Granule-bound starch synthase: structure, function, and phylogenetic utility

Interest in the use of low-copy nuclear genes for phylogenetic analyses of plants has grown rapidly, because highly repetitive genes such as those commonly used are limited in number. Furthermore, because low- copy genes are subject to different evolutionary processes than are plastid genes or highly repetitive nuclear markers, they provide a valuable source of independent phylogenetic evidence. The gene for granule-bound starch synthase (GBSSI or waxy) exists in a single copy in nearly all plants examined so far. Our study of GBSSI had three parts: (1) Amino acid sequences were compared across a broad taxonomic range, including grasses, four dicotyledons, and the microbial homologs of GBSSI. Inferred structural information was used to aid in the alignment of these very divergent sequences. The informed alignments highlight amino acids that are conserved across all sequences, and demonstrate that structural motifs can be highly conserved in spite of marked divergence in amino acid sequence. (2) Maximum-likelihood (ML) analyses were used to examine exon sequence evolution throughout grasses. Differences in probabilities among substitution types and marked among-site rate variation contributed to the observed pattern of variation. Of the parameters examined in our set of likelihood models, the inclusion of among-site rate variation following a gamma distribution caused the greatest improvement in likelihood score. (3) We performed cladistic parsimony analyses of GBSSI sequences throughout grasses, within tribes, and within genera to examine the phylogenetic utility of the gene. Introns provide useful information among very closely related species, but quickly become difficult to align among more divergent taxa. Exons are variable enough to provide extensive resolution within the family, but with low bootstrap support. The combined results of amino acid sequence comparisons, maximum-likelihood analyses, and phylogenetic studies underscore factors that might affect phylogenetic reconstruction. In this case, accommodation of the variable rate of evolution among sites might be the first step in maximizing the phylogenetic utility of GBSSI.      

Environmental change and the phenology of European aphids

Aphids, because of their short generation time and low developmental threshold temperatures, are an insect group expected to respond particularly strongly to environmental changes. Forty years of standardized, daily data on the abundance of flying aphids have been brought together from countries throughout Europe, through the EU Thematic Network 'EXAMINE'. Relationships between phenology, represented by date of first appearance in a year in a suction trap, of 29 aphid species and environmental data have been quantified using the residual maximum likelihood (REML) methodology. These relationships have been used with climate change scenario data to suggest plausible changes in aphid phenology. In general, the date of first record of aphid species in suction traps is expected to advance, the rate of advance varying with location and species, but averaging 8 days over the next 50 years. Strong relationships between aphid phenology and environmental variables have been found for many species, but they are notably weaker in species living all year on trees. Canonical variate analysis and principal coordinate analysis were used to determine ordinations of the 29 species on the basis of the presence/absence of explanatory variables in the REML models. There was strong discrimination between species with different life cycle strategies and between species feeding on herbs and trees, suggesting the possible value of trait-based groupings in predicting responses to environmental changes.     

Evolutionarily stable oviposition and sex ratio in parasitoid wasps with single‐sex broods

Abstract 1. The flexibility of hymenopteran sex ratios is well documented, particularly in structured populations featuring sib mating. 2. Using game theoretic models, the present study examines species producing single‐sex broods in which sib mating is unlikely, and focuses on the role of population density in determining evolutionarily stable oviposition strategies. 3. Since only mated females can produce offspring of both sexes while unmated females produce only male offspring, mated females are under selection to produce more females overall to balance the primary sex ratio. 4. As the proportion of all females that are mated should increase with density, offspring sex ratio of mated females is strongly linked to density at low to moderate densities. The present study shows that when density becomes low enough for fewer than half of all females to have mated, then female offspring generate higher fitness. 5. In this low density situation, females may gain a fitness benefit from waiting at their emergence site or from using other costly means to find and mate with males before ovipositing. 6. The predicted correspondence between females waiting at the emergence site and fewer than half of females in the population containing sperm, can be tested empirically, as can the somewhat counter‐intuitive prediction that greater access to males should yield a more male‐biased sex ratio in the offspring of mated females. 7. The present study also indicates how measuring the variance in giving up times by females waiting for males at low density, can provide insight into mechanisms determining waiting times.     

The diabetic rat kidney mediates inosituria and selective urinary partitioning of D-chiro-inositol

Diabetic nephropathy is a serious complication of diabetes mellitus with a pressing need for effective metabolic markers to detect renal impairment. Of potential significance are the inositol compounds, myo-inositol (MI), and the less abundant stereoisomer, D-chiro-inositol (DCI), which are excreted at increased levels in the urine in diabetes mellitus, a phenomenon known as inosituria. There is also a selective urinary excretion of DCI compared to MI. As the biological origins of altered inositol metabolism in diabetes mellitus are unknown, the aim of this study was to determine whether the diabetic kidney was directly responsible. Kidneys isolated from four-week streptozotocin-induced diabetic rats were characterized by a 3-fold reduction in glomerular filtration rate (GFR) compared to matched non-diabetic kidneys. When perfused with fixed quantities of MI (50 µM) and DCI (5 µM) under normoglycemic conditions (5 mM glucose), GFR-normalized urinary excretion of MI was increased by 1.7-fold in diabetic vs. non-diabetic kidneys. By comparison, GFR-normalized urinary excretion of DCI was increased by 4-fold. Perfusion conditions replicating hyperglycemia (20 mM glucose) potentiated DCI but not MI urinary excretion in both non-diabetic and diabetic kidneys. Overall, there was a 2.4-fold increase in DCI urinary excretion compared to MI in diabetic kidneys that was independent of glucose ambience. This increased urinary excretion of DCI and MI in diabetic kidneys occurred despite increased renal expression of the inositol transporters, sodium myo-inositol transporter subtype 1 and 2 (SMIT1 and SMIT2). These findings show that the diabetic kidney primarily mediates inosituria and altered urinary partitioning of MI and DCI. Urinary inositol levels might therefore serve as an indicator of impaired renal function in diabetes mellitus with wider implications for monitoring chronic kidney disease.     

Evidence for Rosettes as an Unrecognized Stage in the Life Cycle of Leishmania Parasites

ABSTRACT. Leishmania parasites, which afflict 12 million people in 88 countries, exist as promastigotes transmitted by insect vectors and as amastigotes residing in mammalian macrophages. Promastigote cells arranged in rosettes have also been described but universally disregarded as a distinct stage in the life cycle. We present evidence that only rosettes of Leishmania major promastigotes express cell surface poly‐α2,8 N‐acetyl neuraminic acid (PSA) and PSA containing de‐N‐acetyl neuraminic acid (NeuPSA). Expression of rosette‐specific PSA antigens was mosaic, with individual promastigotes expressing PSA, NeuPSA or both. A 50 kDa protein was detected by Western blot analysis of a detergent‐insoluble cell fraction with both PSA and NeuPSA‐reactive antibodies. Frequencies of rosette formation as well as cell surface PSA/NeuPSA expression were temperature dependent. Rosettes also engaged in an unusual swarming behavior, congregating into extended clusters. Distinct structures resembling cellular fusion bodies were formed in and released from rosettes. The results indicate that rosettes are an unrecognized stage in the life cycle of Leishmania. We hypothesize that rosettes initiate mating in Leishmania during which PSA/NeuPSA expression plays an important role. Recognizing rosettes as a distinct form of the Leishmania life cycle opens new possibilities for treatment or prevention of disease and, possibly, in vitro genetic recombination without passage of cells through insect vectors.     

Historical influences dominate the population genetic structure of a sedentary marine fish,Atlantic wolffish (Anarhichas lupus), across the North Atlantic Ocean

Genetic variation was assessed in Atlantic wolffish, Anarhichas lupus, across the North Atlantic Ocean using microsatellite and amplified fragment length polymorphism (AFLP) markers. Despite unusual life history attributes such as large benthic eggs, large larvae, a limited pelagic stage and relatively sedentary adults, which suggest potential for strong population structure, range‐wide F_ST values were comparable to other marine fishes (≤0.035). Nevertheless, both significant genetic differentiation among regions and isolation by distance were observed, suggesting limited dispersal in this species. AFLP loci, evaluated on a subset of samples, revealed slightly higher F_ST values, but similar patterns of differentiation and isolation‐by‐distance estimates, compared to microsatellites. The genetic structure of Atlantic wolffish has likely been shaped by its post‐glacial history of recolonization, North Atlantic current patterns and continuity of habitat on continental shelves.     

Leaf‐litter breakdown in pasture and deciduous woodland streams: a comparison among three European regions

1. Human land‐use has altered catchments on a large scale in most parts of the world, with one of the most profound changes relevant for streams and rivers being the widespread clearance of woody riparian vegetation to make way for livestock grazing pasture. Increasingly, environmental legislation, such as the EU Water Framework Directive (EU WFD), calls for bioassessment tools that can detect such anthropogenic impacts on ecosystem functioning. 2. We conducted a large‐scale field experiment in 30 European streams to quantify leaf‐litter breakdown, a key ecosystem process, in streams whose riparian zones and catchments had been cleared for pasture compared with those in native deciduous woodland. The study encompassed a west–east gradient, from Ireland to Switzerland to Romania, with each of the three countries representing a distinct region. We used coarse‐mesh and fine‐mesh litter bags (10 and 0.5 mm, respectively) to assess total, microbial and, by difference, macroinvertebrate‐mediated breakdown. 3. Overall, total breakdown rates did not differ between land‐use categories, but in some regions macroinvertebrate‐mediated breakdown was higher in deciduous woodland streams, whereas microbial breakdown was higher in pasture streams. This result suggests that overall ecosystem functioning is maintained by compensatory increases in microbial activity in pasture streams. 4. We suggest that simple coefficients of breakdown rates on their own often might not be powerful enough as a bioassessment tool for detecting differences related to land‐use such as riparian vegetation removal. However, shifts in the relative contributions to breakdown by microbial decomposers versus invertebrate detritivores, as revealed by the ratios of their associated breakdown rate coefficients, showed clear responses to land‐use.     

The importance of water regimes operating at small spatial scales for the diversity and structure of wetland vegetation

1. In most cases, the most important determinant of wetland vegetation is the water regime. Although water regime is usually described and managed at the scale of whole wetlands, the patterning of vegetation is likely to be determined by water regimes that are experienced at much finer spatial scales. In this study, we assess the significance of internal heterogeneity in water regimes and the role that this heterogeneity plays in vegetation patterning. 2. The effects of water regime on wetland plant species richness and vegetation structure were studied at Dowd Morass, a 1500 ha, Ramsar‐listed wetland in south‐eastern Australia that is topographically heterogeneous. Data on plant variables and water depth were collected along 45 (50 m) transects throughout the wetland and related to water regimes assigned individually for each transect. Wetland plants were assigned to plant functional groups (PFG) that describe the response of plants to the presence or absence of water at different life stages. 3. The classification of water depth data indicated four distinct water regimes in the wetland that were differentiated primarily by the duration of the dry period. Representatives of all PFGs co‐existed over small spatial scales where topographical variation was present, and the richness and cover of understorey species declined as transects became more deeply and permanently flooded. Some PFGs (e.g. amphibious fluctuation tolerator‐low growing and amphibious fluctuation responder‐morphologically plastic) were eliminated by extended periods of flooding, which increased the cover but not richness of submerged plants. Species richness and foliage projective cover declined as water regimes shifted from shallow and frequently exposed conditions to regimes typified by deeper and longer inundation. Cover of the structurally dominant woody species was compromised by deeply flooded conditions but vegetative regeneration occurred despite high water levels. 4. Internal topographical variation generates mosaics of water regimes at fine spatial scales that allow plant species with different water regime requirements to co‐exist over small distances. Deep water and an absence of dry periods result in decreased cover of plants and an overall loss of species richness in the understorey. Water regimes are described that promote regeneration and cover of structurally dominant taxa and increased species richness in the understorey. The study demonstrates a strong association between vegetation and the diverse water regimes that exist within a single wetland, a pattern that will be useful for modelling the effects of modified water regimes on wetland vegetation.     

How do sucker‐footed bats hold on,and why do they roost head‐up?

Individuals of most bat species hang head‐down by their toenails from rough surfaces, but Madagascar's endemic sucker‐footed bat (Myzopoda aurita) clings head‐up to smooth leaves using specialized pads on its wrists and ankles. We investigated the adhesive performance of 28 individuals and found that attachment performance on brass was not affected by the presence or absence of a seal around the pad–surface interface. Furthermore, on smooth acrylic, the wrist pads were more than nine‐fold weaker when lifted perpendicular to the surface than when pulled parallel to it. The unimportance of a seal and the difference in strength in those directions on a smooth surface are characteristic of wet adhesion, but not of suction. Thus, despite its name, the sucker‐footed bat appears to adhere using wet adhesion. We observed that when wrist pads were pushed anteriorly, they unpeeled easily from the surface because of deformation of the pads. This most likely permits rapid detachment during crawling, but would also cause passive detachment if bats roosted head‐down. This provides an ecomorphological explanation to the head‐up roosting behaviour of these unique bats. The results obtained in the present study thus link morphology, behaviour, and roosting ecology for an enigmatic Malagasy endemic. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 233–240.