Binding of Radioactively Labelled Concanavalin A and Wheat Germ Agglutinin to Normal and Virus-transformed Cells

VARIOUS substances isolated from plants cause animal cells to clump. Several of these lectins¹ preferentially agglutinate cells which have been transformed spontaneously or by chemicals or viruses^2–7. The best known lectins of this class are concanavalin A (Con A) isolated from jack beans⁸ and wheat germ agglutinin⁴, which seem to bind to carbohydrate groups on the cell surface. The determinants recognized by the lectins seem to be N-acetyl-D-glucosamine for WGA⁴ and probably α-methyl-D-glucopyranoside for Con A⁶.     

Methane production by microbial mats under low sulphate concentrations

Cyanobacterial mats collected in hypersaline salterns were incubated in a greenhouse under low sulphate concentrations ([]) and examined for their primary productivity and emissions of methane and other major carbon species. Atmospheric greenhouse warming by gases such as carbon dioxide and methane must have been greater during the Archean than today in order to account for a record of moderate to warm palaeoclimates, despite a less luminous early sun. It has been suggested that decreased levels of oxygen and sulphate in Archean oceans could have significantly stimulated microbial methanogenesis relative to present marine rates, with a resultant increase in the relative importance of methane in maintaining the early greenhouse. We maintained modern microbial mats, models of ancient coastal marine communities, in artificial brine mixtures containing both modern [] (c. 70 mm ) and ‘Archean’[] (<0.2 mm ). At low [], primary production in the mats was essentially unaffected, while rates of sulphate reduction decreased by a factor of three, and methane fluxes increased by up to 10‐fold. However, remineralization by methanogenesis still amounted to less than 0.4% of the total carbon released by the mats. The relatively low efficiency of conversion of photosynthate to methane is suggested to reflect the particular geometry and chemical microenvironment of hypersaline cyanobacterial mats. Therefore, such mats were probably relatively weak net sources of methane throughout their 3.5 Ga history, even during periods of low environmental levels oxygen and sulphate.     

Cryptic variation and the tragedy of unrecognized taxa: the case of international trade in the spiny turtle Heosemys spinosa (Testudines: Geoemydidae)

Loss of habitat and human exploitation have driven many turtle species to the brink of extinction, particularly in many parts of southern Asia. The spiny turtle (Heosemys spinosa) is a terrestrial species distributed throughout the Sundaland region of South‐East Asia. Despite international legislative protection, H. spinosa continues to be illegally collected for the food and traditional medicine markets of China. Given its widespread distribution, taxonomists have reasonably questioned whether H. spinosa truly represents a single evolutionary lineage or multiple undiagnosed species. Recently, a large and illegal shipment of rare, wild‐caught H. spinosa was confiscated in Hong Kong, China, and the turtles were eventually distributed to several zoos and academic collections. Based on analyses of these individuals, along with additional individuals from the pet trade and museum collections, we found concordant genetic and phenotypic variation, indicating that two distinct types of H. spinosa exist in this collection of turtles. Further characterization of this variation will require field surveys and the collection of additional morphological and genetic data from specimens of known geographic provenance. However, our data indicate that this highly exploited, endangered species may contain additional cryptic taxa, and emphasize the critical need for systematic evaluation of species before unrecognized variation is lost forever. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 164 , 811–824.     

Life‐history and ecological correlates of decline and extinction in the endemic Australian frog fauna

Abstract Frog populations are rapidly disappearing throughout the world. An important issue for ecologists to resolve is why some frog species are more susceptible to decline than others. Here, we performed a comparative study of the endemic Australian frog fauna to determine whether the life history and ecology of declining species have predisposed them to extinction. Decline was consistently found to be correlated with geographical range size across contemporary species and in analyses based on phylogenetically independent contrasts (PICs). Species with narrow geographical ranges have been disproportionately more susceptible to decline. Across species, decline was also correlated with large body size and a high proportion of the geographical range overlapping with the distribution of cane toads and landscape stress (e.g. land clearing). We show that with the exception of range size, however, correlates of decline across species are underpinned by a small number of evolutionary events. Hence, the suite of traits that correlate with decline in the cross‐species analysis is only relevant to a small number of clades. We also found that clutch size, testes mass, ova size and distributional overlap with feral pigs were not significantly related to decline. In the ongoing search for life‐history and ecological correlates of decline and extinction, our results highlight the importance of performing analyses across contemporary species and using PICs.     

Perl and Python codes to estimate Hardy–Weinberg‐ and linkage‐disequilibrium‐related parameters

We have developed two pieces of Perl and Python codes to calculate the natural log of lambda, a quantity that expresses deviations from Hardy–Weinberg equilibrium, and R, a weighted correlation coefficient between alleles of locus pairs as a quantity that expresses linkage disequilibrium. These quantities can be used in an estimation approach as tools to facilitate the characterization and the comparison of populations.     

Evidence of a latitudinal gradient in spider diversity in Australian cotton

The most common explanation for species diversity increasing towards the tropics is the corresponding increase in habitats (spatial heterogeneity). Consequently, a monoculture (like cotton in Australia) which is grown along a latitudinal gradient, should have the same degree of species diversity throughout its range. We tested to see if diversity in a dominant cotton community (spiders) changed with latitude, and if the community was structurally identical in different parts of Australia. We sampled seven sites extending over 20° of latitude. At each site we sampled 1–3 fields 3–5 times during the cotton growing season using pitfall traps and beatsheets, recording all the spiders collected to family. We found that spider communities in cotton are diverse, including a large range of foraging guilds, making them suitable for a conservation biological control programme. We also found that spider diversity increased from high to low latitudes, and the communities were different, even though the spiders were in the same monocultural habitat. Spider beatsheet communities around Australia were dominated by different families, and responded differently to seasonal changes, indicating that different pest groups would be targeted at different locations. These results show that diversity can increase from high to low latitudes, even if spatial heterogeneity is held constant, and that other factors external to the cotton crop are influencing spider species composition. Other models which may account for the latitudinal gradient, such as non‐equilibrium regional processes, are discussed.     

Comparison of contemporary mating patterns in continuous and fragmented Eucalyptus globulus native forests

While habitat fragmentation is a central issue in forest conservation studies in the face of broad-scale anthropogenic changes to the environment, its effects on contemporary mating patterns remain controversial. This is partly because of the inherent variation in mating patterns which may exist within species and the fact that few studies have replication at the landscape level. To study the effect of forest fragmentation on contemporary mating patterns, including effective pollen dispersal, we compared four native populations of the Australian forest tree, Eucalyptus globulus . We used six microsatellite markers to genotype 1289 open-pollinated offspring from paired fragmented and continuous populations on the island of Tasmania and in Victoria on mainland Australia. The mating patterns in the two continuous populations were similar, despite large differences in population density. In contrast, the two fragmented populations were variable and idiosyncratic in their mating patterns, particularly in their pollen dispersal kernels. The continuous populations showed relatively high outcrossing rates (86–89%) and low correlated paternity (0.03–0.06) compared with the fragmented populations (65–79% and 0.12–0.20 respectively). A greater proportion of trees contributed to reproduction in the fragmented ( de/d ≥ 0.5) compared with the continuous populations ( de/d  =   0.03–0.04). Despite significant inbreeding in the offspring of the fragmented populations, there was little evidence of loss of genetic diversity. It is argued that enhanced medium- and long-distance dispersal in fragmented landscapes may act to partly buffer the remnant populations from the negative effects of inbreeding and drift.     

Density-dependent germination and the role of seed leachate

Abstract While density dependence is a central issue in much of plant ecology, it is often overlooked during the crucial seed germination period of the plant life-cycle. Here, patterns of germination in relation to initial seed density for 12 phylogenetically-diverse perennial plant species are described from laboratory experiments. When each of the 12 species was analysed individually, seeds of Alysicarpus rugosus, Callistemon citrinus, Eragrostis curvula and Panicum miliaceum showed a significant decrease in the proportion of seeds germinating at high densities of conspecifics. A meta-analysis carried out by grouping 11 of the 12 species together revealed an overall significant effect for a decrease in the proportion of seeds germinating at high conspecific densities compared with low con-specific densities. Significant decreases in the proportion of seeds germinating are interpreted as risk reappraisal by seeds through dormancy in response to potentially hazardous conditions imposed by high density clusters of seeds all germinating at once. The four species that responded significantly to high densities individually were each treated at low densities with a leachate solution obtained from high density conspecifics. For Alysicarpus rugosus and Panicum miliaceum, this resulted in a significant decrease in the proportion of seeds germinating at simulated high densities implicating the leachate as a causative agent. Heterospecific effects were investigated similarly for A. rugosus and E. curvula by the addition of leachate from high density clusters of seeds of one species upon the other. Only A. rugosus decreased germination significantly through the addition of leachate. These results demonstrate the ability of seeds to predict environmental conditions of the habitat into which they will emerge in terms of potential competitive interactions from neighbouring seedlings.     

Estimating Sustainable Harvest in Wolverine Populations Using Logistic Regression

Abstract: Population viability analysis (PVA) is a common tool to evaluate population vulnerability. However, most techniques require reliable estimates of underlying population parameters, which are often difficult to obtain and PVA are, therefore, best used in a qualitative context. Logistic regression is a powerful alternative to traditional PVA methods but has received surprisingly limited attention. Logistic regression fits regression equations to binary output from PVA models at a specific point in time to predict probability of a binary response over a range of parameter values. We used logistic regression on output from stochastic population models to evaluate the relative importance of demographic parameters for wolverine (Gulo gulo) populations and to estimate sustainable harvest in a wolverine population in Alaska. Our analysis indicated that adult survival is the most important demographic parameter to reliably estimate in wolverine populations because it had a greater effect on population persistence than did both fecundity and subadult survival. In accordance with this, harvest rate had a greater effect on population persistence than did any of the other harvest- and migration-related variables we tested. Furthermore, a high proportion of harvested females strengthened the effect of harvest. Hypothetical wolverine populations suffered high probabilities of both extinction and population decline over a range of realistic population sizes and harvest regimes. We suggest that harvested wolverine populations must be regarded as sink populations and that source populations in combination with sufficient dispersal corridors must be secured for any wolverine harvest to be sustainable.     

Mechanisms influencing changes in lake area in Alaskan boreal forest

During the past ～50 years, the number and area of lakes have declined in several regions in boreal forests. However, there has been substantial finer‐scale heterogeneity; some lakes decreased in area, some showed no trend, and others increased. The objective of this study was to identify the primary mechanisms underlying heterogeneous trends in closed‐basin lake area. Eight lake characteristics (δ¹⁸O, electrical conductivity, surface : volume index, bank slope, floating mat width, peat depth, thaw depth at shoreline, and thaw depth at the forest boundary) were compared for 15 lake pairs in Alaskan boreal forest where one lake had decreased in area since ～1950, and the other had not. Mean differences in characteristics between paired lakes were used to identify the most likely of nine mechanistic scenarios that combined three potential mechanisms for decreasing lake area (talik drainage, surface water evaporation, and terrestrialization) with three potential mechanisms for nondecreasing lake area (subpermafrost groundwater recharge through an open talik, stable permafrost, and thermokarst). A priori expectations of the direction of mean differences between decreasing and nondecreasing paired lakes were generated for each scenario. Decreasing lakes had significantly greater electrical conductivity, greater surface : volume indices, shallower bank slopes, wider floating mats, greater peat depths, and shallower thaw depths at the forest boundary. These results indicated that the most likely scenario was terrestrialization as the mechanism for lake area reduction combined with thermokarst as the mechanism for nondecreasing lake area. Terrestrialization and thermokarst may have been enhanced by recent warming which has both accelerated permafrost thawing and lengthened the growing season, thereby increasing plant growth, floating mat encroachment, transpiration rates, and the accumulation of organic matter in lake basins. The transition to peatlands associated with terrestrialization may provide a transient increase in carbon storage enhancing the role of northern ecosystems as major stores of global carbon.