Phylogenetic Analysis Suggests That Habitat Filtering Is Structuring Marine Bacterial Communities Across the Globe

The phylogenetic structure and community composition were analysed in an existing data set of marine bacterioplankton communities to elucidate the evolutionary and ecological processes dictating the assembly. The communities were sampled from coastal waters at nine locations distributed worldwide and were examined through the use of comprehensive clone libraries of 16S ribosomal RNA genes. The analyses show that the local communities are phylogenetically different from each other and that a majority of them are phylogenetically clustered, i.e. the species (operational taxonomic units) were more related to each other than expected by chance. Accordingly, the local communities were assembled non-randomly from the global pool of available bacterioplankton. Further, the phylogenetic structures of the communities were related to the water temperature at the locations. In agreement with similar studies, including both macroorganisms and bacteria, these results suggest that marine bacterial communities are structured by “habitat filtering”, i.e. through non-random colonization and invasion determined by environmental characteristics. Different bacterial types seem to have different ecological niches that dictate their survival in different habitats. Other eco-evolutionary processes that may contribute to the observed phylogenetic patterns are discussed. The results also imply a mapping between phenotype and phylogenetic relatedness which facilitates the use of community phylogenetic structure analysis to infer ecological and evolutionary assembly processes

Egg Production in a Coastal Seabird, the Glaucous-Winged Gull (Larus glaucescens), Declines during the Last Century

Seabirds integrate information about oceanic ecosystems across time and space, and are considered sensitive indicators of marine conditions. To assess whether hypothesized long-term foodweb changes such as forage fish declines may be reflected in a consumer's life history traits over time, I used meta-regression to evaluate multi-decadal changes in aspects of egg production in the glaucous-winged gull (Larus glaucescens), a common coastal bird. Study data were derived from literature searches of published papers and unpublished historical accounts, museum egg collections, and modern field studies, with inclusion criteria based on data quality and geographic area of the original study. Combined historical and modern data showed that gull egg size declined at an average of 0.04 cc y−1 from 1902 (108 y), equivalent to a decline of 5% of mean egg volume, while clutch size decreased over 48 y from a mean of 2.82 eggs per clutch in 1962 to 2.25 in 2009. There was a negative relationship between lay date and mean clutch size in a given year, with smaller clutches occurring in years where egg laying commenced later. Lay date itself advanced over time, with commencement of laying presently (2008–2010) 7 d later than in previous studies (1959–1986). This study demonstrates that glaucous-winged gull investment in egg production has declined significantly over the past ∼50–100 y, with such changes potentially contributing to recent population declines. Though gulls are generalist feeders that should readily be able to buffer themselves against food web changes, they are likely nutritionally constrained during the early breeding period, when egg production requirements are ideally met by consumption of high-quality prey such as forage fish. This study's results suggest a possible decline in the availability of such prey, and the incremental long-term impoverishment of a coastal marine ecosystem bordering one of North America's rapidly growing urban areas

Global Diversity of Ascidiacea

The class Ascidiacea presents fundamental opportunities for research in the fields of development, evolution, ecology, natural products and more. This review provides a comprehensive overview of the current knowledge regarding the global biodiversity of the class Ascidiacea, focusing in their taxonomy, main regions of biodiversity, and distribution patterns. Based on analysis of the literature and the species registered in the online World Register of Marine Species, we assembled a list of 2815 described species. The highest number of species and families is found in the order Aplousobranchia. Didemnidae and Styelidae families have the highest number of species with more than 500 within each group. Sixty percent of described species are colonial. Species richness is highest in tropical regions, where colonial species predominate. In higher latitudes solitary species gradually contribute more to the total species richness. We emphasize the strong association between species richness and sampling efforts, and discuss the risks of invasive species. Our inventory is certainly incomplete as the ascidian fauna in many areas around the world is relatively poorly known, and many new species continue to be discovered and described each year

Invasive species

The second World Ocean Assessment is a collaborative effort of hundreds of experts from all regions of the world, a comprehensive and integrated assessment of the state of marine environment

Invasion genetics of a freshwater mussel (Dreissena rostriformis bugensis) in eastern Europe: High gene flow and multiple introductions

In recent years, the quagga mussel, Dreissena rostriformis bugensis, native to the Dnieper and Bug Limans of the northern Black Sea, has been dispersed by human activities across the basin, throughout much of the Volga River system, and to the Laurentian Great Lakes. We used six published microsatellite markers to survey populations throughout its native and introduced range to identify relationships among potential source populations and introduced ones. Mussels from 12 sites in Eurasia, including the central Caspian Sea and one in North America (Lake Erie), were sampled. Field surveys in the Volga River basin suggested that the species first colonized the middle reach of the river near Kubyshev Reservoir, and thereafter spread both upstream and downstream. Evidence of considerable gene flow among populations was observed and genetic diversity was consistent with a larger, metapopulation that has not experienced bottlenecks or founder effects. We propose that high gene flow, possibly due to multiple invasions, has facilitated establishment of quagga mussel populations in the Volga River system. The Caspian Sea population (D. rostriformis rostriformis (= distincta)) was genetically more distinct than other populations, a finding that may be related to habitat differences. The geographical pattern of genetic divergence is not characteristic of isolation-by-distance but, rather, of long-distance dispersal, most likely mediated by commercial ships\u27 ballast water transfer. © 2005 Nature Publishing Group All rights reserved

Phenotypic Plasticity and Adaptation Potential to Salinity in Early Life Stages of the Tunicate, Ciona intestinalis spB

Species respond to environmental heterogeneity through a variety of mechanisms such as plasticity, genetic adaptation and phenotypic buffering. Determining how gene flow, scale of environmental heterogeneity and trait heritability influence these responses is important for understanding how these different mechanisms arise, which is a central task in the field of evolutionary biology. For many marine organisms salinity is an important driver of environmental heterogeneity and physiological stress. As with many stressors, salinity stress is often more severe for early life-history stages such as embryos and larvae. The main aim of this thesis was to investigate underlying mechanisms that allow species to cope with environmental heterogeneities in their natural environment. More specifically, I focused on strategies to manage salinity differences in early life-history stages of the tunicate Ciona intestinalis. This marine invertebrate has a large geographical distribution and is considered highly invasive in some parts of the world. Plasticity in important fitness related traits is generally considered to promote invasiveness even though there is evidence that local adaptation also could play an important role in range expansions of invasive species. Through investigations of population differences in larval performance, I wanted to understand what mechanisms allowed existing populations to inhabit different salinity regimes, focusing explicitly on the role of transgenerational phenotypic plasticity. Adult acclimation had a predominant effect on tolerance ranges of developing embryos and larvae, but there were also small signs of population differences that could be related to local adaptation and/or persistent environmental effects. To better understand the potential for adaptation of larval salinity tolerance I used quantitative genetic methods to assess the extent to which larval performance in different salinities is a heritable trait. Heritable variation proved to be extremely low, suggesting limited potential for local adaption in investigated populations. The potential for local adaptation can be strongly influenced by gene flow between populations that inhabit different environments. C. intestinalis has pelagic larvae, which could disperse over relatively large areas, thereby preventing local genetic differentiation. Through a population genetic study we found that gene flow at times was restricted at much smaller scales than suggested by the dispersal potential of larvae. Population structures implied that physical barriers, such as density differences between water masses, restricted larval dispersal. The study of sexual selection is an important field in evolutionary biology. Traditionally, it was assumed that sexual selection could not operate in sessile marine invertebrates with external fertilization. Today, however, there are many examples of mechanisms governing gamete interactions that allow eggs to "select" sperm. Our understanding of the underlying selective pressures, and indeed how these mechanisms affect fertilization success between individuals within a species, is however limited. I examined causes of variation in fertilization success in populations of C. intestinalis. I found significant variability in compatibility between parental genotypes, which indicated that this may be a way for individuals to avoid the negative effects of inbreeding

Origin of Spanish invasion by the zebra mussel, Dreissena polymorpha (Pallas, 1771) revealed by amplified fragment length polymorphism (AFLP) fingerprinting.

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