Biochemical and Cytological Evidence for an Overabundance of Mucocysts in the bcd Pattern Mutant of Tetrahymena thermophila

ABSTRACT. Three acidic proteins (42 kD, 43 kD and 50 kD) were present in unusually high concentrations in cortical preparations of the Tetrahymena pattern mutant broadened cortical domains (bcd). Antisera to the 42-kD and 50-kD proteins bound to discharging mucocysts and food vacuole contents in both wild-type and mutant cells. Subsequent analysis revealed that bcd mutant cell pellicles possess five times more "docked" mucocysts than their wild-type counterparts.     

Massive mortality of aspen following severe drought along the southern edge of the Canadian boreal forest

Drought‐induced, regional‐scale dieback of forests has emerged as a global concern that is expected to escalate under model projections of climate change. Since 2000, drought of unusual severity, extent, and duration has affected large areas of western North America, leading to regional‐scale dieback of forests in the southwestern US. We report on drought impacts on forests in a region farther north, encompassing the transition between boreal forest and prairie in western Canada. A central question is the significance of drought as an agent of large‐scale tree mortality and its potential future impact on carbon cycling in this cold region. We used a combination of plot‐based, meteorological, and remote sensing measures to map and quantify aboveground, dead biomass of trembling aspen (Populus tremuloides Michx.) across an 11.5 Mha survey area where drought was exceptionally severe during 2001–2002. Within this area, a satellite‐based land cover map showed that aspen‐dominated broadleaf forests occupied 2.3 Mha. Aerial surveys revealed extensive patches of severe mortality (>55%) resembling the impacts of fire. Dead aboveground biomass was estimated at 45 Mt, representing 20% of the total aboveground biomass, based on a spatial interpolation of plot‐based measurements. Spatial variation in percentage dead biomass showed a moderately strong correlation with drought severity. In the prairie‐like, southern half of the study area where the drought was most severe, 35% of aspen biomass was dead, compared with an estimated 7% dead biomass in the absence of drought. Drought led to an estimated 29 Mt increase in dead biomass across the survey area, corresponding to 14 Mt of potential future carbon emissions following decomposition. Many recent, comparable episodes of drought‐induced forest dieback have been reported from around the world, which points to an emerging need for multiscale monitoring approaches to quantify drought effects on woody biomass and carbon cycling across large areas.     

High‐throughput two‐dimensional root system phenotyping platform facilitates genetic analysis of root growth and development

High‐throughput phenotyping of root systems requires a combination of specialized techniques and adaptable plant growth, root imaging and software tools. A custom phenotyping platform was designed to capture images of whole root systems, and novel software tools were developed to process and analyse these images. The platform and its components are adaptable to a wide range root phenotyping studies using diverse growth systems (hydroponics, paper pouches, gel and soil) involving several plant species, including, but not limited to, rice, maize, sorghum, tomato and Arabidopsis. The RootReader2D software tool is free and publicly available and was designed with both user‐guided and automated features that increase flexibility and enhance efficiency when measuring root growth traits from specific roots or entire root systems during large‐scale phenotyping studies. To demonstrate the unique capabilities and high‐throughput capacity of this phenotyping platform for studying root systems, genome‐wide association studies on rice (Oryza sativa) and maize (Zea mays) root growth were performed and root traits related to aluminium (Al) tolerance were analysed on the parents of the maize nested association mapping (NAM) population.     

Depth selection by Daphnia pulex in response to Chaoborus kairomone

1. The presence of kairomone from the predaceous larval dipteran Chaoborus americanus can result in juvenile Daphnia pulex positioning themselves higher in the water column. Chaoborus normally lives at greater depth during the day, so this behavioural response by Daphnia will reduce its encounter rate with the predator and enhance survival. 2. Behavioural observations of seven clones from a single population were made under four treatments (with and without Chaoborus kairomone prior to and/or during experiments). 3. All clones moved higher when exposed to kairomones during behavioural observations. Six moved higher when kairomone was added prior to the experiment (i.e. pre‐conditioned), while the other clone went lower, providing evidence for the presence of genetic variation in induced behaviour. When this clone was removed from the analysis, the evidence for genetic variation in induced response disappeared. 4. Juvenile Daphnia that were pre‐conditioned had a significantly greater response than those that had no previous exposure. Of the total shift in depth (comparing treatment and control means), 38% was due to prior exposure to the kairomone (‘preconditioning’), while 62% was due to exposure during the 2‐h experiments when the depth selection was assessed. When the effect of the one clone with a qualitatively different response was removed, these two figures became 45% and 55%, respectively. 5. The enhanced effect of prior exposure to the kairomone during development suggests that such exposure causes greater sensitivity to the kairomone.     

Evolutionary process of a tetranucleotide microsatellite locus in Acipenseriformes

The evolutionary dynamics of the tetra-nucleotide microsatellite locus Spl-106 were investigated at the repeat and flanking sequences in 137 individuals of 15 Acipenseriform species, giving 93 homologous sequences, which were detected in 11 out of 15 species. Twenty-three haplotypes of flanking sequences and three distinct types of repeats, type I, type II and type III, were found within these 93 sequences. The MS-Align phylogenetic method, newly applied to microsatellite sequences, permitted us to understand the repeat and flanking sequence evolution of Spl-106 locus. The flanking region of locus Spl-106 was highly conserved among the species of genera Acipenser, Huso and Scaphirhynchus, which diverged about 150 million years ago (Mya). The rate of flanking sequence divergence at the microsatellite locus Spl-106 in sturgeons is between 0.011% and 0.079% with an average at 0.028% per million years. Sequence alignment and phylogenetic trees produced by MS-Align showed that both the flanking and repeat regions can cluster the alleles of different species into Pacific and Atlantic lineages. Our results show a synchronous evolutionary pattern between the flanking and repeat regions. Moreover, the coexistence of different repeat types in the same species, even in the same individual, is probably due to two duplication events encompassing the locus Spl-106 that occurred during the divergence of Pacific lineage. The first occured before the diversification of Pacific species (121–96 Mya) and led to repeat types I and II. The second occurred more recently, just before the speciation of A. sinensis and A. dabryanus (69–10 Mya), and led to repeat type III. Sequences in the same species with different repeat types probably corresponds to paralogous loci. This study sheds a new light on the evolutionary mechanisms that shape the complex microsatellite loci involving different repeat types.     

Host-plant susceptibility to the carrot fly, Psila rosae. 3. The role of oviposition preferences and larval performance

The acceptability of various plant species to ovipositing carrot flies was weakly, but significantly correlated with the host's suitability for larval development. Both adult host-plant preferences and larval performance as determined in laboratory experiments explained a part of the variation in susceptibility among the various test plants observed in the field. Across the whole set of plant species examined, antixenosis contributed more substantially to resistance than antibiosis, while the reverse seemed to be true for carrot cultivars.     

The Abundance and Distribution of Wolverines in British Columbia,Canada

ABSTRACT The abundance and distribution of carnivores and their habitat are key information needed for status assessment, conservation planning, population management, and assessment of the effects of human development on their habitat and populations. We developed a habitat quality rating system, using existing wolverine (Gulo gulo) distribution, wolverine food, ecosystem mapping, and human development data. We used this and empirically derived estimates of wolverine density to predict wolverine distribution and abundance at a provincial scale. Density estimates for wolverines in high-quality habitat averaged 6.2 wolverines/1,000 km² (95% CI = 4.2–9.5). We predicted mean densities ranging from 0.3/1,000 km² in rare-quality habitat to 4.1/1,000 km² in moderate-quality habitat. Our predicted population estimate for wolverines in British Columbia was 3,530 (95% CI = 2,700-4,760). We predicted highest densities of wolverines in interior mountainous regions, moderate densities in interior plateau and boreal forest regions, and low densities in mainland coastal regions and drier interior plateaus. We predicted that wolverines would be rare on Vancouver Island, along the outer mainland coast, and in the dry interior forests, and absent from the Queen Charlotte Islands, interior grassland environments, and areas of intensive urban development.     

Multivariate analysis of morphological variation in Cineraria deltoidea (Asteraceae, Senecioneae)

Cluster analysis and principal coordinates analysis were used to investigate phenetic variation in Cineraria deltoidea , a species that ranges from near sea level in KwaZulu-Natal, South Africa, to 4300 m a.s.l. on the mountains of East Africa and Ethiopia. Earlier taxonomic revisions reduced nine previously recognized species to synonyms of C. deltoidea . Two closely related species, C. decipiens and C. atriplicifolia , were also included in the analyses. Thirty-six morphological characters were examined on 111 specimens. Phenograms and scattergrams show partial clusters of specimens of C. deltoidea from individual mountains or geographical regions, but no groups are sufficiently distinct to warrant formal recognition at any rank. The East African specimens from 3000 m a.s.l. and higher tend to cluster together. Growth at high altitude in East Africa is correlated with fewer, larger capitula on longer peduncles, and an absence of a cobwebby indumentum comprising long, narrow-based trichomes. Cineraria deltoidea is thus a highly variable species with geographical and clinal variation evident throughout its range. Cineraria atriplicifolia and C. decipiens are maintained as distinct species, distinguished from C. deltoidea by their growth form, life span and auricle shape.  © 2007 University of the Witwatersrand, Johannesburg. Journal compilation © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 154 , 497–521.     

The importance of petiole structure on inhabitability by ants in Piper sect. Macrostachys (Piperaceae)

Several Central American species of Piper sect. Macrostachys have obligate associations with ants, in which the ant partner derives food and shelter from modified plant structures and, in turn, protects the plant against fungal infection and herbivory. In addition to these obligate ant-plants (i.e. myrmecophytes), several other species in Piper have resident ants only sometimes (facultative), and still other plant species never have resident ants. Sheathing petioles of sect. Macrostachys form the domatia in which ants nest. Myrmecophytes in sect. Macrostachys have tightly closed petiole sheaths with bases that clasp the stem. These sheathing petioles appear to be the single most important plant character in the association between ants and species of sect. Macrostachys . We examined the structure and variation of petioles in these species, and our results indicate that minor modifications in a small number of petiolar characters make the difference between petioles that are suitable for habitation by ants and those that are not.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 153 , 181–191.