Carbon assimilation mode in mixotrophs and the fatty acid composition of their rotifer consumers

1. We examined an important ecophysiological link between the mixotrophic flagellate Chlamydomonas acidophila and its consumers, the rotifers Elosa worallii, Cephalodella sp. and Brachionus sericus , by comparing their fatty acid profiles.
2. The mixotrophic flagellate was grown under either exclusively autotrophic conditions in the light, under exclusively heterotrophic conditions in the dark with an organic carbon source (glucose), or in the light plus the organic carbon sources (=mixotrophic).
3. Under heterotrophic growth conditions, C. acidophila strongly reduced its content of the n-3 polyunsaturated fatty acid (PUFA) alpha-linolenic acid (ALA, C18:3n-3) compared with auto- and mixotrophic growth conditions. Although PUFAs with more than 18 carbon atoms were not detected in C . acidophila , significant amounts of eicosatetraenoic (ETA, 20:4n-3) and eicosapentaenoic acid (EPA, 20:5n- 3 ) were found in three rotifer consumers.
4. Species-specific differences in the fatty acid profiles with respect to ETA, EPA and the precursor ALA were found in the rotifers: Brachionus and Cephalodella fed on the heterotrophic diets synthesised less EPA. In Elosa , smaller amounts of ALA were detected but were converted efficiently to a constant content of EPA and to an exceptionally high content of ETA.
5. Since in nature the mode of carbon assimilation among mixotrophic organisms differs, and their fatty acid composition varies depending on their mode of carbon assimilation, the availability of ALA might be critical for their consumers. An insufficient dietary supply of this precursor for the synthesis of ETA and EPA can prevent consumers from regulating their content of ETA and EPA. Therefore, observed differences in values of the latter might underly species-specific differences in the competitive capability of consumers.     

Genetic divergence in Greek populations of the genus Leuciscus and its evolutionary and biogeographical implications

In 23 populations of Greek Leuciscus ( Squalius ), the percentage of polymorphic allozyme loci ranged between 0·034 and 0·379 (P=0·19) and expected heterozygosity was 0·011–0·166 (H_e=0·067). Current taxonomy is confusing and does not correspond to genetic data that support the presence in Greece of at least seven different species: L. cephalus , L. peloponnensis , L. prespensis , L. moreoticus , L. borysthenicus , L. keadicus and Leuciscus sp. from Euboea Island. The maximum Nei modified genetic distance was found among L. keadicus and the rest of subgenus Squalius populations D * Nei=0·446–0·705). Accepting the molecular clock hypothesis, speciation for the genus Leuciscus in Greece must have occurred during the Cenozoic period (between the Middle Miocene and the Later Pliocene). The two main biogeographical events causing speciation on mainland Greece were the Uplift of the Pindic cordillera and the isolation of the southern part of Peloponnesus. The faunistic composition of the lakes studied, in which new taxa are reconsidered, suggests the same faunistic origin in the Early Pliocene for Lakes Prespa and Stymphalia and a younger one in the Late Pliocene for Lake Trichonis. Euboea Island was not a zoogeographical unit during the Cenozoic. The isolation of all the freshwater fish fauna of Euboea has occurred since the Pliocene. The biogeographical model proposed here differs from classical hypotheses in considering of lesser importance the dispersion of L. cephalus on the Greek mainland during the Neogene and Quaternary.     

New species of the snakefly genus Mongoloraphidia (Raphidioptera: Raphidiidae) from Japan and Taiwan,with phylogenetic and biogeographical remarks on the Raphidiidae of Eastern Asia

Two species of the snakefly genus Mongoloraphidia Aspöck & Aspöck, 1968 from Japan and Taiwan are described as new to science: Mongoloraphidia (Japanoraphidia) occidentalis sp. nov. and Mongoloraphidia (Formosoraphidia) curvata sp. nov. A key to the species of Mongoloraphidia from Eastern Asia is provided. Phylogenetic and biogeographical aspects on the Raphidiidae from Eastern Asia are discussed.     

Annotated checklist of the living sharks,batoids and chimaeras (Chondrichthyes) of the world,with a focus on biogeographical diversity

An annotated checklist of the chondrichthyan fishes (sharks, batoids and chimaeras) of the world is presented. As of 7 November 2015, the number of species totals 1188, comprising 16 orders, 61 families and 199 genera. The checklist includes nine orders, 34 families, 105 genera and 509 species of sharks; six orders, 24 families, 88 genera and 630 species of batoids (skates and rays); one order, three families, six genera and 49 species of holocephalans (chimaeras). The most speciose shark orders are the Carcharhiniformes with 284 species, followed by the Squaliformes with 119. The most species‐rich batoid orders are the Rajiformes with 285 species and the Myliobatiformes with 210. This checklist represents the first global checklist of chondrichthyans to include information on maximum size, geographic and depth distributions, as well as comments on taxonomically problematic species and recent and regularly overlooked synonymizations. Furthermore, a detailed analysis of the biogeographical diversity of the species across 10 major areas of occurrence is given, including updated figures for previously published hotspots of chondrichthyan biodiversity, providing the detailed numbers of chondrichthyan species per major area, and revealing centres of distribution for several taxa     

The role of phytoplankton photosynthesis in global biogeochemical cycles

Phytoplankton biomass in the world's oceans amounts to only 1–2% of the total global plant carbon, yet these organisms fix between 30 and 50 billion metric tons of carbon annually, which is about 40% of the total. On geological time scales there is profound evidence of the importance of phytoplankton photosynthesis in biogeochemical cycles. It is generally assumed that present phytoplankton productivity is in a quasi steady-state (on the time scale of decades). However, in a global context, the stability of oceanic photosynthetic processes is dependent on the physical circulation of the upper ocean and is therefore strongly influenced by the atmosphere. The net flux of atmospheric radiation is critical to determining the depth of the upper mixed layer and the vertical fluxes of nutrients. These latter two parameters are keys to determining the intensity, and spatial and temporal distributions of phytoplankton blooms. Atmospheric radiation budgets are not in steady-state. Driven largely by anthropogenic activities in the 20th century, increased levels of IR- absorbing gases such as CO₂, CH₄ and CFC's and NO_x will potentially increase atmospheric temperatures on a global scale. The atmospheric radiation budget can affect phytoplankton photosynthesis directly and indirectly. Increased temperature differences between the continents and oceans have been implicated in higher wind stresses at the ocean margins. Increased wind speeds can lead to higher nutrient fluxes. Throughout most of the central oceans, nitrate concentrations are sub-micromolar and there is strong evidence that the quantum efficiency of Photosystem II is impaired by nutrient stress. Higher nutrient fluxes would lead to both an increase in phytoplankton biomass and higher biomass-specific rates of carbon fixation. However, in the center of the ocean gyres, increased radiative heating could reduce the vertical flux of nutrients to the euphotic zone, and hence lead to a reduction in phytoplankton carbon fixation. Increased desertification in terrestrial ecosystems can lead to increased aeolean loadings of essential micronutrients, such as iron. An increased flux of aeolean micronutrients could fertilize nutrient-replete areas of the open ocean with limiting trace elements, thereby stimulating photosynthetic rates. The factors which limit phytoplankton biomass and photosynthesis are discussed and examined with regard to potential changes in the Earth climate system which can lead the oceans away from steady-state. While it is difficult to confidently deduce changes in either phytoplankton biomass or photosynthetic rates on decadal time scales, time-series analysis of ocean transparency data suggest long-term trends have occurred in the North Pacific Ocean in the 20th century. However, calculations of net carbon uptake by the oceans resulting from phytoplankton photosynthesis suggest that without a supply of nutrients external to the ocean, carbon fixation in the open ocean is not presently a significant sink for excess atmospheric CO₂.The submitted paper has been authored under Contract No. DE-AC02-76H00016 with the US Department of Energy. Accordingly, the US Government retains a non-exclusive, royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for US Government purposes.     

Phylogenetic and biogeographical relationships of the Sander pikeperches (Percidae: Perciformes): patterns across North America and Eurasia

North America and Eurasia share several closely related taxa that diverged either from the breakup of the Laurasian supercontinent or later closures of land bridges. Their modern population structures were shaped in Pleistocene glacial refugia and via later expansion patterns, which are continuing. The pikeperch genus Sander contains five species – two in North America (S. canadensis and S. vitreus) and three in Eurasia (S. lucioperca, S. marinus, and S. volgensis) – whose evolutionary relationships and relative genetic diversities were previously unresolved, despite their fishery importance. This is the first analysis to include the enigmatic and rare sea pikeperch S. marinus, nuclear DNA sequences, and multiple mitochondrial DNA regions. Bayesian and maximum‐likelihood trees from three mitochondrial and three nuclear gene regions support the hypothesis that Sander diverged from its sister group Romanichthys/Zingel ～24.6 Mya. North American and Eurasian Sander then differentiated ～20.8 Mya, with the former diverging ～15.4 Mya, congruent with North American fossils dating to ～16.3–13.6 Mya. Modern Eurasian species date to ～13.8 Mya, with S. volgensis being basal and comprising the sister group to S. lucioperca and S. marinus, which diverged ～9.1 Mya. Genetic diversities of the North American species are higher than those in Eurasia, suggesting fewer Pleistocene glaciation bottlenecks. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 156–179.     

Novel lineages of Prochlorococcus and Synechococcus in the global oceans

Picocyanobacteria represented by Prochlorococcus and Synechococcus have an important role in oceanic carbon fixation and nutrient cycling. In this study, we compared the community composition of picocyanobacteria from diverse marine ecosystems ranging from estuary to open oceans, tropical to polar oceans and surface to deep water, based on the sequences of 16S-23S rRNA internal transcribed spacer (ITS). A total of 1339 ITS sequences recovered from 20 samples unveiled diverse and several previously unknown clades of Prochlorococcus and Synechococcus. Six high-light (HL)-adapted Prochlorococcus clades were identified, among which clade HLVI had not been described previously. Prochlorococcus clades HLIII, HLIV and HLV, detected in the Equatorial Pacific samples, could be related to the HNLC clades recently found in the high-nutrient, low-chlorophyll (HNLC), iron-depleted tropical oceans. At least four novel Synechococcus clades (out of six clades in total) in subcluster 5.3 were found in subtropical open oceans and the South China Sea. A niche partitioning with depth was observed in the Synechococcus subcluster 5.3. Members of Synechococcus subcluster 5.2 were dominant in the high-latitude waters (northern Bering Sea and Chukchi Sea), suggesting a possible cold-adaptation of some marine Synechococcus in this subcluster. A distinct shift of the picocyanobacterial community was observed from the Bering Sea to the Chukchi Sea, which reflected the change of water temperature. Our study demonstrates that oceanic systems contain a large pool of diverse picocyanobacteria, and further suggest that new genotypes or ecotypes of picocyanobacteria will continue to emerge, as microbial consortia are explored with advanced sequencing technology.     

Phylogeography of Middle American gophersnakes: mixed responses to biogeographical barriers across the Mexican Transition Zone

Aim We used inferences of phylogeographical structure and estimates of divergence times for three species of gophersnakes (Colubridae: Pituophis) distributed across the Mexican Transition Zone (MTZ) to evaluate the postulated association of three Neogene geological events (marine seaway inundation of the Isthmus of Tehuantepec, formation of the Transvolcanic Belt across central Mexico, and secondary uplifting of the Sierra Madre Occidental) and of Pleistocene climate change with inter‐ and intraspecific diversification. Location Mexico, Guatemala, and the western United States. Methods We combined range‐wide sampling (67 individuals representing three putative species distributed across northern Middle America and western North America) and phylogenetic analyses of 1637 base pairs of mitochondrial DNA to estimate genealogical relationships and divergence times. The hypothesized concordance of inferred gene trees with geological histories was assessed using topology tests. Results We identified three major lineages of Middle American gophersnakes, and strong phylogeographical structure within each lineage. Gene trees were statistically congruent with hypothesized geological histories for two of the three postulated geological events. Estimated divergence dates and the geographical distribution of genetic variation further support mixed responses to these geological events. Considerable phylogeographical structure appears to have been generated during the Pleistocene. Main conclusions Phylogenetic and phylogeographical structure in gophersnakes distributed across northern Middle America and western North America highlights the influence of both Neogene vicariance events and Pleistocene climate change in shaping genetic diversity in this region. Despite the presence of two major geographical barriers in southern Mexico, extreme geological and environmental heterogeneity in this area may have differentially structured genetic diversity in highland taxa. To the north, co‐distributed taxa may display a more predictable pattern of diversification across the warm desert regions. Future studies should incorporate nuclear data to disentangle inferred lineage boundaries and further elucidate patterns of mitochondrial introgression.     

Analysis of rbcL sequences reveals the global biodiversity,community structure,and biogeographical pattern of thermoacidophilic red algae (Cyanidiales)

Thermoacidophilic cyanidia (Cyanidiales) are the primary photosynthetic eukaryotes in volcanic areas. These red algae also serve as important model organisms for studying life in extreme habitats. The global biodiversity and community structure of Cyanidiales remain unclear despite previous sampling efforts. Here, we surveyed the Cyanidiales biodiversity in the Tatun Volcano Group (TVG) area in Taiwan using environmental DNA sequencing. We generated 174 rbcL sequences from eight samples from four regions in the TVG area, and combined them with 239 publicly available rbcL sequences collected worldwide. Species delimita‐tion using this large rbcL data set suggested at least 20 Cyanidiales OTUs (operational taxono‐mic units) worldwide, almost three times the presently recognized seven species. Results from environmental DNA showed that OTUs in the TVG area were divided into three groups: (i) dominant in hot springs with 92%–99% sequence identity to Galdieria maxima; (ii) largely distributed in drier and more acidic microhabitats with 99% identity to G. partita; and (iii) primarily distributed in cooler microhabitats and lacking identity to known cyanidia species (a novel Cyanidiales lineage). In both global and individual area analyses, we observed greater species diversity in non‐aquatic than aquatic habitats. Community structure analysis showed high similarity between the TVG community and West Pacific‐Iceland communities, reflecting their geographic proximity to each other. Our study is the first examination of the global species diversity and biogeographic affinity of cyanidia. Additionally, our data illuminate the influence of microhabitat type on Cyanidiales diversity and highlight intriguing questions for future ecological research.     

The global distribution of ecosystems in a world without fire

This paper is the first global study of the extent to which fire determines global vegetation patterns by preventing ecosystems from achieving the potential height, biomass and dominant functional types expected under the ambient climate (climate potential). To determine climate potential, we simulated vegetation without fire using a dynamic global-vegetation model. Model results were tested against fire exclusion studies from different parts of the world. Simulated dominant growth forms and tree cover were compared with satellite-derived land- and tree-cover maps. Simulations were generally consistent with results of fire exclusion studies in southern Africa and elsewhere. Comparison of global 'fire off' simulations with landcover and treecover maps show that vast areas of humid C(4) grasslands and savannas, especially in South America and Africa, have the climate potential to form forests. These are the most frequently burnt ecosystems in the world. Without fire, closed forests would double from 27% to 56% of vegetated grid cells, mostly at the expense of C(4) plants but also of C(3) shrubs and grasses in cooler climates. C(4) grasses began spreading 6-8 Ma, long before human influence on fire regimes. Our results suggest that fire was a major factor in their spread into forested regions, splitting biotas into fire tolerant and intolerant taxa.     

Revision of the genus Chalcasthenes Arrow (Coleoptera: Scarabaeidae: Dynastinae: Oryctoderini) from the Solomon Islands

The genus Chalcasthenes Arrow (Dynastinae: Oryctoderini), a scarab beetle genus endemic to the Solomon Islands, is reviewed. Based on examination of type specimens, the genus Strehlia Frey (Rutelinae: Rutelini: Parastasiina) is a new junior synonym of Chalcasthenes . The historical classification of these genera (either in the subfamily Dynastinae or Rutelinae) and character-based criteria for assigning the taxa to the Dynastinae are provided. We discuss character states that support the monophyly of members of the genus Chalcasthenes, comment on the distribution and biogeography of species in the genus and provide a key to species. The genus includes four species: Chalcasthenes divinus Endrödi, Chalcasthenes pulcher Arrow, Chalcasthenes squamigerus Frey new combination and Chalcasthenes styracoceros Jameson and Ratcliffe n. sp. Species hypotheses are corroborated based on evidence from Pleistocene geological reconstructions of the Solomon Islands, geographic variation of bird species in the region and development in scarab beetles.     

Species boundaries and global biogeography of the Alexandrium tamarense complex (Dinophyceae)1

Alexandrium catenella (Whedon et Kof.) Balech, A. tamarense (M. Lebour) Balech, and A. fundyense Balech comprise the A. tamarense complex, dinoflagellates responsible for paralytic shellfish poisoning worldwide. The relationships among these morphologically defined species are poorly understood, as are the reasons for increases in range and bloom occurrence observed over several decades. This study combines existing data with new ribosomal DNA sequences from strains originating from the six temperate continents to reconstruct the biogeography of the complex and explore the origins of new populations. The morphospecies are examined under the criteria of phylogenetic, biological, and morphological species concepts and do not to satisfy the requirements of any definition. It is recommended that use of the morphospecies appellations within this complex be discontinued as they imply erroneous relationships among morphological variants. Instead, five groups (probably cryptic species) are identified within the complex that are supported on the basis of large genetic distances, 100% bootstrap values, toxicity, and mating compatibility. Every isolate of three of the groups that has been tested is nontoxic, whereas every isolate of the remaining two groups is toxic. These phylogenetic groups were previously identified within the A. tamarense complex and given geographic designations that reflected the origins of known isolates. For at least two groups, the geographically based names are not indicative of the range occupied by members of each group. Therefore, we recommend a simple group‐numbering scheme for use until the taxonomy of this group is reevaluated and new species are proposed.     

全球气候变化下的海洋浮游植物多样性

理解全球气候变化对地球生态系统的影响是全世界广泛关注的问题, 而相比于陆地生态系统, 海洋生态系统对全球气候变化更为敏感。全球气候变化对海洋的影响主要表现在海洋暖化、海洋酸化、大洋环流系统的改变、海平面上升、紫外线辐射增强等方面。浮游植物是海洋生态系统最重要的初级生产者, 同时对海洋碳循环起到举足轻重的作用, 其对全球气候变化的响应主要体现在物种分布、初级生产力、群落演替、生物气候学等方面。具体表现在以下方面: 暖水种的分布范围在扩大, 冷水种分布范围在缩小; 浮游植物全球初级生产力降低; 浮游植物群落会向细胞体积更小的物种占优势的方向转变; 浮游植物水华发生的时间提前、强度增强; 一些有害物种水华的发生频率也会增加; 海洋表层海水的酸化会影响浮游植物特别是钙化类群的生长和群落多样性; 紫外辐射增强对浮游植物的生长起到抑制作用; 厄尔尼诺、拉尼娜、降水量的增加通常抑制浮游植物生长。浮游植物生长和分布的变化会体现在多样性的各个层面上。对于浮游植物在全球变化各种驱动因子下的生理生态学和长周期变动观测等是今后研究的重要方向, 也将为理解全球变化下的浮游植物-多样性-生态系统响应与反馈机制提供基本信息。     

The biogeography of marine plankton traits

Changes in marine plankton communities driven by environmental variability impact the marine food web and global biogeochemical cycles of carbon and other elements. To predict and assess these community shifts and their consequences, ecologists are increasingly investigating how the functional traits of plankton determine their relative fitness along environmental and biological gradients. Laboratory, field and modelling studies are adopting this trait‐based approach to map the biogeography of plankton traits that underlies variations in plankton communities. Here, we review progress towards understanding the regulatory roles of several key plankton functional traits, including cell size, N₂‐fixation and mixotrophy among phytoplankton, and body size, ontogeny and feeding behaviour for zooplankton. The trait biogeographical approach sheds light on what structures plankton communities in the current ocean, as well as under climate change scenarios, and also allows for finer resolution of community function because community trait composition determines the rates of significant processes, including carbon export. Although understanding of trait biogeography is growing, uncertainties remain that stem, in part, from the paucity of observations describing plankton functional traits. Thus, in addition to recommending widespread adoption of the trait‐based approach, we advocate for enhanced collection, standardisation and dissemination of plankton functional trait data.