Character displacement among bat-pollinated flowers of the genus Burmeistera: analysis of mechanism, process and pattern

Coexisting plants that share pollinators can compete through interspecific pollen transfer. A long-standing idea holds that divergence in floral morphology may reduce this competition by placing pollen on different regions of the pollinator's bodies. However, surprisingly little empirical support for this idea exists. Burmeistera is a diverse neotropical genus that exhibits wide interspecific variation in the degree to which the reproductive parts are exserted outside the corolla. Coexisting Burmeistera share bats as their primary pollinators, and the degree of exsertion determines the site of pollen deposition on the bats' heads. Here we study the mechanism, process and pattern of floral character displacement for assemblages of coexisting Burmeistera. Flight cage experiments with bats and pairs of Burmeistera species demonstrate that the greater the divergence in exsertion length, the less pollen transferred interspecifically. Null model analyses of exsertion lengths for 19 species of Burmeistera across 18 sites (each containing two to four species) demonstrate that observed assemblage structure is significantly overdispersed relative to what would be expected by chance. Local evolution, rather than ecological sorting, appears to be the primary process driving this pattern of overdispersion because local adaptation of the nine widespread species accounts for a large portion of the observed pattern. Taken together, results of this study provide strong support for the idea that competition through interspecific pollen transfer can drive character displacement in plants.     

Interactions between RAMP2 and CRF receptors: The effect of receptor subtypes,splice variants and cell context

Corticotrophin releasing factor (CRF) acts via two family B G-protein-coupled receptors, CRFR1 and CRFR2. Additional subtypes exist due to alternative splicing. CRFR1α is the most widely expressed subtype and lacks a 29-residue insert in the first intracellular loop that is present in CRFR1β. It has been shown previously that co-expression of CRFR1β with receptor activity modifying protein 2 (RAMP2) in HEK 293S cells increased the cell-surface expression of both proteins suggesting a physical interaction as seen with RAMPs and calcitonin receptor-like receptor (CLR). This study investigated the ability of CRFR1α, CRFR1β and CRFR2β to promote cell-surface expression of FLAG-tagged RAMP2. Four different cell-lines were utilised to investigate the effect of varying cellular context; COS-7, HEK 293T, HEK 293S and [ΔCTR]HEK 293 (which lacks endogenous calcitonin receptor). In all cell-lines, CRFR1α and CRFR1β enhanced RAMP2 cell-surface expression. The magnitude of the effect on RAMP2 was dependent on the cell-line ([ΔCTR]HEK 293 > COS-7 > HEK 293T > HEK 293S). RT-PCR indicated this variation may relate to differences in endogenous RAMP expression between cell types. Furthermore, pre-treatment with CRF resulted in a loss of cell-surface FLAG-RAMP2 when it was co-expressed with CRFR1 subtypes. CRFR2β co-expression had no effect on RAMP2 in any cell-line. Molecular modelling suggests that the potential contact interface between the extracellular domains of RAMP2 and CRF receptor subtypes is smaller than that of RAMP2 and CRL, the canonical receptor:RAMP pairing, assuming a physical interaction. Furthermore, a specific residue difference between CRFR1 subtypes (glutamate) and CRFR2β (histidine) in this interface region may impair CRFR2β:RAMP2 interaction by electrostatic repulsion.     

Candidatus Prosiliicoccus vernus,a spring phytoplankton bloom associated member of the Flavobacteriaceae

Microbial degradation of algal biomass following spring phytoplankton blooms has been characterised as a concerted effort among multiple clades of heterotrophic bacteria. Despite their significance to overall carbon turnover, many of these clades have resisted cultivation. One clade known from 16S rRNA gene sequencing surveys at Helgoland in the North Sea, was formerly identified as belonging to the genus Ulvibacter. This clade rapidly responds to algal blooms, transiently making up as much as 20% of the free-living bacterioplankton. Sequence similarity below 95% between the 16S rRNA genes of described Ulvibacter species and those from Helgoland suggest this is a novel genus. Analysis of 40 metagenome assembled genomes (MAGs) derived from samples collected during spring blooms at Helgoland support this conclusion. These MAGs represent three species, only one of which appears to bloom in response to phytoplankton. MAGs with estimated completeness greater than 90% could only be recovered for this abundant species. Additional, less complete, MAGs belonging to all three species were recovered from a mini-metagenome of cells sorted via flow cytometry using the genus specific ULV995 fluorescent rRNA probe. Metabolic reconstruction indicates this highly abundant species most likely degrades proteins and the polysaccharide laminarin. Fluorescence in situ hybridisation showed coccoid cells, with a mean diameter of 0.78 mm, with standard deviation of 0.12 μm. Based on the phylogenetic and genomic characteristics of this clade, we propose the novel candidate genus Candidatus Prosiliicoccus, and for the most abundant and well characterised of the three species the name Candidatus Prosiliicoccus vernus.     

Trilobite ‘pelotons’: possible hydrodynamic drag effects between leading and following trilobites in trilobite queues

Energy saving mechanisms in nature allow following organisms to expend less energy than leaders. Queues, or ordered rows of individuals, may form when organisms exploit the available energy saving mechanism while travelling at near‐maximal sustainable metabolic capacities; compact clusters form when group members travel well below maximal sustainable metabolic capacities. The group size range, given here as the ratio of the difference between the size of the largest and smallest group members, and the size of the largest member (as a percentage), has been hypothesized to correspond proportionately to the energy saving quantity because weaker, smaller, individuals sustain the speeds of stronger, larger, individuals by exploiting the energy saving mechanism (as a percentage). During migration, small individuals outside this range may perish, or form sub‐groups, or simply not participate in migratory behaviour. We approximate drag forces for leading and following individuals in queues of the late Devonian (c. 370 Ma) trilobite Trimerocephalus chopini. Applying data from literature on Rectisura herculea, a living crustacean, we approximate the hypothetical walking speed and maximal sustainable speeds for T. chopini. Our findings reasonably support the hypothesis that among the population of fossilized queues of T. chopini reported in the literature, trilobite size range was 75%, while the size range within queues was 63%; this corresponds reasonably with drag reductions in following positions that permit c. 61.5% energy saving for trilobites following others in optimal low‐drag positions. We model collective trilobite behaviour associated with hydrodynamic drafting.     

The molecular mechanism underlying unconventional secretion of Fibroblast Growth Factor 2 from tumour cells

Fibroblast Growth Factor 2 (FGF2) is a potent cell survival factor involved in tumour‐induced angiogenesis. FGF2 is secreted from cells through an unconventional secretory mechanism based upon direct translocation across the plasma membrane. The molecular mechanism underlying this process depends on a surprisingly small set of trans‐acting factors that are physically associated with the plasma membrane. FGF2 membrane translocation is mediated by the ability of FGF2 to oligomerise and to insert into the plasma membrane in a PI(4,5)P₂‐dependent manner. Membrane‐inserted FGF2 oligomers are dynamic translocation intermediates that are disassembled at the extracellular leaflet mediated by membrane proximal heparan sulphate proteoglycans. This process results in the exposure of FGF2 on cell surfaces as part of its unconventional mechanism of secretion. Although the trans‐acting factors and cis‐elements in FGF2 required for unconventional secretion have been known for a while, the core mechanism of this mysterious process has now been reconstituted with purified components establishing the molecular basis of FGF2 secretion from tumour cells.     

集合群落及其在河流鱼类群聚研究中的应用

集合群落(metacommunity)是指多个潜在相互作用的物种通过它们之间的扩散而连接在一起的一组局域群落,目前已成为斑块生境下生物群落结构、格局和动态的重要理论基础之一。斑块动态、物种排序、群体效应和中性模型等4种理论模型,可用于解释不同情形下集合群落内物种的迁移状况,描述集合群落的动态。可采用群落结构或生态学机制等途径,来阐述所研究的群落是属于哪一种特定的集合群落类型。集合群落可用于研究河流鱼类群聚,解释鱼类的群落结构等问题。另外本文还结合我国水域生态环境及水生生物现状,对今后集合群落的研究作了展望。     

Community Composition of Photosynthetic Picoeukaryotes in a Subtropical Coastal Ecosystem,with Particular Emphasis on Micromonas

Photosynthetic picoeukaryotes (PPEs) are important constituents in picoplankton communities in many marine ecosystems. However, little is known about their community composition in the subtropical coastal waters of the Northwestern Pacific Ocean. In order to study their taxonomic composition, this study constructed 18S rRNA gene libraries using flow cytometric sorting during the warm season. The results show that, after diatoms, prasinophyte clones are numerically dominant. Within prasinophytes, Micromonas produced the most common sequences, and included clades II, III, IV, and VI. We are establishing the new Micromonas clade VI based on our phylogenetic analysis. Sequences of this clade have previously been retrieved from the South China Sea and Red Sea, indicating a worldwide distribution, but this is the first study to detect clade VI in the coastal waters of Taiwan. The TSA‐FISH results indicated that Micromonas clade VI peaked in the summer (~4 × 10² cells/ml), accounting for one‐fifth of Micromonas abundance on average. Overall, Micromonas contributed half of Mamiellophyceae abundance, while Mamiellophyceae contributed 40% of PPE abundance. This study demonstrates the importance of Micromonas within the Mamiellophyceae in a subtropical coastal ecosystem.     

Multi-objective optimization of cascade reservoirs using NSGA-II: A case study of the Three Gorges-Gezhouba cascade reservoirs in the middle Yangtze River,China

A multi-objective optimization model of cascade reservoirs was developed to maximize the power generation and minimizie the appropriate ecological flow shortage index (AEFSI) downstream from the reservoir. Additionally, the non-dominated sorting genetic algorithm (NSGA-II) was used to search for multi-objective Pareto optimal solutions. The paper took the Three Gorges-Gezhouba cascade reservoirs as a case study. After validating the model, data from three typical years were used in the optimization. The results indicated that maximizing power generation by adjusting the optimal rules increased power generation by 1.07%, 0.91%, and 1.03% in normal, wet, and dry hydrological years, respectively, while increasing the AEFSI by 22.12%, 11.78%, and 14.67% (compared to real operations). The AEFSI was improved (decreased) by 21.90%, 10.27%, and 18.52% when the optimal rules favored the downstream ecology, but power generation decreased by 1.61%, 1.06%, and 2.29%, respectively, in the different hydrological years. Moreover, the results provide a set of well-distributed optimal solutions along the Pareto front that allow decision-makers to easily determine the best compromised solutions based on the trade-offs between the economic and ecological benefits. The results of this study provide guidance for decision-makers to improve the comprehensive benefits of the Three Gorges-Gezhouba cascade reservoirs.     

Environmental factors exert predominant effects on testate amoeba metacommunities during droughts in floodplains

Metacommunities have been evaluated as models for the relative importance of environmental and spatial processes in assembling ecological communities. Here, we tested the hypothesis that different hydrological periods (drought and flooding) influence the environmental associations of planktonic testate amoeba metacommunities. We predicted that environmental factors would exert the strongest effects on species dispersal under drought, but that they would be less significant during flooding. Testate amoebae were sampled during drought and flooding, from 72 lakes in four Brazilian floodplains (Amazonian, Araguaia, Pantanal and Paraná). Partial redundancy analysis indicated that only environmental factors were significant; they were significant in all floodplain lakes during the drought. Only the Paraná floodplain had significant results for environmental factors during both hydrological periods. Spatial factors did not contribute significantly to any of the metacommunities. The depth, pH and variables related to environmental productivity were identified as major predictors in the assembly of testate amoeba communities. Our results highlight that different hydrological periods vary in their relative importance in environmental and spatial processes. The species‐sorting model was predominant during drought, while stochastic processes prevailed during flooding in all but the Paraná floodplain. In the Paraná floodplain, the construction of dams could potentially alter the effects of environmental and spatial factors on the dispersal of planktonic testate amoebae. The pH and the environmental productivity factors were largely responsible for species selection and the structuring of the planktonic testate amoebae metacommunities in Brazilian floodplains.     

Competition drives trait evolution and character displacement between Mimulus species along an environmental gradient

Closely related species may evolve to coexist stably in sympatry through niche differentiation driven by in situ competition, a process termed character displacement. Alternatively, past evolution in allopatry may have already sufficiently reduced niche overlap to permit establishment in sympatry, a process called ecological sorting. The relative importance of each process to niche differentiation is contentious even though they are not mutually exclusive and are both mediated via multivariate trait evolution. We explore how competition has impacted niche differentiation in two monkeyflowers, Mimulus alsinoides and M. guttatus, which often co‐occur. Through field observations, common gardens, and competition experiments, we demonstrate that M. alsinoides is restricted to marginal habitats in sympatry and that the impacts of character displacement on niche differentiation are complex. Competition with M. guttatus alters selection gradients and has favored taller M. alsinoides with earlier seasonal flowering at low elevation and floral shape divergence at high elevation. However, no trait exhibits the pattern typically associated with character displacement, higher divergence between species in sympatry than allopatry. Thus, although character displacement was unlikely the process driving initial divergence along niche axes necessary for coexistence, we conclude that competition in sympatry has likely driven trait evolution along additional niche axes.