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PubMed1998

Female choice and manipulations of forceps size and symmetry in the earwig Forficula auricularia L.

The size and asymmetry of male secondary sexual traits are believed to convey reliable information to females concerning the quality of potential mates. Experimental manipulations of male sexual traits provide a powerful approach to the study of preference evolution. Nevertheless, the majority of studies rely on correlational evidence for selection acting on secondary sexual traits. Here we report that in three of four populations of the European earwig, Forficula auricularia, females mated sooner with males with longer forceps although there was no female preference based on forceps asymmetry. We isolated the potentially confounding influences of forceps length and asymmetry by independently manipulating each trait. Manipulations of forceps length confirmed that females preferred males with longer forceps. However, manipulations of asymmetry revealed that although females pay attention to forceps condition, they show no preferences based on asymmetry. No relationships were found between the length and asymmetry of forceps in field populations, and there were no differences in condition between symmetrical and asymmetrical males. Our results are consistent with the notion that female choice has contributed to the sexual dimorphism in earwig forceps. However, they refute the notion that fluctuating asymmetry plays a role in sexual selection. Copyright 1998 The Association for the Study of Animal Behaviour

Journal Article↗
PubMed1986

Duodenal delivery of levodopa for on-off fluctuations in parkinsonism: preliminary observations.

The pathogenesis of on-off motor fluctuations in parkinsonism remains incompletely understood, but slowed or erratic gastric emptying of orally administered levodopa may be involved. In 3 patients with resistant on-off fluctuations, direct duodenal continuous infusion of levodopa via a nasoduodenal tube resulted in a heightened therapeutic effect, including a reduction in motor fluctuations. In 1 of these patients, continuous duodenal levodopa infusion produced greater benefit than did intermittent duodenal levodopa administration. Direct duodenal delivery of levodopa lessens the problems with gastric emptying and may be suitable for long-term therapy in selected patients with resistant on-off motor fluctuations.

Adult↗
PubMed2002

Quasispecies evolution on a fitness landscape with a fluctuating peak.

A quasispecies evolving on a fitness landscape with a single peak of fluctuating height is studied. In the approximation that back mutations can be ignored, the rate equations can be solved analytically. It is shown that the error threshold on this class of dynamic landscapes is defined by the time average of the selection pressure. In the case of a periodically fluctuating fitness peak, we also study the phase shift and response amplitude of the previously documented low-pass filter effect. The special case of a small harmonic fluctuation is treated analytically.

Biological Evolution↗
PubMed2006

The influence of hitchhiking and deleterious mutation upon asexual mutation rates.

The question of how natural selection affects asexual mutation rates has been considered since the 1930s, yet our understanding continues to deepen. The distribution of mutation rates observed in natural bacteria remains unexplained. It is well known that environmental constancy can favor minimal mutation rates. In contrast, environmental fluctuation (e.g., at period T) can create indirect selective pressure for stronger mutators: genes modifying mutation rate may "hitchhike" to greater frequency along with environmentally favored mutations they produce. This article extends a well-known model of Leigh to consider fitness genes with multiple mutable sites (call the number of such sites alpha). The phenotypic effect of such a gene is enabled if all sites are in a certain state and disabled otherwise. The effects of multiple deleterious loci are also included (call the number of such loci gamma). The analysis calculates the indirect selective effects experienced by a gene inducing various mutation rates for given values of alpha, gamma, and T. Finite-population simulations validate these results and let us examine the interaction of drift with hitchhiking selection. We close by commenting on the importance of other factors, such as spatiotemporal variation, and on the origin of variation in mutation rates.

Models, Genetic↗
PubMed1995

Evolutionary predictions from invariant physical measures of dynamic processes.

The invariant physical measure of a dynamic process comprises the information necessary to compute statistical quantities of the system. It allows us to replace time averages over the system's trajectory by integrals over state-space. In particular, it allows us to compute the long-term growth rate of a fluctuating population and hence to make evolutionary predictions. This is explained here using a one-dimensional difference equation. The invariant physical measure reflects three types of selection in this model: K-selection when the resident has a stable equilibrium; r-selection when the resident exhibits complex dynamics; and c-selection, i.e. selection for lower complexity when the resident undergoes large fluctuations. For all three evolutionary scenarios the interaction of the physical measure with the higher moments of the distribution of offspring numbers is crucial. It is also shown how stochastic noise can affect the invariant physical measure and the evolutionary predictions made from it.

Animals↗
PubMed2003

Asymmetry in structural defenses: insights into selective predation in the wild.

Assessment of geographical patterns in fluctuating asymmetry (small, random differences between sides of bilateral characters) among populations shows promise as a tool to resolve the relative biomechanical importance of traits, in addition to being a possible indicator of habitat quality. We used 115 endemic freshwater populations of threespine stickleback (Gasterosteus aculeatus) from Haida Gwaii (Queen Charlotte Islands), British Columbia, Canada, to explore the degree of concordance between geographical variation of asymmetry in a predator defense structure (bony lateral plates) and geographical variation in several indirect measures of predation regime as well as several abiotic habitat variables. We found a geographical cline in the population frequency of lateral plate asymmetries, with reduced asymmetry in the southern clear-water regions of the archipelago characterized by long reaction distances and greater chance of capture by predators, and elevated asymmetry in the northern stained-water regions with poor visibility and low chances of capture. Lateral plate asymmetry was strongly correlated with expression of several defensive armor traits, including total plate numbers among populations, mean cross-sectional diameter of stickleback with the dorsal and pelvic spines erect, and mean degree of overlap between the plates and spine supports. There were no significant correlations between frequency of asymmetric fish and any of our abiotic habitat variables. Stickleback with structural plate asymmetries had fewer trout-induced scars than symmetric fish in the significant majority of populations, and there was a decrease in structural plate asymmetry with age in stained-water habitats, suggesting that trout predators may be selectively removing asymmetric fish in some lakes. This study provides evidence that geographical variation in developmental stability of threespine stickleback, as seen in the frequencies of asymmetry, reflects differences among populations in the importance of structural defenses to fitness rather than differences in habitat quality, and that asymmetry may be a target of selection by predators in wild populations.

Age Factors↗
PubMed1997

Pre-processing variance reducing techniques in multispectral positron emission tomography.

Stochastic fluctuations and systematic errors severely restrict the potential of multispectral acquisition to improve scatter correction by energy-dependent processing in high-resolution positron emission tomography (PET). To overcome this limitation, three pre-processing approaches which reduce stochastic fluctuations and systematic errors without degrading spatial resolution were investigated: statistical variance was reduced by smoothing acquired data in energy space, systematic errors due to nonuniform detector efficiency were minimized by normalizing the data in the spatial domain and the overall variance was further reduced by selecting an optimal pre-processing sequence. Selection of the best protocol to reduce stochastic fluctuations entailed comparisons between four smoothing algorithms (prior constrained (PC) smoothing, weighted smoothing (WS), ideal low-pass filtering (ILF) and mean median (MM) smoothing) and permutations of three pre-processing procedures (smoothing, normalization and subtraction of random events). Results demonstrated that spectral smoothing by WS, ILF and MM efficiently reduces the statistical variance in both the energy and spatial domains without observable spatial resolution loss. The ILF algorithm was found to be the most convenient in terms of simplicity and efficiency. Regardless of the position of subtraction of randoms in the sequence, reduction of the systematic errors by normalization followed by spectral smoothing to suppress statistical noise produced the best results. However, subtraction of random events first in the sequence reduces computation load by half since the need to pre-process this distribution before subtraction is removed. In summary, normalizing data in the spatial domain and smoothing data in energy space are essential steps required to reduce systematic errors and statistical variance independently without degrading spatial resolution of multispectral PET data.

Biophysical Phenomena↗
PubMed2001

Structural properties of the ferrielectric phases of a chiral liquid crystal revealed by dynamic light scattering.

Dynamic light scattering is used to study the antiferro- and ferrielectric phases in a bulk sample of the chiral liquid crystal R-10OTBBB1M7. Comparison of the detected fluctuation modes in the two ferriphases to calculated selection rules for their coupling to light are consistent with the distorted clock structures recently reported by an optical ellipsometry study, but indicate that the distortion has a polar component in both ferriphases. We also find a surprisingly large amplitude and dispersion associated with scattering from fluctuations in the tilt angle magnitude. In terms of the discrete interlayer interaction models currently being used to account for the ferriphases, this finding suggests that the interlayer interaction coefficients are of comparable magnitude to the intralayer coefficients that stabilize the tilt angle.

Journal Article↗
PubMed2003

Insulin resistance and elevated triglyceride in muscle: more important for survival than "thrifty" genes?

Elevated intramyocellular triglyceride (IMTG) is strongly associated with insulin resistance, though a cause and effect relationship has not been fully described. Insulin sensitivity and IMTG content are both dynamic and can alter rapidly in response to dietary variation, physical activity and thermoregulatory response. Physically active humans (athletes) display elevated IMTG content, but in contrast to obese persons, are insulin sensitive. This paradox has created confusion surrounding the role of IMTG in the development of insulin resistance. In this review we consider the modern athlete as the physiological archetype of the Late Palaeolithic hunter-gatherer to whom the selection pressures of food availability, predation and fluctuating environmental conditions applied and to whom the genotype of modern man is virtually identical. As food procurement by the hunter-gatherer required physical activity, "thrifty" genes that encouraged immediate energy storage upon refeeding after food deprivation (Neel, 1962) must have been of secondary importance in survival to genes that preserved physical capacity during food deprivation. Similarly genes that enabled survival during cold exposure whilst starved would be of primary importance. In this context, we discuss the advantage afforded by an elevated IMTG content, and how under these conditions, a concomitant muscle resistance to insulin-mediated glucose uptake would also be advantageous. In sedentary modern man, adiposity is high and skeletal muscle appears to respond as if a state of starvation exists. In this situation, elevated plasma lipids serve to accrue lipid and induce insulin resistance in skeletal muscle. Reversal of this physiological state is primarily dependent on adequate contractile activity, however, in modern Western society, physical inactivity combined with abundant food and warmth has rendered IMTG a redundant muscle substrate.

Animals↗
PubMed1994

Poisson-like fluctuation patterns of revertants of leucine auxotrophy (leu-500) in Salmonella typhimurium caused by delay in mutant cell division.

Leu+ mutants from Salmonella typhimurium leu-500 strain MA412 arise at high frequencies and mutant colonies appear over a broad range of time on selective plates. This observation suggested that these Leu+ mutants might be induced or "directed."= If such a mechanism was responsible, mutants should originate on selective plates rather than in the preceding culture in nonselective conditions and should give rise to Poisson-like fluctuation curves upon plating of sister cultures on selective medium. Poisson-like distribution profiles were indeed observed for Leu+ mutants of S. typhimurium MA412. However, an explanation for the observed Poisson-like fluctuation patterns without a need for selection-induced mutations was found. Microscopical analysis and cell mass/viable count measurements showed that the size of Leu+ mutant cells was often much larger than those of nonmutants. This size difference was a stable characteristic of a large proportion of Leu+ mutants, was observed both in stationary and growing culture and did not measurably affect the division rates of the cells in nutrient broth. As the transition from normal-sized nonmutant to oversized mutant cells during the nonselective culture phase of the fluctuation experiment may have been accompanied by a period with no or few completed cell division cycles, the number of mutant offspring may have been smaller than that of sibling nonmutants. Such underrepresentation of mutants in the final culture is expected to give rise to Poisson-like fluctuation patterns without invoking "directed" mutations.

Cell Division↗
PubMed1995

A general model for the evolution of recombination.

A general representation of multilocus selection is extended to allow recombination to depend on genotype. The equations simplify if modifier alleles have small effects on recombination. The evolution of such modifiers only depends on how they alter recombination between the selected loci, and does not involve dominance in modifier effects. The net selection on modifiers can be found explicitly if epistasis is weak relative to recombination. This analysis shows that recombination can be favoured in two ways: because it impedes the response to epistasis which fluctuates in sign, or because it facilitates the response to directional selection. The first mechanism is implausible, because epistasis must change sign over periods of a few generations: faster or slower fluctuations favour reduced recombination. The second mechanism requires weak negative epistasis between favourable alleles, which may either be increasing, or held in check by mutation. The selection (si) on recombination modifiers depends on the reduction in additive variance of log(fitness) due to linkage disequilibria (v1 < O), and on non-additive variance in log(fitness) (V'2, V'3.. for epistasis between 2, 3.. loci). For unlinked loci and pairwise epistasis, si = --(v1 +4V2/3)deltar, where deltar is the average increase in recombination caused by the modifier. The approximations are checked against exact calculations for three loci, and against Charlesworth's analyses of mutation/selection balance (1990), and directional selection (1993). The analysis demonstrates a general relation between selection on recombination and observable components of fitness variation, which is open to experimental test.

Biological Evolution↗
PubMed2000

Rapid monitoring for the enhanced definition and control of a selective cell homogenate purification by a batch-flocculation process.

Downstream-bioprocess operations, for example, selective flocculation, are inherently variable due to fluctuations in feed material, equipment performance, and quality of additives such as flocculating agents. Due to these fluctuations in operating conditions, some form of process control is essential for reproducible and satisfactory process performance and hence, product quality. Both product (alcohol dehydrogenase) and key contaminants (RNA, protein, cell debris) within a Saccharomyces cerevisiae system were monitored in real-time adopting an at-line enzymatic reaction and rapid UV-VIS spectral-analysis technique every 135 seconds. The real-time measurements were implemented within two control configurations to regulate the batch-flocculation process according to prespecified control objectives, using the flocculant dose as the sole manipulative variable. An adaptive, model-based control arrangement was studied, which combined the rapid measurements with a process model and two model parameter-identification techniques for real-time prediction of process behavior. Based on an up-to-date mathematical description of the flocculation system, process optimization was attained and subsequent feedback control to this optimum operating set point was reproducibly demonstrated with a 92% accuracy. A simpler control configuration was also investigated adopting the cell debris concentration as the control variable. Both control arrangements resulted in superior flocculation-process performances in terms of contaminant removal, product recovery, and excess flocculant usage compared to an uncontrolled system.

Alcohol Dehydrogenase↗
PubMedDate not supplied

The vestibular aqueduct--tomographic evaluation in Meniere's disease--a preliminary report.

Frontal and off-lateral complex motion tomography was performed in 72 consecutive patients selected for endolymphatic sac surgery for episodic vertigo or sensorineural hearing loss. They were selected for this operation because of a fluctuating hearing loss. The morphology and visualization of the vestibular aqueduct and the degree of periaqueductal pneumatization were correlated with surgical results and the presence of bilateral disease. The surgical results were evaluated with use of the classification of the American Academy of Ophthalmology and Otolaryngology. Computer analysis was performed on the data for vestibular aqueduct radiographic anatomy and surgical results or bilateral disease. There was no correlation between visualization or morphology of the vestibular aqueduct and surgical results or presence of bilateral disease.

Follow-Up Studies↗
PubMed1980

Computer experiment for selection of optical isomer during prebiotic polymerization.

Computer experiments simulating prebiotic polymerization were carried out using the Monte Carlo method. A high degree of single optical isomers from racemic monomers occurred by assuming a small asymmetry in their chemical natures, which was included to investigate an amplification of the asymmetry due to parity non-conservation. The asymmetry developed much more slowly than the growth of polymers, and the degree of asymmetry in the polymers increased with the degree of polymerization. Competition between the preferential selection and the disturbance by the statistical fluctuation are discussed.

Computers↗
PubMed1980

The formation of tigroid substance during postnatal maturation of the brain of mice after pre- and perinatal X-irradiation.

Using Nissl stained slices of postnatal brain, tigroid formation in neurons of the cortex, thalamus, cerebellum, hippocampus, gyrus dentatus and nucleus mot. trigemini was examined in X-irradiated mice. Following exposure on days 13, 16, 18.5 or 22 post conception with doses ranging from 0.5 Gy to 3.0 Gy tigroid formation was studied by means of a selective microphotometrical measurement technique. After irradiation, a fluctuating diminution in the tigroid density was observed in relation to the controls. It was dependent both on the dose and on the stage of development during exposure. In several brain regions fluctuating tigroid responses, being most pronounced during the "critical periods" of postnatal brain maturation, resulted in a longterm compensation of a deficit in the tigroid density after irradiation with 0.05 Gy. After the higher doses the density diminution was either not compensated or was progressive. The late tigroid responses decrease from irradiation on day 13 p.c. to irradiation day 22 p.c. Hence, this type of late maturation impairment was either extended through several cell generations or it was induced to a lesser degree in the early postmitotic neurons. Changes in the total RNA-content of the brain are concomitant with the range of the tigroid responses during the second and the beginning of the third week after birth. The tigroid reactions were interpreted as a chain of interdependent processes of retardation and stabilization. Accordingly, to obtain a better understanding of long-term maturation defects, a comprehensive evaluation of the whole chain of events will be required.

Animals↗
PubMed2005

Explaining bank vole cycles in southern Norway 1980-2004 from bilberry reports 1932-1977 and climate.

Correlations between mast fruiting of bilberry Vaccinium myrtillus and peak levels of Clethrionomys-voles have been reported from both Norway and Finland, but there has been a discussion whether this is a bottom-up or a top-down relationship. In a multiple regression model, 65% of the variation in a bilberry production index calculated from game reports from southern Norway 1932-1977 could be explained by the berry index of the two preceding years and climate factors acting during key stages of the flowering cycle. High vole populations in previous years did not contribute to explain the fluctuation in berry production. I used the selected model and climate data to predict bilberry production for the period 1978-2004. Predicted berry indices of the current and previous year explained 38% and the total amount of precipitation in May-June explained 16% of the variation in a log-transformed snap-trapping index of bank vole Clethrionomys glareolus 1980-2004. The vole index was not related to any of the climate variables used to predict berry production. This pattern supports the hypothesis that vole cycles are generated by changes in plant chemistry due to climate-synchronized mast fruiting.

Animals↗
PubMed2006

Environmental variation and the predator-specific responses of tropical stream insects: effects of temperature and predation on survival and development of Australian Chironomidae (Diptera).

The threat posed by predation varies among predator species and with environmental context, and prey species often adjust their responses accordingly. We investigated such effects within an insect assemblage from a tropical Australian stream. These systems are frequently subjected to catastrophic floods, often suggested to reduce the importance of predation in streams, and invertebrate faunas are characterised by relatively broad environmental tolerances. Impacts of the hunting predator Australopelopia prionoptera (Diptera: Chironomidae) and an undescribed ambush predator from the Polycentropodidae (Trichoptera) on survival and development of two species of tubicolous Chironomidae, Echinocladius martini (Orthocladiinae) and Polypedilum australotropicus (Chironominae), were assessed in laboratory microcosms. A further experiment investigated how impacts of Australopelopia varied over a broad range of temperatures, exceeding that experienced annually by the studied populations. Neither predator impacted survivorship for E. martini, but the presence of the polycentropodid caused E. martini to spend longer as larvae and reduced adult longevity, and adult females were smaller-sized and had smaller oocytes. In contrast, both predators reduced survivorship of P. australotropicus, but only Australopelopia affected its development, causing reductions in pupal duration and oocyte size. The observed non-lethal impacts of predation reflect the threat each predator is known to pose to each prey species in situ. Impacts of predation varied little with temperature, reflecting the broad thermal tolerances of all study species. The predator-specific responses of the prey species imply that predation is a significant selective force in tropical Australian streams, although fluctuation in intensity of predation associated with flooding may limit its importance for community structure and prey diversity at larger scales. Our results indicate a more limited scope for environmental modification of predator-prey relationships in faunas characterised by broad physiological tolerances.

Animals↗
PubMed2006

Effects of oestrogen on cognition: what have we learned from basic research?

The results of clinical and basic research conducted over the past two decades have implicated a role for oestrogen in modulating cognitive function. This review focuses on what the results of research using female rodent models have revealed about the effects of oestrogen on mammalian cognition. Increased levels of oestrogen are associated with increased dendritic spine and synapse density in the hippocampus, a brain area important for learning and memory. However, the role of oestrogen in the modulation of performance on tasks of learning and memory is complex because it exerts enhancing effects on some tasks and impairing effects on others. Hypotheses have been offered to explain these varied actions, including differentiating the effects of oestrogen on cognitive processes required to complete tasks and analysing the influence of fluctuating levels of oestrogen on the strategies selected by animals to solve tasks. It is proposed that, when these hypotheses are viewed together and within the context of oestrogen action in the hippocampus and potentially other brain areas, a framework for understanding the varied effects of oestrogen on cognition emerges. The hippocampal-dependent memory system supports the flexible expression of memories and the hippocampal-independent memory system supports development of individual representations. Because of the effects exerted by oestrogen on the structure and function of the hippocampus, it would be expected to enhance performance across a variety of tasks that require hippocampal-dependent flexible expression of memories and would not enhance performance on tasks that involve hippocampal-independent individual representations. This review offers a theoretical model by which the divergent results of studies assessing the role of oestrogen on cognition can be reconciled and suggests that effects of oestrogen on cognition are best understood within the framework of oestrogen action in the brain and the role of those brain areas affected by oestrogen in the mediation of learning and memory.

Animals↗