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The two study species Aeonium davidbramwellii (A) and Aeonium nobile (B). Photographs by Carl Beierkuhnlein and Katharina Staab, respectively.
Source publication
The Crassulacean genus Aeonium is a well-known example for plant species radiation on oceanic archipelagos. However, while allopatric speciation among islands is documented for this genus, the role of intra-island speciation due to population divergence by topographical isolation or ecological heterogeneity has not yet been addressed. The aim of th...
Contexts in source publication
Context 1
... davidbramwellii H.-Y. LIU (Fig. 1A) is a generalist species, growing on rocks, soil banks, and cliffs throughout almost every part of La Palma from 0 to 1000 m a.s.l. (Liu 1989) and up to 1800 m a.s.l. (own observations, see also Fig. 2B). It forms distinct populations but also occurs as scattered individuals and seems to be adapted to a wide range of environmental sit- ...
Context 2
... nobile (PRAEGER) PRAEGER (Fig. 1B) realizes a far more narrow ecological niche, due to its growth site restrictions to dry slopes, banks, and cliffs with high inso- lation (Liu 1989). It is thus much rarer than Ae. david- bramwellii and occurs in distinct and mostly small populations from 0 to 750 m a.s.l. (Liu 1989) and up to 1200 m a.s.l. (own observations). The ...
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... Bayesian STRUCTURE analysis revealed that K = 3 was the most likely number of genetic clusters within Ae. davidbramwellii, although K = 2 and K = 4 also showed high likelihoods, and Evanno's DK had its highest value at K = 2 (Fig. S1). Genetic structure was dominated by one cluster which determined major parts of the geno- types of all individuals ( Fig. 2A, B). However, populations H_d and J_d in the Barranco de las Angustias and its northern edge, as well as C_d in the Barranco de la Madera in the west and A_d in the Barranco Fagundo in the north of La Palma, ...
Context 4
... not definite, our study revealed basic patterns within the two analyzed species and gives additional insights into species evolution on small oceanic islands. Figure S1. Assessment of the most likely number of clus- ters of STRUCTURE runs using the method of Evanno et al. (2005) for Aeonium davidbramwellii. ...
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Citations
... Knowing the distribution of genetic diversity is of chief importance for the conservation of native populations (Francisco-Ortega et al., 2000). Nevertheless, investigations of infraspecific variation and population structure, and therefore of recent eco-evolutionary processes and potential drivers for species divergence in Aeonium, have not taken place yet (Harter et al., 2015). Furthermore, the molecular phylogenies published by Mort et al. (2002) and by Thiv et al. (2010) are largely unresolved, and several clades show very weak support. ...
The rich endemic flora of the Macaronesian Islands places these oceanic archipelagos among the top biodiversity hotspots worldwide. The radiations that have determined the evolution of many of these insular lineages resulted in a wealth of endemic species, many of which occur in a wide range of ecological niches, but show small distribution areas in each of them. Aeonium (Crassulaceae) is the most speciose lineage in the Canary Islands (ca. 40 taxa), and as such can be considered a good model system to understand the diversification dynamics of oceanic endemic floras. The present study aims to assess the genome size variation within Aeonium distribution, i.e., the Macaronesian archipelagos of Madeira, Canaries and Cabo Verde, and analyse it together with information on distribution (i.e., geography and conservation status), taxonomy (i.e., sections), morphological traits (i.e., growth-form), geological data (i.e., island's geological age), and environmental variables (i.e., altitude, annual mean temperature, and precipitation). Based on extensive fieldwork, a cytogeographic screening of 24 Aeonium species was performed. The conservation status of these species was assessed based on IUCN criteria. 61% of the taxa were found to be threatened (4% Endangered and 57% Vulnerable). For the first time, the genome size of a comprehensive sample of Aeonium across the Macaronesian archipelagos was estimated, and considerable differences in Cx-values were found, ranging from 0.984 pg (A. dodrantale) to 2.768 pg (A. gorgoneum). An overall positive correlation between genome size and conservation status was found, with the more endangered species having the larger genomes on average. However, only slight relationships were found between genome size, morphological traits, and environmental variables. These results underscore the importance of characterizing the cytogenomic diversity and conservation status of endemic plants found in Macaronesian Islands, providing, therefore, new data to establish conservation priorities.
... Knowing the distribution of genetic diversity is of chief importance for the conservation of native populations (Francisco-Ortega et al., 2000). Nevertheless, investigations of infraspecific variation and population structure, and therefore of recent eco-evolutionary processes and potential drivers for species divergence in Aeonium, have not taken place yet (Harter et al., 2015). Furthermore, the molecular phylogenies published by Mort et al. (2002) and by Thiv et al. (2010) are largely unresolved, and several clades show very weak support. ...
The rich endemic flora of the Macaronesian Islands places these oceanic archipelagos among the top biodiversity hotspots worldwide. The radiations that have determined the evolution of many of these insular lineages resulted in a wealth of endemic species, many of which occur in a wide range of ecological niches, but show small distribution areas in each of them. Aeonium (Crassulaceae) is the most speciose lineage in the Canary Islands (ca. 40 taxa), and as such can be considered a good model system to understand the diversification dynamics of oceanic endemic floras. The present study aims to assess the genome size variation within Aeonium distribution, i.e., the Macaronesian archipelagos of Madeira, Canaries and Cabo Verde, and analyse it together with information on distribution (i.e., geography and conservation status), taxonomy (i.e., sections), morphological traits (i.e., growth-form), geological data (i.e., island's geological age), and environmental variables (i.e., altitude, annual mean temperature, and precipitation). Based on extensive fieldwork, a cytogeographic screening of 24 Aeonium species was performed. The conservation status of these species was assessed based on IUCN criteria. 61% of the taxa were found to be threatened (4% Endangered and 57% Vulnerable). For the first time, the genome size of a comprehensive sample of Aeonium across the Macaronesian archipelagos was estimated, and considerable differences in Cx-values were found, ranging from 0.984 pg (A. dodrantale) to 2.768 pg (A. gorgoneum). An overall positive correlation between genome size and conservation status was found, with the more endangered species having the larger genomes on average. However, only slight relationships were found between genome size, morphological traits, and Brilhante et al. Aeonium: Genome Size and Conservation Status environmental variables. These results underscore the importance of characterizing the cytogenomic diversity and conservation status of endemic plants found in Macaronesian Islands, providing, therefore, new data to establish conservation priorities.
... We find clear patterns of climatic conditions that are reflected in the diversity and in the proportional contribution of endemic plant species to ecosystem structures and functioning (IRL et al. 2017). On the island of La Palma, habitats in low elevation that exhibit both sufficient water availability (precipitation through rain or clouds) and a high topographic complexity (steep valleys with different aspects) and respective low human impact are hot spots of species richness and also show a high diversity of both, single-island endemics and archipelago endemics (HARTER et al. 2015b). However, with increasing elevation, the proportion of endemic species rises (STEINBAUER et al. 2016(STEINBAUER et al. , 2017. ...
The Island of La Palma (Canary Islands, Spain) is protected as a whole (La Palma World Biosphere Reserve) and within this frame in parts as a national park (Caldera de Taburiente) and additionally through sites of special conservation status, and Natura 2000 sites. The island hosts a large number of archipelago endemic (AE) plant species and also single-island endemic (SIE) plants. These species even contribute substantially to local species richness, biomass and functioning of ecosystems, and they cannot be replaced through species from other regions. In consequence, there is an urgent need to detect spatial patterns and changes in the distribution and performance of these species in order to adapt the management of Protected Areas to the increasing pressures. Here, we present together with local administrative management a detailed analysis of the contribution of endemic species and of the respective threats that need to be addressed in adaptation strategies. Also we show how monitoring and the control of success can be implemented with the support of Earth Observation. The study is part of the H2020 Project ECOPOTENTIAL.
... We find clear patterns of climatic conditions that are reflected in the diversity and in the proportional contribution of endemic plant species to ecosystem structures and functioning (IRL et al. 2017). On the island of La Palma, habitats in low elevation that exhibit both sufficient water availability (precipitation through rain or clouds) and a high topographic complexity (steep valleys with different aspects) and respective low human impact are hot spots of species richness and also show a high diversity of both, single-island endemics and archipelago endemics (HARTER et al. 2015b). However, with increasing elevation, the proportion of endemic species rises (STEINBAUER et al. 2016(STEINBAUER et al. , 2017. ...
... We find clear patterns of climatic conditions that are reflected in the diversity and in the proportional contribution of endemic plant species to ecosystem structures and functioning (IRL et al. 2017). On the island of La Palma, habitats in low elevation that exhibit both sufficient water availability (precipitation through rain or clouds) and a high topographic complexity (steep valleys with different aspects) and respective low human impact are hot spots of species richness and also show a high diversity of both, single-island endemics and archipelago endemics (HARTER et al. 2015b). However, with increasing elevation, the proportion of endemic species rises (STEINBAUER et al. 2016(STEINBAUER et al. , 2017. ...
The Island of La Palma (Canary Islands, Spain) is protected as a whole (La Palma World Biosphere Reserve) and within this frame in parts as a national park (Caldera de Taburiente) and additionally through sites of special conservation status, and Natura 2000 sites. The island hosts a large number of archipelago endemic (AE) plant species and also single-island endemic (SIE) plants. These species even contribute substantially to local species richness, biomass and functioning of ecosystems, and they cannot be replaced through species from other regions. In consequence, there is an urgent need to detect spatial patterns and changes in the distribution and performance of these species in order to adapt the management of Protected Areas to the increasing pressures. Here, we present together with local administrative management a detailed analysis of the contribution of endemic species and of the respective threats that need to be addressed in adaptation strategies. Also we show how monitoring and the control of success can be implemented with the support of Earth Observation. The study is part of the H2020 Project ECOPOTENTIAL.
... This phenomenon is very like the case of Aeonium davidbramwelii and A. nobile on the island of La Palma in the Canarian archipelago: the former is an ecological generalist while the latter is an ecological specialist. There is a lack of species divergence but an obvious population structure exists (Harter et al., 2015). However, in our case, although the niche space of tpe is smaller than that of bar, their spatial distribution predicted by ENM on the basis of six bioclimatic variables is almost overlapping (Supplementary Figure 1). ...
Spatial climate heterogeneity may not only affect adaptive gene frequencies but could also indirectly shape the genetic structure of neutral loci by impacting demographic dynamics. In this study, the effect of local climate on population genetic variation was tested in two phylogenetically close Scutellaria species in Taiwan. Scutellaria taipeiensis, which was originally assumed to be an endemic species of Taiwan Island, is shown to be part of the widespread species S. barbata based on the overlapping ranges of genetic variation and climatic niches as well as their morphological similarity. Rejection of the scenario of “early divergence with secondary contact” and the support for multiple origins of populations of S. taipeiensis from S. barbata provide strong evolutionary evidence for a taxonomic revision of the species combination. Further tests of a climatic effect on genetic variation were conducted. Regression analyses show nonlinear correlations among any pair of geographic, climatic, and genetic distances. However, significantly, the bioclimatic variables that represent the precipitation from late summer to early autumn explain roughly 13% of the genetic variation of our sampled populations. These results indicate that spatial differences of precipitation in the typhoon season may influence the regeneration rate and colonization rate of local populations. The periodic typhoon episodes explain the significant but nonlinear influence of climatic variables on population genetic differentiation. Although, the climatic difference does not lead to species divergence, the local climate variability indeed impacts the spatial genetic distribution at the population level.
... Environmental association studies have formerly concentrated on the correlation between genetic and geographic distances to analyze IBD, while more recent studies also incorporate multiple environmental variables with a main focus on environmental gradients (e.g., climatic-, elevation-, environmental-and habitat gradients) with climatic variables being the most commonly used (Gerber et al. 2004;Nahum et al. 2008;Nakazato et al. 2008;Manel et al. 2012;Jones et al. 2013;Gray et al. 2014;Harter et al. 2015). Environmental association studies by means of climatic variables generally comprise temperature and precipitation that over large geographic distances normally change simultaneously. ...
We analyzed the population genetic pattern of 12 fragmented Geropogon hybridus ecological range edge populations in Israel along a steep precipitation gradient. In the investigation area (45 × 20 km²), the annual mean precipitation changes rapidly from 450 mm in the north (Mediterranean-influenced climate zone) to 300 mm in the south (semiarid climate zone) without significant temperature changes. Our analysis (91 individuals, 12 populations, 123 polymorphic loci) revealed strongly structured populations (AMOVA ΦST = 0.35; P < 0.001); however, differentiation did not change gradually toward range edge. IBD was significant (Mantel test r = 0.81; P = 0.001) and derived from sharply divided groups between the northernmost populations and the others further south, due to dispersal or environmental limitations. This was corroborated by the PCA and STRUCTURE analyses. IBD and IBE were significant despite the micro-geographic scale of the study area, which indicates that reduced precipitation toward range edge leads to population genetic divergence. However, this pattern diminished when the hypothesized gene flow barrier was taken into account. Applying the spatial analysis method revealed 11 outlier loci that were correlated to annual precipitation and, moreover, were indicative for putative precipitation-related adaptation (BAYESCAN, MCHEZA). The results suggest that even on micro-geographic scales, environmental factors play prominent roles in population divergence, genetic drift, and directional selection. The pattern is typical for strong environmental gradients, e.g., at species range edges and ecological limits, and if gene flow barriers and mosaic-like structures of fragmented habitats hamper dispersal.
Premise of the study:
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 hybridisation can play an important role in island evolution. Here we use genotyping-by-sequencing (GBS) to understand the roles of hybridisation, 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 super-matrix and gene tree approaches and hybridisation events were examined using D-statistics and Approximate Bayesian Computation (ABC). Climatic data were analysed to examine the relationship between ecology and diversification.
Key results:
Analysis of the supermatrix dataset resulted in a fully resolved phylogeny. Species networks suggest a hybridisation event has occurred for D. gilva, with these results being supported by ABC 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, hybridisation 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 ILS and gene flow when studying groups prone to hybridisation; patterns that might otherwise be obscured in species trees. This article is protected by copyright. All rights reserved.
1.Climate and topography are among the most fundamental drivers of plant diversity. Here, we assess the importance of climate and topography in explaining diversity patterns of species richness, endemic richness and endemicity on the landscape scale of an oceanic island, and evaluate the independent contribution of climatic and topographic variables to spatial diversity patterns.
2.We constructed a presence/absence matrix of perennial endemic and native vascular plant species (including subspecies) in 890 plots on the environmentally very heterogeneous island of La Palma, Canary Islands. Species richness, endemic richness and endemicity were recorded, interpolated and related to climate (i.e. variables describing temperature, precipitation, variability and climatic rarity) and topography (i.e. topographic complexity, solar radiation, geologic age, slope and aspect). We used multi-model inference, spatial autoregressive models, variance partitioning and linear regression kriging as statistical methods.
3.Species richness is best explained by both climatic and topographic variables. Topographic variables (esp. topographic complexity and solar radiation) explain endemic richness and climatic variables (esp. elevation/temperature and rainfall seasonality) explain endemicity. Spatial patterns of species richness, endemic richness and endemicity were in parts geographically decoupled from each other.
4.Synthesis. We identify several topography-dependent processes ranging from evolutionary processes (micro-refugia, in situ speciation, pre-adaptation to rupicolous conditions, dispersal limitations) to human-induced influences (introduced herbivores, fire, land use) that possibly shape the endemic richness pattern of La Palma. In contrast, climate mainly drives endemicity, which is connected to ecological speciation and specialisation to local conditions. We highlight the importance of incorporating climatic variability into future studies of plant species diversity and endemism. The spatial incongruence in hotspots of species richness, endemic richness and endemicity emphasize the need for an integrated conservation approach acknowledging different diversity measures to protect the complete spectrum of diversity. High-elevation islands such as La Palma are highly suitable to study drivers of diversity and endemism, as they offer environmental gradients of continental magnitude on the landscape scale of a single climatic mini-continent and a large array of in situ-speciated endemics.
