Major Environmental Gradients Research Articles

Gene duplication, shifting selection, and dosage balance of silicon transporter proteins in marine and freshwater diatoms.

Numerous factors shape the evolution of protein-coding genes, including shifts in the strength or type of selection following gene duplications or changes in the environment. Diatoms and other silicifying organisms use a family of silicon transporters (SITs) to import dissolved silicon from the environment. Freshwaters contain higher silicon levels than oceans, and marine diatoms have more efficient uptake kinetics and less silicon in their cell walls, making them better competitors for a scarce resource. We compiled SITs from 37 diatom genomes to characterize shifts in selection following gene duplications and marine-freshwater transitions. A deep gene duplication, which coincided with a whole genome duplication, gave rise to two gene lineages. One of them (SIT1-2) is present in multiple copies in most species and is known to actively import silicon. These SITs have evolved under strong purifying selection that was relaxed in freshwater taxa. Episodic diversifying selection was detected but not associated with gene duplications or habitat shifts. In contrast, genes in the second SIT lineage (SIT3) were present in just half the species, the result of multiple losses. Despite conservation of SIT3 in some lineages for the past 90-100 million years, repeated losses, relaxed selection, and low expression highlighted the dispensability of SIT3, consistent with a model of deterioration and eventual loss due to relaxed selection on SIT3 expression. The extensive but relatively balanced history of duplications and losses, together with paralog-specific expression patterns, suggest diatoms continuously balance gene dosage and expression dynamics to optimize silicon transport across major environmental gradients.

Taxonomic and functional diversity of nematode fauna: two sides of the same coin in the ecological quality assessment of transitional environments

The spatiotemporal variation in taxonomic indices and functional traits of the nematode fauna was investigated along two major environmental (salinity and organic matter enrichment) gradients in the Cabras Lagoon (Sardinia, Italy). We aimed to assess, for the first time in a transitional system of western Mediterranean Sea, how taxonomic and functional components of nematode assemblage respond to such environmental factors. The taxonomic structure was the most sensitive metric to document changes in the nematode assemblage, showing significant differences in relation to all the factors and their interactions. All the taxonomic and functional nematode features, except for the maturity index (MI), proved salinity and organic enrichment to be the primary drivers of nematode distribution. The lack of significant variation in the MI is quite interesting and can be interpreted because of the marked adaptation of nematodes to highly dynamic environmental conditions of brackish and confined habitats. Temperature mainly affected faunal composition, abundance, and diversity, due to its influence on fecundity and biological cycles on almost all species. Integrating the taxonomic and functional components of nematodes as “two-sides of the same coin”, the Shannon diversity index, the percentage of coloniser–persisters and the MI were used together to assess the Ecological Quality Status (EQS) of the study sites, which ranged from poor to bad. Nematodes proved to be good indicators of the environmental variations in the investigated lagoon ecosystem. Importantly, the joint use of taxonomic and functional approaches provided integrative knowledge of nematode response to environmental gradients. We conclude that combining nematode-based taxonomic and functional indicators represent a valuable tool to assess the environmental quality of lagoonal ecosystems and may provide complementary information to macrofauna.

On the biodiversity of diatom communities in lakes of East China: Geochemical effects dominated after eutrophication

AbstractAimOver the last century, lakes all over the world have experienced significant eutrophication and become more susceptible to critical transitions. This has prompted a growing need to understand how community dynamics shift following ecological perturbations. This study aims to elucidate the present status, spatial patterns and determinants of biological diversity, and how they have changed in response to alterations driven by eutrophication.LocationLakes of East China, mostly in the Yangtze River Basin.TaxaBacillariophyceae (163 species in 33 genres, see taxa names in Appendix S1).MethodsThe environmental conditions of over 60 lakes were assessed based on parameters such as water quality, physical characteristics and biogeochemical constituents. Surface sediment samples and high‐resolution sediment records were collected to quantify the biodiversity of diatom communities, and principal component analysis (PCA) was used to determine the major environmental gradients. Meanwhile, linear regression, canonical correlation analysis and Mantel tests were used to quantify the correlations between variables.ResultsBiodiversity metrics showed no distinct geographic patterns, although areas near large lakes showed comparatively high evenness. Smaller pairwise dissimilarities were observed among hypereutrophic lakes in comparison to lakes with a lower trophic status. The past century has witnessed a decrease in both pairwise dissimilarity and the standard deviation of evenness. A significant statistical association was found between dissimilarity and ionic concentration and composition in the surface sediment of lakes, rather than nutrient levels.Main ConclusionsFollowing regional eutrophication and human disturbance, a significant reduction in biodiversity differentiation was observed in lakes located in East China. Currently, the dominant factor in determining the beta diversity of diatom communities is geochemical conditions rather than nutrient concentrations. Long‐term stress caused by cultural eutrophication may also have altered the dominant determinant of regional biodiversity and diatom community dynamics.

Evolutionary Processes Shaping Postglacial Gene Pools of High-Altitude Forests: Evidence from the Endemic Eucalypts of Tasmania

Climatic changes during the Pleistocene were responsible for dramatic redistributions of plant species worldwide. On the rugged southern hemisphere island of Tasmania, temperature increases following the last glaciation saw upslope migration of climatically suitable species from lowland refugia and the expansion of eucalypt-dominated forests and woodlands in the Central Highlands. We integrate multiple lines of evidence (chloroplast and nuclear DNA markers, seedling morphology, and survival in common garden experiments) from a group of closely related endemic eucalypts (the alpine white gums) to argue that (i) the Central Highlands of the island were colonised by multiple glacial refugia with hybridisation among species and previously separated populations, and (ii) natural selection has filtered the admixed populations, resulting in local adaptation to the harsh sub-alpine environment. Chloroplast haplotype diversity decreased and nuclear microsatellite diversity increased with altitude, chloroplast sharing among taxa was common, and nuclear DNA differentiation of morphologically distinct taxa was lower in the Central Highlands compared with lowland regions. Local adaptation in the highlands was signalled by evidence from (i) a glasshouse trial in which directional selection (QST > FST) had shaped seedling morphological trait variation and (ii) population survival differences in 35-year-old reciprocal plantings along the major environmental gradients. We conclude that the evolutionary response of these island endemic trees to past climate change has involved the interplay of both hybridisation and natural selection, highlighting the importance of maintaining species interactions under future climate change.

Comparative analysis of zooplankton diversity in freshwaters: What can we gain from metagenomic analysis?

AbstractMolecular genetic approaches applied to environmental DNA have great potential for biodiversity research and ecosystem monitoring. A metagenome is produced via shotgun sequencing of DNA collected directly from the environment and represents a sample of genetic information from all organisms captured in an environmental sample. Metagenomes have been primarily used to study bacteria and archaea, but promising reports focusing on metazoan diversity are emerging. However, methodological uncertainties remain, and studies are required to validate the power and the limitations of such an approach when applied to macro‐eukaryotes. Here, we analyzed water sample metagenomes to estimate zooplankton diversity in 22 freshwater lakes across eastern Canada. We tested the coherence of data based on field samples collected at the same time: 1) morphologically identified zooplankton specimens and 2) molecular genetic data derived from shotgun sequencing of environmental DNA for which we applied two different bioinformatic workflows: a whole metagenome mapping approach and a small subunit (SSU) rRNA gene prediction approach. We further evaluated diversity trends emerging from each dataset in relation to major environmental gradients. We found a significant correlation between the relative abundance of zooplankton families identified based on SSU rRNA gene prediction and morphology. However, differences in congruence between metagenomes and morphological identifications were detected when varied bioinformatic approaches were applied to the presence–absence data. This study presents one of the first diversity assessments of a group of aquatic metazoans using metagenomes and validates the coherence of the community composition derived from genomic and classical species surveys. Overall, our results suggest that metagenomics has the potential to be further developed to describe metazoan biodiversity in aquatic ecosystems, and to advance this area we provide key recommendations for workflow improvement.

Trait variation, trade-offs, and attributes may contribute to colonization and range expansion of a globally distributed weed.

Trait variation, trade-offs, and attributes can facilitate colonization and range expansion. We explored how those trait features compare between ancestral and nonnative populations of the globally distributed weed Centaurea solstitialis. We measured traits related to survival, size, reproduction, and dispersal in field sampling following major environmental gradients; that of elevation in Anatolia (ancestral range) and that of precipitation in Argentina (nonnative range). We also estimated abundance. We found that overall variation in traits in ancestral populations was similar to that in nonnative populations. Only one trait-seed mass-displayed greater variation in ancestral than nonnative populations; coincidentally, seed mass has been shown to track global range expansion of C. solstitialis. Traits displayed several associations, among which seed mass and number were positively related in both ranges. Many traits varied with elevation in the ancestral range, whereas none varied with precipitation in the nonnative one. Interestingly, most traits varying with elevation within the ancestral range also displayed differences in attributes between ancestral and nonnative ranges. Unexpectedly, ancestral plants were more fecund than nonnative plants, but density was greater in the nonnative than ancestral range, indicating that C. solstitialis survives at larger proportions in the nonnative than ancestral range. Our results suggest that maintaining levels of trait variation in nonnative populations comparable to those in ancestral populations, avoiding trait trade-offs, and developing differences in trait attributes between ranges can play a major role in the success of many weeds in novel environments.

Environmental DNA metabarcoding uncovers environmental correlates of fish communities in spatially heterogeneous freshwater habitats

Biomonitoring of complex heterogeneous environments is highly challenging. Fish in deep water bodies occupy different habitats, so a combination of survey methods has traditionally been used. Environmental DNA (eDNA) metabarcoding is a novel monitoring tool that can overcome spatial heterogeneity in a highly sensitive and entirely non-invasive manner. However, taxon detection probability is dependent on environmental variables. In this study, three reservoirs were sampled in two seasons using a spatiotemporally distributed sampling design covering major environmental gradients. In all sampling campaigns, 31 fish taxa were detected. Data reliability was supported by tight positive correlations between individual taxon scores derived from gillnet sampling and eDNA site occupancy. Analyses confirmed anticipated trends, such as the highest number of taxa in the largest water body, and more taxa in inflows and littoral regions compared to open water. The most important factors for fish distribution were temperature, water age and trophic status (expressed as total Chlorophyll a concentration) of water bodies. Taxon detection reflected ecological niches of individual species, e.g. warm water wels catfish (Silurus glanis) and cold water salmonids. This study provides further evidence that eDNA metabarcoding is a suitable alternative or complement to conventional fish sampling in reservoirs.

Ecological Interactions, Environmental Gradients, and Gene Flow in Local Adaptation.

Despite long-standing interest in local adaptation of plants to their biotic and abiotic environment, existing theory, and many case studies, little work to date has addressed within-species evolution of concerted strategies and how these might contrast with patterns across species. Here we consider the interactions between pollinators, herbivores, and resource availability in shaping plant local adaptation, how these interactions impact plant phenotypes and gene flow, and the conditions where multiple traits align along major environmental gradients such as latitude and elevation. Continued work in emerging model systems will benefit from the melding of classic experimental approaches with novel population genetic analyses to reveal patterns and processes in plant local adaptation.

Calculating cumulative effects in GIS using a stepless multivariate model

The paper present a streamlined workflow, using multivariate analyses of environmental variables in combinations with GIS overlay analyses that provide methods to extract and analyse major environmental and climatic gradients by using fishnet polygons as sample units. The method opens for illustrating multivariate results as geographical maps and as PCA plots using sample scores as coordinates. Then the PCA sample scores can be allocated to fishnets polygons and each sample score can be assigned with its ID and other attributes to each fishnet polygon. This is used to construct a cumulative impact model based on PCA fishnet polygon frequency scores and further to measure representativity of nature protected areas. It also provide possibilities for testing of a range of different hypothesis. The method present the numerical results visually in both the PCA sample score plot and in a geographical map, and can be used as a part of cumulative impact analysis to assess representativeness of mapped or modelled valued environmental components (VECs). It can be applied to existing as well as planned or potential infrastructure and other technical developments. •The Stepless Multivariate Model is an explicit, transferable and reproducible procedure to conduct systematic assessment of cumulative impacts based on an analysis of representativity.•The method can be used to illustrate the analysis both geographically and numerically.•The procedure in the method has a potential wide range of applications and can form a basis for hypothesis testing.

Large‐scale multi‐trophic co‐response models and environmental control of pelagic food webs in Québec lakes

Environmental heterogeneity plays a fundamental role in driving species distributions by, for one, fostering niche dimensionality. Within lake ecosystems, species distributions and concordance patterns are driven by both local and regional heterogeneity, though their relative importance across trophic levels has rarely been explored. We developed a statistical framework to compare responses of taxa from different trophic levels to abiotic factors and determine how this affected multi‐trophic network structures. In particular, we used multi‐species concordance modelling (concordance analysis and RV coefficient) to determine species associations and correlations within and among three trophic levels (phytoplankton, zooplankton and fish communities sampled across 49 southern Québec lakes, covering eight hydrological regions). We then used multiple factor analysis, latent variable modelling and local contributions of sites to beta diversity to assess the relative importance of major environmental gradients in structuring species co‐responses and species interaction turnover across the landscape. Our analyses confirmed that concordant species within each trophic level varied jointly or segregated into different pelagic food webs in Québec lakes where important acidification and eutrophication took place. Some keynote species were indicators of different food web compartments and distinguished groups of lakes along multiple environmental niche dimensions. Among the three trophic levels examined, zooplankton depicted the highest proportion of species concordance and appeared to act as a trophic linkage between phytoplankton and fish. Ultimately, the losses or gains in species richness and species interactions were strongly driven by environmental gradients. This study provides for the first time a combined analysis of the effects of environmental heterogeneity on ecological communities belonging to three trophic levels sampled near simultaneously across an 800 km broad lacustrine landscape. The new framework developed in this study has a great potential to better understand the complex response of aquatic ecosystems in a world increasingly affected by multiple, cumulative stressors.

Behavioural response to simulated avian predation varies with latitude and predation intensity of natural populations

The intensity of ecological interactions is generally expected to increase at lower latitudes, suggesting potential to shape prey behavior at broad spatial scales. Yet, there is relatively limited understanding of how animal behavior varies across major environmental gradients for most taxonomic groups. In this study, I investigated behavioral response of a livebearing fish, Gambusia holbrooki, to a simulated avian predator. Fish originated from 17 populations distributed across 15° latitude. Across this latitudinal expanse, the richness of piscivorous birds varied significantly. Consistent with putative predation pressure, antipredator responses were more frequent in regions with greater inferred predation pressure. Predator richness and latitude covaried significantly across the study region, indicating a need to further disentangle drivers of behavioral evolution including potentially correlated unmeasured variables. Nonetheless, this study demonstrates the importance of environmental variation for shaping patterns of animal behavior at a broad spatial scale (2000+ km), which may be important for understanding a range of ecological processes such as disease transmission and invasion dynamics.

Ecosystem-wide metagenomic binning enables prediction of ecological niches from genomes

The genome encodes the metabolic and functional capabilities of an organism and should be a major determinant of its ecological niche. Yet, it is unknown if the niche can be predicted directly from the genome. Here, we conduct metagenomic binning on 123 water samples spanning major environmental gradients of the Baltic Sea. The resulting 1961 metagenome-assembled genomes represent 352 species-level clusters that correspond to 1/3 of the metagenome sequences of the prokaryotic size-fraction. By using machine-learning, the placement of a genome cluster along various niche gradients (salinity level, depth, size-fraction) could be predicted based solely on its functional genes. The same approach predicted the genomes’ placement in a virtual niche-space that captures the highest variation in distribution patterns. The predictions generally outperformed those inferred from phylogenetic information. Our study demonstrates a strong link between genome and ecological niche and provides a conceptual framework for predictive ecology based on genomic data.

Towards a framework for understanding the context dependence of impacts of non‐native tree species

Abstract Biological invasions are a major driver of ecosystem change but causes of variation in their environmental impacts over space and time remain poorly understood. Most approaches used to quantify the impacts of non‐native species assume there are interactions among per capita (i.e. individual level) effects, species abundance and the area occupied by the species. However, studies rarely evaluate these factors and their interactions and often fail to recognize that the magnitude of impacts can be highly context dependent. Understanding what drives the context dependence of non‐native species impacts can improve our understanding and predictions of ecosystem change and better inform options for mitigation. Conifers, especially pines, are among the most problematic non‐native plant species globally. We use Pinaceae to illustrate how context dependence in biodiversity and environmental impacts of non‐native plant species can be generated by at least four processes: nonlinear density effects; intraspecific variation in functional traits; shifts in impacts over time; and persistence of impacts as biological or ecosystem legacies following non‐native species removal. Using this understanding, we develop a framework to better quantify interactions of impacts along environmental gradients (e.g. soil fertility, climate, ecosystem age). We demonstrate how impacts of non‐native species can occur at both low and high density, and that failing to account for intraspecific variation in effect traits can lead to significant errors in the prediction of impacts. By incorporating context dependence in regard to density and functional traits, we can measure how the interaction of this context dependence will shift along environmental gradients. Moreover, disentangling the roles of species and abundance along such gradients will provide new insights into the net effects of both the native and non‐native components of communities. We use a working example of our framework that incorporates all four processes to demonstrate how to measure fire risk impacts of Pinus contorta. We show that ecosystem impacts of non‐native tree species are not fixed but rather vary predictably along major environmental gradients. Moreover, removal of non‐native species through management provides an important tool for revealing biological and ecosystem legacy effects. Although we focus here on relatively well‐documented Pinaceae, the new insights into context dependence of impacts can be widely applied across species, environments and regions. A free Plain Language Summary can be found within the Supporting Information of this article.

A systematic survey of regional multi-taxon biodiversity: evaluating strategies and coverage

BackgroundIn light of the biodiversity crisis and our limited ability to explain variation in biodiversity, tools to quantify spatial and temporal variation in biodiversity and its underlying drivers are critically needed. Inspired by the recently published ecospace framework, we developed and tested a sampling design for environmental and biotic mapping. We selected 130 study sites (40 × 40 m) across Denmark using stratified random sampling along the major environmental gradients underlying biotic variation. Using standardized methods, we collected site species data on vascular plants, bryophytes, macrofungi, lichens, gastropods and arthropods. To evaluate sampling efficiency, we calculated regional coverage (relative to the known species number per taxonomic group), and site scale coverage (i.e., sample completeness per taxonomic group at each site). To extend taxonomic coverage to organisms that are difficult to sample by classical inventories (e.g., nematodes and non-fruiting fungi), we collected soil for metabarcoding. Finally, to assess site conditions, we mapped abiotic conditions, biotic resources and habitat continuity.ResultsDespite the 130 study sites only covering a minute fraction (0.0005%) of the total Danish terrestrial area, we found 1774 species of macrofungi (54% of the Danish fungal species pool), 663 vascular plant species (42%), 254 bryophyte species (41%) and 200 lichen species (19%). For arthropods, we observed 330 spider species (58%), 123 carabid beetle species (37%) and 99 hoverfly species (33%). Overall, sample coverage was remarkably high across taxonomic groups and sufficient to capture substantial spatial variation in biodiversity across Denmark. This inventory is nationally unprecedented in detail and resulted in the discovery of 143 species with no previous record for Denmark. Comparison between plant OTUs detected in soil DNA and observed plant species confirmed the usefulness of carefully curated environmental DNA-data. Correlations among species richness for taxonomic groups were predominantly positive, but did not correlate well among all taxa suggesting differential and complex biotic responses to environmental variation.ConclusionsWe successfully and adequately sampled a wide range of diverse taxa along key environmental gradients across Denmark using an approach that includes multi-taxon biodiversity assessment and ecospace mapping. Our approach is applicable to assessments of biodiversity in other regions and biomes where species are structured along environmental gradient.

Native American Land-Use Impacts on a Temperate Forested Ecosystem, West Central New York State

Land survey records (LSRs) describing forest species composition prior to extensive European American settlement are critical sources of information on past environmental controls of forest dynamics in eastern North America. Embedded within these historical data sources is evidence of prior Native American land use. This study expands on previous LSR-based analyses of Seneca and Iroquoian populations’ impacts on the temperate forests of west central New York State. We use an enhanced array of geospatial LSR vegetation data beyond conventional bearing tree data and implement, for the first time, combined indirect ordination of vegetation data along major environmental gradients and numerical classification of discrete upland vegetation communities. Nonmetric multidimensional scaling revealed three main drivers of vegetation dynamics in the study area: (1) fire frequency (53.7 percent of total variance); (2) soil productivity (22.6 percent variance); and (3) Native American land use (15.9 percent variance). Agglomerative hierarchical clustering reinforced the primacy of these gradients by delineating two major forest types differentiated primarily by fire frequency and secondarily by soil productivity. Seneca and Iroquoian agricultural villages were preferentially concentrated within fire-tolerant dry upland forests on high-productivity soils within the interior portion of the Lake Ontario Lowland. Fire-tolerant, dry upland forests on low-productivity soils were situated on the adjacent Appalachian Plateau, which was likely used by indigenous populations for silvicultural land-use activities. Native American disturbance of temperate forested ecosystems likely varied across the diverse culture areas of eastern North America, with the Seneca and Iroquois representing an extreme end-member within a broad continuum of anthropogenic disturbance. Key Words: forest composition, land survey records, land-use history, Native Americans, vegetation disturbance.

Carbon forms, nutrients and water velocity filter hydrophyte and riverbank species differently: A trait‐based study

AbstractQuestionsThe majority of theories of trait‐based plant community assembly have been developed and tested predominantly in terrestrial ecosystems. Studies investigating the functional trait composition of aquatic plant communities and their relation to environmental determinants remain scarce. Macrophytes are essential components of aquatic ecosystems, and a more detailed knowledge of their trait‐based assembly is crucial for their management. We identified how plant functional traits respond to environmental gradients in streams and rivers.LocationDanube River Catchment, Hungary.MethodsWe studied the processes governing community assembly along major environmental gradients related to carbon‐ and nutrient‐limiting factors as well as physical strain. We used six continuous traits (leaf area, specific leaf area, leaf dry matter content, seed weight, seed shape, woodiness) and calculated community‐weighted mean and standardised effect size of functional diversity for each community. We then used stepwise regression analyses for each trait along the environmental gradients to test which environmental factors explain the changes in community‐weighted mean and functional diversity. All analyses were conducted for aquatic (hydato‐helophyte) and riverbank species separately.ResultsWe found that the effect of environmental filtering significantly increased toward higher pH, indicating the response of functional traits to carbon limitation. Our results showed trait convergence among riverbank species in rivers with higher productivity. Larger functional diversity (i.e., trait divergence) among hydato‐helophyte species suggests an increase in the diversity of resource acquisition strategies under higher productivity.ConclusionsHere, we have shown that the functional trait distribution of aquatic and riverbank plant communities responds to major environmental drivers related to nutrient and carbon availability. The understanding of how community assembly mechanisms varied along environmental gradients might be useful when proposing future management and restoration plans and actions towards the conservation of the aquatic vegetation in streams and rivers.

Subsea tunnel reinforced sprayed concrete subjected to deterioration harbours distinct microbial communities

Deterioration of concrete is a large societal cost. In the Oslofjord subsea tunnel (Norway), deterioration of sprayed concrete and corrosion of reinforcing steel fibres occur under biofilm formed at sites with intrusion of saline groundwater. In this study, the microbial community structure, in situ environmental gradients and chemical composition of the biofilms were examined at three tunnel sites. Ammonia- and nitrite-oxidising microorganisms, in particular Nitrosopumilus sp., and iron-oxidising bacteria within Mariprofundus sp., were omnipresent, together with a diversity of presumably heterotrophic bacteria. Alpha- and beta diversity measures showed significant differences in richness and community structure between the sites as well as over time and null-models suggested that deterministic factors were important for the community assembly. The superficial flow of water over the biofilm had a strong effect on oxygen penetration in the biofilm and was identified as one major environmental gradient that varied between the sites, likely being important for shaping the microbial communities.

A global analysis of terrestrial plant litter dynamics in non-perennial waterways

Perennial rivers and streams make a disproportionate contribution to global carbon (C) cycling. However, the contribution of intermittent rivers and ephemeral streams (IRES), which sometimes cease to flow and can dry completely, is largely ignored although they represent over half the global river network. Substantial amounts of terrestrial plant litter (TPL) accumulate in dry riverbeds and, upon rewetting, this material can undergo rapid microbial processing. We present the results of a global research collaboration that collected and analysed TPL from 212 dry riverbeds across major environmental gradients and climate zones. We assessed litter decomposability by quantifying the litter carbon-to-nitrogen ratio and oxygen (O2) consumption in standardized assays and estimated the potential short-term CO2 emissions during rewetting events. Aridity, cover of riparian vegetation, channel width and dry-phase duration explained most variability in the quantity and decomposability of plant litter in IRES. Our estimates indicate that a single pulse of CO2 emission upon litter rewetting contributes up to 10% of the daily CO2 emission from perennial rivers and stream, particularly in temperate climates. This indicates that the contributions of IRES should be included in global C-cycling assessments.

Influence of environmental variation on the bacterioplankton community and its loss to viral lysis in the Curonian Lagoon

Coastal lagoons are continuously exposed to strong environmental gradients that determine the distribution and trophic interactions of microbial communities. Therefore, in this study we assessed whether and how environmental changes influence the bacterial community and its vulnerability to viral infection and lysis along the major environmental gradient in the Curonian Lagoon. We found significant differences in bacterial community profiles, their richness and evenness between the riverine, freshwater southern part and the Baltic Sea water intrusion-influenced northern part of the lagoon, suggesting strong environmental control of the structure of bacterial communities. Viruses were found to be play an important role in bacterial mortality in the Curonian Lagoon, being responsible for the removal of 20–50% of the bacterial standing stock. We observed differences in virioplankton decay rates and virus burst sizes between the northern and southern parts of the lagoon. However, no relationships were found between viral activity and bacterial communities within the lagoon ecosystem. The frequency of infected cells and virus-mediated bacterial mortality (VMBM) remained constant among the sampling sites irrespective of differences in bacteria community assemblages and environmental conditions. The results indicate that factors determining changes in bacterial diversity are different from the factors limiting their vulnerability to viral infection and lysis. This study also suggests that under changing environmental conditions, virus-bacteria interactions are more stable than the interacting viral and bacterial communities themselves. These findings are important for understanding the functioning of the coastal ecosystems under the rapidly changing local (spatial and temporal) and global (e.g. eutrophication, climate change) conditions.

An intercontinental comparison of niche conservatism along a temperature gradient

AbstractAimsPhylogenetic niche conservatism (PNC) predicts that closely related species will have similar distributions along major environmental gradients, e.g. temperature. We test this theory by comparing the central tendencies of temperature for selected woody genera, and investigating whether these genera have a similar rank order (sequence) across continents and hemispheres. A strong correlation may indicate niche conservatism, as inherited temperature tolerance would best explain a positive correlation.LocationPeru (Andes) and Nepal (Himalaya).MethodsElevation and temperature ranges for all species belonging to eight disjunct genera of woody plants were compiled. Central tendencies of congeneric species along the temperature gradient were established by means of reciprocal averaging and weighted average temperature. We correlated the rank order of genera from the Himalaya and Andes, and tested if the order in the Himalaya could predict the order in the Andes, using permutation procedure.ResultsMost genera exhibit a bell‐shaped or curvilinear pattern with the maximum number of congeneric species in the centre of the temperature range, but some curvilinear responses and monotonic increases are found in Andes. The order of generic optima along the temperature gradient in each region is highly correlated (ρ > 0.81), as well as the size of the temperature range and minimum temperature limit (ρ > 0.90).ConclusionThe analyses verify the conjecture that the maximum number of congeneric species is found towards the centre of the temperature range of the genus. This may be caused by newly evolving species not dispersing very far from their ancestors and inherent temperature tolerances. Inherent temperature tolerance and covariates such as primary production and soil conditions are the main factors that may explain consistency of the rank order of disjunct genera along temperature gradients between continents and hemispheres. Hence temperature tolerances within a clade are conserved over time and space.