Effects of low-pH stress on the morphology and activity of bacteria from lakes receiving acid precipitation

Field and laboratory studies on the effects of low-pH stress are reported here for lacustrine bacteria. Two biochemical parameters, respiration and substrate utilization, reveal a marked decrease under severe low-pH stress. Bacterial ultrastructure and cell diversity can be correlated with a given level of pH. Structural changes in the cell envelope as a function of pH are highlighted. The biochemical, physiological and morphological observations are united into a hypothesis which seeks to relate cell adaptation to environmental stress.     

Hydrogen turnover by psychrotrophic homoacetogenic and mesophilic methanogenic bacteria in anoxic paddy soil and lake sediment

Abstract The effect of temperature on CH₄ production, turnover of dissolved H₂, and enrichment of H₂-utilizing anaerobic bacteria was studied in anoxic paddy soil and sediment of Lake Constance. When anoxic paddy soil was incubated under an atmosphere of H₂/CO₂, rates of CH₄ production increased 25°C, but decreased at temperatures lower than 20°C. Chloroform completely inhibited methano-genesis in anoxic paddy soil and lake sediment, but did not or only partially inhibit the turnover of dissolved H₂, especially at low incubation temperatures. Cultures with H₂ as energy source resulted in the enrichment of chemolithotrophic homoacetogenic bacteria whenever incubation temperatures were lower than 20°C. Hydrogenotrophic methanogens could only be enriched at 30°C from anoxic paddy soil. A homoacetogen     

A stochastic discrete generation birth,continuous death population growth model and its approximate solution

This paper describes a single species growth model with a stochastic population size dependent number of births occurring at discrete generation times and a continuous population size dependent death rate. An integral equation for a suitable transformation of the limiting population size density function is not in general soluble, but a Gram-Charlier representation procedure, previously used in storage theory, is successfully extended to cover this problem. Examples of logistic and Gompertz type growth are used to illustrate the procedure, and to compare with growth models in random environments. Comments on the biological consequences of these models are also given.Currently at Department of Mathematics, University of MarylandWork partially supported by the Danish Natural Science Research Council and Monash University     

Natural,human and spatial constraints to expanding populations of otters in the Iberian Peninsula

Aim To determine the relationships between otter (Lutra lutra) distribution dynamics and environmental and spatial constraints over a 20‐year period. Location Andalusia, southern Iberian Peninsula. Methods We synthesized otter distribution data from three otter surveys (1985, 1995 and 2005) using subcatchment areas defined by hydrological barriers. Subcatchments were characterized by two ‘natural’ (climatic and orographic variables) and two ‘human’ (land use and population density) gradients. In addition, we calculated two contagion variables (the distance to previously occupied subcatchments and the percentage of occupied subcatchments within a 50 km buffer) for consecutively surveyed subcatchments. Results Between 1985 and 2005 the percentage of subcatchments with otters present increased from 42% to 72%. Otters tended to be rare or absent from human‐dominated areas. Anthropogenic gradients were better predictors of otter distribution than natural ones. Human and natural gradients showed strong covariation, but for any value of the natural gradients otters tended to be present in subcatchments with lower human impacts. Colonization of new subcatchments was found to be strongly related to contagion variables and expansion rates were slower than those estimated in other studies. Newly colonized areas tended to be located in areas with intermediate human influence, while repeated absences occurred mainly in areas where human impact was most severe. Main conclusions Our results suggest that recent otter expansion across Andalusia is a reflection of large‐scale improvement in environmental conditions. Otter populations that survived the period of strong and generalized declines appear to be acting as sources from which neighbouring areas are colonized, probably aided by improved water quality and increases in food availability. However, the further expansion of otters into their full original range is likely to be constrained by human‐impacted landscapes.     

Post settlement behaviour of brachiopods on hard and soft substrates

Abstract

This paper describes the variation in shell and pedicle morphology of three species of brachiopods. Two are specialists that live on hard or soft surfaces, respectively, and the third is a generalist that can live on either. The interaction between behaviour and substrate explains (1) the morphology of the specialists, (2) variability in the lifestyle of the generalists, and (3) diversity in fossil brachiopods.     

Evolutionary biogeography of Manihot (Euphorbiaceae), a rapidly radiating Neotropical genus restricted to dry environments

Aim The aims of this study were to reconstruct the phylogeny of Manihot, a Neotropical genus restricted to seasonally dry areas, to yield insight into its biogeographic history, and to identify the closest wild relatives of a widely grown, yet poorly known, crop: cassava (Manihot esculenta). Location Dry and seasonally dry regions of Meso‐ and South America. Methods We collected 101 samples of Manihot, representing 52 species, mostly from herbaria, and two outgroups (Jatropha gossypiifolia and Cnidoscolus urens). More than half of the currently accepted Manihot species were included in our study; our sampling covered the whole native range of the genus, and most of its phenotypic and ecological variation. We reconstructed phylogenetic relationships among Manihot species using sequences for two nuclear genes and a non‐coding chloroplast region. We then reconstructed the history of traits related to growth form, dispersal ecology and regeneration ability. Results Manihot species from Mesoamerica form a grade basal to South American species. The latter species show a strong biogeographic clustering: species from the cerrado form well defined clades, species from the caatinga of north‐eastern Brazil form another, and so do species restricted to forest gaps along the rim of the Amazon basin. Vine and tree growth habits evolved repeatedly in the genus, as did fruit indehiscence and loss of ant‐mediated seed dispersal. Main conclusions The genus Manihot probably originated in Mesoamerica, where it diversified prior to colonizing South America. Within South America, several groups then radiated southwards and eastwards within all kinds of seasonally dry lowland habitats. Some species also adapted to more humid environments, such as forest gaps, around the rim of the Amazon basin. Given the limited dispersal abilities of Manihot species, we propose that this radiation is most likely to have occurred only after, or shortly before, the completion of the Isthmus of Panama, around 3.5 Ma. Our results are in agreement with the past existence of a corridor of dry vegetation through Amazonia or along the eastern South American coast. In addition, our phylogeny allows identification of cassava’s closest wild relatives.     

Asymmetric Spatiotemporal Evolution of Prebiotic Homochirality

The role of asymmetry on the evolution of prebiotic homochirality is investigated in the context of autocatalytic polymerization reaction networks. A model featuring enantiometric cross-inhibition and chiral bias is used to study the diffusion equations controlling the spatiotemporal development of left and right-handed domains. Bounds on the chiral bias are obtained based on present-day constraints on the emergence of life on early Earth. The viability of biasing mechanisms such as weak neutral currents and circularly polarized UV light is discussed. The results can be applied to any hypothetical planetary platform.     

Human challenges in polar and space environments

This paper reviews literature on psychosocial adaptation in isolated and confined extreme (ICE) environments, focusing on polar work groups and expedition teams, and simulation and actual space crews. Long-duration missions may involve chronic exposure to many stressors that can negatively impact behavioral health, performance and even safety. In the last decades, anecdotal evidence has been replaced by scientific studies, identifying temporal, social, and individual determinants of psychosocial adaptation, and pointing to countermeasures that may minimize or prevent potential problems. Still, many issues remain that require additional investigation, specifically in relation to the integration of psychosocial and neurobiological adaptation. A recognition of ICE environments as natural laboratories for studies of fundamental questions within psychology may attract more scientists to the field.     

An evaluation of factors affecting vertical distribution among recruits of Calanus finmarchicus in three adjacent high-latitude localities

The vertical distributions of populations of Calanus finmarchicus are described in three different fjord areas near Tromse, northern Norway during May 1986. These localities (Malangen, Grøtsund and Balsfjorden) had characteristic differences in temperature, phytoplankton and population density of copepods. They probably are representative annual situations during the spring and summer period for coastal and fjord areas in northern Norway. Copepodite stage I and II C. finmarchicus are found in the surface waters (0–30 m) during a 24 h cycle, while the other stages appear to have a different diel depth distribution in Malangen. Pronounced differences in the depth distribution of the various copepodite stages and adult females were found in Grøtsund and Balsfjorden during the same period of the day on 20 and 21 May. The tendency for vertical overlap among CI–CV was clearly less pronounced in an environment with low phytoplankton standing stock and high population density of copepods. The patterns of vertical distribution are analysed by multidimentional scaling (MDS) and it is evident that the distribution pattern of C. finmarchicus is different at each locality. These preliminary results, are discussed in relation to ontogenetic vertical migration and aspects of resource partitioning and the possible importance of vertical separation for reducing competitive interactions between the different life stages of C. finmarchicus.     

Extreme environments: microbiology leading to specialized metabolites

The prevalence of multidrug-resistant microbial pathogens due to the continued misuse and overuse of antibiotics in agriculture and medicine is raising the prospect of a return to the preantibiotic days of medicine at the time of diminishing numbers of drug leads. The good news is that an increased understanding of the nature and extent of microbial diversity in natural habitats coupled with the application of new technologies in microbiology and chemistry is opening up new strategies in the search for new specialized products with therapeutic properties. This review explores the premise that harsh environmental conditions in extreme biomes, notably in deserts, permafrost soils and deep-sea sediments select for micro-organisms, especially actinobacteria, cyanobacteria and fungi, with the potential to synthesize new druggable molecules. There is evidence over the past decade that micro-organisms adapted to life in extreme habitats are a rich source of new specialized metabolites. Extreme habitats by their very nature tend to be fragile hence there is a need to conserve those known to be hot-spots of novel gifted micro-organisms needed to drive drug discovery campaigns and innovative biotechnology. This review also provides an overview of microbial-derived molecules and their biological activities focusing on the period from 2010 until 2018, over this time 186 novel structures were isolated from 129 representatives of microbial taxa recovered from extreme habitats.