Petra Lenz Publication Summaries
Escape behavior of planktonic copepods in response to hydrodynamic disturbances:
high speed video analysis
Edward J. Buskey, Petra H. Lenz and Daniel K. Hartline
Mar. Ecol. Progr. Ser. 235: 135-146 (2002)
Full text via MEPS
Planktonic copepods exhibit rapid escape behavior in response to
hydrodynamic disturbances. Small disturbances of brief duration were produced by a
piezoelectric transducer moving a small cylinder. The escape responses of
free-swimming adult males and females of the copepods Acartia tonsa and A.
lilljeborgii were recorded using high-speed video and quantified using computerized
motion analysis techniques. Response latency, swimming speed, acceleration and
turning rate during escape behavior were measured. Acartia spp. typically responded
within 4 msto the hydrodynamic disturbance, giving multiple power strokes of the
swimming legs. Each stroke and recovery was of ca. 7 ms duration with maximum
speeds often exceeding 500 mm/s and minimum speeds between strokes rarely
falling below 100 mm/s. Acceleration during initial escape usually exceeded 100 m/s^2.
Escapes often began with rapid reorientation away from the source of the
disturbance, with maximum turning rates of about 30 degrees/ms. Significant differences
were found between the kinetics of escape responses of adult male and female
copepods of each species, with males having greater maximum speeds and
accelerations, and females having longer duration jumps. Significant differences
were also found between the two species, for both males and females, with A. lilljeborgii
exhibiting greater speeds and more rapid acceleration than the smaller A. tonsa.
Mechanoreceptors in calanoid copepods: designed for high sensitivity
Weatherby, T.M. and Lenz, P.H. (2000)
Arthropod Struct. Dev. 29: 275-288.
Article via Science Direct.
Mechanoreceptors of the first antennae of the mesopelagic calanoid copepod, Pleuromamma xiphias, are critical for the detection of
potential predators. These receptors exceed the physiological performance of other crustacean mechanoreceptors in sensitivity to relative water
velocities as well as in frequency response. A study of these receptors was initiated to elucidate structure-function relationships.
Morphologically, the receptors resemble arthropod scolopidial organs in the occurrence of a scolopale tube. However, the rigidity of the
copepod receptors greatly exceeds that described for other crustaceans and as well as other arthropods. The scolopale tube completely encloses
the distal dendrites and is firmly anchored to the cuticle. Microtubules are organized in register and arise from microtubule subfibers associated with
crescent-shaped rods that extend from the basal body region to the setal socket. The distal dendrites are filled with a large number of
cross-linked microtubules. Termination of the distal dendrites inside the lumen of the setae is gradual with firm anchoring to the cuticle. A
likely mechanism for mechanotransduction would involve a linkage between individual microtubules and mechanically-gated channels in the
dendritic membrane. The rigidity probably contributes to the high frequency sensitivity, and termination of the dendrite inside the seta
rather than at its base (as in insects) increases the overall sensitivity of these receptors.
The need for speed. I. Fast reactions and myelinated axons in copepods
Petra H. Lenz, Daniel K. Hartline and April D. Davis
J. comp. Physiol. A 186: 337-345 (2000)
Full text via JCP
A rapid and powerful escape response decreases predation risk in planktonic
copepods. Calanoid copepods are sensitive to small and brief hydrodynamic
disturbances: they respond with multiple nerve impulses to hydrodynamic disturbances produced by a vibrating sphere.
Some species, such as Pleuromamma xiphias and Labidocera madurae, respond with
very large spikes (1 to 4 mV), whereas maximum spike heights are an order of
magnitude smaller in others, such as Undinula vulgaris and Neocalanus gracilis.
A comparative study of the escape responses showed that all species reacted
within 10 milliseconds of the initiation of a hydrodynamic stimulus. However, U.
vulgaris and N. gracilis had significantly shorter reaction times (minimum
reaction times: 1.5 and 1.6 msec) than the other two, P. xiphias (6.6
msec) and L. madurae (3.1 msec). Examination of the first
antenna and the central nervous system using transmission electron microscopy
revealed extensive myelination of sensory and motor and central axons in the two species with
the shorter reaction times. Axons of the other two species resembled typical
crustacean unmyelinated fibers. A survey of 20 calanoids revealed that none of
the species in two of the more ancient superfamilies possessed myelin, but
myelination was present in the species from three more recently evolved
superfamilies. Myelin may be a major innovation in copepods, providing increased
resistance to predator pressure and allowing penetration and survival in riskier
The need for speed. II. Myelin in calanoid copepods
Tina M. Weatherby, April D. Davis, Daniel K. Hartline and Petra H. Lenz
J. comp. Physiol. A 186: 347-357 (2000)
Full text via JCP
The conduction speed of nerve impulses is greatly increased by myelin, a
multilayered membranous sheath surrounding axons. Myelinated axons are
ubiquitous among the vertebrates, but relatively rare among invertebrates.
Electron microscopy of calanoid copepods using rapid cryofixation techniques
revealed the widespread presence of myelinated axons. Myelin sheaths of up to 60
layers were found around both sensory and motor axons of the first antenna and
interneurons of the ventral nerve cord. Except at nodes, individual lamellae
appeared to be continuous and circular, without seams, as opposed to the spiral
structure of vertebrate and annelid myelin. The highly organized myelin was
characterized by the complete exclusion of cytoplasm from the intracellular
spaces of the cell generating it. In regions of compaction, extracytoplasmic
space was also eliminated. Focal or fenestration nodes, rather than
circumferential ones, were locally common. Myelin lamellae terminated in
stepwise fashion at these nodes, appearing to fuse with the axolemma or adjacent
myelin lamellae. As with vertebrate myelin, copepod sheaths are designed to
minimize both resistive and capacitive current flow through the internodal
membrane, greatly speeding nerve impulse conduction. Copepod myelin differs from
that of any other group described, while sharing features of every group.
Rapid jumps and bioluminescence elicited by controlled hydrodynamic stimuli
in a mesopelagic copepod, Pleuromamma xiphias
Daniel K. Hartline, Edward J. Buskey and Petra H. Lenz
Biol. Bull. 197: 132-143 (1999)
Actively vertically migrating mesopelagic copepods
are preyed upon by a wide variety of fishes and invertebrates. Their responses to
predatory attacks include vigorous escape jumps and discharge of bioluminescent
material. Escape jumps and bioluminescent discharge in the calanoid copepod,
Pleuromamma xiphias were elicited by quantified hydrodynamic disturbances. Brief
weak stimuli (peak water velocity 63 ± 21 ?m s-1) elicited weak (peak force 6.5
dynes) propulsive responses ("jumps") and no bioluminescence. Moderate stimuli
(1580 ± 780 ?m s-1) produced strong propulsive responses consisting of long
trains of coordinated powerstrokes by the four pairs of swimming legs ("kicks").
Peak forces averaged 42 dynes. Strong stimuli (5250 ± 3220 ?m s-1) were required
to elicit both a jump and a bioluminescent discharge. In several cases, multiple
stimuli were needed to evoke bioluminescence, given the limits on stimulus
magnitude imposed by the apparatus. Repeated bioluminescent discharges could be
evoked, but this responsiveness waned rapidly. Latencies for the jump response
(mean = 13 ms) were considerably shorter than for the accompanying bioluminescent
discharge (mean = 56 ms). The higher threshold for eliciting bioluminescent
discharge compared to escape jumps suggests that the copepods save this defense
mechanism for what is perceived to be a stronger threat.
Reaction times and force production during escape behavior of a calanoid
copepod, Undinula vulgaris.
Petra H. Lenz and Daniel K. Hartline
Mar. Biol. 133: 249-258 (1999)
Effective escape behavior contributes to the success of copepods in
planktonic communities. The kinematics of the escape was studied in
tethered Undinula vulgaris (Calanoida) by analyzing the timing and
magnitude of the powerstrokes to a precisely controlled sudden mechanical
perturbation in the surrounding water. Copepods responded with rapid swims
to water velocities of 36 to 86 um/sec. Reaction times were under 2.5 ms
following stimulus onset. The time course of force exerted was complex
but reproducible from stimulus to stimulus. Multiple powerstrokes
("kicks") were frequently observed in response to single stimuli. Time
intervals of 5 milliseconds were observed between the end of one escape
kick and the beginning of the next. U. vulgaris developed maximum forces
of 40 to over 100 dynes during a rapid swim. The behavioral reaction
times and intervals between multiple responses observed in this calanoid
are among the shortest reported in aquatic invertebrates.
Physiological and behavioral studies of escape responses in calanoid copepods
Daniel K. Hartline, Petra H.Lenz, and Christen M. Herren
Mar. Fresh. Behav. Physiol. 27: 199-212 (1996)
Copepods are among the more numerous and diverse of zooplankton groups in aquatic ecosystems.
Inhabiting a pelagic environment with little cover, they are subject to intense predation pressure.
Thus their abilities to detect and escape from potential predators is a major factor in their success.
Owing to their small size (mm), their sensory capabilities have not, until recently, been investigated with
the tools of sensory physiology. Much might be learned about copepod survival mechanisms and evolutionary
pressures through application of such techniques. In this paper we describe electrophysiological approaches
for monitoring sensory discharges from the first antennae of calanoid copepods. Nerve impulses can be recorded
extracellularly from both mechanoreceptors and putative chemoreceptors. "Giant" spikes (mV) with unusual
characteristics are found in Augaptiloids and Centropagoids, but not more recently diverging calanoid groups.
There are two such giant antennal mechanoreceptor units (GAMs) in each antenna. These originate in the sensory
setae of each distal tip. They are sensitive to very small (<10 nm) hydrodynamic signals, including abrupt
displacements and sinusoidal vibrations. Their frequency range for oscillatory stimuli is unusual for aquatic
arthropods, extending up to and above 2 kHz. Behavioral studies in the shallow-water calanoid Labidocera
madurae show that rapid escape reactions can be triggered by the same types of disturbances as elicit
firing in the GAMs. Sensitivities as low as 4 nm were found at frequencies of ca. 900 Hz.
Behavioral sensitivities over a range of frequencies are similar to those measured
physiologically and suggest that firing of the GAMs is capable of triggering escape behavior.
It may be that even a single nerve impulse can elicit the reaction in these animals.
Mechanoreception in zooplankton first antennae: electrophysiological techniques
Donald V. Gassie, Petra H. Lenz, Jeannette Yen and Daniel K. Hartline
Bulletin of Marine Science 53(1): 96-105 (1993)
We describe methods for delivering calibrated mechanical displacements to antennal
mechanoreceptors in zooplankton while simultaneously recording related neural traffic.
Mechanosensory neural responses to small water displacements (0.01-1 um) were studied
over a wide frequency range (30 to > 3000 Hz). Receptors could be localized and properties
(thresholds, phase locking, habituation) examined. These methods have been tested on
calanoid copepod first antennae (antennules), but may be suitable for other preparations.
Extracellular recordings are made by holding the animal in stainless steel forceps and
raising it into a layer of mineral oil, leaving one of the first antennae projecting
into the underlying sea water. Nerve impulse traffic is recorded between the forceps
and a chlorided silver wire in the seawater. Antennae are stimulated by water displacements
produced by a vibrating sphere attached to either an electromagnetic or piezoelectric
transducer. A fiberoptic sensor continuously monitors displacement. A computer-controlled
waveform generator and amplifier drive the transducer with various frequencies, amplitudes
and waveforms. The amplified sensor output and neural activity are digitized for later analysis.
Mechanoreception in marine copepods: electrophysiological studies on the first antennae
Jeannette Yen, Petra H. Lenz, Donald V. Gassie and Daniel K. Hartline
J. Plankton Res. 14(4):495-512 (1992)
Neural activity was recorded extracellularly at the base of the first antenna in 15 marine
copepods. Controlled mechanical stimuli were delivered with a vibrator driven by a waveform
generator. Many species exhibited responses characterized by a large number of small spikes, while
others were characterized by the presence of a small number of large units. Two bay species,
Labidocera madurae and Acarfia fossae , exhibited large units that could be easily
distinguished from the background activity of smaller units. In these species, the antennal receptors
fired short latency (>5 ms) trains of one to several impulses in response to a brief mechanical
stimulus and sustained trains to a prolonged sinusoidal stimulus. They were extremely
sensitive to small displacements and sensitivity increased with stimulus frequency. The
receptors responded to stimuli between 40 and 1000 Hz and receptors required displacement
velocities of 20 um s-1 or more to fire. Displacements as small as 10 nm were capable of
triggering spikes. With an increase in the amplitude of the displacement, a decrease in
the latency and an increase in the number of units recruited and/or firing frequency was
recorded. Phase-locking to oscillatory stimuli was observed over a frequency range of 80-500 Hz.
Neural activity increased in response to bending of individual setae. Setae appear innervated
and structurally constrained to movements in specific directions. These experiments suggest
that (i) some copepod setal receptors may be more nearly velocity detectors than purely
displacement sensors, (ii) they may be capable of sensing closely spaced stimuli, (iii) the
patterns of response may code for intensity and duration of the stimulus, and (iv) receptors
may be capable of supplying directional information.