eustele) yet, they contain shared developmental stages which generate stem morphologies with deconstructed boundaries of morphological categories (continuum morphology). Unlike our a priori hypotheses, interxylary phloem is reconstructed as the ancestral character for the family, with three ontogenies characterized as successive cambia evolving in few taxa. Cambial variants are not contingent on habits, and their transitions are independent from species diversification.

CONCLUSIONS

Our findings suggest that multiple developmental mechanisms, such as heterochrony and heterotopy, generate the transitions between interxylary phloem and successive cambia. Intermediate between these two extremes are present in Nyctaginaceae, suggesting a continuum morphology across the family as a generator of anatomical diversity.

Plastid phylogenomics of the Sansevieria Clade of Dracaena (Asparagaceae) resolves a recent radiation

Best known as low maintenance houseplants, sansevierias are a diverse group of flowering plants native to Africa, Madagascar, the Arabian Peninsula, and the Indian subcontinent. Traditionally recognised as a distinct genus, Sansevieria was recently merged with the larger genus Dracaena based on molecular phylogenetic data. Within the Sansevieria Clade of Dracaena, taxonomic uncertainties remain despite attempts to unravel the relationships between the species. To investigate the evolutionary relationships, morphological evolution and biogeographical history in the group, we aim to reconstruct a robust dated phylogenetic hypothesis. Using genome skimming, a chloroplast genome (cpDNA) dataset and a nuclear ribosomal (nrDNA) dataset were generated. The sampling included representatives of all sections and informal groups previously described in Sansevieria based on morphology. Analysis of the cpDNA dataset using a maximum likelihood approach resulted in a well-supported phylogeny. The time-calibrated phylogeny indicated a recent radiation with five main clades emerging in the Pliocene. Two strongly supported clades align with previously defined groups, i.e., Sansevieria section Dracomima, characterised by the Dracomima-type inflorescence, and the Zeylanica informal group, native to the Indian subcontinent. Other previously defined groups were shown to be polyphyletic; a result of convergent evolution of the identifying characters. Switches between flat and cylindrical leaves occurred multiple times in the evolution of the Sansevieria Clade. Similarly, the Cephalantha-type inflorescence has originated multiple times from an ancestor with a Sansevieria-type inflorescence. Analysis of the nrDNA dataset resulted in a phylogenetic hypothesis with low resolution, yet it supported the same two groups confirmed by the cpDNA dataset. This study furthers our understanding of the evolution of the Sansevieria Clade, which will benefit taxonomic and applied research, and aid conservation efforts.

Hidden Diversity—A New Speciose Gall Midge Genus (Diptera: Cecidomyiidae) Associated with Succulent Aizoaceae in South Africa

Simple Summary

Succulent Aizoaceae (often called “mesembs” or ice plants) form a dominant component of the Succulent Karoo in southern Africa, constituting one of the most species-rich families within the Greater Cape Floristic Region (GCFR). Despite the diversity and abundance of these plants, the diversity of insects specialized on them has never been surveyed methodically prior to this study. In a three-year study of the galling insects associated with succulent Aizoaceae in South Africa, we found that they support a rich community of gall midges (Diptera: Cecidomyiidae), virtually all of which are new to science. This is not surprising, given that knowledge of the Afrotropical fauna of gall midges is scarce, with most species described in the 1900s. Here, we describe the new genus Ruschiola with ten species from succulent Aizoaceae in Namaqualand, the Knersvlakte and the Cedarberg regions of South Africa based on morphological, molecular and life history data. The genetic data were particularly important in this study for differentiating taxa, given that Ruschiola species are very similar morphologically. Members of this genus develop in leaf galls or in plant tissues without visible gall formation, and are highly host specific.

Abstract

Aizoaceae (Caryophyllales) constitute one of the major floral components of the unique Greater Cape Floristic Region (GCFR), with more than 1700 species and 70% endemism. Within succulent Aizoaceae, the subfamily Ruschioideae is the most speciose and rapidly diversifying clade, offering potential niches for the diversification of specialized herbivorous insects. Nevertheless, insect diversity on these plants has not been studied to date, and knowledge of gall-inducing insects in the Afrotropics is generally scarce. Our recent observations indicate that succulent Aizoaceae in the GCFR support a rich and largely unstudied community of gall midges (Diptera: Cecidomyiidae). Here, we provide a first report of their diversity with a description of a new genus, Ruschiola Dorchin, and ten new species, based on morphological and molecular analyses of material collected during a three-year targeted survey across major GCFR vegetation types. A high degree of morphological uniformity in Ruschiola suggests recent diversification and necessitated the use of molecular data and laboratory rearing from host plants to verify species boundaries and host ranges.

Limited dispersal and local adaptation promote allopatric speciation in a biodiversity hotspot

Recently diverged or diverging populations can offer unobstructed insights into early barriers to gene flow during the initial stages of speciation. The current study utilised a novel insect system (order Mantophasmatodea) to shed light on the early drivers of speciation. The members of this group have limited dispersal abilities, small allopatric distributions and strong habitat associations in the Cape Floristic Region biodiversity hotspot in South Africa. Sister taxa from the diverse family Austrophasmatidae were chosen as focal species (Karoophasma biedouwense, K. botterkloofense). Population genetics and Generalized Dissimilarity Modelling (GDM) were used to characterise spatial patterns of genetic variation and evaluate the contribution of environmental factors to population divergence and speciation. Extensive sampling confirmed the suspected allopatry of these taxa. However, hybrids were identified in a narrow region occurring between the species' distributions. Strong population structure was found over short geographic distances; particularly in K. biedouwense in which geographic distance accounted for 32% of genetic variation over a scale of 50 km (r = .56, p < .001). GDM explained 42%-78% of the deviance in observed genetic dissimilarities. Geographic distance was consistently indicated to be important for between species and within population differentiation, suggesting that limited dispersal ability may be an important neutral driver of divergence. Temperature, altitude, precipitation and vegetation were also indicated as important factors, suggesting the possible role of adaptation to local environmental conditions for species divergence. The discovery of the hybrid-zone, and the multiple allopatric species pairs in Austrophasmatidae support the idea that this could be a promising group to further our understanding of speciation modes.

Recent Progress on Plant-Inspired Soft Robotics with Hydrogel Building Blocks: Fabrication, Actuation and Application

Millions of years’ evolution has imparted life on earth with excellent environment adaptability. Of particular interest to scientists are some plants capable of macroscopically and reversibly altering their morphological and mechanical properties in response to external stimuli from the surrounding environment. These intriguing natural phenomena and underlying actuation mechanisms have provided important design guidance and principles for man-made soft robotic systems. Constructing bio-inspired soft robotic systems with effective actuation requires the efficient supply of mechanical energy generated from external inputs, such as temperature, light, and electricity. By combining bio-inspired designs with stimuli-responsive materials, various intelligent soft robotic systems that demonstrate promising and exciting results have been developed. As one of the building materials for soft robotics, hydrogels are gaining increasing attention owing to their advantageous properties, such as ultra-tunable modulus, high compliance, varying stimuli-responsiveness, good biocompatibility, and high transparency. In this review article, we summarize the recent progress on plant-inspired soft robotics assembled by stimuli-responsive hydrogels with a particular focus on their actuation mechanisms, fabrication, and application. Meanwhile, some critical challenges and problems associated with current hydrogel-based soft robotics are briefly introduced, and possible solutions are proposed. We expect that this review would provide elementary tutorial guidelines to audiences who are interested in the study on nature-inspired soft robotics, especially hydrogel-based intelligent soft robotic systems.

Diversification, disparification and hybridization in the desert shrubs Encelia

There are multiple hypotheses for the spectacular plant diversity found in deserts. We explore how different factors, including the roles of ecological opportunity and selection, promote diversification and disparification in Encelia, a lineage of woody plants in the deserts of the Americas. Using a nearly complete species-level phylogeny based on double-digest restriction-aided sequencing along with a broad set of phenotypic traits, we estimate divergence times and diversification rates, identify instances of hybridization, quantify trait disparity and assess phenotypic divergence across environmental gradients. We show that Encelia originated and diversified recently (mid-Pleistocene) and rapidly, with rates comparable to notable adaptive radiations in plants. Encelia probably originated in the hot deserts of North America, with subsequent diversification across steep environmental gradients. We uncover multiple instances of gene flow between species. The radiation of Encelia is characterized by fast rates of phenotypic evolution, trait lability and extreme disparity across environments and between species pairs with overlapping geographic ranges. Encelia exemplifies how interspecific gene flow in combination with high trait lability can enable exceptionally fast diversification and disparification across steep environmental gradients.

Quaternary diversification of a columnar cactus in the driest place on earth

PREMISE

The cactus family (Cactaceae) is a speciose lineage with an almost entirely New World distribution. The genus Eulychnia with eight currently recognized species is endemic to the Atacama and Peruvian Deserts. Here we investigated the phylogeny of this group based on a complete taxon sampling to elucidate species delimitation and biogeographic history of the genus.

METHODS

A family-wide Bayesian molecular clock dating based on plastid sequence data was conducted to estimate the age of Eulychnia and its divergence from its sister genus Austrocactus. A second data set obtained from genotyping by sequencing (GBS) was analyzed, using the family-wide age estimate as a secondary calibration to date the GBS phylogeny using a penalized likelihood approach. Ancestral ranges were inferred employing the dispersal extinction cladogenesis approach.

RESULTS

Our GBS phylogeny of Eulychnia was fully resolved with high support values nearly throughout the phylogeny. The split from Austrocactus occurred in the late Miocene, and Eulychnia diversified during the early Quaternary. Three lineages were retrieved: Eulychnia ritteri from Peru is sister to all Chilean species, which in turn fall into two sister clades of three and four species, respectively. Diversification in the Chilean clades started in the early Pleistocene. Eulychnia likely originated at the coastal range of its distribution and colonized inland locations several times.

CONCLUSIONS

Diversification of Eulychnia during the Pleistocene coincides with long periods of hyperaridity alternated with pluvial phases. Hyperaridity caused habitat fragmentation, ultimately leading to speciation and resulting in the current allopatric distribution of taxa.

OCBIL theory examined: reassessing evolution, ecology and conservation in the world’s ancient, climatically buffered and infertile landscapes

OCBIL theory was introduced as a contribution towards understanding the evolution, ecology and conservation of the biological and cultural diversity of old, climatically buffered, infertile landscapes (OCBILs), especially in the Southern Hemisphere. The theory addresses some of the most intransigent environmental and cultural trends of our time – the ongoing decline of biodiversity and cultural diversity of First Nations. Here we reflect on OCBILs, the origins of the theory, and its principal hypotheses in biological, anthropological and conservation applications. The discovery that threatened plant species are concentrated in the Southwest Australian Floristic Region (SWAFR) on infertile, phosphorous-impoverished uplands within 500 km of the coast formed the foundational framework for OCBIL theory and led to the development of testable hypotheses that a growing literature is addressing. Currently, OCBILs are recognized in 15 Global Biodiversity Hotspots and eight other regions. The SWAFR, Greater Cape Floristic Region of South Africa and South America’s campos rupestres (montane grasslands) are those regions that have most comprehensively been investigated in the context of OCBIL theory. We summarize 12 evolutionary, ecological and cultural hypotheses and ten conservation-management hypotheses being investigated as recent contributions to the OCBIL literature.

Niche specificity influences gene flow across fine-scale habitat mosaics in Succulent Karoo plants

While the tempo of diversification in biodiversity hotspots has received much attention, the spatial scale of diversification has often been overlooked. Addressing this deficiency requires understanding the drivers of population divergence and the spatial scales at which they operate in species-rich clades and ecosystems. South Africa's Succulent Karoo (SK) hotspot provides an excellent system for such research, being both compact (ca. 110,000 km² ) and home to spectacular in-situ radiations, such as the ruschioid Aizoaceae. Here we use GBS to document genetic structure in two co-occurring ruschioid species, at both coarse (>10 km) and fine (<500 m) spatial scales. Where Ruschia burtoniae shows strong between-population genetic differentiation and no gene flow, Conophytum calculus shows weak differentiation, with high levels of admixture suggesting recent or ongoing gene flow. Community analysis and transplant experiments reveal that R. burtoniae occupies a narrow, low-pH edaphic niche, and at scales of a few hundred metres, areas of elevated genetic turnover correspond to patches of edaphically unsuitable habitat. In contrast, C. calculus occupies a broader niche and exhibits isolation-by-distance without a habitat effect. We suggest that edaphic specialisation, coupled with highly restricted seed and pollen dispersal in heterogeneous landscapes, has played a major role in driving rapid diversification at small spatial scales in this system. However, the contrasting patterns in our study species show that these factors do not influence all organisms uniformly, being strongly modulated by lineage-specific traits that influence both the spatial scale of gene flow and habitat specificity.

Is the age of plant communities predicted by the age, stability and soil composition of the underlying landscapes? An investigation of OCBILs

Old, climatically buffered, infertile landscapes (OCBILs) have been hypothesized to harbour an elevated number of persistent plant lineages and are predicted to occur across different parts of the globe, interspersed with other types of landscapes. We tested whether the mean age of a plant community is associated with occurrence on OCBILs, as predicted by climatic stability and poor soil environments. Using digitized occurrence data for seed plants occurring in Australia (7033 species), sub-Saharan Africa (3990 species) and South America (44 482 species), regions that comprise commonly investigated OCBILs (Southwestern Australian Floristic Region, Greater Cape Floristic Region and campos rupestres), and phylogenies pruned to match the species occurrences, we tested for associations between environmental data (current climate, soil composition, elevation and climatic stability) and two novel metrics developed here that capture the age of a community (mean tip length and mean node height). Our results indicate that plant community ages are influenced by a combination of multiple environmental predictors that vary globally; we did not find statistically strong associations between the environments of OCBIL areas and community age, in contrast to the prediction for these landscapes. The Cape Floristic Region was the only OCBIL that showed a significant, although not strong, overlap with old communities.

Comparative Analyses of the Self-Sealing Mechanisms in Leaves of Delosperma cooperi and Delosperma ecklonis (Aizoaceae)

Within the Aizoaceae, the genus Delosperma exhibits a vast diversification colonizing various ecological niches in South-Africa and showing evolutionary adaptations to dry habitats that might include rapid self-sealing. Leaves of Delosperma react to external damage by the bending or contraction of the entire leaf until wound edges are brought into contact. A study of leaf morphology and anatomy, biomechanics of entire leaves and individual tissues and self-sealing kinematics after a ring incision under low and high relative humidity (RH) was carried out comparing the closely related species Delosperma cooperi and Delosperma ecklonis, which are indigenous to semi-arid highlands and regions with an oceanic climate, respectively. For both species, the absolute contractions of the examined leaf segments ("apex", "incision", "base") were more pronounced at low RH levels. Independent of the given RH level, the absolute contractions within the incision region of D. cooperi were significantly higher than in all other segments of this species and of D. ecklonis. The more pronounced contraction of D. cooperi leaves was linked mainly to the elastic properties of the central vascular strand, which is approximately twice as flexible as that of D. ecklonis leaves.

Phylogenetic relationships in the southern African genus Drosanthemum (Ruschioideae, Aizoaceae)

BACKGROUND

Drosanthemum, the only genus of the tribe Drosanthemeae, is widespread over the Greater Cape Floristic Region in southern Africa. With 114 recognized species, Drosanthemum, together with the highly succulent and species-rich tribe Ruschieae, constitute the 'core ruschioids' in Aizoaceae. Within Drosanthemum, nine subgenera have been described based on flower and fruit morphology. Their phylogenetic relationships, however, have not yet been investigated, hampering understanding of monophyletic entities and patterns of geographic distribution.

METHODS

Using chloroplast and nuclear DNA sequence data, we performed network- and tree-based phylogenetic analyses of 73 species of Drosanthemum with multiple accessions for widespread species. A well-curated, geo-referenced occurrence dataset comprising the 134 genetically analysed and 863 further accessions was used to describe the distributional ranges of intrageneric lineages and the genus as a whole.

RESULTS

Phylogenetic inference supports nine clades within Drosanthemum, seven of which group in two major clades, while the remaining two show ambiguous affinities. The nine clades are generally congruent to previously described subgenera within Drosanthemum, with exceptions such as cryptic species. In-depth analyses of sequence patterns in each gene region were used to reveal phylogenetic affinities inside the retrieved clades in more detail. We observe a complex distribution pattern including widespread, species-rich clades expanding into arid habitats of the interior (subgenera Drosanthemum p.p., Vespertina, Xamera) that are genetically and morphologically diverse. In contrast, less species-rich, genetically less divergent, and morphologically unique lineages are restricted to the central Cape region and more mesic conditions (Decidua, Necopina, Ossicula, Quastea, Quadrata, Speciosa). Our results suggest that the main lineages arose from an initial rapid radiation, with subsequent diversification in some clades.

Recent diversification of Chrysoritis butterflies in the South African Cape (Lepidoptera: Lycaenidae)

Although best known for its extraordinary radiations of endemic plant species, the South African fynbos is home to a great diversity of phytophagous insects, including butterflies in the genus Chrysoritis (Lepidoptera: Lycaenidae). These butterflies are remarkably uniform morphologically; nevertheless, they comprise 43 currently accepted species and 68 currently valid taxonomic names. While many species have highly restricted, dot-like distributions, others are widespread. Here, we investigate the phylogenetic and biogeographic history underlying their diversification by analyzing molecular markers from 406 representatives of all described species throughout their respective ranges. We recover monophyletic clades for both C. chrysaor and C. thysbe species-groups, and identify a set of lineages that fall between them. The estimated age of divergence for the genus is 32 Mya, and we document significantly rapid diversification of the thysbe species-group in the Pleistocene (~2 Mya). Using ancestral geographic range reconstruction, we show that West Fynbos is the most likely region of origin for the radiation of the thysbe species-group. The colonization of this region occurred 9 Mya and appears to have been followed by a long period of relative stasis before a recent increase in diversification. Thus, the thysbe radiation does not appear to have resulted from the colonization of new biogeographic areas. Rather, the impact of species interactions (with ants and plants), the appearance of key innovations, and/or the opening of new ecological niche space in the region might explain the sudden burst of speciation that occurred in this group 2 Mya. The biogeographic model suggests two different diversification processes with few historical cross-colonisations, one in eastern South Africa for the C. chrysaor group and the other in western South Africa for the remaining taxa. Distributional range assessments and ecological niche models for each species show important niche overlap, and in a few cases, complete overlap. However, these shared traits are not explained by phylogenetic history. Chrysoritis taxa frequently fly in sympatry and gene tree reticulation appears to be widespread at the species level, suggesting that several episodes of range shifts might have led to secondary sympatries, allowing limited gene flow that challenges species delimitation efforts. In addition, the unusually high diversification rate for the thysbe clade of 1.35 [0.91-1.81] lineages per million years also suggests the possibility of taxonomic oversplitting. The phylogeny presented here provides a framework for a taxonomic revision of the genus. We highlight cases of potential synonymy both in allopatry and sympatry, and stress the importance of dedicated studies to assess potential pre- and post-zygotic barriers giving rise to species delimitations of the thysbe group.

The genetics of evolutionary radiations

With the realization that much of the biological diversity on Earth has been generated by discrete evolutionary radiations, there has been a rapid increase in research into the biotic (key innovations) and abiotic (key environments) circumstances in which such radiations took place. Here we focus on the potential importance of population genetic structure and trait genetic architecture in explaining radiations. We propose a verbal model describing the stages of an evolutionary radiation: first invading a suitable adaptive zone and expanding both spatially and ecologically through this zone; secondly, diverging genetically into numerous distinct populations; and, finally, speciating. There are numerous examples of the first stage; the difficulty, however, is explaining how genetic diversification can take place from the establishment of a, presumably, genetically depauperate population in a new adaptive zone. We explore the potential roles of epigenetics and transposable elements (TEs), of neutral process such as genetic drift in combination with trait genetic architecture, of gene flow limitation through isolation by distance (IBD), isolation by ecology and isolation by colonization, the possible role of intra-specific competition, and that of admixture and hybridization in increasing the genetic diversity of the founding populations. We show that many of the predictions of this model are corroborated. Most radiations occur in complex adaptive zones, which facilitate the establishment of many small populations exposed to genetic drift and divergent selection. We also show that many radiations (especially those resulting from long-distance dispersal) were established by polyploid lineages, and that many radiating lineages have small genome sizes. However, there are several other predictions which are not (yet) possible to test: that epigenetics has played a role in radiations, that radiations occur more frequently in clades with small gene flow distances, or that the ancestors of radiations had large fundamental niches. At least some of these may be testable in the future as more genome and epigenome data become available. The implication of this model is that many radiations may be hard polytomies because the genetic divergence leading to speciation happens within a very short time, and that the divergence history may be further obscured by hybridization. Furthermore, it suggests that only lineages with the appropriate genetic architecture will be able to radiate, and that such a radiation will happen in a meta-population environment. Understanding the genetic architecture of a lineage may be an essential part of accounting for why some lineages radiate, and some do not.

Phylogenetic Relationships and Evolutionary Trends in the Cactus Family

Members of the cactus family are keystone species of arid and semiarid biomes in the Americas, as they provide shelter and resources to support other members of ecosystems. Extraordinary examples are the several species of flies of the genus Drosophila that lay eggs and feed in their rotting stems, which provide a model system for studying evolutionary processes. Although there is significant progress in understanding the evolution of Drosophila species, there are gaps in our knowledge about the cactus lineages hosting them. Here, we review the current knowledge about the evolution of Cactaceae, focusing on phylogenetic relationships and trends revealed by the study of DNA sequence data. During the last several decades, the availability of molecular phylogenies has considerably increased our understanding of the relationships, biogeography, and evolution of traits in the family. Remarkably, although succulent cacti have very low growth rates and long generation times, they underwent some of the fastest diversifications observed in the plant kingdom, possibly fostered by strong ecological interactions. We have a better understanding of the reproductive biology, population structure and speciation mechanisms in different clades. The recent publication of complete genomes for some species has revealed the importance of phenomena such as incomplete lineage sorting. Hybridization and polyploidization are common in the family, and have been studied using a variety of phylogenetic methods. We discuss potential future avenues for research in Cactaceae, emphasizing the need of a concerted effort among scientists in the Americas, together with the analyses of data from novel sequencing techniques.

Extinction pulse at Eocene-Oligocene boundary drives diversification dynamics of two Australian temperate floras

The diversification dynamics of the Australian temperate flora remains poorly understood. Here, we investigate whether differences in plant richness in the southwest Australian (SWA) biodiversity hotspot and southeast Australian (SEA) regions of the Australian continent can be attributed to higher net diversification, more time for species accumulation, or both. We assembled dated molecular phylogenies for the 21 most species-rich flowering plant families found across mesic temperate Australia, encompassing both SWA and SEA regions, and applied a series of diversification models to investigate responses across different groups and timescales. We show that the high richness in SWA can be attributed to a higher net rate of lineage diversification and more time for species accumulation. Different pulses of diversification were retrieved in each region. A decrease in diversification rate across major flowering plant lineages at the Eocene-Oligocene boundary (ca 34 Ma) was witnessed in SEA but not in SWA. Our study demonstrates the importance of historical diversification pulses and differential responses to global events as drivers of present-day diversity. More broadly, we show that diversity within the SWA biodiversity hotspot is not only the result of recent radiations, but also reflects older events over the history of this planet.

Species Selection Regime and Phylogenetic Tree Shape

Species selection, the effect of heritable traits in generating between-lineage diversification rate differences, provides a valuable conceptual framework for understanding the relationship between traits, diversification, and phylogenetic tree shape. An important challenge, however, is that the nature of real diversification landscapes—curves or surfaces which describe the propensity of species-level lineages to diversify as a function of one or more traits—remains poorly understood. Here, we present a novel, time-stratified extension of the QuaSSE model in which speciation/extinction rate is specified as a static or temporally shifting Gaussian or skewed-Gaussian function of the diversification trait. We then use simulations to show that the generally imbalanced nature of real phylogenetic trees, as well as their generally greater than expected frequency of deep branching events, are typical outcomes when diversification is treated as a dynamic, trait-dependent process. Focusing on four basic models (Gaussian-speciation with and without background extinction; skewed-speciation; Gaussian-extinction), we also show that particular features of the species selection regime produce distinct tree shape signatures and that, consequently, a combination of tree shape metrics has the potential to reveal the species selection regime under which a particular lineage diversified. We evaluate this idea empirically by comparing the phylogenetic trees of plant lineages diversifying within climatically and geologically stable environments of the Greater Cape Floristic Region, with those of lineages diversifying in environments that have experienced major change through the Late Miocene-Pliocene. Consistent with our expectations, the trees of lineages diversifying in a dynamic context are less balanced, show a greater concentration of branching events close to the present, and display stronger diversification rate-trait correlations. We suggest that species selection plays an important role in shaping phylogenetic trees but recognize the need for an explicit probabilistic framework within which to assess the likelihoods of alternative diversification scenarios as explanations of a particular tree shape. [Cape flora; diversification landscape; environmental change; gamma statistic; species selection; time-stratified QuaSSE model; trait-dependent diversification; tree imbalance.]

Ecophysiology of constitutive and facultative CAM photosynthesis

In plants exhibiting crassulacean acid metabolism (CAM), CAM photosynthesis almost always occurs together with C3 photosynthesis, and occasionally with C4 photosynthesis. Depending on species, ontogeny, and environment, CAM input to total carbon gain can vary from values of <1% to 100%. The wide range of CAM phenotypes between and within species is a fascinating example of functional diversity and plasticity, but poses a significant challenge when attempting to define CAM. CO2 gas exchange experiments designed for this review illustrate key patterns of CAM expression and highlight distinguishing features of constitutive and facultative CAM. Furthermore, they help to address frequently recurring questions on CAM terminology. The functional and evolutionary significance of contrasting CAM phenotypes and of intermediate states between extremes is discussed. Results from a study on nocturnal malate accumulation in 50 species of Aizoaceae exposed to drought and salinity stress suggest that facultative CAM is more widespread amongst vascular plants than previously thought.

Analysis of temporal diversification of African Cyprinidae (Teleostei, Cypriniformes)

Recent evidence that freshwater fishes diversify faster than marine fishes signifies that the evolutionary history of biodiversity in freshwater system is of particular interest. Here, the evolutionary diversification events of African Cyprinidae, a freshwater fish family with wide geographic distribution, were reconstructed and analysed. The overall diversification rate of African Cyprinidae is 0.08 species per million year (when extinction rate is very high, i.e., ε = 0.9) and 0.11 species per million year (when ε = 0). This overall rate is lower than the rate reported for African Cichlids, suggesting that African freshwaters might be less conducive for a rapid diversification of Cyprinidae. However, the observed diversification events of African Cyprinidae occurred in the last 10 million years. The temporal pattern of these events follows a non-constant episodic birth-death model (Bayes Factor > 28) and the rate-constant model never outperformed any of the non-constant models tested. The fact that most diversification events occurred in the last 10 million years supports the pattern reported for Cyprinidae in other continent, e.g., Asia, perhaps pointing to concomitant diversification globally. However, the diversification events coincided with major geologic and paleo-climatic events in Africa, suggesting that geological and climatic events may have mediated the diversification patterns of Cyprinidae on the continent.

Insights into the historical assembly of global dryland floras: the diversification of Zygophyllaceae

BACKGROUND

Drylands cover nearly 41% of Earth's land surface and face a high risk of degradation worldwide. However, the actual timeframe during which dryland floras rose on a global scale remains unknown. Zygophyllaceae, an important characteristic component of dryland floras worldwide, offers an ideal model group to investigate the diversification of dryland floras. Here, we used an integration of the phylogenetic, molecular dating, biogeographic, and diversification methods to investigate the timing and patterns of lineage accumulation for Zygophyllaceae overall and regionally. We then incorporated the data from other dominant components of dryland floras in different continents to investigate the historical construction of dryland floras on a global scale.

RESULTS

We provide the most comprehensive phylogenetic tree for Zygophyllaceae so far based on four plastid and nuclear markers. Detailed analyses indicate that Zygophyllaceae colonized Africa, Asia, Australia, and the New World at different periods, sometimes multiple times, but Zygophyllaceae lineages in the four regions all experienced a rapid accumulation beginning at the mid-late Miocene (~ 15-10 Ma). Other eleven essential elements of dryland floras become differentiated at the same time.

CONCLUSIONS

Our results suggest that the rise of global dryland floras is near-synchronous and began at the mid-late Miocene, possibly resulting from the mid-Miocene global cooling and regional orogenetic and climate changes. The mid-late Miocene is an essential period for the assembly and evolution of global dryland floras.

Crassula, insights into an old, arid-adapted group of southern African leaf-succulents

The Crassulaceae is an important family in the Greater Cape Floristic Region of southern Africa and is the seventh largest family in the arid Succulent Karoo Biome. After the Aizoaceae it is the largest group of leaf-succulents in southern Africa. This is the first investigation of a broad selection (68%) of the ±170 species of Crassula. We used data from three chloroplast and two nuclear gene-regions, which yielded many informative characters and provided good resolution among the species. We show that only five of the 20 sections in Crassula are monophyletic. However, the clades recovered show close correlation with the two subgenera that were once recognized. Crassula contains more than 25 succulent annual species which are not closely related to each other but form early-diverging branches in each of the three major clades. One of these major clades contains far more perennial species than the others and is the greatest diversification within Crassula. This diversification mostly arose within the last 10 million years (my) and spread across much of southern Africa. Members of the smaller two major clades are often soft- and flat-leaved perennials (many with basic chromosome number x = 8, with high levels of polyploidy). Those in the largest diversification (where a basic chromosome number of x = 7 predominates) show other arid-adaptations (more highly succulent leaves with a dense covering of hairs or papillae or a smooth xeromorphic epidermis). Their flowers are also more variable in shape and bee-, moth- and butterfly-pollinated species are known among them. We establish that Crassula arose in the Greater Cape Floristic Region of southern Africa. While much of its diversity has evolved in the last 10 my, Crassula nevertheless contains species that are much older and itself arose ±46 my ago. Since all its species are succulent it is possible that they are part of an early arid-adapted flora that contributed to the Succulent Karoo Biome in the western part of southern Africa. Consequently this Biome may not be assembled only from 'young lineages' as is usually thought to be the case.

Decoding ice plants: challenges associated with barcoding and phylogenetics in the diverse succulent family Aizoaceae

Aizoaceae is the largest succulent plant family in the world, including in excess of 1800 species. Despite its richness, a large proportion of its taxa are listed as data deficient and as such, has been identified as the top priority for taxonomic research in South Africa. Limitations to accurate taxonomic identification of taxa in the family may be partly attributed to the degree of technical knowledge required to identify taxa in the Aizoaceae. DNA barcoding may provide an alternative method of identification; however, the suitability of commonly used gene regions has not been tested in the family. Here, we analyse variable and parsimony informative characters (PIC), as well as the barcoding gap, in commonly used plastid regions (atpB-rbcL, matK, psbA-trnH, psbJ-petA, rpl16, rps16, trnD-trnT, trnL-trnF, trnQ-rps16, and trnS-trnG) and the nuclear region ITS (for Aizooideae only) across two subfamilies and two expanded clades within the Aizoaceae. The relative percentage of PIC was much greater in subfamilies Aizooideae and Mesembryanthemoideae than in Ruschioideae. Although nrITS had the highest percentage of PIC, barcoding gap analyses identified neither ITS nor any chloroplast region as suitable for barcoding of the family. From the results, it is evident that novel barcoding regions need to be explored within the Aizoaceae.

Niche conservatism and elevated diversification shape species diversity in drylands: evidence from Zygophyllaceae

The integrated contributions of climate and macroevolutionary processes to global patterns of species diversity are still controversial in spite of a long history of studies. The niche conservatism hypothesis and the net diversification rate hypothesis have gained wide attention in recent literature. Many studies have tested these two hypotheses for woody species in humid forests; however, the determinants of species diversity patterns for arid-adapted plants remain largely ignored. Here, using a molecular phylogeny and the global distributions of Zygophyllaceae, a typical arid-adapted plant family, we assessed the effects of contemporary climate and net diversification rates on species diversity patterns in drylands. We found the variables representing water availability to be the best predictors for Zygophyllaceae diversity. Specifically, Zygophyllaceae species diversity significantly decreased with the increase in water availability, probably owing to phylogenetic conservatism of water-related niches. The net diversification rates of Zygophyllaceae accelerated sharply in the recent 10 Myr, coinciding roughly with the period of global aridification. The species diversity of Zygophyllaceae significantly increased with the increase in mean net diversification rates per geographical unit, especially in the Old World, supporting the net diversification rate hypothesis. Our study provides a case exploring climatic and evolutionary mechanisms of dryland species diversity patterns, and suggests that the conservatism in water-related niches and elevated net diversification rates in drylands may have jointly determined the global patterns of dryland species diversity.

Finite element modelling of complex movements during self-sealing of ring incisions in leaves of Delosperma cooperi

A numerical computer model was developed in order to describe the complex self-sealing mechanism of injured Delosperma cooperi leaves. For this purpose, the leaf anatomy was simplified to a model consisting of five concentric tissue layers. Specific parameters (modulus of elasticity, permeability, porosity, etc.) were assigned to each tissue type for modelling its physical properties. These parameters were either determined experimentally from living plant material or taken from literature. The developed computer model considers the leaf as a liquid-filled porous body within a continuum approach in order to determine the governing equations. The modelling of the wound accounts for both the injury of peripheral tissues and the free surfaces caused by the incision. The loss of water through these free surfaces initiates the self-sealing process. It is further shown that the tissue permeability and the reflection coefficient (relative permeability of a cell membrane for solutes) are the determining parameters of the self-sealing process, whereas the modulus of elasticity has a negligible influence. Thus, the self-sealing mechanism is a hydraulically driven process which leads to a local (incision region) and global (total leaf) contraction of the leaf. The accuracy of the modelled self-sealing process was validated by comparing simulation results with experiments conducted on natural plant leaves. The results will serve as valuable input for developing novel, bio-inspired technical products with self-sealing function.

Current progress and future prospects in phylofloristics

The species composition of regional plant assemblages can in large part be explained by a long history of biogeographical and evolutionary events. Traditional attempts of floristic studies typically focus on the analyses of taxonomic composition, often ignoring the rich context that evolutionary history can provide. In 2014, Swenson and Umaña introduced the term 'phylofloristics' to define a phylogenetically enabled analysis of the species composition of regional floras. Integrating phylogenetic information into traditional floristic analysis can provide a promising way to explore the ecological, biogeographic, and evolutionary processes that drive plant assemblies at multiple spatial scales. In this review, we summarize the current progress on the phylogenetic structure, spatial phylogenetic pattern, origin and diversification, phylogenetic regionalization of floristic assemblages, and application of phylogenetic information in biodiversity conservation. These summaries highlight the importance of incorporating phylogenetic information to improve our understanding of floristic assembly from an evolutionary perspective. The review ends with a brief outlook on future challenges for phylofloristic studies, including generating a highly resolved species-level phylogenetic tree, compiling detailed and refined information regarding the geographic distribution of all plant life, extracting trait information from publications and herbarium specimens, and developing technological and methodological approaches for big data analysis.

Fire and Plant Diversification in Mediterranean-Climate Regions

Despite decades of broad interest in global patterns of biodiversity, little attention has been given to understanding the remarkable levels of plant diversity present in the world's five Mediterranean-type climate (MTC) regions, all of which are considered to be biodiversity hotspots. Comprising the Mediterranean Basin, California, central Chile, the Cape Region of South Africa, and southwestern Australia, these regions share the unusual climatic regime of mild wet winters and warm dry summers. Despite their small extent, covering only about 2.2% of world land area, these regions are home to approximately one-sixth of the world vascular plant flora. The onset of MTCs in the middle Miocene brought summer drought, a novel climatic condition, but also a regime of recurrent fire. Fire has been a significant agent of selection in assembling the modern floras of four of the five MTC regions, with central Chile an exception following the uplift of the Andes in the middle Miocene. Selection for persistence in a fire-prone environment as a key causal factor for species diversification in MTC regions has been under-appreciated or ignored. Mechanisms for fire-driven speciation are diverse and may include both directional (novel traits) and stabilizing selection (retained traits) for appropriate morphological and life-history traits. Both museum and nursery hypotheses have important relevance in explaining the extant species richness of the MTC floras, with fire as a strong stimulant for diversification in a manner distinct from other temperate floras. Spatial and temporal niche separation across topographic, climatic and edaphic gradients has occurred in all five regions. The Mediterranean Basin, California, and central Chile are seen as nurseries for strong but not spectacular rates of Neogene diversification, while the older landscapes of southwestern Australia and the Cape Region show significant components of both Paleogene and younger Neogene speciation in their diversity. Low rates of extinction suggesting a long association with fire more than high rates of speciation have been key to the extant levels of species richness.

Leaf stable isotopes suggest shared ancestry is an important driver of functional diversity

Plant physiological strategies of carbon (C) and nitrogen (N) uptake and metabolism are often regarded as outcomes of environmental selection. This is likely true, but the role of evolutionary history may also be important in shaping patterns of functional diversity. Here, we used leaf C and N stable isotope ratios (δ¹³C, δ¹⁵N) as integrators of physiological processes to assess the relative roles of phylogenetic history and environment in a diverse group of Ericaceae species native to North America. We found strong phylogenetic signal in both leaf δ¹³C and δ¹⁵N, suggesting that close relatives have similar physiological strategies. The signal of phylogeny was generally stronger than that of the local environment. However, within some specialized environments (e.g., wetlands, sandy soils), we found environmental effects and/or niche conservatism. Phylogenetic signal in δ¹³C appears to be most closely related to the constraints on metabolic demand and supply of C, and δ¹⁵N appears to be most strongly related to mycorrhizal associations within the family.

Accelerated diversification and functional trait evolution in Velloziaceae reveal new insights into the origins of the campos rupestres' exceptional floristic richness

Background and Aims

The greater diversity of plant clades in the Neotropics compared to their relatives in Africa is a pervasive pattern in biogeography. To better understand the causes of this imbalance, we studied the diversification dynamics of the monocot family Velloziaceae. In addition to being conspicuously richer in the Neotropics compared to the Palaeotropics, many species of Velloziaceae exhibit extreme desiccation tolerance (i.e. 'resurrection' behaviour), and other ecological specializations to life on rocky outcrops, poor sandy soils, open vegetation and seasonally dry climates. Velloziaceae is also ecologically dominant in the campos rupestres, a habitat having exceptionally high plant diversity and endemism in Brazil.

Methods

We reconstructed a densely sampled time-calibrated molecular phylogeny and used state-dependent and state-independent models to estimate rates of lineage diversification in relation to continent-scale geographical occurrence and functional traits associated with desiccation tolerance and water storage capacity.

Key Results

Independent shifts to faster diversification occurred within two Neotropical lineages, Vellozia and Barbacenia. The Vellozia radiation was associated with the presence of conspicuous aerial stems, and was followed by decreasing diversification rates during the Oligocene, a time of rising global temperatures and expanding open areas around the world. The Barbacenia radiation was faster and more recent, occurring during the cooling conditions of the Miocene, and associated with the acquisition of aquiferous parenchyma on the leaves.

Conclusions

High species richness of Velloziaceae in South America has been driven by faster diversification in lineages predominantly occurring in the campos rupestres, putatively by the evolution of adaptive strategies in response to independent climatic events. The radiation of Vellozia in particular might have played a key role in the assembly of the campos rupestres vegetation.

Feeding ecology and sexual dimorphism in a speciose flower beetle clade (Hopliini: Scarabaeidae)

The relationship between feeding ecology and sexual dimorphism is examined in a speciose South African monkey beetle clade. We test whether feeding and mating at a fixed site (embedding guild) is associated with greater levels of sexual dimorphism and possibly sexual selection than species using unpredictable feeding resources (non-embedding guild). Sexual dimorphism was measured using a point scoring system for hind leg and colour across the two feeding guilds for >50% of the regional fauna. Quantification of hind leg dimorphism using a scoring system and allometric scaling were used to identify traits subject to sexual selection. Feeding guild had a significant effect on hind leg dimorphism, with embedders having high and non-embedders low scores. The sessile and defendable distribution of females on stable platform flowers may favour contests and associated hind leg weaponry. In contrast, degree of colour dimorphism between the sexes was not associated with any particular feeding guild, and may serve to reduce male conflict and combat. Embedder males had high proportions (∼76%) of species with positive allometric slopes for almost all hind leg traits. For male non-embedders, only ∼37% of species showed positive scaling relationships. Phylogenetic data, in conjunction with behavioural data on the function of leg weaponry and visual signalling among males is needed to better understand the link between sexual dimorphism and sexual selection in the radiation of the monkey beetles.

Humidity-dependent wound sealing in succulent leaves of Delosperma cooperi - An adaptation to seasonal drought stress

During evolution, plants evolved various reactions to wounding. Fast wound sealing and subsequent healing represent a selective advantage of particular importance for plants growing in arid habitats. An effective self-sealing function by internal deformation has been found in the succulent leaves of Delosperma cooperi. After a transversal incision, the entire leaf bends until the wound is closed. Our results indicate that the underlying sealing principle is a combination of hydraulic shrinking and swelling as the main driving forces and growth-induced mechanical pre-stresses in the tissues. Hydraulic effects were measured in terms of the relative bending angle over 55 minutes under various humidity conditions. The higher the relative air humidity, the lower the bending angle. Negative bending angles were found when a droplet of liquid water was applied to the wound. The statistical analysis revealed highly significant differences of the single main effects such as "humidity conditions in the wound region" and "time after wounding" and their interaction effect. The centripetal arrangement of five tissue layers with various thicknesses and significantly different mechanical properties might play an additional role with regard to mechanically driven effects. Injury disturbs the mechanical equilibrium, with pre-stresses leading to internal deformation until a new equilibrium is reached. In the context of self-sealing by internal deformation, the highly flexible wide-band tracheids, which form a net of vascular bundles, are regarded as paedomorphic tracheids, which are specialised to prevent cell collapse under drought stress and allow for building growth-induced mechanical pre-stresses.

Evolutionary dynamism in bryophytes: Phylogenomic inferences confirm rapid radiation in the moss family Funariaceae

Rapid diversifications of plants are primarily documented and studied in angiosperms, which are perceived as evolutionarily dynamic. Recent studies have, however, revealed that bryophytes have also undergone periods of rapid radiation. The speciose family Funariaceae, including the model taxon Physcomitrella patens, is one such lineage. Here, we infer relationships among major lineages within the Entosthodon-Physcomitrium complex from virtually complete organellar exomes (i.e., 123 genes) obtained through high throughput sequencing of genomic libraries enriched in these loci via targeted locus capture. Based on these extensive exonic data we (1) reconstructed a robust backbone topology of the Funariaceae, (2) confirmed the monophyly of Funaria and the polyphyly of Entosthodon, Physcomitrella, and Physcomitrium, and (3) argue for the occurrence of a rapid radiation within the Entosthodon-Physcomitrium complex that began 28 mya and gave rise more than half of the species diversity of the family. This diversification may have been triggered by a whole genome duplication and coincides with global Eocene cooling that continued through the Oligocene and Miocene. The Funariaceae join a growing list of bryophyte lineages whose history is marked by at least one burst of diversification, and our study thereby strengthens the view that bryophytes are evolutionarily dynamic lineages and that patterns and processes characterizing the evolution of angiosperms may be universal among land plants.

Adaptive radiations should not be simplified: The case of the danthonioid grasses

Although much of extant diversity is probably the product of evolutionary radiations, the special case of adaptive radiations has not yet been thoroughly explored. Adaptive radiations are postulated to occur when a lineage is exposed to new ecological opportunities, where it can diversify ecologically. We argue that adaptive radiations have two characteristics. Firstly, the diversification rate accelerates initially, and is then followed by a density-dependent slow-down. Secondly, traits relevant to the new ecological opportunity should evolve at or just before the radiation. We also argue that a correct identification of adaptive radiations is dependent on the phylogenies underlying the diversification dynamics being sampled adequately (i.e. comprehensive species sampling), and that the traits should be treated continuously if they exhibit a biological continuum and not be over-simplified into binary traits. Here, we test the hypothesis that much of the extant diversity of the south-temperate grass subfamily Danthonioideae is the result of two geographically separated but contemporaneous adaptive radiations, in response to Late-Miocene-Pliocene aridification and increasingly seasonal climates. We show that both Pentameris (83 African species) and Rytidosperma (73 Australasian-South American species) exhibit accelerations in diversification rates followed by linear density-dependent declines. We also show that two selected traits show differential evolutionary regimes with different evolutionary optima, and that these are linked to changes in the diversification rate. These results are consistent with these being adaptive, and putatively parallel, radiations. However, by mapping traits over the whole danthonioid phylogeny, it is evident that no identified trait or trait combination is sufficient and necessary for adaptive radiations. Furthermore, we show that simplifying the traits to binary gives a strong but potentially erroneous link between trait shift and diversification rate shift.

Plant size: a key determinant of diversification?

Explaining the variation in diversification rate across groups of plants has long been an important goal of botanists. In plants, complex scenarios involving a combination of extrinsic opportunities and intrinsic traits have been used to explain rapid diversification in certain groups. However, we feel that a very simple trait has been neglected from theories of plant diversification, namely plant height. Here, we argue that decreasing plant size should generally lead to an increase in speciation rate and a decrease in extinction rate. Theory suggests that all population genetic processes involved in speciation are influenced by plant size and its correlates, including seed dispersal distance, population size, generation time and the spatial scale at which plants perceive environmental heterogeneity. In addition, several of these variables, notably population size, also influence rates of extinction. We support our arguments with an empirical analysis showing that plant height is indeed negatively correlated with net diversification rate across families of angiosperms. Finally, we outline how the finer aspects of our hypothesis could be tested, at both micro- and macroevolutionary scales. In addition to strengthening our understanding of the effect of plant size on evolutionary processes, such a research agenda should contribute novel insights to speciation theory in general.

RADseq dataset with 90% missing data fully resolves recent radiation of Petalidium (Acanthaceae) in the ultra-arid deserts of Namibia

Deserts, even those at tropical latitudes, often have strikingly low levels of plant diversity, particularly within genera. One remarkable exception to this pattern is the genus Petalidium (Acanthaceae), in which 37 of 40 named species occupy one of the driest environments on Earth, the Namib Desert of Namibia and neighboring Angola. To contribute to understanding this enigmatic diversity, we generated RADseq data for 47 accessions of Petalidium representing 22 species. We explored the impacts of 18 different combinations of assembly parameters in de novo assembly of the data across nine levels of missing data plus a best practice assembly using a reference Acanthaceae genome for a total of 171 sequence datasets assembled. RADseq data assembled at several thresholds of missing data, including 90% missing data, yielded phylogenetic hypotheses of Petalidium that were confidently and nearly fully resolved, which is notable given that divergence time analyses suggest a crown age for African species of 3.6-1.4 Ma. De novo assembly of our data yielded the most strongly supported and well-resolved topologies; in contrast, reference-based assembly performed poorly, perhaps due in part to moderate phylogenetic divergence between the reference genome, Ruellia speciosa, and the ingroup. Overall, we found that Petalidium, despite the harshness of the environment in which species occur, shows a net diversification rate (0.8-2.1 species per my) on par with those of diverse genera in tropical, Mediterranean, and alpine environments.

Out of southern Africa: Origin, biogeography and age of the Aizooideae (Aizoaceae)

The Aizooideae is an early-diverging lineage within the Aizoaceae. It is most diverse in southern Africa, but also has endemic species in Australasia, Eurasia and South America. We derived a phylogenetic hypothesis from Bayesian and Maximum Likelihood analyses of plastid DNA-sequences. We find that one of the seven genera, the fynbos-endemic Acrosanthes, does not belong to the Aizooideae, but is an ancient sister-lineage to the subfamilies Mesembryanthemoideae & Ruschioideae. Galenia and Plinthus are embedded inside Aizoon and Aizoanthemum is polyphyletic. The Namibian endemic Tetragonia schenckii is sister to Tribulocarpus of the Sesuvioideae. For the Aizooideae, we explored their possible age by means of relaxed Bayesian dating and used Bayesian Binary MCMC reconstruction of ancestral areas to investigate their area of origin. Early diversification occurred in southern Africa in the Eocene-Oligocene, with a split into a mainly African lineage and an Eurasian-Australasian-African-South American lineage. These subsequently radiated in the early Miocene. For Tetragonia, colonisation of Australasia via long-distance dispersal from Eurasia gave rise to the Australasian lineage from which there were subsequent dispersals to South America and Southern Africa. Despite the relatively old age of the Aizooideae, more than half the species have radiated since the Pleiocene, coinciding with the large and rapid diversification of the Ruschioideae. The lineage made up of Tetragonia schenckii &Tribulocarpus split from the remainder of the Sesuvioideae already in the mid Oligocene and its disjunct distribution between Namibia and north-east Africa may be the result of a previously wider distribution within an early Arid African flora. Our reconstruction of ancestral character-states indicates that the expanding keels giving rise to hygrochastic fruits originated only once, i.e. after the split of the Sesuvioideae from the remainder of the Aizoaceae and that they were subsequently lost many times. Variously winged and spiky fruits, adapted to dispersal by wind and animals, have evolved independently in the Aizooideae and the Sesuvioideae. There is then a greater diversity of dispersal systems in the earlier lineages than in the Mesembryanthemoideae and Ruschioideae, where dispersal is mainly achieved by rain.

Evolutionary history of a keystone pollinator parallels the biome occupancy of angiosperms in the Greater Cape Floristic Region

The Greater Cape Floristic Region (GCFR) in South Africa has been extensively investigated for its phenomenal angiosperm diversity. A key emergent pattern is the occurrence of older plant lineages in the southern Fynbos biome and younger lineages in the northern Succulent Karoo biome. We know practically nothing, however, about the evolutionary history of the animals that pollinate this often highly-specialized flora. In this study, we explore the evolutionary history of an important GCFR fly pollinator, Megapalpus capensis, and ask whether it exhibits broadly congruent genetic structuring and timing of diversification to flowering plants within these biomes. We find that the oldest M. capensis lineages originated in Fynbos during the Miocene, while younger Succulent Karoo lineages diverged in the Pliocene and correspond to the proposed age of this recent biome. A strong signature of population expansion is also recovered for flies in this arid biome, consistent with recent colonization. Our first investigation into the evolutionary history of GCFR pollinators thus supports a recent origin of the SK biome, as inferred from angiosperm phylogenies, and suggests that plants and pollinators may have co-diverged within this remarkable area.