Deformation of the Active Space in the Low Reynolds Number Feeding Current of Calanoid Copepods

Andrews, John C.

doi:10.1139/f83-147

Cited by 81 publications

(60 citation statements)

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“…This supports theoretical arguments that the orientation of the main axis of deformation relative to the flow direction plays no role in its detection (Ki~rboe & Visser 1999). This is different from chemical detection of prey in a feeding current, which is enhanced by a shear deformation component in the feeding current (Andrews 1983). The variation in estimated threshold values for deformation rate with variation in copepod size is consistent with a set threshold signal strength, also as hypothesised.…”

Section: Perception Of Velocity Gradientssupporting

confidence: 74%

Hydrodynamic signal perception in the copepod Acartia tonsa

Kiørboe¹,

Saiz²,

Visser³

1999

Mar. Ecol. Prog. Ser.

185

200

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Copepods may remotely detect predators from the velocity gradients these generate in the ambient water. Each of the different components and characteristics of a velocity gradient (acceleration, vorticity, longitudinal and shear deformation) can cause a velocity difference between the copepod and the ambient water and may, therefore, be perceived by mechanoreceptory setae. We hypothesised that the threshold value for escape response to a particular component depends solely on the magnitude of the velocity difference (= signal strength) it generates. In experiments we isolated the different components and noted the minimum intensities to which the copepod Acartia tonsa responded. As hypothesised, threshold signal strengths due to longitudinal and shear deformation were similar, -0.015 cm S-', and were invariant with developmental stage. The latter implies that the threshold deformation rate for response scales inversely with size, i.e. that large stages respond to lower fluid deformation rates than small stages and, hence, may detect predators at longer distances. Signals due to vorticity and acceleration did not elicit escape responses, even though their magnitude exceeded threshold signal strength due to deformation. We suggest that A. tonsa cannot distinguish such signals from those due to their own behaviour (sinking, swimming, passive reorientation due to gravity) because they cause a similar spatial distributions of the signal across the body. Reinterpretation of data from the literature revealed that threshold signal strength due to deformation varies by ca 2 orders of magnitude between copepods and exceeds the neurophysiological response threshold by more than a factor of 10. In contrast, threshold deformation rates vary much less, -0.5 to 5 S-' Model calculations suggest that such threshold deformation rates are just sufficient to allow efficient predator detection while at the same time just below maximum turbulent deformation rates, thus preventing inordinate escapes.

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Section: Perception Of Velocity Gradientssupporting

confidence: 74%

Hydrodynamic signal perception in the copepod Acartia tonsa

Kiørboe¹,

Saiz²,

Visser³

1999

Mar. Ecol. Prog. Ser.

185

200

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“…and E. pileatus collect algae by altering the flow direction of part of the current towards the copepod's median with flicks of individual mouthparts. Each flick is thought to be elicited by chemical exudates which, through accelerated flow of the feeding current, precede a phytoplankton cell and provide signals to chemoreceptors on A1 and other mouthparts (Andrews 1983). MXP and A2 are the mouthparts which most frequently aid in gathering food particles.…”

Section: Discussionmentioning

confidence: 99%

Why is Acartia tonsa (Copepoda: Calanoida) restricted to nearshore environments?

Paffenhöfer¹,

Stearns²

1988

Mar. Ecol. Prog. Ser.

152

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The copepod Acartia tonsa is adapted to high food concentrations which it encounters in estuaries and upwelled waters. It cannot obtain sufficient food for reproduction on the middle and outer shelf, where food concentrations are usually low, because it decreases clearance rates when concentrations of Thalassiosira weissflogii fall below 0.25 mm3 1-' In comparison, the offshore copepod Paracalanus sp. continues to increase its clearance rate when food levels are below the abovementioned concentration. Several factors are thought to be responsible for this reduction of clearance rates of A. tonsa feeding on T. weissflogii: ( l ) The proportion of time during which water is transported towards the copepod decreases with decreasing food concentration. (2) The efficiency of capturing food particles decreases below 22 pg C I-' (= 0.28 mm3 I-' of T. weissflogb]. (3) A. tonsa does not seem to reroute phytoplankton cells individually towards its median, and therefore cannot use a, hypothesized, increased sensitivity of its chemoreceptors at low chlorophyll concentrations to increase clearance rate.

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“…Atema (1988) further contrasts the turbulent plumes followed by lobsters which have very di¡erent temporal lives and spatial structures from the odours entrained in the viscous copepod feeding current (Andrews 1983;Strickler 1985). Moore et al (1994) empirically showed how the copepod feeding current pulls the di¡use algal phycosphere into its laminar £ow ¢eld where the odour becomes streamlined and more localized within a sheared ¢lament.…”

Section: (B) Spatiotemporal Coordination Of Mating Eventsmentioning

confidence: 99%

The fluid physics of signal perception by mate-tracking copepods

Yen

Weissburg

Doall

1998

Phil. Trans. R. Soc. Lond. B

111

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Within laboratory-induced swarms of the marine copepod Temora longicornis, the male exhibits chemically mediated trail-following behaviour, concluding with £uid mechanical provocation of the mate-capture response.The location and structure of the invisible trail were determined by examining the speci¢c behaviour of the female copepods creating the signal, the response of the male to her signal, and the £uid physics of signal persistence. Using the distance of the mate-tracking male from the ageing trail of the female, we estimated that the molecular di¡usion coe¤cient of the putative pheromonal stimulant was 2.7 Â10 À5 cm 2 s À1 , or 1000 times slower than the di¡usion of momentum. Estimates of signal strength levels, using calculations of di¡usive properties of odour trails and attenuation rates of £uid mechanical signals, were compared to the physiological and behavioural threshold detection levels. Males ¢nd trails because of strong across-plume chemical gradients; males sometimes go the wrong way because of weak along-plume gradients; males lose the trail when the female hops because of signal dilution; and mate-capture behaviour is elicited by suprathreshold £ow signals. The male is stimulated by the female odour to accelerate along the trail to catch up with her, and the boundary layer separating the signal from the chemosensitive receptors along the copepod antennule thins. Di¡usion times, and hence reaction times, shorten and behavioural orientation responses can proceed more quickly. While`perceptive' distance to the odour signal in the trail or the £uid mechanical signal from the female remains within 1^2 body lengths (55 mm), the`reactive' distance between males and females was an order of magnitude larger. Therefore, when nearest-neighbour distances are 5 cm or less, as in swarms of 10 4 copepods m À3 , mating events are facilitated. The strong similarity in the structure of mating trails and vortex tubes (isotropic, millimetre^centimetre scale, 10:1 aspect ratio, 10 s persistence), indicates that these trails are constrained by the same physical forces that in£uence water motion in a low Reynolds number £uid regime, where viscosity limits forces to the molecular scale. The exploratory reaches of mating trails appear inscribed within Kolmogorov eddies and may represent a measure of eddy size. Biologically formed mating trails, however, are distinct in their £ow velocity and chemical composition from common small-scale turbulent features; and mechanoreceptive and chemoreceptive copepods use their senses to discriminate these di¡erences. Zooplankton are not aimless wanderers in a featureless environment. Their ambit is replete with clues that guide them in their e¡orts for survival in the ocean.

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Deformation of the Active Space in the Low Reynolds Number Feeding Current of Calanoid Copepods

Cited by 81 publications

References 0 publications

Hydrodynamic signal perception in the copepod Acartia tonsa

Hydrodynamic signal perception in the copepod Acartia tonsa

Why is Acartia tonsa (Copepoda: Calanoida) restricted to nearshore environments?

The fluid physics of signal perception by mate-tracking copepods

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