Allopatric diversification, multiple habitat shifts, and hybridization in the evolution of Pericallis (Asteraceae), a Macaronesian endemic genus

The role of geography, ecology, and hybridization in the evolutionary history of Canary Island Descurainia

PREMISE

Oceanic islands offer the opportunity to understand evolutionary processes underlying rapid diversification. Along with geographic isolation and ecological shifts, a growing body of genomic evidence has suggested that hybridization can play an important role in island evolution. Here we use genotyping-by-sequencing (GBS) to understand the roles of hybridization, ecology, and geographic isolation in the radiation of Canary Island Descurainia (Brassicaceae).

METHODS

We carried out GBS for multiple individuals of all Canary Island species and two outgroups. Phylogenetic analyses of the GBS data were performed using both supermatrix and gene tree approaches and hybridization events were examined using D-statistics and Approximate Bayesian Computation. Climatic data were analyzed to examine the relationship between ecology and diversification.

RESULTS

Analysis of the supermatrix data set resulted in a fully resolved phylogeny. Species networks suggest a hybridization event has occurred for D. gilva, with these results being supported by Approximate Bayesian Computation analysis. Strong phylogenetic signals for temperature and precipitation indicate one major ecological shift within Canary Island Descurainia.

CONCLUSIONS

Inter-island dispersal played a significant role in the diversification of Descurainia, with evidence of only one major shift in climate preferences. Despite weak reproductive barriers and the occurrence of hybrids, hybridization appears to have played only a limited role in the diversification of the group with a single instance detected. The results highlight the need to use phylogenetic network approaches that can simultaneously accommodate incomplete lineage sorting and gene flow when studying groups prone to hybridization; patterns that might otherwise be obscured in species trees.

Insect Antifeedant Benzofurans from Pericallis Species

In this work, we have studied the benzofurans of Pericallis echinata (aerial parts and transformed roots), P. steetzii (aerial parts and transformed roots), P. lanata (aerial parts), and P. murrayi (aerial parts and roots). This work has permitted the isolation of the new benzofurans 10-ethoxy-11-hydroxy-10,11-dihydroeuparin (10), (-)-eupachinin A ethyl ether (12), 11,15-didehydro-eupachinin A (13), 10,12-dihydroxy-11-angelyloxy-10,11-dihydroeuparin (14), 2,4-dihydroxy-5-formyl-acetophenone (15) isolated for the first time as a natural product, 11-angelyloxy-10,11-dihydroeuparin (16), and 12-angelyloxyeuparone (17), along with several known ones (1-9, 11). In addition, the incubation of the abundant component, 6-hydroxytremetone (1), with the fungus Mucor plumbeus has been studied. Benzofurans in the tremetone series (1, 1a, 2-5, 18, 18a), the euparin series (6, 7, 7a, 8-10, 14, 16), and the eupachinin-type (11, 12) were tested for antifeedant effects against the insect Spodoptera littoralis. The antifeedant compounds (1, 4, 6, 11, 12) were further tested for postingestive effects on S. littoralis larvae. The most antifeedant compounds were among the tremetone series, with 3-ethoxy-hydroxy-tremetone (4) being the strongest antifeedant. Glucosylation of 1 by its biotransformation with Mucor plumbeus gave inactive products. Among the euparin series, the dihydroxyangelate 14 was the most active, followed by euparin (6). The eupachinin-type compounds (11, 12) were both antifeedants. Compounds 4, 11, and 12 showed antifeedant effects without postingestive toxicity to orally dosed S. littoralis larvae. Euparin (6) had postingestive toxicity that was enhanced by the synergist piperonyl butoxide.

Evolution and conservation genetics of an insular hemiparasitic plant lineage at the limit of survival: the case of Thesium sect. Kunkeliella in the Canary Islands

PREMISE

The diversification of island flora has been widely studied. However, the role of environmental niches in insular radiation processes has been less investigated. We combined population genetic analyses with species distribution modelling to clarify the genetic relationships, diversification patterns, species niche requirements, and conservation of Thesium sect. Kunkeliella, a clade of rare hemiparasitic plants endemic to the Canaries.

METHODS

We studied the three extant Thesium species and a new taxon from La Palma Island. We developed 12 microsatellites and performed population genetic analysis and studied the demographic history of the group. To evaluate the role of niche conservatism in the diversification of the group, we performed species distribution modelling (ESM) with four algorithms.

RESULTS

All species presented moderate genetic diversity values for rare endemics. Thesium canariense (Gran Canaria) showed high differentiation, whereas T. subsucculentum, T. retamoides (Tenerife), and La Palma populations are closely related. The lineage may have undergone a recent diversification with colonization proceeding east to west, with T. canariense as sister to the others. We detected a climatic niche shift, as taxa showed different distributions across the temperature gradient. There is enough evidence to describe La Palma populations as a new species.

CONCLUSIONS

We characterized the evolutionary history of Thesium sect. Kunkeliella by integrating genetic and ecological assessments. Our results indicate that this clade has undergone a recent radiation process with niche differentiation among species. The results increase our knowledge about insular radiations and will inform the conservation management of the study species.

Plastome Diversity and Phylogenomic Relationships in Asteraceae

Plastid genomes are in general highly conserved given their slow evolutionary rate, and thus large changes in their structure are unusual. However, when specific rearrangements are present, they are often phylogenetically informative. Asteraceae is a highly diverse family whose evolution is long driven by polyploidy (up to 48x) and hybridization, both processes usually complicating systematic inferences. In this study, we generated one of the most comprehensive plastome-based phylogenies of family Asteraceae, providing information about the structure, genetic diversity and repeat composition of these sequences. By comparing the whole-plastome sequences obtained, we confirmed the double inversion located in the long single-copy region, for most of the species analyzed (with the exception of basal tribes), a well-known feature for Asteraceae plastomes. We also showed that genome size, gene order and gene content are highly conserved along the family. However, species representative of the basal subfamily Barnadesioideae-as well as in the sister family Calyceraceae-lack the pseudogene rps19 located in one inverted repeat. The phylogenomic analysis conducted here, based on 63 protein-coding genes, 30 transfer RNA genes and 21 ribosomal RNA genes from 36 species of Asteraceae, were overall consistent with the general consensus for the family's phylogeny while resolving the position of tribe Senecioneae and revealing some incongruences at tribe level between reconstructions based on nuclear and plastid DNA data.

Macaronesia as a Fruitful Arena for Ecology, Evolution, and Conservation Biology

Research in Macaronesia has led to substantial advances in ecology, evolution and conservation biology. We review the scientific developments achieved in this region, and outline promising research avenues enhancing conservation. Some of these discoveries indicate that the Macaronesian flora and fauna are composed of rather young lineages, not Tertiary relicts, predominantly of European origin. Macaronesia also seems to be an important source region for back-colonisation of continental fringe regions on both sides of the Atlantic. This group of archipelagos (Azores, Madeira, Selvagens, Canary Islands, and Cabo Verde) has been crucial to learn about the particularities of macroecological patterns and interaction networks on islands, providing evidence for the development of the General Dynamic Model of oceanic island biogeography and subsequent updates. However, in addition to exceptionally high richness of endemic species, Macaronesia is also home to a growing number of threatened species, along with invasive alien plants and animals. Several innovative conservation and management actions are in place to protect its biodiversity from these and other drivers of global change. The Macaronesian Islands are a well-suited field of study for island ecology and evolution research, mostly due to its special geological layout with 40 islands grouped within five archipelagos differing in geological age, climate and isolation. A large amount of data is now available for several groups of organisms on and around many of these islands. However, continued efforts should be made toward compiling new information on their biodiversity, to pursue various fruitful research avenues and develop appropriate conservation management tools.

The importance of environmental conditions in maintaining lineage identity in Epithelantha (Cactaceae)

The use of environmental variables to explain the evolution of lineages has gained relevance in recent studies. Additionally, it has allowed the recognition of species by adding more characters to morphological and molecular information. This study focuses on identifying environmental and landscape variables that have acted as barriers that could have influenced the evolution of Epithelantha species and its close genera.Our results show that soil pH, isothermality, temperature seasonality, and annual precipitation have a significant phylogenetic signal for Epithelantha. Soil type and landforms are also relevant as ecological barriers that maintain the identity of Epithelantha species.The variables associated with the soil (pH) have influenced the evolution of Epithelantha and probably in other genera of Cactaceae. Additionally, Epithelantha is frequent in the piedmont and haplic kastanozems. Bioclimatic variables reinforce the recognition of E. micromeris, and E. cryptica as independent species. Therefore, ecology can be considered as a factor to explain the high level of endemism in Cactaceae.

Reconstruction of the spatio-temporal diversification and ecological niche evolution of Helianthemum (Cistaceae) in the Canary Islands using genotyping-by-sequencing data

BACKGROUND AND AIMS

Several biogeographical models have been proposed to explain the colonization and diversification patterns of Macaronesian lineages. In this study, we calculated the diversification rates and explored what model best explains the current distribution of the 15 species endemic to the Canary Islands belonging to Helianthemum sect. Helianthemum (Cistaceae).

METHODS

We performed robust phylogenetic reconstructions based on genotyping-by-sequencing data and analysed the timing, biogeographical history and ecological niche conservatism of this endemic Canarian clade.

KEY RESULTS

Our phylogenetic analyses provided strong support for the monophyly of this clade, and retrieved five lineages not currently restricted to a single island. The pristine colonization event took place in the Pleistocene (~1.82 Ma) via dispersal to Tenerife by a Mediterranean ancestor.

CONCLUSIONS

The rapid and abundant diversification (0.75-1.85 species per million years) undergone by this Canarian clade seems the result of complex inter-island dispersal events followed by allopatric speciation driven mostly by niche conservatism, i.e. inter-island dispersal towards niches featuring similar environmental conditions. Nevertheless, significant instances of ecological niche shifts have also been observed in some lineages, making an important contribution to the overall diversification history of this clade.

Geographical isolation, habitat shifts and hybridisation in the diversification of the Macaronesian endemic genus Argyranthemum (Asteraceae)

Inferring the processes responsible for the rich endemic diversity of oceanic island floras is important for our understanding of plant evolution and setting practical conservation priorities. This requires an accurate knowledge of phylogenetic relationships, which have often been difficult to resolve due to a lack of genetic variation. We employed genotyping-by-sequencing (GBS) to investigate how geographical isolation, habitat shifts, and hybridisation have contributed to the evolution of diversity observed in Argyranthemum Webb (Asteraceae), the largest genus of flowering plants endemic to the Macaronesian archipelagos. Species relationships were resolved, and biogeographical stochastic mapping identified intra-island speciation as the most frequent biogeographic process underlying diversification, contrary to the prevailing view in Argyranthemum and the Canary Islands. D-statistics revealed significant evidence of hybridisation between lineages co-occurring on the same island, however there was little support for the hypothesis that hybridisation may be responsible for the occurrence of nonmonophyletic multi-island endemic (MIE) species. Geographic isolation, habitat shifts and hybridisation have all contributed to the diversification of Argyranthemum, with intra-island speciation found to be more frequent than previously thought. Morphological convergence is also proposed to explain the occurrence of nonmonophyletic MIE species. This study reveals greater complexity in the evolutionary processes generating Macaronesian endemic diversity.

Molecular phylogenetics of Lotus (Leguminosae) with emphasis in the tempo and patterns of colonization in the Macaronesian region

With a wide distribution range including Europe and Asia, Lotus (Leguminosae) represents the largest genus within Loteae. It is particularly diverse in the Mediterreanean region and in the five archipelagos of Macaronesia (Atlantic Ocean). However, little is known about the relationships among the 14 sections currently recognized within Lotus and about the timing and patterns of its colonization in the Macaronesian region. In this investigation, we use four DNA regions (nuclear ribosomal ITS plus three plastid regions) in the most comprehensive sampling of Lotus species to date (some endemic species within the Canary Islands were poorly represented in previous phylogenetic analyses) to infer relationships within this genus and to establish patterns of colonization in Macaronesia. Divergence time estimates and habitat reconstruction analyses indicate that Lotus likely diverged about 7.86 Ma from its sister group, but all colonization events to Macaronesia occurred more recently (ranging from the last 0.23 to 2.70 Ma). The diversification of Lotus in Macaronesia involved between four and six independent colonization events from four sections currently distributed in Africa and Europe. A major aspect shaping the current distribution of taxa involved intra-island colonization of mainly new habitats and inter-island colonization of mostly similar habitats, with Gran Canaria and Tenerife as the major sources of diversification and of further colonization events. Section Pedrosia is the most diverse in terms of colonization events, number of species, and habitat heterogeneity, including a back-colonization event to the continent. Subsections within Pedrosia radiated into diverse habitat types recently (late Pleistocene, ca 0.23-0.29 Ma) and additional molecular markers and sampling would be necessary to understand the most recent dispersal events of this group within the Canary Islands and Cape Verde.

Fernández de Castro A, Seguí J, Traveset A, Sosa PA. Alpine species in dynamic insular ecosystems through time: conservation genetics and niche shift estimates of the endemic and vulnerable Viola cheiranthifolia

BACKGROUND AND AIMS

Alpine oceanic ecosystems are considered amongst the most ephemeral and restricted habitats, with a biota highly vulnerable to climate changes and disturbances. As an example of an alpine insular endemic, the past and future population genetic structure and diversity, and the future distribution of Viola cheiranthifolia (Violaceae), endemic to Tenerife (Canary Islands), were estimated. The main goals were to predict distribution changes of this alpine oceanic plant under climate change, and to assist in actions for its conservation.

METHODS

To perform population genetic analysis, 14 specific microsatellite markers and algorithms which considered the polyploid condition of V. cheiranthifolia were employed. The niche modelling approach incorporated temperature gradients, topography and snow cover maps. Models were projected into climate change scenarios to assess the extent of the altitudinal shifts of environmental suitability. Finally, simulations were performed to predict whether the environmental suitability loss will affect the genetic diversity of populations.

KEY RESULTS

Viola cheiranthifolia presents short dispersal capacity, moderate levels of genetic diversity and a clear population genetic structure divided into two main groups (Teide and Las Cañadas Wall), showing signs of recolonization dynamics after volcanic eruptions. Future estimates of the distribution of the study populations also showed that, despite being extremely vulnerable to climate change, the species will not lose all its potential area in the next decades. The simulations to estimate genetic diversity loss show that it is correlated to suitability loss, especially in Las Cañadas Wall.

CONCLUSIONS

The low dispersal capacity of V. cheiranthifolia, coupled with herbivory pressure, mainly from rabbits, will make its adaptation to future climate conditions in this fragile alpine ecosystem difficult. Conservation actions should be focused on herbivore control, population reinforcement and surveillance of niche shifts, especially in Guajara, which represents the oldest isolated population and a genetic reservoir for the species.

How repeatable is microevolution on islands? Patterns of dispersal and colonization-related plant traits in a phylogeographical context

BACKGROUND AND AIMS

Archipelagos provide a valuable framework for investigating phenotypic evolution under different levels of geographical isolation. Here, we analysed two co-distributed, widespread plant lineages to examine if incipient island differentiation follows parallel patterns of variation in traits related to dispersal and colonization.

METHODS

Twenty-one populations of two anemochorous Canarian endemics, Kleinia neriifolia and Periploca laevigata, were sampled to represent mainland congeners and two contrasting exposures across all the main islands. Leaf size, seed size and dispersability (estimated as diaspore terminal velocity) were characterized in each population. For comparison, dispersability was also measured in four additional anemochorous island species. Plastid DNA data were used to infer genetic structure and to reconstruct the phylogeographical pattern of our focal species.

KEY RESULTS

In both lineages, mainland-island phenotypic divergence probably started within a similar time frame (i.e. Plio-Pleistocene). Island colonization implied parallel increases in leaf size and dispersability, but seed size showed opposite patterns of variation between Kleinia and Periploca species pairs. Furthermore, dispersability in our focal species was low when compared with other island plants, mostly due to large diaspore sizes. At the archipelago scale, island exposure explained a significant variation in leaf size across islands, but not in dispersability or seed size. Combined analyses of genetic and phenotypic data revealed two consistent patterns: (1) extensive within-island but very limited among-island dispersal, and (2) recurrent phenotypic differentiation between older (central) and younger (peripheral) island populations.

CONCLUSIONS

Leaf size follows a more predictable pattern than dispersability, which is affected by stochastic shifts in seed size. Increased dispersability is associated with high population connectivity at the island scale, but does not preclude allopatric divergence among islands. In sum, phenotypic convergent patterns between species suggest a major role of selection, but deviating traits also indicate the potential contribution of random processes, particularly on peripheral islands.

Phylogeography of the Macaronesian Lettuce Species Lactuca watsoniana and L. palmensis (Asteraceae)

The phylogenetic relationships and phylogeography of two relatively rare Macaronesian Lactuca species, Lactuca watsoniana (Azores) and L. palmensis (Canary Islands), were, until this date, unclear. Karyological information of the Azorean species was also unknown. For this study, a chromosome count was performed and L. watsoniana showed 2n = 34. A phylogenetic approach was used to clarify the relationships of the Azorean endemic L. watsoniana and the La Palma endemic L. palmensis within the subtribe Lactucinae. Maximum parsimony, Maximum likelihood and Bayesian analysis of a combined molecular dataset (ITS and four chloroplast DNA regions) and molecular clock analyses were performed with the Macaronesian Lactuca species, as well as a TCS haplotype network. The analyses revealed that L. watsoniana and L. palmensis belong to different subclades of the Lactuca clade. Lactuca watsoniana showed a strongly supported phylogenetic relationship with North American species, while L. palmensis was closely related to L. tenerrima and L. inermis, from Europe and Africa. Lactuca watsoniana showed four single-island haplotypes. A divergence time estimation of the Macaronesian lineages was used to examine island colonization pathways. Results obtained with BEAST suggest a divergence of L. palmensis and L. watsoniana clades c. 11 million years ago, L. watsoniana diverged from its North American sister species c. 3.8 million years ago and L. palmensis diverged from its sister L. tenerrima, c. 1.3 million years ago, probably originating from an African ancestral lineage which colonized the Canary Islands. Divergence analyses with *BEAST indicate a more recent divergence of the L. watsoniana crown, c. 0.9 million years ago. In the Azores colonization, in a stepping stone, east-to-west dispersal pattern, associated with geological events might explain the current distribution range of L. watsoniana.

Genetic diversity and differentiation patterns in Micromeria from the Canary Islands are congruent with multiple colonization dynamics and the establishment of species syngameons

Background

Especially on islands closer to the mainland, such as the Canary Islands, different lineages that originated by multiple colonization events could have merged by hybridization, which then could have promoted radiation events (Herben et al., J Ecol 93: 572–575, 2005; Saunders and Gibson, J Ecol 93: 649–652, 2005; Caujapé-Castells, Jesters, red queens, boomerangs and surfers: a molecular outlook on the diversity of the Canarian endemic flora, 2011). This is an alternative to the scenario where evolution is mostly driven by drift (Silvertown, J Ecol 92: 168–173, 2004; Silvertown et al., J Ecol 93: 653–657, 2005). In the former case hybridization should be reflected in the genetic structure and diversity patterns of island species. In the present work we investigate Micromeria from the Canary Islands by extensively studying their phylogeographic pattern based on 15 microsatellite loci and 945 samples. These results are interpreted according to the hypotheses outlined above.

Results

Genetic structure assessment allowed us to genetically differentiate most Micromeria species and supported their current classification. We found that populations on younger islands were significantly more genetically diverse and less differentiated than those on older islands. Moreover, we found that genetic distance on younger islands was in accordance with an isolation-by-distance pattern, while on the older islands this was not the case. We also found evidence of introgression among species and islands.

Conclusions

These results are congruent with a scenario of multiple colonizations during the expansion onto new islands. Hybridization contributes to the grouping of multiple lineages into highly diverse populations. Thus, in our case, islands receive several colonization events from different sources, which are combined into sink populations. This mechanism is in accordance with the surfing syngameon hypothesis. Contrary to the surfing syngameon current form, our results may reflect a slightly different effect: hybridization might always be related to colonization within the archipelago as well, making initial genetic diversity to be high to begin with. Thus the emergence of new islands promotes multiple colonization events, contributing to the establishment of hybrid swarms that may enhance adaptive ability and radiation events. With time, population sizes grow and niches start to fill. Consequently, gene-flow is not as effective at maintaining the species syngameon, which allows genetic differentiation and reproductive isolation to be established between species. This process contributes to an even further decrease in gene-flow between species.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-017-1031-y) contains supplementary material, which is available to authorized users.

Why do different oceanic archipelagos harbour contrasting levels of species diversity? The macaronesian endemic genus Pericallis (Asteraceae) provides insight into explaining the 'Azores diversity Enigma'

Background

Oceanic archipelagos typically harbour extensive radiations of flowering plants and a high proportion of endemics, many of which are restricted to a single island (Single Island Endemics; SIEs). The Azores represents an anomaly as overall levels of endemism are low; there are few SIEs and few documented cases of intra-archipelago radiations. The distinctiveness of the flora was first recognized by Darwin and has been referred to as the ‘Azores Diversity Enigma’ (ADE). Diversity patterns in the Macaronesian endemic genus Pericallis (Asteraceae) exemplify the ADE. In this study we used morphometric, Amplified Length Polymorphisms, and bioclimatic data for herbaceous Pericallis lineages endemic to the Azores and the Canaries, to test two key hypotheses proposed to explain the ADE: i) that it is a taxonomic artefact or Linnean shortfall, ie. the under description of taxa in the Azores or the over-splitting of taxa in the Canaries and (ii) that it reflects the greater ecological homogeneity of the Azores, which results in limited opportunity for ecological diversification compared to the Canaries.

Results

In both the Azores and the Canaries, morphological patterns were generally consistent with current taxonomic classifications. However, the AFLP data showed no genetic differentiation between the two currently recognized Azorean subspecies that are ecologically differentiated. Instead, genetic diversity in the Azores was structured geographically across the archipelago. In contrast, in the Canaries genetic differentiation was mostly consistent with morphology and current taxonomic treatments. Both Azorean and Canarian lineages exhibited ecological differentiation between currently recognized taxa.

Conclusions

Neither a Linnean shortfall nor the perceived ecological homogeneity of the Azores fully explained the ADE-like pattern observed in Pericallis. Whilst variation in genetic data and morphological data in the Canaries were largely congruent, this was not the case in the Azores, where genetic patterns reflected inter-island geographical isolation, and morphology reflected intra-island bioclimatic variation. The combined effects of differences in (i) the extent of geographical isolation, (ii) population sizes and (iii) geographical occupancy of bioclimatic niche space, coupled with the morphological plasticity of Pericallis, may all have contributed to generating the contrasting patterns observed in the archipelagos.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-016-0766-1) contains supplementary material, which is available to authorized users.

Viola woosanensis, a recurrent spontaneous hybrid between V. ulleungdoensis and V. chaerophylloides (Violaceae) endemic to Ulleung Island, Korea

Ulleung Island is an oceanic volcanic island in Korea, which has never been connected to the adjacent continent. Previous studies highlighted Ulleung Island as an excellent system to study the pattern and process of early stages of flowering plant evolutions on oceanic island. The predominant mode of speciation in flowering plants on Ulleung Island appears to be anagenesis. However, the potentially important role of hybrid speciation among incompletely reproductively isolated lineages cannot be ruled out. Viola woosanensis (Violaceae) is of purportedly hybrid origin between V. ulleungdoensis (i.e., formerly recognized as V. selkirkii in Ulleung Island) and V. chaerophylloides, based on morphology. To examine the origin of V. woosanensis, we sampled a total of 80 accessions, including V. woosanensis and its putative parental species and sequenced nrDNA ITS, and four highly variable chloroplast noncoding regions (trnL-trnF, rpl16 intron, atpF-atpH, and psbA-trnH). Representative species of Viola from Korea were also included in the phylogenetic analyses (maximum parsimony, maximum likelihood, and Bayesian inference). Additive polymorphic sites in the nrDNA ITS regions were confirmed by cloning amplicons from representative species. The molecular data strongly supported the hybrid origin of V. woosanensis, and the maternal and paternal parent were determined to be V. ulleungdoensis and V. chaerophylloides, respectively. The presence of two parental ribotypes in V. woosanensis (with the exception in one population) was confirmed by cloning, suggesting V. woosanensis is primarily the F1 generation. No trace of backcrossing and introgression with its parents was detected due to low fertility of hybrid species. We found a multiple and unidirectional hybrid origin of V. woosanensis. Additional studies are required to determine which factors contribute to asymmetric gene flow of Viola species in Ulleung Island.

Diversity hotspots of the laurel forest on Tenerife, Canary Islands: a phylogeographic study of Laurus and Ixanthus

BACKGROUND AND AIMS

Macaronesian laurel forest is among the worldwide hotspots of threatened biodiversity. With increasing evidence that woodland composition on the Canary Islands changed dramatically during the last few thousand years, the aim of this study was to find evidence for substantial recent population dynamics of two representative species from laurel forest.

METHODS

Amplified fragment length polymorphism (AFLP) was used to evaluate fine-scaled genetic variation of the paradigmatic tree Laurus novocanariensis (Lauraceae) and a long-lived herbaceous gentian from core laurel forest, Ixanthus viscosus (Gentianaceae), on Tenerife. Bioclimatic variables were analysed to study the respective climate niches. A chloroplast DNA screening was performed to evaluate additional genetic variation.

KEY RESULTS

Genetic diversity of the laurel tree showed severe geographic partitioning. On Tenerife, fine-scaled Bayesian clustering of genetic variation revealed a western and an eastern gene pool, separated by a zone of high admixture and with a third major gene pool. Compared with genetic clusters found on the other Canary Islands, the East-West differentiation on Tenerife seems to be more recent than differentiation between islands. This is substantiated by the finding of extremly low levels of chloroplast DNA-based polymorphisms. Ixanthus showed no geographic structuring of genetic variation.

CONCLUSIONS

Genetic data from Tenerife indicate contemporary gene flow and dispersal on a micro/local scale rather than reflecting an old and relic woodland history. In particular for Laurus, it is shown that this species occupies a broad bioclimatic niche. This is not correlated with its respective distribution of genetic variation, therefore indicating its large potential for contemporary rapid and effective colonization. Ixanthus is more specialized to humid conditions and is mostly found in the natural Monteverde húmedo vegetation types, but even for this species indications for long-term persistence in the respective bioclimatically differentiated regions was not find.

Genetic structure of Micromeria (Lamiaceae) in Tenerife, the imprint of geological history and hybridization on within-island diversification

Geological history of oceanic islands can have a profound effect on the evolutionary history of insular flora, especially in complex islands such as Tenerife in the Canary Islands. Tenerife results from the secondary connection of three paleo‐islands by a central volcano, and other geological events that further shaped it. This geological history has been shown to influence the phylogenetic history of several taxa, including genus Micromeria (Lamiaceae). Screening 15 microsatellite markers in 289 individuals representing the eight species of Micromeria present in Tenerife, this study aims to assess the genetic diversity and structure of these species and its relation with the geological events on the island. In addition, we evaluate the extent of hybridization among species and discuss its influence on the speciation process. We found that the species restricted to the paleo‐islands present lower levels of genetic diversity but the highest levels of genetic differentiation suggesting that their ranges might have contracted over time. The two most widespread species in the island, M. hyssopifolia and M. varia, present the highest genetic diversity levels and a genetic structure that seems correlated with the geological composition of the island. Samples from M. hyssopifolia from the oldest paleo‐island, Adeje, appear as distinct while samples from M. varia segregate into two main clusters corresponding to the paleo‐islands of Anaga and Teno. Evidence of hybridization and intraspecific migration between species was found. We argue that species boundaries would be retained despite hybridization in response to the habitat's specific conditions causing postzygotic isolation and preserving morphological differentiation.

Multiplexed-shotgun-genotyping data resolve phylogeny within a very recently derived insular lineage

PREMISE OF THE STUDY

Endemic plants on oceanic islands have long served as model systems for studying patterns and processes of evolution. However, phylogenetic studies of island plants frequently illustrate a decoupling of molecular divergence and ecological/morphological diversity, resulting in phylogenies lacking the resolution required to interpret patterns of evolution in a phylogenetic context. The current study uses the primarily Macaronesian flowering plant genus Tolpis to illustrate the utility of multiplexed shotgun genotyping (MSG) for resolving relationships at relatively deep (among archipelagos) and very shallow (within archipelagos) nodes in this small, yet diverse insular plant lineage that had not been resolved with other molecular markers.

METHODS

Genomic libraries for 27 accessions of Macaronesian Tolpis were generated for genotyping individuals using MSG, a form of reduced-representation sequencing, similar to restriction-site-associated DNA markers (RADseq). The resulting data files were processed using the program pyRAD, which clusters MSG loci within and between samples. Phylogenetic analyses of the aligned data matrix were conducted using RAxML.

KEY RESULTS

Analysis of MSG data recovered a highly resolved phylogeny with generally strong support, including the first robust inference of relationships within the highly diverse Canary Island clade of Tolpis.

CONCLUSIONS

The current study illustrates the utility of MSG data for resolving relationships in lineages that have undergone recent, rapid diversification resulting in extensive ecological and morphological diversity. We suggest that a similar approach may prove generally useful for other rapid plant radiations where resolving phylogeny has been difficult.

The explosive radiation of Cheirolophus (Asteraceae, Cardueae) in Macaronesia

Background

Considered a biodiversity hotspot, the Canary Islands have been the key subjects of numerous evolutionary studies concerning a large variety of organisms. The genus Cheirolophus (Asteraceae) represents one of the largest plant radiations in the Canarian archipelago. In contrast, only a few species occur in the Mediterranean region, the putative ancestral area of the genus. Here, our main aim was to reconstruct the phylogenetic and biogeographic history of Cheirolophus with special focus on explaining the origin of the large Canarian radiation.

Results

We found significant incongruence in phylogenetic relationships between nuclear and plastid markers. Each dataset provided resolution at different levels in Cheirolophus: the nuclear markers resolved the backbone of the phylogeny while the plastid data provided better resolution within the Canarian clade. The origin of Cheirolophus was dated in the Mid-Late Miocene, followed by rapid diversification into the three main Mediterranean lineages and the Macaronesian clade. A decrease in diversification rates was inferred at the end of the Miocene, with a new increase in the Late Pliocene concurrent with the onset of the Mediterranean climate. Diversification within the Macaronesian clade started in the Early-Mid Pleistocene, with unusually high speciation rates giving rise to the extant insular diversity.

Conclusions

Climate-driven diversification likely explains the early evolutionary history of Cheirolophus in the Mediterranean region. It appears that the exceptionally high diversification rate in the Canarian clade was mainly driven by allopatric speciation (including intra- and interisland diversification). Several intrinsic (e.g. breeding system, polyploid origin, seed dispersal syndrome) and extrinsic (e.g. fragmented landscape, isolated habitats, climatic and geological changes) factors probably contributed to the progressive differentiation of populations resulting in numerous microendemisms. Finally, hybridization events and emerging ecological adaptation may have also reinforced the diversification process.