Vegetative reproduction as a stabilizing feature of the population dynamics of Yucca glauca

Summary The life history of Yucca glauca in the Great Plains was the subject of a four year field study. Data were incorporated in a stage transition model (based on rosette size) to explain how populations are maintained in spite of large regional and temporal variation in sexual reproductive success. Rosette size was found to be a good predictor of flowering effort, but a poor predictor of fruit set. Large rosettes that failed to set fruit, however, exhibited an increased capacity for vegetative reproduction. Asexual reproduction contributes to population stability by reducing the variance in annual recruitment, and perhaps by damping oscillations caused by departures from a stable stage distribution.     

Yeast communities in a natural tequila fermentation

Fresh and cooked agave,Drosophila spp., processing equipment, agave molasses, agave extract, and fermenting must at a traditional tequila distillery (Herradura, Amatitan, Jalisco, México) were studied to gain insight on the origin of yeasts involved in a natural tequila fermentations. Five yeast communities were identified. (1) Fresh agave contained a diverse mycobiota dominated byClavispora lusitaniae and an endemic species,Metschnikowia agaveae. (2)Drosophila spp. from around or inside the distillery yielded typical fruit yeasts, in particularHanseniaspora spp.,Pichia kluyveri, andCandida krusei. (3)Schizosaccharomyces pombe prevailed in molasses. (4) Cooked agave and extract had a considerable diversity of species, but includedSaccharomyces cerevisiae. (5) Fermenting juice underwent a gradual reduction in yeast heterogeneity.Torulaspora delbrueckii, Kluyveromyces marxianus, andHanseniaspora spp. progressively ceded the way toS. cerevisiae, Zygosaccharomyces bailii, Candida milleri, andBrettanomyces spp. With the exception ofPichia membranaefaciens, which was shared by all communities, little overlap existed. That separation was even more manifest when species were divided into distinguishable biotypes based on morphology or physiology. It is concluded that crushing equipment and must holding tanks are the main source of significant inoculum for the fermentation process.Drosophila species appear to serve as internal vectors. Proximity to fruit trees probably contributes to maintaining a substantialDrosophila community, but the yeasts found in the distillery exhibit very little similarity to those found in adjacent vegetation. Interactions involving killer toxins had no apparent direct effects on the yeast community structure.     

Physiology as a caste-defining feature

Division of labour is a key factor in the ecological success of social insects. Groups of individuals specializing on a particular behaviour are known as castes and are usually distinguished by morphology or age. Physiology plays a key role in both these types of caste, in either the developmental physiology which determines morphology, or the temporal changes in physiology over an insect’s life. Physiological correlates of morphological or temporal caste include differences in gland structure, secretory products, leanness, neuroanatomy and neurochemistry. However, purely physiological castes could also occur. Physiological castes are discrete groups of same-age same-size individuals with particular physiological competencies, or groups of individuals with similar physiology crossing age or size groups. A stable physiological caste occurs in the monomorphic Pharaoh’s ant, where some ants can detect old pheromone trails and retain this specialization over time. These ants differ physiologically from other workers, and the differences arise before eclosion. More temporary physiological castes occur in the ant Ectatomma where brood care specialists have more developed ovarioles than other same-aged workers, and in the honeybee where nurses, wax-workers and soldiers all differ physiologically from same-aged nestmates. Physiology is an important aspect of caste, not only in its contribution to age-related and morphological castes, but also in its own right as a caste grouping factor. While age and morphological differences make caste structures accessible for study, more cryptic physiological castes may play just as important a role in division of labour. Received 19 December 2007; revised 24 July and 18 September 2008; accepted 19 September 2008.     

Biological invasion as a natural experiment of the evolutionary processes: introduction of the special feature

Although biological invasion has a devastating impact on biodiversity, it also provides a valuable opportunity for natural experiments on evolutionary responses. Alien populations are often subject to strong natural selection when they are exposed to new abiotic and biotic conditions. Native populations can also undergo strong selection when interacting with introduced enemies and competitors. This special feature aims to highlight how evolutionary studies take advantage of biological invasion and, at the same time, emphasizes how studying evolutionary processes deepens our understanding of biological invasions. We hope this special feature stimulates more invasion studies taking evolutionary processes into account. Those studies should provide fundamental information essential for formulating effective measures in conserving native biodiversity, as well as valuable empirical tests for evolutionary theories.     

Melatonin as a universal stabilizing factor of mental activity

Pineal hormone melatonin stabilizes mental activity of man and animals due to its somnogenic, anxiolytic, antidepressant and nootropic properties. Melatonin effects are based on the synchronization of biological rhythms via the influence on the cerebral structures which control biological rhythms and emotions and normalize endocrine and immune state.     

On the stabilizing effect of predators and competitors on ecological communities

Ecological communities can lose their permanence if a predator or a competitor is removed: the remaining species no longer coexist. This well-known phenomenon is analysed for some low dimensional examples of Lotka-Volterra type, with special attention paid to the occurrence of heteroclinic cycles.     

Experimental manipulation of natural plant communities

Attempts to elucidate the factors controlling the structure of plant communities have relied increasingly on field experiments. This is a powerful approach for testing theoretical predictions that offers important advantages over observational and comparative studies. However, field experiments suffer from intrinsic difficulties as well as more-easily remediable limitations. Recent progress has been made by new approaches including the use of multifactor experiments, and the development and dissemination of better statistical tools.     

Scleraldehyde as a stabilizing agent for collagen scaffold preparation

Schizophyllan is a natural polysaccharide, produced by fungi of the genus Schizophyllum. Periodate oxidation specifically cleaves the vicinal glycols in schizophyllan to form their dialdehyde derivatives. The present study investigates the interaction of scleraldehyde with Type I collagen membrane. The formation of the inter and intra interaction between scleraldehyde and the collagen fibres results in significant increase in viscosity of collagen. Crosslinking efficiency of scleraldehyde was found to increase with concentration of scleraldehyde. Scleraldehyde interacted collagen membrane exhibited an increase in thermal stability by 29 °C at pH 8. The gelling time of collagen fibrils was found to decrease with increase in concentration of scleraldehyde due to shift in nucleation centre. Swelling degree of collagen membrane was also found to decrease with increase in concentration of scleraldehyde. Scleraldehyde treated collagen membrane exhibited 93% resistance to collagenase. The modified collagen membrane exhibited non-toxicity towards the fibroblasts cells. The modified collagen membrane by scleraldehyde finds application as a stabilizing agent in scaffold preparation.     

Omnivory and the stability of simple food webs

Traditional ecological theory predicts that the stability of simple food webs will decline with an increasing number of trophic levels and increasing amounts of omnivory. These ideas have been tested using protozoans in laboratory microcosms. However, the results are equivocal, and contrary to expectation, omnivory is common in natural food webs. Two recent developments lead us to re-evaluate these predictions using food webs assembled from protists and bacteria. First, recent modelling work suggests that omnivory is actually stabilizing, providing that interactions are not too strong. Second, it is difficult to evaluate the degree of omnivory of some protozoan species without explicit experimental tests. This study used seven species of ciliated protozoa and a mixed bacterial flora to assemble four food webs with two trophic levels, and four webs with three trophic levels. Protist species were assigned a rank for their degree of omnivory using information in the literature and the results of experiments that tested whether the starvation rate of predators was influenced by the amount of bacteria on which they may have fed and whether cannibalism (a form of omnivory) occurred. Consistent with recent modelling work, both bacterivorous and predatory species with higher degrees of omnivory showed more stable dynamics, measured using time until extinction and the temporal variability of population density. Systems with two protist species were less persistent than systems with one protist species, supporting the prediction that longer food chains will be less stable dynamically. Received: 28 December 1997 / Accepted: 22 June 1998     

Population genomics in natural microbial communities

Little is known about the evolutionary processes that structure and maintain microbial diversity because, until recently, it was difficult to explore individual-level patterns of variation at the microbial scale. Now, community-genomic sequence data enable such variation to be assessed across large segments of microbial genomes. Here, we discuss how population-genomic analysis of these data can be used to determine how selection and genetic exchange shape the evolution of new microbial lineages. We show that once independent lineages have been identified, such analyses enable the identification of genome changes that drive niche differentiation and promote the coexistence of closely related lineages within the same environment. We suggest that understanding the evolutionary ecology of natural microbial populations through population-genomic analyses will enhance our understanding of genome evolution across all domains of life.     

Predator-prey interactions in natural communities.

The familiar concepts of harvest and yield are developed for the purpose of describing predator-prey interactions in a community context. In this regard the functional response (appropriate for one predator-one prey systems) is replaced by a community harvest function. Conditions for the stability of an ecological community are obtained. Exploring the dynamics of predator-prey interactions within this framework leads to new interpretations of other dynamical models such as the Lotka-Volterra model. The concept of a community moving attractor point is introduced in order to describe the changes in all populations over time.     

Omnivory and the stability of food webs

The ecological concept of omnivory, feeding at more than a single trophic level, is formulated as an intermediate stage between any two of three classical three-dimensional species interaction systems-tritrophic chain, competition, and polyphagy. It is shown that omnivory may be either stabilizing or destabilizing, depending, in part, on the conditions of the parent systems from which it derives. It is further conjectured that the tritrophic to competition gradient cannot be entirely stable, that there must be an instability at some level of intermediate omnivory.     

Impacts of parasitic plants on natural communities

Parasitic plants have profound effects on the ecosystems in which they occur. They are represented by some 4000 species and can be found in most major biomes. They acquire some or all of their water, carbon and nutrients via the vascular tissue of the host's roots or shoots. Parasitism has major impacts on host growth, allometry and reproduction, which lead to changes in competitive balances between host and nonhost species and therefore affect community structure, vegetation zonation and population dynamics. Impacts on hosts may further affect herbivores, pollinators and seed vectors, and the behaviour and diversity of these is often closely linked to the presence and abundance of parasitic plants. Parasitic plants can therefore be considered as keystone species. Community impacts are mediated by the host range of the parasite (the diversity of species that can potentially act as hosts) and by their preference and selection of particular host species. Parasitic plants can also alter the physical environment around them--including soil water and nutrients, atmospheric CO2 and temperature--and so may also be considered as ecosystem engineers. Such impacts can have further consequences in altering the resource supply to and behaviour of other organisms within parasitic plant communities.     

Acidophilic microbial communities associated with a natural, biodegraded hydrocarbon seepage

Characterization of microbial communities present in a surface petroleum seep in which hydrocarbons have been biodegraded for thousands of years in order to improve the understanding on natural petroleum biodegradation. DNA was extracted from a natural, surface petroleum seep and subjected to culture independent analysis (rRNA gene-based denaturing gradient gel electrophoresis and phylogenetic analysis of clone libraries). Molecular analysis suggested dominance by acidophilic bacteria, especially Alphaproteobacteria (mainly bacteria related to Acidiphilium and Acidocella). Archaea were not detected, but fungi were present. pH of the samples was around 3.5. Acidophilic microbial communities are associated with an acidic petroleum seep. Microbial community structure analysis gives information on the environmental conditions under which petroleum biodegradation occurs. This knowledge could be applied to define conditions for specific cultivation or activity measurements. The activity of acidophilic micro-organisms deserves more attention with respect to their involvement in natural petroleum degradation. This knowledge will contribute to the design of oil bioremediation strategies for polluted acidic settings.     

Amyloid as a natural product

Amyloid fibrils, such as those found in Alzheimer's and the gelsolin amyloid diseases, result from the misassembly of peptides produced by either normal or aberrant intracellular proteolytic processing. A paper in this issue by Marks and colleagues (Berson et al., 2003) demonstrates that intra-melanosome fibrils are formed through normal biological proteolytic processing of an integral membrane protein. The resulting peptide fragment assembles into fibrils promoting the formation of melanin pigment granules. These results, along with the observation that amyloid fibril formation by bacteria is highly orchestrated, suggest that fibril formation is an evolutionary conserved biological pathway used to generate natural product nanostructures.