Jonathan B. Armstrong

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1. The neck muscle biventer cervicis is supplied by five separate nerve bundles that originate from segments C2-C5 and enter the muscle at different rostrocaudal levels. We have used the glycogen-depletion method to investigate the distribution of muscle fibers supplied by each nerve bundle and also the extent of motor-unit territories supplied by single(More)
Cattle grazing St. Augustine grass growing on peaty muck soils in the Florida Everglades developed anemia associated with the presence of Heinz bodies and suboptimal concentrations of selenium in blood. Selenium supplementation corrected the anemia, prevented Heinz body formation, increased the body weight of cows and calves, and elevated blood selenium.(More)
1. Biventer cervicis (BC) is an anatomically complex muscle that is divided by tendinous inscriptions into five in-series compartments of motor units. We have analyzed the fiber architecture and fiber-type composition of these different compartments using microdissection and histochemical methods. 2. BC narrows as it runs rostrally, but its in-series(More)
Beginning at mid-neurulation, a wave of somite segmentation passes down the axolotl body axis in a cephalocaudal direction. At 20 degrees C a somite forms every 2.57 hr. Fate-mapping of the presomitic mesoderm indicates that the primordia for the next few somites occupy nearly the same space that they will after segmentation, but that the remaining somites(More)
A central challenge for predators is achieving positive energy balance when prey are spatially and temporally heterogeneous. Ecological heterogeneity produces evolutionary trade-offs in the physiological design of predators; this is because the ability to capitalize on pulses of food abundance requires high capacity for food-processing, yet maintaining such(More)
Vertical heterogeneity in the physical characteristics of lakes and oceans is ecologically salient and exploited by a wide range of taxa through diel vertical migration to enhance their growth and survival. Whether analogous behaviors exploit horizontal habitat heterogeneity in streams is largely unknown. We investigated fish movement behavior at daily(More)
The development of the axial musculature, its innervation and early locomotion in Xenopus laevis embryos are described. Between stages 17 and 40 some 45 myotomes are formed on each side of the body. During this period the animals develop from non-motile to free swimming embryos. Using fluorescein-conjugated bungarotoxin the acquisition of acetylcholine(More)
A critical challenge for ecologists is to understand the functional significance of habitat heterogeneity and connectivity for mobile animals. Here, we explore how a thermo-regulating fish responds to annual variation in the spatial patterning of thermal and trophic resources. In a third-order stream in coastal Alaska, juvenile coho salmon forage on sockeye(More)
T he greatest challenges in ecology and evolution are in understanding how physical and biological processes that play out over extensive spatial, temporal, and taxonomic scales interact to affect the dynamics of genes, phenotypes, populations, and ecosystems. The fact that many biological properties are " scale-dependent " has been recognized for decades;(More)
1. Quantifying the variability in the delivery of ecosystem services across the landscape can be used to set appropriate management targets, evaluate resilience and target conservation efforts. Ecosystem functions and services may exhibit portfolio-type dynamics, whereby diversity within lower levels promotes stability at more aggregated levels. Portfolio(More)