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Period Duration (period + duration)
Selected AbstractsEXTREME SELECTION ON SIZE IN THE EARLY LIVES OF FISHEVOLUTION, Issue 8 2010Kestrel O. Perez Although fitness typically increases with body size and selection gradients on size are generally positive, much of this information comes from terrestrial taxa. In the early life history of fish, there is evidence of selection both for and against larger size, leaving open the question of whether the general pattern for terrestrial taxa is valid for fish. We reviewed studies of size-dependent survival in the early life history of fish and obtained estimates of standardized selection differentials from 40 studies. We found that 77% of estimated selection differentials favored larger size and that the strength of selection was more than five times that seen in terrestrial taxa. Selection decreased with study period duration and initial length, and disruptive selection occurred significantly more frequently than stabilizing selection. Contrary to expectations from Bergmann's rule, selection on size did not increase with latitude. [source] Microgeographic life history variation in an alpine caddisfly: plasticity in response to seasonal time constraintsFRESHWATER BIOLOGY, Issue 1 2009LISA N. S. SHAMA Summary 1.,Temporally constrained environments, such as habitats with short growth seasons or short hydroperiods, cause potentially strong selection on life histories. Depending on the predictability of these events and the extent of spatial and temporal heterogeneity, local populations could become adapted either via a fixed phenotype or via life history plasticity in response to these environmental cues. 2.,We used a common garden experiment to investigate microgeographic variation in life history responses to combined changes in photoperiod (ambient/late) and hydroperiod (constant/drying) time constraint cues in an alpine caddisfly (Trichoptera). We compared six populations (three permanent/three temporary streams) originating from a small, alpine floodplain and which spanned an expected gradient in growth period duration (GPD) with distance from glaciers. 3.,We made two main predictions in relation to locally varying selection pressures: (i) populations nearest glaciers (shorter GPD and strongest time constraints) should have the fastest development rates and (ii) populations from permanent streams should be less able to respond to drying hydroperiods than populations from temporary streams. 4.,All populations and both sexes accelerated development in response to late season photoperiod cues. However, only permanent stream populations showed an increase in development time with increasing GPD, suggesting that other factors were influencing populations in temporary streams. 5.,Permanent stream populations showed countergradient variation (genetic and environmental influences were in opposition) in development time, and under-compensation of growth rates resulted in a converse Bergmann cline in body size (smaller body size along gradients of declining season length). The extent of plasticity in response to hydroperiod, and the combined effects of both time constraints, differed between populations and sexes, but were not consistent among populations. 6.,Taken together, our results suggest adaptive plasticity in response to season length. The lack of a predictable pattern in response to hydroperiod may be due to gene flow or weak selection. We conclude that spatially structured populations can strongly differ in phenotypic plasticity even at microgeographic scales. [source] Experimental evidence on trading behavior, market efficiency and price formation in double auctions with unknown trading durationMANAGERIAL AND DECISION ECONOMICS, Issue 8 2005Darren Duxbury The reasons for the highly efficient market outcomes observed under the double auction remain unclear. This paper presents a series of experimental financial markets designed to investigate the importance of unknown trading period duration on trading behavior and the convergence tendencies of such markets. Using panel data techniques the results support the conclusions that individuals generally display more aggressive trading strategies, trading earlier in a period, and that markets exhibit reduced levels of informational efficiency when unknown duration is present. Markets with imperfect information structures are also studied and, in a unique result, are associated with significantly slower rates of trade, as traders become more cautious over their trading strategies. Investigation of the price formation process provides evidence that the pricing error varies over time and the estimation of a fixed effects model provides unique support that learning effects and unknown trading period duration influence the price formation process. Future refinement of theoretical models of the price formation process or institutions of exchange should recognize the effect of unknown trading period duration on market behavior, along with potential learning effects. Copyright © 2005 John Wiley & Sons, Ltd. [source] Altered corticomotor representation in patients with Parkinson's diseaseMOVEMENT DISORDERS, Issue 8 2003Florian A. Kagerer PhD Abstract In 6 patients with Parkinson's disease (PD) and 6 age-matched controls, transcranial magnetic stimulation was applied at 56 regions over the motor cortex and premotor cortex of each hemisphere, with the first dorsal interosseous (FDI) muscle of both hands activated at 15% maximum voluntary contraction during stimulation. For each site, motor evoked potential (MEP) landmarks were recovered, including MEP amplitude, MEP onset latency, and silent period duration. Scaled MEP amplitudes were used to construct individual cortical maps of the FDI muscles. The maps revealed an anterior displacement of the muscle representation in PD patients. This anterior shift over motor cortical areas may reflect increased contributions of corticocortical connections between motor cortex and premotor cortical areas, possibly enhanced by the visual feedback aspect of the task. These alterations may reflect adaptations to the impairments in striatocortical circuits in PD. © 2003 Movement Disorder Society [source] Toxicity and Synergism in the Feeding Deterrence of Some Coumarins on Spodoptera frugiperdaSmith (Lepidoptera: Noctuidae)CHEMISTRY & BIODIVERSITY, Issue 1 2006Nancy Vera Abstract The phagodepression activity of five coumarins (=2H -1-benzopyran-2-ones), 6-hydroxy-7-isoprenyloxycoumarin (1), 6-methoxy-7-isoprenyloxycoumarin (2), 6,7-methylenedioxycoumarin (3), 5-methoxy-6,7-methylenedioxycoumarin (4), and 6-methoxy-7-(2-hydroxyethoxy)coumarin (5), from the Argentine native herb Pterocaulon polystachyum, was tested against Spodoptera frugiperda (Lepidoptera: Noctuidae) larvae. Two analogs, scopoletin (6) and 2-methoxy-2-methyl-3,4,5,6,7,8-hexahydro-3H -chromen-5-one (7), synthesized in our laboratory, were also evaluated for comparison. The compounds were added to an artificial diet at doses ranging from 50 to 200,,g per g of diet. Natural coumarins induced 100% of phagodepression when 200,,g were added per g of diet. Binary equimolar mixtures of the natural coumarins were phagodepressors against S. frugiperda surpassing the expected additive responses, indicating that these compounds can act synergistically against S. frugiperda larvae. Compounds 1 and 3 (non-methoxylated coumarins), and the equimolar mixture of both, displayed the strongest phagodepression. Additionally, 50,,g/g of 1 and 3 incorporated to the larval diet caused 80 and 50% of pupal mortality, respectively, while a 100,,g/g dose of compounds 2, 4, 6, and 7 produced 60, 50, 10, and 80% pupal mortality, respectively. Larval growing rate during the early larval instars was significantly reduced by treatments with the methylenedioxycoumarins 3 and 4. Coincidentally, the larval period duration was significantly increased by the latter compounds. [source] Asymmetric corticomotor excitability correlations in early Parkinson's diseaseMOVEMENT DISORDERS, Issue 11 2007Allan D. Wu MD Abstract We studied corticomotor excitability (CE) between the more and less affected sides in early Parkinson's disease (PD) patients using transcranial magnetic stimulation (TMS). Sixteen-PD patients within the first 3 years of diagnosis were studied with single-pulse TMS over each motor cortex with intensities from 40% to 100% stimulator output. Active motor evoked potentials (MEP) and cortical silent period durations (CSP) were recorded, fitted with sigmoid curves, summarized as maximal MEP/CSP, maximal MEP/CSP slope, and intensity where MEP/CSP is half-maximal (MEP/CSP-Int50), and correlated with Unified Parkinson's Disease Rating Scale scores (UPDRS). On the more affected side, higher (worse) UPDRS scores were correlated with shorter maximal CSP (r = ,0.51, P = 0.046). On the less affected side, higher UPDRS scores were correlated with higher MEP-Int50 (r = 0.51, P = 0.043) and CSP-Int50 (r = 0.54, P = 0.029). For the less affected side, altered CE, as indexed by higher MEP or CSP-Int50 intensities, may contribute to early clinical symptoms. On the more affected side, increases in CE, indexed by shorter CSP, may account for a greater proportion of PD symptoms. These findings are consistent with an evolution of neurophysiologic correlates in early PD patients from a less to more symptomatic state. © 2007 Movement Disorder Society [source] | ||||||||||