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Chala D, Zimmermann N, Brochmann C, Bakkestuen V (2017)
Migration corridors for alpine plants among the ‘sky islands’ of eastern Africa: do they, or did they exist?
Alpine Botany 1-12.
The tropical alpine ecosystem in eastern Africa is highly fragmented among biological ‘sky islands’, where populations of frost-tolerant organisms are isolated from each other by a ‘sea’ of tropical lowlands. One-third of the species in the afroalpine flora are exclusively alpine, but the other species can to varying degrees extend into grasslands and open forests of lower vegetation belts. A long-debated question is whether colonization of the alpine zone of these mountains and subsequent intermountain gene flow entirely depend on long-distance dispersal across unsuitable habitats, or whether suitable habitats shifted far enough downslope under past colder climates to form bridges enabling gradual migration. Here we address this question using a classification tree model. We mapped the extent of the current alpine habitat and projected it to the last glacial maximum (LGM) climate to assess whether gradual migration was possible for exclusively alpine taxa during this glacial period, and thus potentially also during earlier Pleistocene glaciations. Next, we modelled landcover under current and LGM climates to assess whether grassland and open forests could have served as migration corridors for alpine taxa that today extend into lower vegetation belts. We estimated that the LGM treeline was about 1000 m lower and the alpine habitat was about eight times larger than that today. At the LGM, we found that most of the currently fragmented alpine habitat of the Ethiopian highlands was interconnected except across the Great Rift Valley, whereas the solitary mountains of East/Central Africa remained isolated for exclusively alpine species. However, for drought-tolerant alpine species that today extend below the treeline, gradual migration through habitat corridors may have been possible among mountains during the dry glacial periods, and possibly also under the current climate before agriculture transformed the low-lying landscapes.
Keywords: Afroalpine, CART, Gene flow, Habitat connectivity, Last glacial maximum, Treeline
Mairal M, Sanmartín I, Pellissier L (2017)
Journal of Biogeography.
Aim The disjunct distribution patterns of sister taxa can arise when previously continuous distribution ranges are fragmented by environmental changes such as major climatic events. Populations become isolated on either side of the newly established environmental barrier, and absence of gene flow promotes allopatric speciation, in a process that is known as ecological vicariance. If climate change altered the ancestral range gradually, such as along temporal temperature or moisture gradients, the age of divergence of disjunct species should be related to the lineage tolerance to climatic conditions. Here, we investigate this hypothesis using as a study model the African Rand Flora, a continental-scale floristic pattern that relates sister taxa distributed on either side of the Saharan Desert. Location Africa, Macaronesia, Mediterranean Basin and the Middle East. Methods We estimated the extant climatic tolerances of 14 Rand Flora lineages based on present occurrence data, and correlated the phylogenetic age of divergence between vicariant clades. We tested whether the tempo of the vicariance in the Rand Flora lineages was associated with the average values of their climatic niches in agreement with niche-driven divergence. We hindcasted species ranges using species distribution models combined with palaeoclimate simulations to infer the potential distribution of each lineage's ancestors. Results We found a positive relationship between the lineage temperature niche and the age of the Rand Flora disjunction: lineages with subtropical affinities diverged first, whereas those with a higher tolerance to drier conditions (temperate or sub-xeric adaptations) exhibited younger disjunctions. The range reconstructions showed the existence of climatic corridors south of the Sahara in the wetter Late Miocene, which became interrupted during the mid-Pliocene warming event. Main conclusions Our results suggest that climate change leading to the formation of the Sahara Desert drove Rand Flora lineages divergences along a temporal sequence that matched the climatic niche of species.
Keywords: Rand Flora, continental disjunctions, extinction, niche conservatism, refuges, vicariance
Zeng X, Durka W, Welk E, Fischer M (2017)
Heritability of early growth traits and their plasticity in 14 woody species of Chinese subtropical forest
Journal of Plant Ecology 10(1) 222-231.
Aims Genetic variation in plant traits represents the raw material for future adaptive evolution. Its extent can be estimated as heritability based on the performance of experimental plants of known relatedness, such as maternal half-sib seed families. While there is considerable heritability information for herbaceous plants and commercially important trees, little is known for woody species of natural subtropical forest. Moreover, it is open whether heritability is higher for species with r- or K-strategies, for more common species with larger distribution ranges than for rarer ones, or for populations closer to the centres of distributional ranges. Methods For 14 woody species in Chinese subtropical forest, we collected 13–38 maternal seed families, assessed seed size, grew replicates of each seed family in one more and one less benign nursery environment and measured stem diameter and plant height after 7 months. Important findings For the different species, plants grew 1.8–8.1 times taller in the more benign environment. For all 14 species, variation between seed families (and thus heritability) was significant (with very few exceptions at the P < 0.001 level) for seed size and for stem diameter and plant height in both nurseries. Moreover, significant seed family by nursery interactions for stem diameter and plant height for all species (P < 0.001) indicated significant heritability for plasticity in these traits. Multiple regression analysis suggests that heritabilities were higher for species with higher age at reproduction and higher wood density (traits indicating a K strategy) but also for species with higher specific leaf area (a trait rather indicating an r strategy). Furthermore, heritabilities were higher for species with larger range sizes, while there was no significant relationship between heritabilities and the distance of the study area to the range margins of our study species. In conclusion, the detected large heritability estimates suggest considerable potential for the evolution of plant performance and its plasticity for trees of subtropical forest. Moreover, our study shows that the simple method of comparing plants of different maternal seed families is valuable to address evolutionary ecological questions for so far understudied species.
Keywords: heritability, phenotypic plasticity, plant performance, subtropical forest
Zurano J, Martinez P, Canto-Hernandez J, Montoya-Burgos J, Costa G (2017)
Journal of Biogeography.
Aim Closely related species are expected to be similar in their ecological attributes. However, clades colonizing new environments and diversifying due to ecological processes often show morphological and ecological divergence. Canids arrived in South America after the formation of the Isthmus of Panama and diversified to occupy a variety of habitats. We test whether the diversification of this group was followed by divergence in species niches. If ecological processes are associated with species divergences, we expect to see species occupying distinct climatic niches, showing divergent phenotypes, and showing a close association between their phenotypes and ecological attributes. Location South America Methods We use comparative and multivariate climatic niche analysis, geometric morphometric (skull and jaw), and distance-based phylogenetic regressions to test whether the diversification of South American canids was followed by divergence in their climatic niches and phenotypic traits. Results We found a pattern of continental niche occupancy (north to south) along a complex climatic gradient. As species diverged, they evolved distinct climatic tolerances. Climatic niche similarities are not related to species phylogenetic relationships, indicating that closely related species may have distinct climatic tolerances. Our morphological analysis also showed strong phenotypic divergence between species. Our results suggest that these differences were related to climatic and trophic niches. Results show divergent phenotypes in both the skull and jaw, and that there is a close association between phenotype and ecological strategies. Main conclusions Our study integrates phylogenetic history, ecological and morphological data to study the evolution of South American canids. Canid colonization of South America was followed by species ecological divergences. Our results support the hypothesis that ecological processes are the main drivers of diversification of this clade and illustrate a complex biogeographical history of ecological diversification of canids at continental scale.
Keywords: heritability, phenotypic plasticity, plant performance, subtropical forest
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.
Keywords: heritability, phenotypic plasticity, plant performance, subtropical forest
Antonelli A, Hettling H, Condamine F, Vos K, Nilsson R, Sanderson M et al. (2016)
Toward a Self-Updating Platform for Estimating Rates of Speciation and Migration, Ages, and Relationships of Taxa
Systematic Biology syw066.
Rapidly growing biological data –including molecular sequences and fossils– hold an unprecedented potential to reveal how evolutionary processes generate and maintain biodiversity. However, researchers often have to develop their own idiosyncratic workflows to integrate and analyse these data for reconstructing time-calibrated phylogenies. In addition, divergence times estimated under different methods and assumptions, and based on data of various quality and reliability, should not be combined without proper correction. Here we introduce a modular framework termed SUPERSMART (Self-Updating Platform for Estimating Rates of Speciation and Migration, Ages, and Relationships of Taxa), and provide a proof of concept for dealing with the moving targets of evolutionary and biogeographical research. This framework assembles comprehensive datasets of molecular and fossil data for any taxa and infers dated phylogenies using robust species tree methods, also allowing for the inclusion of genomic data produced through next-generation sequencing techniques. We exemplify the application of our method by presenting phylogenetic and dating analyses for the mammal order Primates and for the plant family Arecaceae (palms). We believe that this framework will provide a valuable tool for a wide range of hypothesis-driven research questions in systematics, biogeography, and evolution. SUPERSMART will also accelerate the inference of a “Dated Tree of Life” where all node ages are directly comparable.
Keywords: Bayesian phylogenetics, GenBank, data mining, divide-and-conquer methods, multilocus multispecies coalescent, next-generation sequencing, palms, primates, tree calibration
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
Benedict J, Smith S, Specht C, Collinson M, Leong-Škorničková J, Parkinson D et al. (2016)
Species diversity driven by morphological and ecological disparity: a case study of seeds of Zingiberales (bananas, gingers, and relatives).
AoB PLANTS plw063.
Phenotypic variation can be attributed to genetic heritability as well as biotic and abiotic factors. Across Zingiberales, there is a high variation in the number of species per clade and in phenotypic diversity. Factors contributing to this phenotypic variation have never been studied in a phylogenetic or ecological context. Seeds of 166 species from all eight families in Zingiberales were analyzed for 51 characters using synchrotron based 3D X-ray tomographic microscopy to determine phylogenetically informative characters and to understand the distribution of morphological disparity within the order. All families are distinguishable based on seed characters. Non-metric multidimensional scaling analyses show Zingiberaceae occupy the largest seed morphospace relative to the other families, and environmental analyses demonstrate that Zingiberaceae inhabit both temperate and tropical regions, while other Zingiberales are almost exclusively tropical. Temperate species do not cluster in morphospace nor do they share a common suite of character states. This suggests that the diversity seen is not driven by adaptation to temperate niches; rather, the morphological disparity seen likely reflects an underlying genetic plasticity that allowed Zingiberaceae to repeatedly colonize temperate environments. The notable morphoanatomical variety in Zingiberaceae seeds may account for their extraordinary ecological success and high species diversity as compared to other Zingiberales.
Keywords: Cannaceae, Costaceae, Heliconiaceae, Lowiaceae, Marantaceae, Musaceae, Strelitziaceae, Zingiberaceae
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