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Aliabadian M, Alaei-Kakhki N, Mirshamsi O, Nijman V, Roulin A (2016)
Biological Journal of the Linnean Society.
The existence of substantial morphological variation has resulted in the description of numerous subspecies of the cosmopolitan barn owl, Tyto alba. However, preliminary studies have revealed a high degree of genetic variation between Old and New World barn owls, suggesting that the T. alba complex may consist of several species. We present a comprehensive study of its taxonomy and propose a spatiotemporal framework to explain the origin and patterns of dispersal and diversification within these cosmopolitan owls. We used a Bayesian relaxed molecular clock approach to assess the timing of diversification. To evaluate the biogeographical pattern, we considered dispersal in addition to temporal connectivity between areas. Finally, we used ecological niche modelling to evaluate their ecological niches. Our phylogenetic analyses suggest that barn owls of the Old and New World show a high degree of genetic divergence, and the barn owls of South and South-east Asia (Tyto alba stertens and Tyto alba javanica) cluster with the Australian barn owl Tyto delicatula. We propose to treat the T. alba complex as three species: T. alba (Africa, Europe), Tyto furcata (New World), and Tyto javanica (Australasia). The dating analyses indicate that the early divergence among the species of the T. alba complex took place in the Middle Miocene and we hypothesize that a common ancestor of the T. alba complex lived in Africa. A potential scenario suggests that T. alba dispersed to Europe and south-western Asia during the interglacial periods of the Miocene/Pliocene, and dispersed into the New World either via an eastern Asian route or a western north Atlantic one.
Ballesteros-Mejia L, Kitching I, Jetz W, Beck J (2016)
Putting insects on the map: Near-global variation in sphingid moth richness along spatial and environmental gradients
Despite their vast diversity and vital ecological role, insects are notoriously underrepresented in biogeography and conservation, and key broad-scale ecological hypotheses about them remain untested – largely due to generally incomplete and very coarse spatial distribution knowledge. Integrating records from publications, field work and natural history collections, we used a mixture of species distribution models and expert estimates to provide geographic distributions and emergent richness patterns for all ca. 1,000 sphingid moth species found outside the Americas in high spatial detail. Total sphingid moth richness, the first for a higher insect group to be documented at this scale, shows distinct maxima in the wet tropics of Africa and the Oriental with notable decay toward Australasia. Using multivariate models controlling for spatial autocorrelation, we found that primary productivity is the dominant environmental variable associated with moth richness, while temperature, contrary to our predictions, is an unexpectedly weak predictor. This is in stark contrast to the importance we identify for temperature as a niche variable of individual species. Despite divergent life histories, both main sub-groups of moths exhibit these relationships. Tribal-level deconstruction of richness and climatic niche patterns indicate idiosyncratic effects of biogeographic history for some of the less species-rich tribes, which in some cases exhibit distinct richness peaks away from the tropics. The study confirms, for a diverse insect group, overall richness associations of remarkable similarity to those documented for vertebrates and highlights the significant within-taxon structure that underpins emergent macroecological patterns. Results do not, however, meet predictions from vertebrate-derived hypotheses on how thermoregulation affects the strength of temperature-richness effects. Our study thus broadens the taxonomic focus in this data-deficient discourse. Our procedures of processing incomplete, scattered distribution data are a template for application to other taxa and regions.
Keywords: Distribution modelling, Lepidoptera, Productivity, Spatial scale, Sphingidae, Tropics
Bocksberger G, Schnitzler J, Chatelain C, Daget P, Janssen T, Schmidt M et al. (2016)
Journal of Vegetation Science.
Questions Which environmental variables influence grass diversity in West Africa? What are the effects of climate and grass functional traits on the spatial patterns (richness and abundance) of the grass clades Andropogoneae, Paniceae and Chloridoideae? Location West Africa, demarcated by the Atlantic Ocean in the west and south (20° W and 4° N), the Sahara desert in the north (25° N) and the border between Niger and Chad in the east (20° E). Methods Based on 38 912 georeferenced occurrence records, we modelled the distribution of 302 grass species (51% of West African grass diversity). We integrated species richness, abundance and functional traits (life cycle, photosynthetic type and height) to determine the contribution of the most speciose grass clades (Andropogoneae, Paniceae and Chloridoideae) to overall grass diversity in West Africa. Results Precipitation is the variable most often influencing the species distribution models of grasses in West Africa. Richness and relative abundance of the tribe Andropogoneae show a centre of diversity in Sudanian savanna regions. The height of Andropogoneae species, generally >150 cm, is driving this ecological dominance. Species richness of the tribe Paniceae is more dispersed and shows two main centres of abundance: The southern regions with higher mean annual precipitation and tree density are dominated by C3 Paniceae species. The Sahelian regions in the north are dominated by short Paniceae species with the C4 NAD-ME photosynthetic subtype, as well as Chloridoideae possessing the same functional attributes. Conclusions Our study provides insight into the environmental correlates of grass species richness in West Africa and contributes to the much-needed research on tropical rangelands. Moreover, the integration of evolutionary history significantly improves our understanding of large-scale biodiversity patterns.
Keywords: Andropogoneae, Chloridoideae, Maxent, Paniceae, Poaceae, Savanna, Species distribution modelling, West Africa, species richness
Boucher F, Lavergne S, Basile M, Choler P, Aubert S (2016)
Perspectives in Plant Ecology, Evolution and Systematics 20 22-31.
Cushion-forming species occur in all cold and dry environments worldwide, where they play important engineering roles. Understanding the origins of cushion plants may thus provide insights into the evolutionary assembly of biomes under extreme climatic conditions. Here we investigate the evolutionary and biogeographic history of cushions in Angiosperms based on a global checklist of all cushion plants, along with phylogenetic, climatic, and biogeographic information. Our aim is to measure the frequency of this evolutionary convergence and to identify its historic, environmental, and biogeographic drivers. We show that cushions appeared at least 115 times in Angiosperms and that they mainly belong to families that occupy the coldest and driest environments on Earth. We found that cushions have intensively diversified in the Himalayas, the Andes, or New Zealand, while other regions like Patagonia have probably been hubs enabling cushion species to migrate between different alpine regions. We conclude that the cushion life form is a remarkable example of convergent key innovation, which has favored the colonization of cold and dry habitats.
Keywords: Alpine, Angiosperms, Arctic, Biogeography, Cushion plants, Evolutionary convergence
Dufresnes C, Litvinchuk S, Leuenberger J, Ghali K, Zinenko O, Stöck M et al. (2016)
Evolutionary melting pots: a biodiversity hotspot shaped by ring diversifications around the Black Sea in the Eastern tree frog ( Hyla orientalis )
Hotspots of intraspecific genetic diversity, which are of primary importance for the conservation of species, have been associated to glacial refugia, i.e. areas where species survived the Quaternary climatic oscillations. However, the proximate mechanisms generating these hotspots remain an open issue. Hotspots may reflect the long-term persistence of large refugial populations; alternatively, they may result from allopatric differentiation between small and isolated populations, that later admixed. Here we test these two scenarios in a widely distributed species of tree frog, Hyla orientalis, which inhabits Asia Minor and Southeastern Europe. We apply a fine-scale phylogeographic survey, combining fast-evolving mitochondrial and nuclear markers, with a dense sampling throughout the range, as well as ecological niche modeling, to understand what shaped the genetic variation of this species. We documented an important diversity center around the Black Sea, composed of multiple allopatric and/or parapatric diversifications, likely driven by a combination of Pleistocene climatic fluctuations and complex regional topography. Remarkably, this diversification forms a ring around the Black Sea, from the Caucasus through Anatolia and Eastern Europe, with terminal forms coming into contact and partially admixing in Crimea. Our results support the view that glacial refugia generate rather than host genetic diversity, and can also function as evolutionary melting pots of biodiversity. Moreover, we report a new case of ring diversification, triggered by a large, yet cohesive dispersal barrier, a very rare situation in nature. Finally, we emphasize the Black Sea region as an important center of intraspecific diversity in the Palearctic with implications for conservation.
Keywords: Alpine, Angiosperms, Arctic, Biogeography, Cushion plants, Evolutionary convergence
Ferreira G, Ferreira P, Chautems A, Waechter J (2016)
Subtropical species of Sinningia (Gesneriaceae): distribution patterns and limiting environmental factors
Flora - Morphology, Distribution, Functional Ecology of Plants 222 86-95.
The neotropical genus Sinningia Nees encompasses tuberous herbs or subshrubs which occupy a wide range of environments with respect to climate and soil or substrate types. The genus has more than 70 species distributed from Southern Mexico to Northern Argentina, with a diversity centre in the Brazilian Atlantic Rainforest. In this ecosystem, a large number of species occur in several particular vegetation types, occupying terrestrial, rupestrial and epiphytic substrates. The aims of this study were to describe the distribution patterns of subtropical Sinningia species, and to determine possible limiting factors for their range extension. We summarized environmental data for 21 subtropical species. Ten geographical and ecological variables were subdivided into several regional or local conditions. The occurrence of species in each of these conditions was obtained from published material, herbarium reviews and field expeditions. We used exploratory multivariate approaches, (cluster and ordination analyses) to assess the contribution of these variables to species’ ecological and geographical distributions. Comparisons between groups of species were evaluated using randomization tests. Two major patterns of geographic distribution were identified for subtropical Sinningia species: widespread and restricted. Species richness according to spatial and climatic variables showed four distinct patterns. Habitat tolerance of the species also distinguished two groups in a wider continuum context. Cluster analysis resulted in two stable groups, which coincided almost entirely with an a priori classification based on geographic range. Ordination analysis showed a distinction between widespread and restricted species, as well as a gradient of substrate occupancy. Patterns of ecological and geographical distribution were strongly related to the evolutionary history of the genus. The southern distribution limit of Sinningia is mainly linked to shifts in vegetation types around the 30°S parallel, where the northern forested Atlantic and Paranean biogeographic provinces give place to the southern non-forested Espinal and Pampean provinces.
Keywords: Biogeography, Corytholoma, Dircaea, Ecology, Plasticity
Fuchs J, Lemoine D, Parra J, Pons J, Raherilalao M, Prys-Jones R et al. (2016)
Long-distance dispersal and inter-island colonization across the western Malagasy Region explain diversification in brush-warblers (Passeriformes: Nesillas )
Biological Journal of the Linnean Society.
The present study examines the colonization history and phylogeography of the brush-warblers (Nesillas), a genus of passerines endemic to islands of the western Indian Ocean (Madagascar, Comoros, and Aldabra Atoll). The phylogeny of all recognized Nesillas taxa was reconstructed employing Bayesian phylogenetic methods and divergence times were estimated using a range of substitution rates and clock assumptions. Spatiotemporal patterns of population expansion were inferred and niches of different lineages were compared using ecological niche modelling. Our results indicate that taxa endemic to the Comoros are paraphyletic and that the two endemic species on Madagascar (Nesillas typica and Nesillas lantzii) are not sister taxa. The brush-warblers started to diversify approximately 1.6 Mya, commencing with the separation of the clade formed by two species endemic to the Comoros (Nesillas brevicaudata and Nesillas mariae) from the rest of the genus. The lineages leading to the two Malagasy species diverged approximately 0.9 Mya; each with significantly different modern ecological niches and the subject of separate demographic processes. Patterns of diversification and endemism in Nesillas were shaped by multiple long distance dispersal events and inter-island colonization, a recurring pattern for different lineages on western Indian Ocean islands. The diversification dynamics observed for Nesillas are also consistent with the taxon cycle hypothesis.
Keywords: MAXENT, demographic history, ecological niche modelling, island biogeography, mitochondrial sequence data, phylogenetic constraints, taxon cycle
Keller B, de Vos J, Schmidt-Lebuhn A, Thomson J, Conti E (2016)
Both morph- and species-dependent asymmetries affect reproductive barriers between heterostylous species
Ecology and Evolution 6(17) 6223-6244.
The interaction between floral traits and reproductive isolation is crucial to explaining the extraordinary diversity of angiosperms. Heterostyly, a complex floral polymorphism that optimizes outcrossing, evolved repeatedly and has been shown to accelerate diversification in primroses, yet its potential influence on isolating mechanisms remains unexplored. Furthermore, the relative contribution of pre- versus postmating barriers to reproductive isolation is still debated. No experimental study has yet evaluated the possible effects of heterostyly on pre- and postmating reproductive mechanisms. We quantify multiple reproductive barriers between the heterostylous Primula elatior (oxlip) and P. vulgaris (primrose), which readily hybridize when co-occurring, and test whether traits of heterostyly contribute to reproductive barriers in unique ways. We find that premating isolation is key for both species, while postmating isolation is considerable only for P. vulgaris; ecogeographic isolation is crucial for both species, while phenological, seed developmental, and hybrid sterility barriers are also important in P. vulgaris, implicating sympatrically higher gene flow into P. elatior. We document for the first time that, in addition to the aforementioned species-dependent asymmetries, morph-dependent asymmetries affect reproductive barriers between heterostylous species. Indeed, the interspecific decrease of reciprocity between high sexual organs of complementary floral morphs limits interspecific pollen transfer from anthers of short-styled flowers to stigmas of long-styled flowers, while higher reciprocity between low sexual organs favors introgression over isolation from anthers of long-styled flowers to stigmas of short-styled flowers. Finally, intramorph incompatibility persists across species boundaries, but is weakened in long-styled flowers of P. elatior, opening a possible backdoor to gene flow through intramorph pollen transfer between species. Therefore, patterns of gene flow across species boundaries are likely affected by floral morph composition of adjacent populations. To summarize, our study highlights the general importance of premating isolation and newly illustrates that both morph- and species-dependent asymmetries shape boundaries between heterostylous species.
Keywords: Diversification, Primula elatior (oxlip), Primula vulgaris (primrose), floral heteromorphism, heterostyly, hybridization, mechanical isolation, morph-dependent asymmetry, reciprocal herkogamy, speciation, species-dependent asymmetry
Lee-Yaw J, Kharouba H, Bontrager M, Mahony C, Csergő A, Noreen A et al. (2016)
A synthesis of transplant experiments and ecological niche models suggests that range limits are often niche limits
Global change has made it important to understand the factors that shape species' distributions. Central to this area of research is the question of whether species' range limits primarily reflect the distribution of suitable habitat (i.e. niche limits) or arise as a result of dispersal limitation. Over-the-edge transplant experiments and ecological niche models are commonly used to address this question, yet few studies have taken advantage of a combined approach for inferring the causes of range limits. Here, we synthesise results from existing transplant experiments with new information on the predicted suitability of sites based on niche models. We found that individual performance and habitat suitability independently decline beyond range limits across multiple species. Furthermore, inferences from transplant experiments and niche models were generally concordant within species, with 31 out of 40 cases fully supporting the hypothesis that range limits are niche limits. These results suggest that range limits are often niche limits and that the factors constraining species' ranges operate at scales detectable by both transplant experiments and niche models. In light of these findings, we outline an integrative framework for addressing the causes of range limits in individual species.
Keywords: Abiotic constraints, climate, dispersal limitation, fitness, geographical distribution, over the edge transplant, species distribution modelling
Oberlander K, Dreyer L, Goldblatt P, Suda J, Linder H (2016)
Species-rich and polyploid-poor: Insights into the evolutionary role of whole-genome duplication from the Cape flora biodiversity hotspot
American Journal of Botany 103(7) 1336-1347.
PREMISE OF THE STUDY: Whole-genome duplication (WGD) in angiosperms has been hypothesized to be advantageous in unstable environments and/or to increase diversification rates, leading to radiations. Under the first hypothesis, floras in stable environments are predicted to have lower proportions of polyploids than highly, recently disturbed floras, whereas species-rich floras would be expected to have higher than expected proportions of polyploids under the second. The South African Cape flora is used to discriminate between these two hypotheses because it features a hyperdiverse flora predominantly generated by a limited number of radiations (Cape clades), against a backdrop of climatic and geological stability. METHODS: We compiled all known chromosome counts for species in 21 clades present in the Cape (1653 species, including 24 Cape clades), inferred ploidy levels for these species by inspection or derived from the primary literature, and compared Cape to non-Cape ploidy levels in these clades (17,520 species) using G tests. KEY RESULTS: The Cape flora has anomalously low proportions of polyploids compared with global levels. This pattern is consistently observed across nearly half the clades and across global latitudinal gradients, although individual lineages seem to be following different paths to low levels of WGD and to differing degrees. CONCLUSIONS: This pattern shows that the diversity of the Cape flora is the outcome of primarily diploid radiations and supports the hypothesis that WGD may be rare in stable environments.
Keywords: Cape flora, diversification, environmental stability, evolutionary radiation, polyploidy, whole-genome duplication