Life history plasticity of Nemoura trispinosa (Plecoptera: Nemouridae) along a permanent-temporary water habitat gradient

1. The life history of the small herbivorous stonefly Nemoura trispinosa Claassen was studied in a variety of small springs in southern Ontario, Canada. Nymphs generally were able to tolerate a wide range of environmental conditions and were found in 78% of habitats sampled, although population densities differed markedly. 2. Life-cycle patterns varied from a univoltine, slow seasonal type to a univoltine, fast seasonal type with extended egg development. In one, highly stable, spring the life cycle was semivoltine. Inter-year variation was studied for 5 years in one spring and was found to be low relative to among-spring variation. 3. Differences in the life history traits of N. trispinosa populations from our spring series were most probably an expression of phenotypic plasticity rather than of genetic differentiation. 4. Maximum annual water temperature was the factor most influential on nymphal growth rate (non-linear relationship), whereas range in generation time was related to the degree of habitat permanence.     

A new species of Ramazzottius (Tardigrada, Hypsibiidae) in a rain gutter sediment from England

Five species of tardigrades were extracted from a sample of sediment from a rain gutter. Four of these, the heterotardigrade Echiniscus testudo and the eutardigrades Milnesium tardigradum, Ramazzottius oberhaeuseri , and probably Macrobiotus cf. sandrae are typical of xerophilous habitats. The fifth species, Ramazzottius varieornatus sp. nov. , is new to science, and it can be readily distinguished from the others of the same genus by egg shell morphology, placoids and the type of cuticle.     

Measuring the impact of sewage effluent on the macroinvertebrate community of an upland stream: The effect of different levels of taxonomic resolution and quantification

Abstract Benthic macroinvertebrates were sampled from four sites on upland streams in the Wentworth Falls area of the Blue Mountains, NSW. One site received effluent from a sewage treatment plant and the others were reference sites. Five replicate collections were taken from each site on four occasions at intervals of 3 months. Macroinvertebrate community data were analysed using univariate (ANOVA) and multivariate (NMDS) techniques and comparisons were made between analyses at different levels of taxonomic aggregation and using different methods of data transformation. Similar patterns were observed at both species and family levels, and even the order level showed a clear community response to effluent input. Binary (presence/ absence) data provided similar results to quantitative data for the species and family levels. However, when binary data were used at the order level, the distinctions between the reference sites became blurred. We discuss the implications of these findings for environmental monitoring.     

Frequency-dependent food selection by arthropods: a review

We review published studies in which arthropods were presented with a choice of food types at a range of relative densities. Twenty-four of 28 studies showed frequency-independent preference; 11 studies also showed frequency-dependent preference. Both pro- and anti-apostatic selection were found. In the light of these studies we discuss possible behavioural mechanisms which produce such selection; the potential benefits to the predators and the consequences of such selection for diversity both within and between species.     

RNA Homologies Between Protozoa

SYNOPSIS. Comparison of RNA molecules between certain protozoa using the technic of nucleic acid hybridisation revealed that there are complementary sequences for ribosomal RNA molecules in the genomes of such cells. Furthermore the genes for ribosomal RNA have been conserved during evolution in this group of organisms. On the other hand, RNA molecules from these protozoa which can be considered to be "messengers" show little in the way of sequence relationships. By utilising the technic of hybridisation it was found that Oxytricha can compete effectively against Paramecium ribosomal RNA for Tetrahymena DNA but the ribosomal RNA sequences of the latter could not compete completely against Paramecium ribosomal RNA for Oxytricha DNA. The result is interpreted to show that different ribosomal sequences were hybridising with each of the DNA samples from Tetrahymena and Oxytricha. A general interpretation of this result in terms of ribosome evolution is presented.     

Effects of Electrolyte and Non-Electrolyte Solutions on the Tropic Responses of Avena Coleoptiles

Solutions of mannitol and carbowax 1540 reduced the geotropicresponse of Avena sativa coleoptiles to at least the same extentas a potassium chloride solution of equal osmotic potential.Similar results were obtained with the phototropic response.The magnitude of these decreases increased almost linearly withthe osmotic concentration of the solutions over the range 0.025–0.45J cm^–3. In contrast, the geotropic and phototropic responseswere scarcely affected by exposing the coleoptiles to solutionsof glycerol. The absence of an effect with glycerol is probably due to thepenetration of the coleoptile cells by this solute. The similaror greater reduction in tropic curvature brought about by mannitoland carbowax 1540 solutions, as compared with a potassium chloridesolution of equal osmotic potential, makes untenable a previoussuggestion attributing the inhibitory effects of electrolytesolutions to a shunting of the electro-potential differenceson the plant surface.     

Information theory and plant growth substance analysis

Abstract. Reeve & Crozier (1980) have recently proposed a method of evaluating the accuracy of a plant growth substance analysis by using information theory to estimate whether the analysis would distinguish the growth substance from all other components of the sample. In the present article, it is argued that their method requires knowledge of the relevant analytical characteristics of all potential components of the sample, and hence is not applicable to plant extracts. Instead, the identity of a growth substance in a plant extract can only be conclusively established using techniques which yield information on its chemical structure.     

Field evidence for indirect interactions between foliar‐feeding insect and root‐feeding nematode communities on Nicotiana tabacum

Abstract 1. As herbivory often elicits systemic changes in plant traits, indirect interactions via induced plant responses may be a pervasive feature structuring herbivore communities. Although the importance of this phenomenon has been emphasised for herbivorous insects, it is unknown if and how induced responses contribute to the organisation of other major phytoparasitic taxa. 2. Survey and experimental field studies were used to investigate the role of plants in linking the dynamics of foliar‐feeding insects and root‐feeding nematodes on tobacco, Nicotiana tabacum. 3. Plant‐mediated interactions between insects and nematodes could largely be differentiated by insect feeding guild, with positive insect–nematode interactions predominating with leaf‐chewing insects (caterpillars) and negative interactions occurring with sap‐feeding insects (aphids). For example, insect defoliation was positively correlated with the abundance of root‐feeding nematodes, but aphids and nematodes were negatively correlated. Experimental field manipulations of foliar insect and nematode root herbivory also tended to support this outcome. 4. Overall, these results suggest that plants indirectly link the dynamics of divergent consumer taxa in spatially distinct ecosystems. This lends support to the growing perception that plants play a critical role in propagating indirect effects among a diverse assemblage of consumers.     

Landscape genetics and least-cost path analysis reveal unexpected dispersal routes in the California tiger salamander (Ambystoma californiense)

A major goal of landscape genetics is to understand how landscapes structure genetic variation in natural populations. However, landscape genetics still lacks a framework for quantifying the effects of landscape features, such as habitat type, on realized gene flow. Here, we present a methodology for identifying the costs of dispersal through different habitats for the California tiger salamander ( Ambystoma californiense ), an endangered species restricted to grassland/vernal pool habitat mosaics. We sampled larvae from all 16 breeding ponds in a geographically restricted area of vernal pool habitat at the Fort Ord Natural Reserve, Monterey County, California. We estimated between-pond gene flow using 13 polymorphic microsatellite loci and constructed GIS data layers of habitat types in our study area. We then used least-cost path analysis to determine the relative costs of movement through each habitat that best match rates of gene flow measured by our genetic data. We identified four measurable rates of gene flow between pairs of ponds, with between 10.5% and 19.9% of larvae having immigrant ancestry. Although A. californiense is typically associated with breeding ponds in grassland habitat, we found that dispersal through grassland is nearly twice as costly as dispersal through chaparral and that oak woodland is by far the most costly habitat to traverse. With the increasing availability of molecular resources and GIS data, we anticipate that these methods could be applied to a broad range of study systems, particularly those with cryptic life histories that make direct observation of movement challenging.     

Phylogeography of lions (Panthera leo ssp.) reveals three distinct taxa and a late Pleistocene reduction in genetic diversity

Lions were the most widespread carnivores in the late Pleistocene, ranging from southern Africa to the southern USA, but little is known about the evolutionary relationships among these Pleistocene populations or the dynamics that led to their extinction. Using ancient DNA techniques, we obtained mitochondrial sequences from 52 individuals sampled across the present and former range of lions. Phylogenetic analysis revealed three distinct clusters: (i) modern lions, Panthera leo ; (ii) extinct Pleistocene cave lions, which formed a homogeneous population extending from Europe across Beringia (Siberia, Alaska and western Canada); and (iii) extinct American lions, which formed a separate population south of the Pleistocene ice sheets. The American lion appears to have become genetically isolated around 340 000 years ago, despite the apparent lack of significant barriers to gene flow with Beringian populations through much of the late Pleistocene. We found potential evidence of a severe population bottleneck in the cave lion during the previous interstadial, sometime after 48 000 years, adding to evidence from bison, mammoths, horses and brown bears that megafaunal populations underwent major genetic alterations throughout the last interstadial, potentially presaging the processes involved in the subsequent end-Pleistocene mass extinctions.