606 research outputs found
Differences in the trophic ecology of micronekton driven by diel vertical migration.
Many species of micronekton perform diel vertical migrations (DVMs), which ultimately contributes to carbon export to the deep sea. However, not all micronekton species perform DVM, and the nonmigrators, which are often understudied, have different energetic requirements that might be reflected in their trophic ecology. We analyze bulk tissue and whole animal stable nitrogen isotopic compositions (δ 15N values) of micronekton species collected seasonally between 0 and 1250 m depth to explore differences in the trophic ecology of vertically migrating and nonmigrating micronekton in the central North Pacific. Nonmigrating species exhibit depth-related increases in δ 15N values mirroring their main prey, zooplankton. Higher variance in δ 15N values of bathypelagic species points to the increasing reliance of deeper dwelling micronekton on microbially reworked, very small suspended particles. Migrators have higher δ 15N values than nonmigrators inhabiting the epipelagic zone, suggesting the consumption of material during the day at depth, not only at night when they migrate closer to the surface. Migrating species also appear to eat larger prey and exhibit a higher range of variation in δ 15N values seasonally than nonmigrators, likely because of their higher energy needs. The dependence on material at depth enriched in 15N relative to surface particles is higher in migratory fish that ascend only to the lower epipelagic zone. Our results confirm that stark differences in the food habits and dietary sources of micronekton species are driven by vertical migrations
Predicting essential components of signal transduction networks: a dynamic model of guard cell abscisic acid signaling
Plants both lose water and take in carbon dioxide through microscopic
stomatal pores, each of which is regulated by a surrounding pair of guard
cells. During drought, the plant hormone abscisic acid (ABA) inhibits stomatal
opening and promotes stomatal closure, thereby promoting water conservation.
Here we synthesize experimental results into a consistent guard cell signal
transduction network for ABA-induced stomatal closure, and develop a dynamic
model of this process. Our model captures the regulation of more than forty
identified network components, and accords well with previous experimental
results at both the pathway and whole cell physiological level. Our analysis
reveals the novel predictions that the disruption of membrane depolarizability,
anion efflux, actin cytoskeleton reorganization, cytosolic pH increase, the
phosphatidic acid pathway or of K+ efflux through slowly activating K+ channels
at the plasma membrane lead to the strongest reduction in ABA responsiveness.
Initial experimental analysis assessing ABA-induced stomatal closure in the
presence of cytosolic pH clamp imposed by the weak acid butyrate is consistent
with model prediction. Our method can be readily applied to other biological
signaling networks to identify key regulatory components in systems where
quantitative information is limited.Comment: 17 pages, 8 figure
Uniform semiclassical wave function for coherent 2D electron flow
We find a uniform semiclassical (SC) wave function describing coherent
branched flow through a two-dimensional electron gas (2DEG), a phenomenon
recently discovered by direct imaging of the current using scanned probed
microscopy. The formation of branches has been explained by classical
arguments, but the SC simulations necessary to account for the coherence are
made difficult by the proliferation of catastrophes in the phase space. In this
paper, expansion in terms of "replacement manifolds" is used to find a uniform
SC wave function for a cusp singularity. The method is then generalized and
applied to calculate uniform wave functions for a quantum-map model of coherent
flow through a 2DEG. Finally, the quantum-map approximation is dropped and the
method is shown to work for a continuous-time model as well.Comment: 9 pages, 7 figure
The role of enzyme activation state in limiting carbon assimilation under variable light conditions
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