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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
Grossenbacher D, Brandvain Y, Auld J, Burd M, Cheptou P, Conner J et al. (2017)
Because establishing a new population often depends critically on finding mates, individuals capable of uniparental reproduction may have a colonization advantage. Accordingly, there should be an over-representation of colonizing species in which individuals can reproduce without a mate, particularly in isolated locales such as oceanic islands. Despite the intuitive appeal of this colonization filter hypothesis (known as Baker's law), more than six decades of analyses have yielded mixed findings. We assembled a dataset of island and mainland plant breeding systems, focusing on the presence or absence of self-incompatibility. Because this trait enforces outcrossing and is unlikely to re-evolve on short timescales if it is lost, breeding system is especially likely to reflect the colonization filter. We found significantly more self-compatible species on islands than mainlands across a sample of > 1500 species from three widely distributed flowering plant families (Asteraceae, Brassicaceae and Solanaceae). Overall, 66% of island species were self-compatible, compared with 41% of mainland species. Our results demonstrate that the presence or absence of self-incompatibility has strong explanatory power for plant geographical patterns. Island floras around the world thus reflect the role of a key reproductive trait in filtering potential colonizing species in these three plant families.
Keywords: Baker's law, biogeography, ecological filtering, island, mainland, self‐incompatibility
Lommen S, Jolidon E, Sun Y, Bustamante eduardo J, Muller-scharer H (2017)
An early suitability assessment of two exotic Ophraella species (Coleoptera: Chrysomelidae) for biological control of invasive ragweed in Europe
European Journal of Entomology 114(1) 160-169.
Classical biological control is an important means of managing the increasing threat of invasive plants. It constitutes the introduction of natural enemies from the native range of the target plant into the invaded area. This method may be the only cost-effective solution to control the rapidly expanding common ragweed, Ambrosia artemisiifolia, in non-crop habitats in Europe. Therefore, candidate biocontrol agents urgently need to be assessed for their suitability for ragweed control in Europe. A previous literature review prioritized the host-specific leaf beetle Ophraella slobodkini as a candidate agent for ragweed control in Europe, whereas it rejected its oligophagous congener O. communa. Meanwhile, O. communa was accidentally introduced and became established south of the European Alps, and we show here that it is expanding its European range. We then present a short version of the traditional pre-release risk-benefit assessment for these two candidate agents to facilitate fast decision-making about further research efforts. We selected two complementary tests that can be conducted relatively rapidly and inform about essential risks and benefits. We conducted a comparative no-choice juvenile performance assay using leaves of ragweed and sunflower, the most important non-target plant, in Petri dishes in climatic conditions similar to that in the current European range of O. communa. This informs on the fundamental host range and potential for increasing abundance on these host plants. The results confirm that O. slobodkini does not survive on, and is hence unlikely to cause severe damage to sunflower, while O. communa can survive but develops more slowly on sunflower than on ragweed. In parallel, our species distribution models predict no suitable area for the establishment of O. slobodkini in Europe, while O. communa is likely to expand its current range to include a maximum of 18% of the European ragweed distribution. Based on this early assessment, the prioritization and further assessment of O. slobodkini seem unwarranted whereas the results urgently advocate further risk-benefit analysis of O. communa. Having revealed that most of the European area colonized by ragweed is unlikely to be suitable for these species of Ophraella we suggest the use of such relatively short and cheap preliminary assessment to prioritise other candidate agents or strains for these areas.
Keywords: Ambrosia artemisiifolia, Chrysomelidae, Coleoptera, Ophraella, biological control, invasive plant
Li Y, Zhang Q, Liu Q, Meissle M, Yang Y, Wang Y et al. (2017)
Plant Biotechnology Journal.
Bt rice can control yield losses caused by lepidopteran pests but may also harm non-target species and reduce important ecosystem services. A comprehensive data set on herbivores, natural enemies, and their interactions in Chinese rice fields was compiled. This together with an analysis of the Cry protein content in arthropods collected from Bt rice in China indicated which non-target species are most exposed to the insecticidal protein and should be the focus of regulatory risk assessment.
Keywords: Bt rice, ecosystem services, environmental risk assessment, non-target effects, surrogate species
Liedtke H, Müller H, Hafner J, Penner J, Gower D, Mazuch T et al. (2017)
Proceedings of the Royal Society B: Biological Sciences 284(1851) 20162598.
How evolutionary novelties evolve is a major question in evolutionary biology. It is widely accepted that changes in environmental conditions shift the position of selective optima, and advancements in phylogenetic comparative approaches allow the rigorous testing of such correlated transitions. A longstanding question in vertebrate biology has been the evolution of terrestrial life histories in amphibians and here, by investigating African bufonids, we test whether terrestrial modes of reproduction have evolved as adaptations to particular abiotic habitat parameters. We reconstruct and date the most complete species-level molecular phylogeny and estimate ancestral states for reproductive modes. By correlating continuous habitat measurements from remote sensing data and locality records with life-history transitions, we discover that terrestrial modes of reproduction, including viviparity evolved multiple times in this group, most often directly from fully aquatic modes. Terrestrial modes of reproduction are strongly correlated with steep terrain and low availability of accumulated water sources. Evolutionary transitions to terrestrial modes of reproduction occurred synchronously with or after transitions in habitat, and we, therefore, interpret terrestrial breeding as an adaptation to these abiotic conditions, rather than an exaptation that facilitated the colonization of montane habitats.
Keywords: Bufonidae, amphibian, evolution, reproductive mode, terrestrial life history, viviparity
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
Pitteloud C, Arrigo N, Suchan T, Mastretta-Yanes A, Vila R, Dincă V et al. (2017)
Climatic niche evolution is faster in sympatric than allopatric lineages of the butterfly genus Pyrgus
Proceedings of the Royal Society of London B: Biological Sciences 284(1852).
Understanding how speciation relates to ecological divergence has long fascinated biologists. It is assumed that ecological divergence is essential to sympatric speciation, as a mechanism to avoid competition and eventually lead to reproductive isolation, while divergence in allopatry is not necessarily associated with niche differentiation. The impact of the spatial context of divergence on the evolutionary rates of abiotic dimensions of the ecological niche has rarely been explored for an entire clade. Here, we compare the magnitude of climatic niche shifts between sympatric versus allopatric divergence of lineages in butterflies. By combining next-generation sequencing, parametric biogeography and ecological niche analyses applied to a genus-wide phylogeny of Palaearctic Pyrgus butterflies, we compare evolutionary rates along eight climatic dimensions across sister lineages that diverged in large-scale sympatry versus allopatry. In order to examine the possible effects of the spatial scale at which sympatry is defined, we considered three sets of biogeographic assignments, ranging from narrow to broad definition. Our findings suggest higher rates of niche evolution along all climatic dimensions for sister lineages that diverge in sympatry, when using a narrow delineation of biogeographic areas. This result contrasts with significantly lower rates of climatic niche evolution found in cases of allopatric speciation, despite the biogeographic regions defined here being characterized by significantly different climates. Higher rates in allopatry are retrieved when biogeographic areas are too widely defined—in such a case allopatric events may be recorded as sympatric. Our results reveal the macro-evolutionary significance of abiotic niche differentiation involved in speciation processes within biogeographic regions, and illustrate the importance of the spatial scale chosen to define areas when applying parametric biogeographic analyses.
Keywords: climatic niche, macro-evolutionary processes, next-generation sequencing, parametric biogeography
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