Phenology of a northern hardwood forest canopy

While commonplace in other parts of the world, long‐term and ongoing observations of the phenology of native tree species are rare in North America. We use 14 years of field survey data from the Hubbard Brook Experimental Forest to fit simple models of canopy phenology for three northern hardwood species, sugar maple (Acer saccharum), American beech (Fagus grandifolia), and yellow birch (Betula alleghaniensis). These models are then run with historical meteorological data to investigate potential climate change effects on phenology. Development and senescence are quantified using an index that ranges from 0 (dormant, no leaves) to 4 (full, green canopy). Sugar maple is the first species to leaf out in the spring, whereas American beech is the last species to drop its leaves in the fall. Across an elevational range from 250 to 825 m ASL, the onset of spring is delayed by 2.7±0.4 days for every 100 m increase in elevation, which is in reasonable agreement with Hopkin's law. More than 90% of the variation in spring canopy development, and just slightly less than 90% of the variation in autumn canopy senescence, is accounted for by a logistic model based on accumulated degree‐days. However, degree‐day based models fit to Hubbard Brook data appear to overestimate the rate at which spring development occurs at the more southerly Harvard Forest. Autumn senescence at the Harvard Forest can be predicted with reasonable accuracy in sugar maple but not American beech. Retrospective modeling using five decades (1957–2004) of Hubbard Brook daily mean temperature data suggests significant trends (P≤0.05) towards an earlier spring (e.g. sugar maple, rate of change=0.18 days earlier/yr), consistent with other studies documenting measurable climate change effects on the onset of spring in both North America and Europe. Our results also suggest that green canopy duration has increased by about 10 days (e.g. sugar maple, rate of change=0.21 days longer/yr) over the period of study.     

Empirical evaluation of preservation methods for faecal DNA

We evaluate the relative effectiveness of four methods for preserving faecal samples for DNA analysis. PCR assays of fresh faecal samples collected from free-ranging baboons showed that amplification success was dependent on preservation method, PCR-product size, and whether nuclear or mitochondrial DNA was assayed. Storage in a DMSO/EDTA/Tris/salt solution (DETs) was most effective for preserving nuclear DNA, but storage in 70% ethanol, freezing at –20°C and drying performed approximately equally well for mitochondrial DNA and short (<200 bp) nuclear DNA fragments. Because faecal DNA is diluted and degraded, repeated extractions from faeces may be necessary and short nuclear markers should be employed for genotyping. A review of molecular scatology studies further suggests that three to six faeces per individual should be collected.     

Virulence of Agrobacterium on Larix decidua and Their Cellular Interactions as Depicted by Scanning Electron Microscopy

European larch (Larix decidua Mill.) seedlings were inoculatedwith a number of Agrobacterium strains to screen susceptibilityto infection by agrobacteria. Nine of fourteen Agrobacteriumstrains tested were virulent on this conifer species. The attachmentof virulent Agrobacterium to larch seedling tissues was examinedusing scanning electron microscopy. Electron micrographs showedthe attachment specificity of virulent Agrobacterium to larchcells at wound sites in a manner similar to that described forcells of susceptible dicotyledonous angiosperms, indicatinga host-parasite relationship between oncogenic Agrobacteriumspp. and young seedlings of European larch. These unique electronmicrographs provide the first opportunity to document the compatibleinteractions of Agrobacterium and a conifer at the cellularlevel. Further, the evaluation of tumour formation frequencysuggested that the interactions between Agrobacterium and Europeanlarch were affected by wound site, position of inoculation,age of plant tissues, and time of co-culture. Successful infectionof Agrobacterium resulted in genetic transformation of hostcells. Agrobacterium-mediated DNA transfer and expression of bacterialgenes in larch tissues were confirmed by both Southern blotanalysis and opine assay with the transformed tissues. Key words: Agrobacterium, Larix decidua, cellular interaction, transformation, DNA transfer, scanning electron microscopy     

Molecular genetics of the most endangered canid: the Ethiopian wolf Canis simensis

The world's most endangered canid is the Ethiopian wolf Canis simensis , which is found in six isolated areas of the Ethiopian highlands with a total population of no more than 500 individuals. Ethiopian wolf populations are declining due to habitat loss and extermination by humans. Moreover, in at least one population, Ethiopian wolves are sympatric with domestic dogs, which may hybridize with them, compete for food, and act as disease vectors. Using molecular techniques, we address four questions concerning Ethiopian wolves that have conservation implications. First, we determine the relationships of Ethiopian wolves to other wolf-like canids by phylogenetic analysis of 2001 base pairs of mitochondrial DNA (mtDNA) sequence. Our results suggest that the Ethiopian wolf is a distinct species more closely related to gray wolves and coyotes than to any African canid. The mtDNA sequence similarity with gray wolves implies that the Ethiopian wolf may hybridize with domestic dogs, a recent derivative of the gray wolf. We examine this possibility through mtDNA restriction fragment analysis and analysis of nine microsatellite loci in populations of Ethiopian wolves. The results imply that hybridization has occurred between female Ethiopian wolves and male domestic dogs in one population. Finally, we assess levels of variability within and between two Ethiopian wolf populations. Although these closely situated populations are not differentiated, the level of variability in both is low, suggesting long-term effective population sizes of less than a few hundred individuals. We recommend immediate captive breeding of Ethiopian wolves to protect their gene pool from dilution and further loss of genetic variability.     

A Computer Model for Reshaping of Cells in Epithelia Due to In-plane Deformation and Annealing

Although cell reshaping is fundamental to the mechanics of epithelia, technical barriers have prevented the methods of mechanics from being used to investigate it. These barriers have recently been overcome by the cell-based finite element formulation of Chen and Brodland. Here, parameters to describe the fabric of an epithelium in terms of cell shape and orientation and cell edge density are defined. Then, rectangular "patches" of model epithelia having various initial fabric parameters are generated and are either allowed to anneal or are subjected to one of several patterns of in-plane deformation. The simulations show that cell reshaping lags the deformation history, that it is allayed by cell rearrangement and that it causes the epithelium as a whole to exhibit viscoelastic mechanical properties. Equations to describe changes in cell shape due to annealing and in-plane deformation are presented.     

More for less: a study of environmental flows during drought in two Australian rivers

1. In rivers affected by drought, flow regulation can further reduce flow and intensify its effects. We measured ecological responses to environmental flows, during a prolonged drought in a regulated river (Cotter River), compared with a drought affected, unregulated river (Goodradigbee River) in south‐eastern Australia. 2. Environmental flows in the regulated Cotter River were reduced from a monthly average base flow of 15 MLd^?1 to only 5 MLd^?1, which was implemented as two test flow regimes. Initially, flows were delivered in cycles of 14 days at 3 MLd^?1 followed by 3 days at 14 MLd^?1 and then another 14 days at 3 MLd^?1 to make up the monthly average of 5 MLd^?1. This flow regime continued for 6 months, after which a preliminary ecological assessment indicated deterioration in river condition. Consequently, the flow regime was altered to a cycle of 2 MLd^?1 for 28 days followed by 20 MLd^?1 for either 3 or 4 days. This new flow regime continued for another 5 months. 3. The ecological outcomes of the test flow regimes were assessed in terms of (i) the provision of available habitat (wetted channel) for aquatic biota; (ii) the accumulation of periphyton; and (iii) the structure and richness of macroinvertebrate assemblages. 4. Flow of 20 MLd^?1 covered most of the streambed in the Cotter River, thus providing more wetted area and connectivity between habitats than flows of 2, 3 or 14 MLd^?1. Depth and velocity were always less in the Cotter River than in the unregulated Goodradigbee River. Periphyton decreased in the Cotter River during the 2/20 MLd^?1 flow regime, which combined the lowest and greatest test flow volumes, while periphyton did not change significantly in the unregulated river. 5. The reduced flow in the Cotter River resulted in fewer macroinvertebrates than expected (13) compared with unregulated Goodradigbee sites (19), although the magnitude of the differences did not depend on the test flow releases. Macroinvertebrates in the Cotter River became numerically dominated by Diptera and Oligochaeta, while Ephemeroptera, Plecoptera and Trichoptera decreased in abundance. 6. In the Cotter River, the monthly average flow of 5 MLd^?1 (exceeded 97% of the time pre‐regulation) was insufficient to maintain the macroinvertebrate assemblages in reference condition, regardless of release patterns. However, short‐term ecological objectives were achieved, such as reduced periphyton accumulation and increased habitat availability, and the environmental flows maintained the river’s ability to recover (resilience) when higher flows returned.     

Cannabis use and the risk of developing a psychotic disorder

We briefly review the evidence that cannabis use in adolescence and young adulthood is a contributory cause of schizophreniform psychoses, by summarising longitudinal studies that: a) have examined relationships between cannabis use and the risk of psychosis or psychotic symptoms; and b) have controlled for potential confounders, such as other forms of drug use and personal characteristics that predict an increased risk of psychosis. There is now reasonable evidence from longitudinal studies that regular cannabis use predicts an increased risk of schizophrenia and of reporting psychotic symptoms. These relationships have persisted after controlling for confounding variables such as personal characteristics and other drug use. The relationships did not seem to be explained by cannabis being used to self-medicate symptoms of psychosis. A contributory causal relationship is biologically plausible because psychotic disorders involve disturbances in the dopamine neurotransmitter system with which the cannabinoid system interacts, as has been shown by animal studies and a human provocation study. We briefly explore the clinical and public health implications of the most plausible hypothesis, that cannabis use precipitates schizophrenia in persons who are vulnerable because of a personal or family history of schizophrenia.     

Dispersal, philopatry, and genetic relatedness in a social carnivore: comparing males and females

A balance must be maintained between the proportion of individuals dispersing and the proportion remaining philopatric such that inbreeding and resource competition are minimized. Yet the relative importance of dispersal and philopatric behaviour is uncertain, especially for species with complex social systems. We examine the influence of dispersal on genetic relationships of a white-nosed coati ( Nasua narica : Procyonidae) population from Panama. Field studies of the coati indicate a social system in which all females are highly philopatric and live in bands while all adult males become solitary at maturity, but do not disperse from the home range of their natal band. Based on analyses of multilocus DNA fingerprints, we confirm that female philopatry is the rule, long-distance dispersal is rare, and that relatedness between most bands is low. However, some new bands result from fission events and these bands retain relatively high relatedness to one another for several years. Adult males inhabiting the home range of a band are closely related to band members. In contrast, males and band members whose ranges do not overlap are unrelated or only slightly related. Adult males are also more closely related to other males whose home ranges they overlap extensively than to males whose home ranges they overlap only slightly. These results indicate that males initially disperse from their natal bands to reduce resource competition and not to avoid inbreeding. Inbreeding avoidance, if it occurs, results from more extensive range movements by males during the mating season.