bluuebunny/crossref_metadata_2025_split huggingface dataset:
Consequences of non‐random species loss for decomposition dynamics: experimental evidence for additive and non‐additive effects
Authors: Ball Becky A. , Hunter Mark D. , Kominoski John S. , Swan Christopher M. , Bradford Mark A. 
Published: February 2008

SummaryAlthough litter decomposition is a fundamental ecological process, most of our understanding comes from studies of single‐species decay. Recently, litter‐mixing studies have tested whether monoculture data can be applied to mixed‐litter systems. These studies have mainly attempted to detect non‐additive effects of litter mixing, which address potential consequences of random species loss – the focus is not on which species are lost, but the decline in diversityper se.Under global change, species loss is likely to be non‐random, with some species more vulnerable to extinction than others. Under such scenarios, the effects of individual species (additivity) as well as of species interactions (non‐additivity) on decomposition rates are of interest.To examine potential impacts of non‐random species loss on ecosystems, we studied additive and non‐additive effects of litter mixing on decomposition. A full‐factorial litterbag experiment was conducted using four deciduous leaf species, from which mass loss and nitrogen content were measured. Data were analysed using a statistical approach that first looks for additive identity effects based on the presence or absence of species and then significant species interactions occurring beyond those. It partitions non‐additive effects into those caused by richness and/or composition.This approach addresses questions key to understanding the potential effects of species loss on ecosystem processes. If additive effects dominate, the consequences for decomposition dynamics will be predictable based on our knowledge of individual species, but not statistically predictable if non‐additive effects dominate.We found additive (identity) effects on mass loss and non‐additive (composition) effects on litter nitrogen dynamics, suggesting that non‐random species loss could significantly affect this system. We were able to identify the species responsible for effects that would otherwise have been considered idiosyncratic or absent when analysed by the methods used in previous work.Synthesis. We observed both additive and non‐additive effects of litter‐mixing on decomposition, indicating consequences of non‐random species loss. To predict the consequences of global change for ecosystem functioning, studies should examine the effects of both random and non‐random species loss, which will help identify the mechanisms that influence the response of ecosystems to environmental change.
Somatic mutation and the Antarctic ozone hole
Authors: Clarke Laurence J. , Ayre David J. , Robinson Sharon A. 
Published: February 2008

Summary

Previous studies of Antarctic clonal moss populations using RAPD markers have reported extraordinarily high levels of genetic variation. This has been claimed to reflect somatic mutation, possibly resulting from elevated UV‐B radiation.
Our study used microsatellite markers to compare the genetic variation present within continental Antarctic, sub‐Antarctic and temperate populations of the moss Ceratodon purpureus.
In contrast to the RAPD studies, microsatellite data revealed that C. purpureus populations from continental Antarctica display less intra‐population genetic diversity than populations from a range of temperate and sub‐Antarctic sites.
Analysis of molecular variation (amova) revealed that populations within the Windmill Islands region of Antarctica were more genetically differentiated than populations spread among more widely separated temperate regions.
Synthesis. Our data provide no evidence of elevated mutation rates in the Antarctic, and imply climate change will present ongoing challenges for continental Antarctic moss populations that appear weakly interconnected and with less potential than temperate populations to adapt to environmental change.
Biological Flora of the British Isles: Mercurialis perennis L.
Authors: Jefferson Richard G. 
Published: February 2008

Summary

This account reviews information on all aspects of the biology of Mercurialis perennis that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history and conservation.
Mercurialis perennis is a dioecious, clonal, perennial forb of woodland, hedgerows, limestone pavement, screes and tall‐herb communities. It is very tolerant of low light; it can also grow in unshaded conditions, although higher light flux densities result in lower shoot biomass. It is Eurocaucasic, occurring throughout temperate areas of Europe as far east as the Russian border.
Mercurialis perennis occurs on a wide variety of soil types over a pH range from 4.3 to 8.5, although it is most abundant on more base‐rich clay or loam soils with a low organic content. It seldom occurs on peat or very sandy soils. It can grow in soils with low availability of macronutrients but it responds positively to nutrient addition from atmospheric or agricultural sources. It is intolerant of waterlogging, mainly because of poor aerenchyma development; its limited capacity to oxygenate the root environment can lead to ferrous ion toxicity. The resulting superficial root development on heavy soils may confer drought susceptibility in summer.
Mercurialis perennis is predominantly wind‐pollinated. Ants are the main dispersal agents and the seed bears an elaiosome which offers them a lipid‐rich reward. Establishment from seed is uncommon and vegetative propagation is the main means of expansion, often leading to dense clonal stands of aerial shoots.
Mercurialis perennis has been described as a stress‐tolerant competitor. The persistence of its clones and slow dispersal have led to it being regarded an as indicator of ancient, semi‐natural woodland.
Landscape features affect gene flow of Scottish Highland red deer (Cervus elaphus)
Authors: PÉREZ‐ESPONA S. , PÉREZ‐BARBERÍA F. J. , MCLEOD J. E. , JIGGINS C. D. , GORDON I. J. , PEMBERTON J. M. 
Published: February 2008

AbstractLandscape features have been shown to strongly influence dispersal and, consequently, the genetic population structure of organisms. Studies quantifying the effect of landscape features on gene flow of large mammals with high dispersal capabilities are rare and have mainly been focused at large geographical scales. In this study, we assessed the influence of several natural and human‐made landscape features on red deer gene flow in the Scottish Highlands by analysing 695 individuals for 21 microsatellite markers. Despite the relatively small scale of the study area (115 × 87 km), significant population structure was found usingF‐statistics (FST = 0.019) and the programstructure, with major differentiation found between populations sampled on either side of the main geographical barrier (the Great Glen). To assess the effect of landscape features on red deer population structure, the ArcMap GIS was used to create cost‐distance matrices for moving between populations, using a range of cost values for each of the landscape features under consideration. Landscape features were shown to significantly affect red deer gene flow as they explained a greater proportion of the genetic variation than the geographical distance between populations. Sea lochs were found to be the most important red deer gene flow barriers in our study area, followed by mountain slopes, roads and forests. Inland lochs and rivers were identified as landscape features that might facilitate gene flow of red deer. Additionally, we explored the effect of choosing arbitrary cell cost values to construct least cost‐distance matrices and described a method for improving the selection of cell cost values for a particular landscape feature.
°Molecular evidence for sequential colonization and taxon cycling in freshwater decapod shrimps on a Caribbean island
Authors: COOK BENJAMIN D. , PRINGLE CATHERINE M. , HUGHES JANE M. 
Published: February 2008

AbstractTaxon cycling, i.e. sequential phases of expansions and contractions in species’ distributions associated with ecological or morphological shifts, are postulated to characterize dynamic biogeographic histories in various island faunas. The Caribbean freshwater shrimp assemblage is mostly widespread and sympatric throughout the region, although one species (Atyidae: Atya lanipes) is geographically restricted and ecologically and morphologically differentiated from other Atya species. Using patterns of nucleotide variation at the COI mtDNA gene in five species of freshwater shrimp (A. lanipes, A. scabra, A. innocuous; Xiphocarididae: Xiphocaris elongata; Palaemonidae: Macrobrachium faustinum) from Puerto Rico, we expected to detect a signature of sequential colonization in these shrimp, consistent with the concept of taxon cycling, and expected that A. lanipes would be at a different taxon stage (i.e. an early stage species) to all other species. We also examined patterns of genetic population structure in each species expected with poor, intermediate and well‐developed abilities for among‐river dispersal. Population expansions were detected in all species, although the relative timing of the expansions varied among them. Assuming that population expansions followed colonization of Puerto Rico by freshwater shrimp, results bear the hallmarks of sequential colonization and taxon cycling in this fauna. A. lanipes had a star phylogeny, low mean pairwise nucleotide differences and recent (Holocene) estimates for an in situ population expansion in Puerto Rico, and it was inferred as an early stage species in the taxon cycle undergoing a secondary phase of expansion. All other species were inferred as late stage species undergoing regional population expansions, as their mean pairwise nucleotide differences were relatively high and phylogenetic patterns were more complex than A. lanipes. High rates of gene flow without isolation by distance among rivers were detected in all species, although results should be treated cautiously as some populations are unlikely to be in mutation–drift equilibrium. Nested clade analysis produced inconsistent results among species that all have high rates of gene flow and expanding populations.
Divergence with gene flow between Ponto‐Caspian refugia in an anadromous cyprinid Rutilus frisii revealed by multiple gene phylogeography
Authors: KOTLÍK PETR , MARKOVÁ SILVIA , CHOLEVA LUKÁŠ , BOGUTSKAYA NINA G. , EKMEKÇI F. GULER , IVANOVA PETYA P. 
Published: February 2008

AbstractThe Black and Caspian Seas have experienced alternating periods of isolation and interconnection over many Milankovitch climate oscillations and most recently became separated when the meltwater overflow from the Caspian Sea ceased at the end of the last glaciation. Climate‐induced habitat changes have indisputably had profound impacts on distribution and demography of aquatic species, yet uncertainties remain about the relative roles of isolation and dispersal in the response of species shared between the Black and Caspian Sea basins. We examined these issues using phylogeographical analysis of an anadromous cyprinid fish Rutilus frisii. Bayesian coalescence analyses of sequence variation at two nuclear and one mitochondrial genes suggest that the Black and Caspian Seas supported separate populations of R. frisii during the last glaciation. Parameter estimates from the fitted isolation‐with‐migration model showed that their separation was not complete, however, and that the two populations continued to exchange genes in both directions. These analyses also suggested that majority of migrations occurred during the Pleistocene, showing that the variation shared between the Black and Caspian Seas is the result of ancient dispersal along the temporary natural connections between the basins, rather than of incomplete lineage sorting or recent human‐mediated dispersal. Gene flow between the refugial populations was therefore an important source of genetic variation, and we suggest that it facilitated the evolutionary response of the populations to changing climate.
Colonization history, ecological shifts and diversification in the evolution of endemic Galápagos weevils
Authors: SEQUEIRA A. S. , LANTERI A. A. , ALBELO L. ROQUE , BHATTACHARYA S. , SIJAPATI M. 
Published: February 2008

AbstractMitochondrial DNA sequence data were obtained for eight species of flightless Galapaganus endemic weevils and one winged close relative in order to study their colonization history and modes of diversification in the Galápagos Archipelago. Contrary to most other insular radiations, the phylogeny estimates we recovered for Galapaganus do not follow the progression rule of island biogeography. The penalized likelihood age estimates of colonization of the archipelago exceed the age of the emerged islands and underscore the potential role of now sunken seamounts for the early evolution of Galapaganus. The phylogeny proposes one intra‐island origin for Galapaganus endemics, but monophyly tests suggest a larger contribution of in‐situ speciation on older islands. Generalist habitat preferences were reconstructed as ancestral while shifts to highland habitats were reconstructed as having evolved independently on different islands. Magnitudes and patterns of diversification rate were found to differ between older and younger islands. Our analyses reveal that the colonization sequence of islands and timing of colonization of Galapaganus could be linked with the geological and volcanic history of the islands in a rather complex scenario. Even though most islands appear to have been colonized soon after their emergence, there are notable deviations from the pattern of sequential colonization expected under the progression rule when considering only the extant emerged islands. Patterns of diversification rate variation on older and younger islands correspond to the volcanic activity or remnants of such activity, while the pattern of independent evolution of restricted habitat preferences in different islands suggests that habitat shifts could also have contributed to species diversity in Galapaganus.
Reproductive isolation among two interfertileRhododendronspecies: low frequency of post‐F1hybrid genotypes in alpine hybrid zones
Authors: MILNE RICHARD I. , ABBOTT RICHARD J. 
Published: February 2008

AbstractHybrids between the acid‐loving speciesRhododendron ferrugineumand the basic soil speciesRhododendron hirsutumoccur on soils of intermediate pH in the European Alps. Material from two hybrid zones ~500 m apart, and also nearby populations of each parent species, was surveyed for presence/absence of 31 random amplified polymorphic DNA markers that distinguish parents. Based on morphological assessment, the material comprised 51 putative hybrids, 18 putativeR. ferrugineumindividuals and 26 putativeR. hirsutumplants. RAPD data were analysed using a Bayesian approach implemented by the programnewhybrids, and also by principal coordinates analysis. The identity of allR. ferrugineumplants examined was confirmed; however, of the putativeR. hirsutumindividuals examined, two were certainly and 11 possibly hybrid derivatives. Among all hybrid derivatives examined, about half were designated as F1s or a similar class, otherwise backcrosses toR. hirsutumappeared to be common whereas other hybrid classes were rare and backcrosses toR. ferrugineumpossibly absent. Despite this, artificially generated seed of F2class and backcrosses in each direction showed greater viability than one parent (R. hirsutum). Introgression fromR. ferrugineumwas also detected in a population that from morphology appeared to contain onlyR. hirsutum. Hence, the direction of backcrossing might be highly asymmetric within hybrid zones, causing unidirectional gene flow fromR. ferrugineumintoR. hirsutum. Conversely, the rarity of backcrosses toR. ferrugineum, F2s and later hybrid generations, which might be due to phenology effects and habitat‐mediated selection, could play a part in restricting gene flow towardsR. ferrugineum.
Mating for variety increases foraging activity in the harvester ant, Pogonomyrmex occidentalis
Authors: WIERNASZ DIANE C. , HINES JESSICA , PARKER DARA G. , COLE BLAINE J. 
Published: February 2008

AbstractMultiple mating by females characterizes most insect species, but is relatively uncommon in social insects. Females may mate with multiple mates because they experience the direct benefits of increased survival or fecundity, to acquire high quality mates, or to lower the risk of reduced fecundity by mating with incompatible males. We used the extensive natural variation in mating frequency in the western harvester ant, Pogonomyrmex occidentalis, to test the hypothesis that increased mating by the queen leads to an increase in colony performance. Colonies with greater genetic diversity began to forage earlier in the day and foraged for longer time periods. The workers which initiated foraging were a nonrandom subset of the genotypes present in the colony. We used a statistical approach to correctly predict the direction and magnitude of the correlation between genetic diversity and colony foraging activity.
Cryptic speciation in the vermilion rockfish (Sebastes miniatus) and the role of bathymetry in the speciation process
Authors: HYDE J. R. , KIMBRELL C. A. , BUDRICK J. E. , LYNN E. A. , VETTER R. D. 
Published: February 2008

AbstractA recent phylogenetic review of the genus Sebastes suggested the existence of a cryptic species of vermilion rockfish (Sebastes miniatus). To evaluate the geographical and bathymetric range of the Type 1 and Type 2 forms reported in that study, cytochrome b sequences were examined from 548 fish. Type 1 fish were found primarily south of Point Conception on reefs deeper than 100 m. Type 2 fish were common range‐wide at sites shallower than 100 m. Reproductive isolation between the two types was tested using nine microsatellite loci. Estimates of genetic divergence were made using the fixation index (FST) and correspondence between haplotype and genotype was tested by Bayesian population assignment and multivariate plotting of individual genotypes. Microsatellite analyses gave strong support for the presence of two distinct groups of genotypes. All fish with Type 1 haplotypes and fish with Type 2 haplotypes from < 100 m depth had genotypes unique to their haplotype group. However, most (68%) fish with Type 2 haplotypes from > 100 m depth assigned strongly to the Type 1 genotype group. Morphometric comparisons between the two genotypic groups revealed significant differences at three of the six examined measurements. Differences in both genetics, depth of occurrence, and morphology suggest these are separate species. This observation along with evidence of depth segregation in many recent species pairs led us to hypothesize a speciation model for Sebastes spp. by which the loss or truncation of a depth‐related ontogenetic migration can lead to the creation of reproductively isolated populations.
Novel ultrastructures of Treponema primitia and their implications for motility
Authors: Murphy Gavin E. , Matson Eric G. , Leadbetter Jared R. , Berg Howard C. , Jensen Grant J. 
Published: February 2008

SummaryMembers of the bacterial phylum Spirochaetes are generally helical cells propelled by periplasmic flagella. The spirochete Treponema primitia is interesting because of its mutualistic role in the termite gut, where it is believed to cooperate with protozoa that break down cellulose and produce H2 as a by‐product. Here we report the ultrastructure of T. primitia as obtained by electron cryotomography of intact, frozen‐hydrated cells. Several previously unrecognized external structures were revealed, including bowl‐like objects decorating the outer membrane, arcades of hook‐shaped proteins winding along the exterior and tufts of fibrils extending from the cell tips. Inside the periplasm, cone‐like structures were found at each pole. Instead of the single peptidoglycan layer typical of other Gram‐negative bacteria, two distinct periplasmic layers were observed. These layers formed a central open space that contained two flagella situated adjacent to each other. In some areas, the inner membrane formed flattened invaginations that protruded into the cytoplasm. High‐speed light microscopic images of swimming T. primitia cells showed that cell bodies remained rigid and moved in a helical rather than planar motion. Together, these findings support the ‘rolling cylinder’ model for T. primitia motility that posits rotation of the protoplasmic cylinder within the outer sheath.
Self‐tolerance of Human Natural Killer Cells Lacking Self‐HLA‐specific Inhibitory Receptors
Authors: Hasenkamp J. , Borgerding A. , Uhrberg M. , Falk C. , Chapuy B. , Wulf G. , Jung W. , Trümper L. , Glass B. 
Published: February 2008

AbstractNatural killer (NK) cells identify cells with altered human leucocyte antigen (HLA) expression as targets through lacking engagement of self‐HLA‐specific inhibitory receptors (e.g. killer cell immunoglobulin‐like receptor, KIR). Thus, they eliminate cells with ‘missing self’ because of viral or malignant transformation. We performed analysis of HLA, KIR genotypes and KIR receptor expression patterns at single cell level in NK cells in 17 donors. The function of NK cell subsets is determined by degranulation assays using target cells expressing self, cognate, control or no HLA class I. Donors could be grouped into three groups: their NK cells possess potential for alloreactivity, autoreactivity based on the presence of NK cells expressing particular KIR only (mono‐KIR) in the absence of its ligand or lack alloreactivity. All donors possess NK cells lacking all detectable inhibitory receptors. Both potential autoreactive subpopulations did not respond to HLA class I‐positive target cells. They retain partial reactivity against HLA class I‐negative tumour target cells. Mono‐KIR NK cells without the corresponding ligands in the individuals and NK cells lacking all inhibitory receptors behave self‐tolerant. Our results suggest alternative mechanisms than HLA‐specific inhibitory receptors to control NK cell activity. But HLA seems to be involved in shaping effector function of the NK cell repertoire.