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Fluctuating Environment (fluctuating + environment)
Selected AbstractsTHE EVOLUTION OF ENVIRONMENTAL AND GENETIC SEX DETERMINATION IN FLUCTUATING ENVIRONMENTSEVOLUTION, Issue 12 2003Tom J. M. Van Dooren Abstract Twenty years ago, Bulmer and Bull suggested that disruptive selection, produced by environmental fluctuations, can result in an evolutionary transition from environmental sex determination (ESD) to genetic sex determination (GSD). We investigated the feasibility of such a process, using mutation-limited adaptive dynamics and individual-based computer simulations. Our model describes the evolution of a reaction norm for sex determination in a metapopulation setting with partial migration and variation in an environmental variable both within and between local patches. The reaction norm represents the probability of becoming a female as a function of environmental state and was modeled as a sigmoid function with two parameters, one giving the location (i.e., the value of the environmental variable for which an individual has equal chance of becoming either sex) and the other giving the slope of the reaction norm for that environment. The slope can be interpreted as being set by the level of developmental noise in morph determination, with less noise giving a steeper slope and a more switchlike reaction norm. We found convergence stable reaction norms with intermediate to large amounts of developmental noise for conditions characterized by low migration rates, small differential competitive advantages between the sexes over environments, and little variation between individual environments within patches compared to variation between patches. We also considered reaction norms with the slope parameter constrained to a high value, corresponding to little developmental noise. For these we found evolutionary branching in the location parameter and a transition from ESD toward GSD, analogous to the original analysis by Bulmer and Bull. Further evolutionary change, including dominance evolution, produced a polymorphism acting as a GSD system with heterogamety. Our results point to the role of developmental noise in the evolution of sex determination. [source] Modelling potential spawning habitat of sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) in the Bay of BiscayFISHERIES OCEANOGRAPHY, Issue 1 2007BENJAMIN PLANQUE Abstract Large amplitude variations in recruitment of small pelagic fish result from interactions between a fluctuating environment and population dynamics processes such as spawning. The spatial extent and location of spawning, which is critical to the fate of eggs and larvae, can vary strongly from year to year, as a result of changing population structure and environmental conditions. Spawning habitat can be divided into ,potential spawning habitat', defined as habitat where the hydrographic conditions are suitable for spawning, ,realized spawning habitat', defined as habitat where spawning actually occurs, and ,successful spawning habitat', defined as habitat from where successful recruitment has resulted. Using biological data collected during the period 2000,2004, as well as hydrographic data, we investigate the role of environmental parameters in controlling the potential spawning habitat of anchovy and sardine in the Bay of Biscay. Anchovy potential spawning habitat appears to be primarily related to bottom temperature followed by surface temperature and mixed-layer depth, whilst surface and bottom salinity appear to play a lesser role. The possible influence of hydrographic factors on the spawning habitat of sardine seems less clear than for anchovy. Modelled relationships between anchovy and sardine spawning are used to predict potential spawning habitat from hydrodynamical simulations. The results show that the seasonal patterns in spawning are well reproduced by the model, indicating that hydrographic changes may explain a large fraction of spawning spatial dynamics. Such models may prove useful in the context of forecasting potential impacts of future environmental changes on sardine and anchovy reproductive strategy in the north-east Atlantic. [source] A structured model for the simulation of bioreactors under transient conditionsAICHE JOURNAL, Issue 11 2009Jérôme Morchain Abstract Modeling the transient behavior of continuous culture is of primary importance for the scale-up of biological processes. Spatial heterogeneities increase with the reactor size and micro-organisms have to cope with a fluctuating environment along their trajectories within the bioreactor. In this article, a structured model for bioreactions expressed in terms of biological extensive variables is proposed. A biological variable is introduced to calculate the growth rate of the population. The value is updated on the basis of the difference between the composition in the liquid and biotic phase. The structured model is able to predict the transient behavior of different continuous cultures subject to various drastic perturbations. This performance is obtained with a minimum increase in the standard unstructured model complexity (one additional time constant). In the final part, the consequences of decoupling the growth rate from the substrate uptake rate are discussed. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Molecular ecology of zebra mussel invasionsMOLECULAR ECOLOGY, Issue 4 2006GEMMA E. MAY Abstract The invasion of the zebra mussel, Dreissena polymorpha, into North American waters has resulted in profound ecological disturbances and large monetary losses. This study examined the invasion history and patterns of genetic diversity among endemic and invading populations of zebra mussels using DNA sequences from the mitochondrial cytochrome oxidase I (COI) gene. Patterns of haplotype frequency indicate that all invasive populations of zebra mussels from North America and Europe originated from the Ponto-Caspian Sea region. The distribution of haplotypes was consistent with invasive populations arising from the Black Sea drainage, but could not exclude the possibility of an origin from the Caspian Sea drainage. Similar haplotype frequencies among North American populations of D. polymorpha suggest colonization by a single founding population. There was no evidence of invasive populations arising from tectonic lakes in Turkey, while lakes in Greece and Macedonia contained only Dreissena stankovici. Populations in Turkey might be members of a sibling species complex of D. polymorpha. Ponto-Caspian derived populations of D. polymorpha (, = 0.0011) and Dreissena bugensis (one haplotype) exhibited low levels of genetic diversity at the COI gene, perhaps as a result of repeated population bottlenecks. In contrast, geographically isolated tectonic lake populations exhibited relatively high levels of genetic diversity (, = 0.0032 to 0.0134). It is possible that the fluctuating environment of the Ponto-Caspian basin facilitated the colonizing habit of invasive populations of D. polymorpha and D. bugensis. Our findings were concordant with the general trend of destructive freshwater invaders in the Great Lakes arising from the Ponto-Caspian Sea basin. [source] Ab Initio Molecular Dynamics Simulation of a Water,Hydrogen Fluoride Equimolar MixtureCHEMPHYSCHEM, Issue 1 2005Christian Simon Abstract Hydrogen fluoride and water can be mixed in any proportion. The resulting solutions have unique acidic properties. In particular, hydrogen fluoride undergoes a weak-to-strong acidity transition with increasing concentration of HF. To supplement the knowledge already obtained on dilute or moderately concentrated solutions and gas-phase aggregates, an equimolar mixture is studied here by Car,Parrinello molecular dynamics. The natures of the ions and of the complexes formed in the equimolar liquid were determined. Specifically, H3O+, H5O2+, FHOH2, and HF2,were spontaneously obtained while only hydronium and fluoride ions pre-exist in the equimolar crystal. The behaviour of the proton in the equimolar liquid was compared with mixtures of other proportions simulated previously in an attempt to relate proton dynamics to acidity. In the same way, the behaviour of HF2,was also examined. In this case, proton localization and transfer appeared to be driven by the fluctuating environment of the solvated ion. [source] | |||||||||||||