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Weissburg,
Marc J.
Weissburg,
Marc J.
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ItemChemoreception in the salmon louse (Lepeophtheirus salmonis): an electrophysiology approach(Georgia Institute of Technology, 2007-12-13) Fields, David M. ; Weissburg, Marc J. ; Browman, H. I.The search for effective and long-term solutions to the problems caused by salmon lice Lepeophtheirus salmonis (Krøyer, 1837) has increasingly included biological/ecological mechanisms to combat infestation. One aspect of this work focuses on the host-associated stimuli that parasites use to locate and discriminate a compatible host. In this study we used electrophysiological recordings made directly from the antennule of adult lice to investigate the chemosensitivity of L salmonis to putative chemical attractants from fish flesh, prepared by soaking whole fish tissue in seawater. There was a clear physiological response to whole fish extract (WFX) with threshold sensitivity at a dilution of 10–4. When WFX was size fractionated, L. salmonis showed the greatest responses to the water-soluble fractions containing compounds between 1 and 10 kDa. The results suggest that the low molecular weight, water-soluble compounds found in salmon flesh may be important in salmon lice host choice.
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ItemCue hierarchy and foraging in calanoid copepods: ecological implications of oceanographic structure(Georgia Institute of Technology, 2007-01) Woodson, Clifton Brock ; Webster, Donald R. ; Weissburg, Marc J. ; Yen, JeannetteFine-scale water column structure was mimicked in a laboratory plane jet flume to examine responses of the calanoid copepods Temora longicornis and Acartia tonsa to layers consisting of a velocity gradient, density gradient, phytoplankton exudates and food (phytoplankton). Copepods were exposed to isolated layers and combinations of cues as defined by in situ conditions. Behaviors elicited by the velocity gradient and chemical exudate layers included increased swimming speed and turn frequency consistent with excited area-restricted search behavior, which led to increased proportional residence time in the layers. Both species had significant responses to isolated layers of velocity gradients and chemical exudates, with T. longicornis responding more intensely to chemical cues than velocity gradients and A. tonsa responding equally to both. Combined fluid mechanical and chemical cues elicited species-specific responses. For T. longicornis, chemical presence induced responses that strengthened or cancelled initial reactions to the velocity gradient. These results suggest a cue hierarchy where a velocity gradient acts as an initial cue for narrowing search regions, and chemical cues and food presence determine consequent responses. For A. tonsa, combining velocity gradient and chemical cues had the same effect on copepod behavior as the individual cues, which suggests both cues are equal sources of information but are not closely associated. In both species, physical contact with particles or cells initiated feeding behavior, resulting in lower swimming speeds. Fluid density had a potentially aversive effect, as neither species responded with an area-restricted search response and individuals rarely crossed a strong density gradient. Observed behaviors may lead to aggregation, especially when superimposed on rhythmic movements such as diel vertical migration.
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ItemClamming up: environmental forces diminish the perceptive ability of bivalve prey(Georgia Institute of Technology, 2006-06) Smee, Delbert L. ; Weissburg, Marc J.The lethal and nonlethal impacts of predators in marine systems are often mediated via reciprocal detection of waterborne chemical signals between consumers and prey. Local flow environments can enhance or impair the chemoreception ability of consumers, but the effect of hydrodynamics on detection of predation risk by prey has not been investigated. Using clams as our model organism, we investigated two specific questions: (1) Can clams decrease their mortality by responding to predators? (2) Do fluid forces affect the ability of clams to detect approaching predators? Previous research has documented a decrease in clam feeding (pumping) in response to a neighboring predator. We determined the benefits of this behavior to survivorship by placing clams in the field with knobbed whelk or blue crab predators caged nearby and compared mortality between these clams and clams near a cage-only control. Significantly more clams survived in areas containing a caged predator, suggesting that predator-induced alterations in feeding reduce clam mortality in the field. We ascertained the effect of fluid forces on clam perception of predators in a laboratory flume by comparing the feeding (pumping) behavior of clams in response to crabs and whelks in flows of 3 and 11 cm/s. Clams pumped significantly less in the presence of predators, but their reaction to blue crabs diminished in the higher velocity flow, while their response to whelks remained constant in both flows. Thus, clam reactive distance to blue crabs was affected by fluid forces, but hydrodynamic effects on clam perceptive distance was predator specific. After predators were removed, clams exposed to whelks took significantly longer to resume feeding than those exposed to blue crabs. Our results suggest that prey perception of predators can be altered by physical forces. Prey detection of predators is the underlying mechanism for trait-mediated indirect interactions (TMIIs), and recent research has documented the importance of TMIIs to community structure. Since physical forces can influence prey perception, the prevalence of TMIIs in communities may, in part, be related to the sensory ability of prey, physical forces in the environment that impact sensory performance, and the type of predator detected.
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ItemEvolutionary and ecological significance of mechanosenor morphology: copepods as a model system(Georgia Institute of Technology, 2005-02-18) Fields, David M. ; Weissburg, Marc J.The ability to sense fluid motion is strongly influenced by morphological properties of setae and by the way in which they are organized into an ensemble along the mechanosensory organ (i.e. the antennule). Setal length and orientation affect how setae encode basic properties such as velocity, frequency and direction, whereas the arraignment of setae mediate perception of more complicated properties, such as shear. Morphological and physiological data indicate that the design of setae and antennules bias an organism towards detecting particular types of disturbances, or for efficient operation in certain environments. These structure-function relationships provide potential insight into trophic status, predator detection abilities or distributions, and perhaps can explain the fantastic degree of variation in setal morphology. However, structure-function predictions remain largely unverified, because we generally lack complementary data on both the design and ecological roles of the mechanosensory system in a particular organism. Thus, an important challenge is to use a comparative approach to determine whether design principles of mechanosensory systems can explain organismal properties, and therefore provide insights into ecological interactions in the plankton.
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ItemRole of olfactory appendages in chemically mediated orientation of blue crabs(Georgia Institute of Technology, 2003-10-17) Keller, Troy A. ; Powell, Ian ; Weissburg, Marc J.Benthic crustaceans such as the blue crab Callinectes sapidus use various sensory appendages to navigate chemical plumes. We characterized the role of different sensory structures in blue crabs during olfactory search by deafferenting (i.e. removing or rendering inactive) particular sensor populations and by quantifying odor-plume structure and flow dynamics. Our results indicate that blue crabs use both cephalic and thoracic appendages for olfactory-mediated orientation. Cephalic chemosensor deafferentation decreased search success, reduced walking speed and increased the duration of stationary periods. All these deficiencies are manifestations of the inability of crabs to sustain upstream progress. Crabs subjected to deafferentation of thoracic sensilla failed to correctly track the narrowing plume and showed an increased frequency of large course-corrections. Whereas cephalic sensors clearly function in motivating upstream movement during the search process, thoracic receptors aid in source localization. The differing functional roles of these 2 sets of appendages may be associated with different signal characteristics impinging on their chemosensor populations. Intermittent but intense signals received by the cephalic appendages may enable the crabs to identify attractive odors and sustain searching. Chemical signals impinging on legs are more homogeneous and may allow the crabs to acquire better information on the spatial patterns of chemical signal structure that are important for navigation. The simultaneous use of chemical signals at differing heights in the plume suggest that the 3D structure of these plumes is important for foraging success, and that different populations of neural receptors may be tuned to operate optimally in particular signal environments.
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ItemMechanical and neural responses from the mechanosensory hairs on the antennule of Gaussia princeps(Georgia Institute of Technology, 2002-02-13) Fields, David M. ; Shaeffer, D. S. ; Weissburg, Marc J.This study investigated the physical and physiological response of individual setae on the antennule of Gaussia princeps. We found significant differences in the physical and physiological responses of the setae to various intensities of water flow. No physiological evidence was found to suggest that individual setae are dually innervated; however, directional bias in both the displacement and subsequent physiological responses was evident. Although more easily displaced by fluid flow, the shortest hairs were physiologically less sensitive to angular deflection than were the longer setae, so that slow flows produced a greater neural response in the long seta. The combination of high resistance to movement and acute physiological sensitivity allows the long seta to respond to biologically driven, low-intensity flows while filtering out high-frequency background noise. This suggests that the most prominent, long, distal setae function as low-flow detectors whereas the short hairs respond to more rapid fluid motion. Each seta responds to only a portion of the overall range of water velocity in the copepod's habitat. Thus, the entire sensory appendage, which consists of an ensemble of setae of different morphologies and lengths, may function as a unit to code the intensity and directionality of complex fluid disturbances.