Invasive and Non-Invasive Congeners Show Similar Trait Shifts between Their Same Native and Non-Native Ranges

Differences in morphological or ecological traits expressed by exotic species between their native and non-native ranges are often interpreted as evidence for adaptation to new conditions in the non-native ranges. In turn this adaptation is often hypothesized to contribute to the successful invasion of these species. There is good evidence for rapid evolution by many exotic invasives, but the extent to which these evolutionary changes actually drive invasiveness is unclear. One approach to resolving the relationship between adaptive responses and successful invasion is to compare traits between populations from the native and non-native ranges for both exotic invaders and congeners that are exotic but not invasive. We compared a suite of morphological traits that are commonly tested in the literature in the context of invasion for three very closely related species of Centaurea, all of which are sympatric in the same native and non-native ranges in Europe and North America. Of these, C. solstitialis is highly invasive whereas C. calcitrapa and C. sulphurea are not. For all three species, plants from non-native populations showed similar shifts in key traits that have been identified in other studies as important putative adaptive responses to post-introduction invasion. For example, for all three species plants from populations in non-native ranges were (i) larger and (ii) produced seeds that germinated at higher rates. In fact, the non-invasive C. calcitrapa showed the strongest trait shift between ranges. Centaurea solstitialis was the only species for which plants from the non-native range increased allocation to defensive spines, and allocated proportionally less resources to reproduction, patterns contrary to what would be predicted by theory and other empirical studies to enhance invasion. Our results suggest caution when interpreting the commonly observed increase in size and reproductive capacity as factors that cause exotics to become invaders.     

Invasive Congeners Differ in Successional Impacts across Space and Time

Invasive species can alter the succession of ecological communities because they are often adapted to the disturbed conditions that initiate succession. The extent to which this occurs may depend on how widely they are distributed across environmental gradients and how long they persist over the course of succession. We focus on plant communities of the USA Pacific Northwest coastal dunes, where disturbance is characterized by changes in sediment supply, and the plant community is dominated by two introduced grasses – the long-established Ammophila arenaria and the currently invading A. breviligulata. Previous studies showed that A. breviligulata has replaced A. arenaria and reduced community diversity. We hypothesize that this is largely due to A. breviligulata occupying a wider distribution across spatial environmental gradients and persisting in later-successional habitat than A. arenaria. We used multi-decadal chronosequences and a resurvey study spanning 2 decades to characterize distributions of both species across space and time, and investigated how these distributions were associated with changes in the plant community. The invading A. breviligulata persisted longer and occupied a wider spatial distribution across the dune, and this corresponded with a reduction in plant species richness and native cover. Furthermore, backdunes previously dominated by A. arenaria switched to being dominated by A. breviligulata, forest, or developed land over a 23-yr period. Ammophila breviligulata likely invades by displacing A. arenaria, and reduces plant diversity by maintaining its dominance into later successional backdunes. Our results suggest distinct roles in succession, with A. arenaria playing a more classically facilitative role and A. breviligulata a more inhibitory role. Differential abilities of closely-related invasive species to persist through time and occupy heterogeneous environments allows for distinct impacts on communities during succession.     

How Humans Differ from Other Animals in Their Levels of Morphological Variation

Animal species come in many shapes and sizes, as do the individuals and populations that make up each species. To us, humans might seem to show particularly high levels of morphological variation, but perhaps this perception is simply based on enhanced recognition of individual conspecifics relative to individual heterospecifics. We here more objectively ask how humans compare to other animals in terms of body size variation. We quantitatively compare levels of variation in body length (height) and mass within and among 99 human populations and 848 animal populations (210 species). We find that humans show low levels of within-population body height variation in comparison to body length variation in other animals. Humans do not, however, show distinctive levels of within-population body mass variation, nor of among-population body height or mass variation. These results are consistent with the idea that natural and sexual selection have reduced human height variation within populations, while maintaining it among populations. We therefore hypothesize that humans have evolved on a rugged adaptive landscape with strong selection for body height optima that differ among locations.     

Invasive Populations of Elephantgrass Differ in Morphological and Growth Characteristics from Clones Selected for Biomass Production

Elephantgrass (Pennisetum purpureum Schum.) has demonstrated potential for use as a biomass crop, but in Florida, some naturalized types are invasive weeds in sugarcane (Saccharum sp.) fields, along roadsides, and in natural areas. It is not known whether elephantgrass introductions and breeding lines developed for biomass production (i.e., “selected”clones) differ from naturalized populations sufficiently that risk assessment and regulatory decisions should be made at the level of the clone instead of the species. The objective was to compare morphological and physiological traits of elephantgrass-naturalized populations and selected clones. Ten naturalized populations and six selected clones were evaluated in replicated trials at two field locations during 2 years. Selected clones were 8–14 % taller and had leaf blade length that was 48–87 % longer, and leaf blade width that was 61–89 % wider than naturalized clones. Selected types averaged 5.7 to 7.2 fewer tillers per plant than naturalized types, but tiller mass of selected types was 70 % greater than naturalized types. Leaf N concentration was 43 % greater for selected types and was associated with greater light-saturated leaf photosynthesis, stomatal conductance, leaf transpiration rate, and leaf dark respiration than naturalized types. Photosynthetic parameters indicated a greater maximum photosynthetic rate, leaf dark respiration, and light compensation point for selected versus naturalized clones. Clones selected for use as biomass crops differ widely in morphology and physiological response from naturalized populations, supporting a conclusion that risk assessment of elephantgrass should occur at the level of the clone rather than the species.     

The Genetic Properties of the Primary Endosymbionts of Mealybugs Differ from Those of Other Endosymbionts of Plant Sap-Sucking Insects

Mealybugs (Hemiptera, Coccoidea, Pseudococcidae), like aphids and psyllids, are plant sap-sucking insects that have an obligate association with prokaryotic endosymbionts that are acquired through vertical, maternal transmission. We sequenced two fragments of the genome of Tremblaya princeps, the endosymbiont of mealybugs, which is a member of the β subdivision of the Proteobacteria. Each of the fragments (35 and 30 kb) contains a copy of 16S-23S-5S rRNA genes. A total of 37 open reading frames were detected, which corresponded to putative rRNA proteins, chaperones, and enzymes of branched-chain amino acid biosynthesis, DNA replication, protein translation, and RNA synthesis. The genome of T. princeps has a number of properties that distinguish it from the genomes of Buchnera aphidicola and Carsonella ruddii, the endosymbionts of aphids and psyllids, respectively. Among these properties are a high G+C content (57.1 mol%), the same G+C content in intergenic spaces and structural genes, and similar G+C contents of the genes encoding highly and poorly conserved proteins. The high G+C content has a substantial effect on protein composition; about one-third of the residues consist of four amino acids with high-G+C-content codons. Sequence analysis of DNA fragments containing the rRNA operon and adjacent regions from endosymbionts of several mealybug species suggested that there was a single duplication of the rRNA operon and the adjacent genes in an ancestor of the present T. princeps. Subsequently, in one mealybug lineage rpS15, one of the duplicated genes, was retained, while in another lineage it decayed. These results extend the diversity of the types of endosymbiotic associations found in plant sap-sucking insects.     

Adaptation of the Thermal Responses of Insects

SYNOPSIS. Some insects adjust heat production and heat loss,while others depend upon adjustments in location and postureto regulate body temperature. Many activities oE insects aretuned to internal temperature. These two features predict thatthe nature and form of temperature control in insects interactstrongly in adaptation to climate, energy demand, niche specialization,and population size of insects.     

ATP-dependent Proteases Differ Substantially in Their Ability to Unfold Globular Proteins

ATP-dependent proteases control the concentrations of hundreds of regulatory proteins and remove damaged or misfolded proteins from cells. They select their substrates primarily by recognizing sequence motifs or covalent modifications. Once a substrate is bound to the protease, it has to be unfolded and translocated into the proteolytic chamber to be degraded. Some proteases appear to be promiscuous, degrading substrates with poorly defined targeting signals, which suggests that selectivity may be controlled at additional levels. Here we compare the abilities of representatives from all classes of ATP-dependent proteases to unfold a model substrate protein and find that the unfolding abilities range over more than 2 orders of magnitude. We propose that these differences in unfolding abilities contribute to the fates of substrate proteins and may act as a further layer of selectivity during protein destruction.Energy-dependent proteolysis is responsible for more than 90% of the protein turnover inside the cell (1). This process both removes misfolded and aggregated proteins as part of the response of the cell to stress and controls the concentrations of regulatory proteins (2, 3). In prokaryotes and eukaryotic organelles, energy-dependent proteases fall into five classes as follows: ClpAP, ClpXP, Lon, HslUV (also referred to as ClpYQ), and HflB (also referred to as FtsH). In Archaea, analogous functions are performed by the archaebacterial proteasome, consisting of the proteasome-activating nucleotidase (PAN),³ working with the 20 S proteasome (4); in the cytoplasm and nucleus of eukaryotes, these same functions are performed by the 26 S proteasome (5). These different proteases show little sequence conservation outside the ATP-binding domains, but they share their overall architecture. They all form oligomeric, barrel-shaped complexes composed of one or more rings with the active sites of proteolysis sequestered inside a central degradation chamber (6). Access channels to these sites are narrow, and proteins have to be unfolded to gain entry (6). Regulatory particles belonging to the AAA family of molecular chaperones assemble on either end of the proteolytic chamber and recognize substrates destined for degradation. After recognition, the regulatory particles translocate the substrate through a central channel to the proteolytic chamber and in doing so unravel folded domains within the substrate. Translocation and unfolding are driven by ATP hydrolysis by the regulatory particles, with conformational changes in the protease transmitted to the substrate by conserved residues in the loops lining the channel (7–10).Protein degradation by AAA proteases is tightly regulated. Most proteins are targeted to ClpAP, ClpXP, HslUV, Lon, HflB, and PAN by sequence motifs in their primary structure (11–17). Sometimes adaptor proteins recognize and bind sequence elements in substrates and deliver them to the protease, and other times the protease recognizes sequence elements directly (18, 19). In contrast, proteins are typically targeted to the 26 S proteasome through the covalent attachment of polyubiquitin chains (20). Thus, substrates appear to be selected for degradation based on the presence of specific recognition elements in the protein substrates.However, other mechanisms may also affect the specificity of degradation by prokaryotic proteases. Individual proteases recognize a wide range of targeting signals (11, 16). (For example, Escherichia coli ClpXP recognizes sequences belonging to five distinct classes of consensus sequences (11), and ClpAP, Lon, and FtsH can bind to unstructured regions in proteins with a wide range of amino acid sequences (21–23).) One illustration of the loose specificity in targeting signals is the ability of a mitochondrial presequence to target proteins to the proteases ClpAP (24) and HslUV in vitro (see below). In addition, substrates are commonly acted upon by several different proteases in E. coli. For instance, proteins containing the 11-residue ssrA peptide at their C termini can be recognized by ClpAP, ClpXP, FtsH, Lon, and the archaebacterial proteasome (4, 25–27). Similarly, some substrates of Lon can be degraded by HslUV in vivo (28).It is not clear how degradation remains selective despite the loose specificity of targeting signals. We propose that the intrinsic protein unfolding ability of AAA proteases and the stabilities of substrates against unfolding play a role in determining the fate of cellular proteins. For example, ClpXP releases hard-to-unfold substrates when it encounters them and degrades destabilized titin variants 20-fold faster than wild type titin (29). The membrane-bound AAA protease FtsH has a weak unfolding ability, which allows this protease to act selectively on damaged and unfolded polypeptides (30). Here we find that the relative unfolding abilities of ATP-dependent proteases vary more than 100-fold and that the unfolding abilities of proteases belonging to the same class but originating from different species appear to be conserved. The unfolding abilities also seem to be intrinsic properties of the proteases themselves rather than other cytosolic factors, such as chaperones. Differences in protease unfolding abilities may contribute to substrate selectivity during protein degradation. For example, expression of a protease with a weak unfolding ability during a stress response could allow the selective elimination of unfolded, misfolded, or otherwise aberrant proteins and spare stable proteins from destruction (30).     

Astrocytes from Forebrain, Cerebellum, and Spinal Cord Differ in Their Responses to Vasoactive Intestinal Peptide

Astrocytes from cortex, cerebellum, and spinal cord responded to isoproterenol and vasoactive intestinal peptide (VIP) with increases in intracellular cyclic AMP levels. The response to VIP was as great as that to isoproterenol in cortical astrocytes (180-fold and 185-fold, respectively), and the effect of VIP in combination with isoproterenol was partially additive. Spinal cord astrocytes also responded to VIP and isoproterenol with equal potency (seven- to ninefold and eight- to 13-fold, respectively), but the level of response was much smaller than in cortex. Spinal cord astrocytes were synergistic in their response to VIP and isoproterenol. The response to VIP was lowest in cerebellar astrocytes (only threefold), and no additivity was observed when VIP was added together with isoproterenol. A small response to alpha-melanocyte stimulating hormone (alpha-MSH) was also observed in cortex and cerebellum, but not in spinal cord. Somatostatin inhibited the response to isoproterenol in cortex and cerebellum, but had no effect in spinal cord. The results from the above study show that astrocytes obtained from these three regions of the rat CNS express quite different responses to VIP and alpha-MSH and further point to possible astrocyte heterogeneity.     

Posterior Midgut Epithelial Cells Differ in Their Organization of the Membrane Skeleton from Other Drosophila Epithelia

In epithelial cells, the various components of the membrane skeleton are segregated within specialized subregions of the plasma membrane, thus contributing to the development and stabilization of cell surface polarity. It has previously been shown that, in various Drosophila epithelia, the membrane skeleton components ankyrin and alphabeta-spectrin reside at the lateral surface, whereas alphabeta(H)-spectrin is restricted to the apical domain. By use of confocal immunofluorescence microscopy, the present study characterizes the membrane skeleton of epithelial cells in the posterior midgut, leading to a number of unexpected results. First, ankyrin and alphabeta-spectrin are not detected on the entire lateral surface but appear to be restricted to the apicolateral area, codistributing with fasciclin III at smooth septate junctions. The presumptive ankyrin-binding proteins neuroglian and Na(+),K(+)-ATPase, however, do not colocalize with ankyrin. Second, alphabeta(H)-spectrin is enriched at the apical domain but is also present in lower amounts on the entire lateral surface, colocalizing apicolaterally with ankyrin/alphabeta-spectrin. Finally, despite the absence of zonulae adherentes, F-actin, beta(H)-spectrin, and nonmuscle myosin-II are enriched in the midlateral region. Thus, the model established for the organization of the membrane skeleton in Drosophila epithelia does not hold for the posterior midgut, and there is quite some variability between the different epithelia with respect to the organization of the membrane skeleton.     

Sub-Sets of Cancer Stem Cells Differ Intrinsically in Their Patterns of Oxygen Metabolism

The glycolytic response of hypoxic cells is primarily mediated by the hypoxia inducible factor alpha (HIF-1α) but even in the presence of abundant oxygen tumours typically show high rates of glycolysis. Higher levels of HIF-1α in tumours are associated with a poorer prognosis and up-regulation of markers of epithelial mesenchymal transition (EMT) due to HIF-1α actions. We have recently shown that EMT occurs within the CD44^high cancer stem cell (CSC) fraction and that epithelial and EMT CSCs are distinguished by high and low ESA expression, respectively. We here show that hypoxia induces a marked shift of the CSC fraction towards EMT leading to altered cell morphology, an increased proportion of CD44^high/ESA^low cells, patterns of gene expression typical of EMT, and enhanced sphere-forming ability. The size of EMT fractions returned to control levels in normoxia indicating a reversible process. Surprisingly, however, even under normoxic conditions a fraction of EMT CSCs was present and maintained high levels of HIF-1α, apparently due to actions of cytokines such as TNFα. Functionally, this EMT CSC fraction showed decreased mitochondrial mass and membrane potential, consumed far less oxygen per cell, and produced markedly reduced levels of reactive oxygen species (ROS). These differences in the patterns of oxygen metabolism of sub-fractions of tumour cells provide an explanation for the general therapeutic resistance of CSCs and for the even greater resistance of EMT CSCs. They also identify potential mechanisms for manipulation of CSCs.     

Nascent Astrocyte Particles Differ from Lipoproteins in CSF

Abstract: Little is known about lipid transport and metabolism in the brain. As a further step toward understanding the origin and function of CNS lipoproteins, we have characterized by size and density fractionation lipoprotein particles from human CSF and primary cultures of rat astrocytes. The fractions were analyzed for esterified and free cholesterol, triglyceride, phospholipid, albumin, and apolipoproteins (apo) E, AI, AII, and J. As determined by lipid and apolipoprotein profiles, gel electrophoresis, and electron microscopy, nascent astrocyte particles contain little core lipid, are primarily discoidal in shape, and contain apoE and apoJ. In contrast, CSF lipoproteins are the size and density of plasma high-density lipoprotein, contain the core lipid, esterified cholesterol, and are spherical. CSF lipoproteins were heterogeneous in apolipoprotein content with apoE, the most abundant apolipoprotein, localized to the largest particles, apoAI and apoAII localized to progressively smaller particles, and apoJ distributed relatively evenly across particle size. There was substantial loss of protein from both CSF and astrocyte particles after density centrifugation compared with gel-filtration chromatography. The differences between lipoproteins secreted by astrocytes and present in CSF suggest that in addition to delivery of their constituents to cells, lipoprotein particles secreted within the brain by astrocytes may have the potential to participate in cholesterol clearance, developing a core of esterified cholesterol before reaching the CSF. Study of the functional properties of both astrocyte-secreted and CSF lipoproteins isolated by techniques that preserve native particle structure may also provide insight into the function of apoE in the pathophysiology of specific neurological diseases such as Alzheimer's disease.     

Some Thermal Requirements of Fiddler Crabs of the Temperate and Tropical Zones and Their Influence on Geographic Distribution

Thermal stress is one environmental parameter that has greatlyinfluenced the migration of crustaceans from the sea to land.Since a greater number of species of terrestrial crabs are foundin the tropics than in the temperate zone, comparative studiesof the influence of temperature on latitudinally separated populationswere undertaken. Two tropical species, U. rapax and U. thayeri,may occur as far north as St. Augustine, Florida, or, followinga severe winter, may be rare north of Cape Kennedy. The lethaleffect of the low temperatures recorded during one severe winter(1957–58) is supported by laboratory studies in whichLD₅₀, deaths occurred in 4.5 days at 10°C for U. rapax acclimatedto 18°C. The experiment demonstrates that U. rapax cannotacclimate to and survive low temperatures. This contrasts markedlywith the situation in semi-terrestrial crabs of the temperatezone, which are able to acclimate to cold. The distribution of Uca around Cape Cod Bay correlates wellwith the coastal hydrographic thermal gradient and supportsPassano's suggestion that temperatures below 20° may belimiting as they inhibit proecdysis in U. pugnax. Such an inhibitionis found experimentally in U. pugilator and in the tropicalspecies, U. rapax. It is hypothesized that a shift in the thermodynamicsof the processes underlying molting has not occurred in Ucaof the temperate zone. The paucity of semi-terrestrial Brachyurain the temperate zone may be due to the failure of many speciesto evolve capacity-adaptations to carry out all requisite lifeprocesses at temperatures below 20°, or the resistance-adaptationsnecessary to survive the low temperatures of winter.     

Synaptic and Non-Synaptic Mitochondria in Hippocampus of Adult Rats Differ in Their Sensitivity to Hypothyroidism

Hypothyroidism in humans provokes various neuropsychiatric disorders, movement, and cognitive abnormalities that may greatly depend on the mitochondrial energy metabolism. Brain cells contain at least two major populations of mitochondria that include the non-synaptic mitochondria, which originate from neuronal and glial cell bodies (CM), and the synaptic (SM) mitochondria, which primarily originate from the nerve terminals. Several parameters of oxidative stress and other parameters in SM and CM fractions of hippocampus of adult rats were compared among euthyroid (control), hypothyroid (methimazol-treated), and thyroxine (T4)-treated hypothyroid states. nNOS translocation to CM was observed with concomitant increase of mtNOS??s activity in hypothyroid rats. In parallel, oxidation of cytochrome c oxidase and production of peroxides with substrates of complex I (glutamate?+?malate) were enhanced in CM, whereas the activity of aconitase and mitochondrial membrane potential (????_m) were decreased. Furthermore, the elevation of mitochondrial hexokinase activity in CM was also found. No differences in these parameters between control and hypothyroid animals were observed in SM. However, in contrast to CM, hypothyroidism increases the level of pro-apoptotic K-Ras and Bad in SM. Our results suggest that hypothyroidism induces moderate and reversible oxidative/nitrosative stress in hippocampal CM, leading to the compensatory elevation of hexokinase activity and aerobic glycolysis. Such adaptive activation in glycolytic metabolism does not occur in SM, suggesting that synaptic mitochondria differ in their sensitivity to the energetic disturbance in hypothyroid conditions.     

High Prevalence of Co-Infections by Invasive and Non-Invasive Chlamydia trachomatis Genotypes during the Lymphogranuloma Venereum Outbreak in Spain

The evolution of Chlamydia trachomatis is mainly driven by recombination events. This fact can be fuelled by the coincidence in several European regions of the high prevalence of non-invasive urogenital genotypes and lymphogranuloma venereum (LGV) outbreaks. This scenario could modify the local epidemiology and favor the selection of new C. trachomatis variants. Quantifying the prevalence of co-infection could help to predict the potential risk in the selection of new variants with unpredictable results in pathogenesis or transmissibility. In the 2009-2013 period, 287 clinical samples with demonstrated presence of C. trachomatis were selected. They were divided in two groups. The first group was constituted by 137 samples with C. trachomatis of the LGV genotypes, and the second by the remaining 150 samples in which the presence of LGV genotypes was previously excluded. They were analyzed to detect the simultaneous presence of non-LGV genotypes based on pmpH and ompA genes. In the first group, co-infections were detected in 10.9% of the cases whereas in the second group the prevalence was 14.6%, which is the highest percentage ever described among European countries. Moreover, bioinformatic analyses suggested the presence among men who have sex with men of a pmpH-recombinant variant, similar to strains described in Seattle in 2002. This variant was the result of genetic exchange between genotypes belonging to LGV and members of G-genotype. Sequencing of other genes, phylogenetically related to pathotype, confirmed that the putative recombinant found in Madrid could have a common origin with the strains described in Seattle. Countries with a high prevalence of co-infections and high migration flows should enhance surveillance programs in at least their vulnerable population.     

Plant Functional Types Differ in Their Long-term Nutrient Response to eCO2 in an Extensive Grassland

Ecosystems - Increasing atmospheric CO2 enhances plant biomass production and may thereby change nutrient concentrations in plant tissues. The objective of this study was to identify the effect of...     

Ecological and Evolutionary Interactions between Wild Crucifers and Their Herbivorous Insects

Abstract Insects feeding on ten species of wild crucifer were investigated. Differences in host plant range and insect community structure were examined with regard to anti-herbivore defense mechanisms. Most of the crucifer species deterred insect herbivory by disappearing in the summer or by lowering their intrinsic quality as food for insects. Species with these defense mechanisms were exploited by only a few specialized herbivorous insects that seemed to have counter defenses. The plants without these defense mechanisms were used by many herbivorous insect species. Rorippa indica lacked direct defenses, but supported a low total density of herbivore individuals. This crucifer has an indirect defense mechanism: ants attracted to floral nectar defended the plant from deleterious herbivores. Crucifers that disappeared seasonally lacked other anti-herbivore defense mechanisms. This suggests that the phonological response is an alternative other responses to herbivore attack.