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Articles 1 - 11 of 11

Full-Text Articles in Life Sciences

Latitudinal Differences In The Hibernation Characteristics Of Woodchucks (Marmota Monax), Stam M. Zervanos, Christine R. Maher, Jerry A. Waldvogel, Gregory L. Florant Feb 2010

Latitudinal Differences In The Hibernation Characteristics Of Woodchucks (Marmota Monax), Stam M. Zervanos, Christine R. Maher, Jerry A. Waldvogel, Gregory L. Florant

Faculty Publications

There is little information on the phenotypic flexibility of hibernation characteristics within species. To address this issue, we observed differences in hibernation characteristics of three free-ranging populations of woodchucks (Marmota monax) distributed along a latitudinal gradient from Maine to South Carolina. Data from free-ranging animals exhibited a direct relationship between latitude and length of the hibernation season. As expected, woodchucks in the northern latitudes hibernated longer than those in the southern latitudes. Also, the length of interbout arousals decreased with increase in latitude, whereas the length of torpor bouts and the number of arousals increased. Thus, we observed phenotypic plasticity ...


Gis-Based Analysis Of Ice-Breeding Seal Strandings In The Gulf Of Maine, David Harris Ph.D., Sat Gupta Jan 2006

Gis-Based Analysis Of Ice-Breeding Seal Strandings In The Gulf Of Maine, David Harris Ph.D., Sat Gupta

Faculty Publications

Phoca groenlandica (harp seals) and Cystophora cristata (hooded seals), two species of ice-breeding seals, are being sighted more frequently onshore in the Gulf of Maine since 1990, but little is known about their behavior in this ecosystem. We obtained records of 904 ice-breeding seal stranding locations in the Gulf of Maine between 1996 and 2002 from NOAA Fisheries and used a geographic information system (GIS) to conduct group-wise comparisons by species (using non-parametric techniques), and to determine the predictors of high seal-stranding density (using ordinal logistic regression analysis). Compared to harp seals, hooded seals stranded closer to deep water, farther ...


Ecotypic Variation In Phosphorus Acquisition Mechanisms Within Marine Picocyanobacteria, Lisa Moore, M. Ostrowski, D. J. Scanlan, K. Feren, T. Sweetsir Jun 2005

Ecotypic Variation In Phosphorus Acquisition Mechanisms Within Marine Picocyanobacteria, Lisa Moore, M. Ostrowski, D. J. Scanlan, K. Feren, T. Sweetsir

Faculty Publications

Prochlorococcus and Synechococcus are major prokaryotic primary producers in the oligotrophic oceans that may be affected by the climate-related increases in nitrogen fixation and subsequent phosphorus (P) limitation in some parts of the oceans. Evidence that Prochlorococcus populations in the North Pacific subtropical gyre (NPSG) have increased over the past decades, possibly due to having a competitive advantage under conditions of P limitation, suggests aspects of their Pphysiology that are important for dictating their in situ success. Here, we compared the physiology of P acquisition and response to P stress (indicated by alkaline phosphatase activity, APA) among isolates of Prochlorococcus ...


Constraints On Adaptive Evolution: The Functional Trade-Off Between Reproduction And Fast-Start Swimming Performance In The Trinidadian Guppy (Poecilia Reticulata), Cameron K. Ghalambor, David N. Reznick, Jeffrey A. Walker Jul 2004

Constraints On Adaptive Evolution: The Functional Trade-Off Between Reproduction And Fast-Start Swimming Performance In The Trinidadian Guppy (Poecilia Reticulata), Cameron K. Ghalambor, David N. Reznick, Jeffrey A. Walker

Faculty Publications

The empirical study of natural selection reveals that adaptations often involve trade-offs between competing functions. Because natural selection acts on whole organisms rather than isolated traits, adaptive evolution may be constrained by the interaction between traits that are functionally integrated. Yet, few attempts have been made to characterize how and when such constraints are manifested or whether they limit the adaptive divergence of populations. Here we examine the consequences of adaptive life-history evolution on locomotor performance in the live-bearing guppy. In response to increased predation from piscivorous fish, Trinidadian guppies evolve an increased allocation of resources toward reproduction. These populations ...


Dynamics Of Pectoral Fin Rowing In A Fish With An Extreme Rowing Stroke: The Threespine Stickleback (Gasterosteus Aculeatus), Jeffrey A. Walker Ph.D. May 2004

Dynamics Of Pectoral Fin Rowing In A Fish With An Extreme Rowing Stroke: The Threespine Stickleback (Gasterosteus Aculeatus), Jeffrey A. Walker Ph.D.

Faculty Publications

The dynamics of pectoral fin rowing in the threespine stickleback are investigated by measuring the instantaneous force balance on freely swimming fish throughout the stroke cycle and comparing the measured forces with fin motions and an unsteady, blade-element model of pectoral fin propulsion. Both measured and modeled forces suggest that attached vortex and circulatory forces and not inertial (added mass) forces dominate the force balance. Peak forces occur at midstrokes. There is no evidence for large force peaks at the stroke transitions due to either rapid fin rotation (supination) or rapid fin closure against the body. The energetics of pectoral ...


Nitric Oxide Mediates Seasonal Muscle Potentiation In Clam Gills, Louis F. Gainey Jr., Michael J. Greenberg Oct 2003

Nitric Oxide Mediates Seasonal Muscle Potentiation In Clam Gills, Louis F. Gainey Jr., Michael J. Greenberg

Faculty Publications

The physiology and timing of gill muscle potentiation were explored in the clam Mercenaria mercenaria. When isolated demibranchs were exposed twice (with an intervening wash) to the same concentration of 5-hydroxytryptamine, the second contraction was larger than the first. This potentiation was seasonal: it was present from November through June, and absent from July through October. Potentiation was not affected by the geographic origin of the clams, nor by their acclimation temperature. Potentiation was inhibited by the nitric oxide synthase (NOS) inhibitor L-NAME and mimicked by the nitric oxide (NO) donor DEANO. During the season of potentiation, immunoreactive NOS appeared ...


Rotational Lift: Something Different Or More Of The Same?, Jeffrey A. Walker Ph.D. Dec 2002

Rotational Lift: Something Different Or More Of The Same?, Jeffrey A. Walker Ph.D.

Faculty Publications

This paper addresses the question, do the rotational forces in the hovering fruit fly Drosophila melanogaster reflect something different (the Magnus effect) or more of the same (circulatory-and-attached-vortex force)? The results of an unsteady blade-element model using empirically derived force coefficients from translating (root-oscillating) wings are compared with recent results derived from both the measured forces on a dynamically scaled Drosophila wing and the computational fluid dynamic (CFD)-modeled forces on a virtual Drosophila wing. The behavior of the forces in all three models during wing rotation supports the hypothesis that rotational lift is not a novel aerodynamic mechanism but ...


Fluid Dynamics Of Flapping Aquatic Flight In The Bird Wrasse: Three-Dimensional Unsteady Computations With Fin Deformation, Ravi Ramamurti, William C. Sandberg, Rainald Lӧhner, Jeffrey A. Walker Ph.D., Mark W. Westneat Oct 2002

Fluid Dynamics Of Flapping Aquatic Flight In The Bird Wrasse: Three-Dimensional Unsteady Computations With Fin Deformation, Ravi Ramamurti, William C. Sandberg, Rainald Lӧhner, Jeffrey A. Walker Ph.D., Mark W. Westneat

Faculty Publications

Many fishes that swim with the paired pectoral fins use fin-stroke parameters that produce thrust force from lift in a mechanism of underwater flight. These locomotor mechanisms are of interest to behavioral biologists, biomechanics researchers and engineers. In the. present study, we performed the first three-dimensional unsteady computations of fish swimming with oscillating and deforming fins. The objective of these computations was to investigate the fluid dynamics of force production associated with the flapping aquatic flight of the bird wrasse Gomphosus varius. For this computational work, we used the geometry of the wrasse and its pectoral fin, and previously measured ...


Performance Limits Of Labriform Propulsion And Correlates With Fin Shape And Motion, Jeffrey A. Walker Ph.D., Mark W. Westneat Jan 2002

Performance Limits Of Labriform Propulsion And Correlates With Fin Shape And Motion, Jeffrey A. Walker Ph.D., Mark W. Westneat

Faculty Publications

Labriform locomotion, which is powered by oscillating the paired pectoral fins, varies along a continuum from rowing the fins back and forth to flapping the fins up and down. It has generally been assumed (i) that flapping is more mechanically efficient than rowing, a hypothesis confirmed by a recent simulation experiment, and (ii) that flapping should be associated with wing-shaped fins while rowing should be associated with paddle-shaped fins, To determine whether these hypotheses and the results of the simulation experiment are consistent with natural variation, we compared the steady swimming performance (critical swimming speed) of four species of labrid ...


Does A Rigid Body Limit Maneuverability?, Jeffrey A. Walker Ph.D. Oct 2000

Does A Rigid Body Limit Maneuverability?, Jeffrey A. Walker Ph.D.

Faculty Publications

Whether a rigid body limits maneuverability depends on how maneuverability is defined. By the current definition, the minimum radius of the turn, a rigid-bodied, spotted boxfish Ostracion meleagris approaches maximum maneuverability, i.e. it can spin around with minimum turning radii near zero. The radius of the minimum space required to turn is an alternative measure of maneuverability. By this definition, O. meleagris is not very maneuverable. The observed space required by O. meleagris to turn is slightly greater than its theoretical minimum but much greater than that of highly flexible fish. Agility, the rate of turning, is related to ...


Teaching The Ethics Of Biology, David Harris Ph.D., Carol K. Johansen May 2000

Teaching The Ethics Of Biology, David Harris Ph.D., Carol K. Johansen

Faculty Publications

Discusses the basic principles of ethics and ethical decision making as applied to biology. Ethical issues associated with biology; Theoretical basis of ethical decision-making; Models of ethical decision-making; Social implications of scientific experimentation and discovery.