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First published online February 29, 2008
Journal of Experimental Biology 211, 873-882 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.006031
Dynamic properties of a locomotory muscle of the tobacco hornworm Manduca sexta during strain cycling and simulated natural crawling
Tufts University, Department of Biology, Dana Laboratories, 163 Packard Avenue, Medford, MA 02155, USA
* Author for correspondence (e-mail: William.woods{at}tufts.edu)
Accepted 14 January 2008
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Summary |
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 TOP Summary INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Key words: muscle, caterpillar, soft-bodied locomotion, hydrostatic locomotion, passive muscle properties, work loop, Manduca sexta
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INTRODUCTION |
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TOPSummaryINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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; Brackenbury,
1997; Brackenbury,
1999; Brackenbury,
2000; Cacciatore et al.,
2000; O'Reilly et al.,
1997; Quillin,
1999; Quillin,
2000; Trueman,
1975). In general their skeletons are hydrostatic, with muscles
acting upon a flexible body wall under tension surrounding largely
incompressible tissues and fluid under pressure. Among terrestrial soft-bodied
animals, caterpillars such as Manduca sexta, the subject of this
study, not only crawl but, as herbivores, climb on branching and irregular
surfaces at all angles, including inverted ones. During crawling, forward
motion is in anterograde waves in which as many as three pairs of prolegs and
the segments bearing them are simultaneously lifted, swung forward, and
returned to the substrate. Manduca larvae even burrow, tunneling
underground before pupating. Additionally, caterpillars can be capable of
rapid movement (e.g. Brackenbury,
1997; Brackenbury,
1999; Walters et al.,
2001). Yet, the properties of the muscles with which they
accomplish these activities have been little studied except for the work of
Rheuben and Kammer (Rheuben and Kammer,
1980).
The muscles driving these activities are small, each consisting of
2–14 fibers, typically 4–6 mm long in an early fifth instar larva.
There are about 70 muscles per larval segment layered beneath the soft cuticle
to which they are attached (Barth,
1937; Beckel, 1958;
Levine and Truman, 1985). Most
lie within a single segment and are innervated by a single motoneuron
(Levine and Truman, 1985).
Nearly all are oriented longitudinally or obliquely, and none
circumferentially as in earthworms or other organisms that accomplish motion
by peristalsis (Quillin, 1998;
Quillin, 2000). During
crawling, these muscles might be expected to function quite differently from
skeletal or adult arthropod muscles, which typically contract rapidly while
undergoing limited shortening, using levers to move appendages distances
several times that of muscle strain. For example, dorsoventral wing muscles of
adult M. sexta cycle through a strain of about 7% (approximately 0.5
mm) during flight, shortening in about 0.018 s
(Stevenson and Josephson,
1990) and driving the wingtips via a jointed lever
through a path much greater in length than muscle shortening distance. By
contrast, muscle movement in a caterpillar is more directly linked to exterior
motions, and some natural caterpillar motions would appear to require
considerable changes in length
(Brackenbury, 1997;
Brackenbury, 1999;
Walters et al., 2001).
It is probable that Manduca muscles, or at least some of them,
play a role in maintaining turgor, whether actively or passively. Barth
proposed that some muscles function primarily to maintain turgor whereas
others are primarily locomotory, though his evidence was entirely anatomical
(Barth, 1937); it is also
possible that individual muscles alternate between these functions. The
oblique muscles are at a comparatively narrow angle to the longitudinal axis,
a configuration that would be expected to develop low flexural stiffness and
provide minimal resistance to the dorsoventral motion of the anterograde waves
while still contributing to turgor (Vogel,
2003; Wainwright,
1988). However, the roles of specific body wall muscles in
locomotion or turgor maintenance are still not known.
Structurally, M. sexta muscles are distinct from vertebrate
skeletal muscle or even from the wing muscles of adult M. sexta
(Rheuben and Kammer, 1980).
Compared to wing muscles, they have few mitochondria, long sarcomeres, poorly
defined and non-aligned Z-bands, very high tetanus-to-twitch ratios and far
slower force development (Rheuben and
Kammer, 1980). Additionally, where skeletal muscle is attached to
the bone by tendons that have high resilience and therefore comparatively
efficient elastic energy storage (Biewener
and Roberts, 2000; Vogel,
2003), caterpillar muscles lack discrete tendons; elastic energy
storage in larval muscle is limited to the capacity of the muscle's
contractile elements and fibrous titin- and collagen-class proteins.
Almost nothing is known about the dynamic properties of caterpillar muscle or its role in crawling or other activities. However, the complex motions accomplished by caterpillars with their comparatively simple central nervous system (CNS) raise intriguing possibilities. Some information processing may be embedded in the properties of the muscle material, and if so, these properties might differ from those of skeletal or cuticular muscle. To understand the role of caterpillar muscle during locomotion, we need to know not only the stimulus patterns but also the dynamic properties of active and passive muscle. In this article, we address these questions, focusing on the ventral interior longitudinal muscle (VIL) of the third abdominal segment (A3). A3 VIL is a comparatively large muscle in the innermost layer of muscles, spanning the proximal end of each A3 proleg and extending laterally almost to the spiracles (Fig. 1); its attachment points, like those of most of the muscles, lie just within the segment. Specifically, we ask (1) can caterpillar muscle function as an actuator over a broad strain range; (2) how effectively can the muscle store elastic energy; (3) what are its fundamental damping characteristics; and (4) what is the role of A3 VIL during crawling?
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MATERIALS AND METHODS |
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TOPSummaryINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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) at
27°C on a 17 h:7 h light:dark photoperiod. Second day, fifth instars of
both sexes were used for experiments. Proleg pairs are present on the third to
sixth abdominal segments (designated A3 to A6) as well on the more specialized
terminal segment. Although the muscles in segments A3 to A6 are similar in
appearance and organization, crawling loop experiments were always performed
on the same muscles of the same segment for which kinematic and electromyogram
(EMG) data were obtained.
Muscle preparations
Animals were anaesthetized by cooling on crushed ice for at least 20 min.
The resting length of VIL was determined using external markers established by
prior dissections and the animal was weighed to the nearest 0.01 g. After a
full-length dorsal midline incision, the gut was removed and the larvae were
pinned out in `flatterpillar' fashion, with the muscles and nerve cord
dorsally exposed, in physiological saline
(Weeks and Truman, 1984). In
such a preparation, VIL is in an uppermost position. Ipsilateral transverse
and ventral nerves and all contralateral nerves were cut from the A3 ganglion.
Longitudinal incisions were made through exterior muscles and cuticle
alongside VIL, and the cuticle and remaining muscles exterior to VIL were
removed by gently sliding dissecting scissors underneath the ends of VIL. The
cuticle anterior and posterior to A3 insertion points was cut, and the muscle,
together with attached cuticle and the dorsal nerve and ganglion, was removed.
The muscle was transferred to a horizontal bath in which one end was pinned to
an elastomer `island' by the attached cuticle so that the muscle was suspended
horizontally in saline. The other end of the muscle was secured to an Aurora
model 300B-LR lever-arm ergometer (Aurora Scientific Inc., Aurora, ON, Canada)
by means of a hook fashioned from an insect pin (size 000). Bath temperature
was regulated to 25±0.5°C by a Peltier device built into the
platform holding the bath and controlled by a Newport model INFCT-010B
thermocouple temperature controller (Newport Electronics Inc., Santa Ana, CA,
USA). Saline was replaced constantly and the bath was kept aerated.
The lever arm position was controlled and force, position and time recorded
by Aurora DMC software. Muscles were subjected to sinusoidal cycling over a
range of frequencies and to constant velocity stretching at a range of
velocities; the strain rates imposed included those encountered by A3 VIL
during crawling (see below) as well as higher rates. Stimulus trains (30 V, 20
Hz) were administered by a Grass S48 stimulator and SIU5 isolation unit (Grass
Instruments Inc., Quincy, MA, USA) via a suction electrode applied to
the dorsal nerve between the muscle and the ganglion. Separate preparations
were subjected to strain cycles and stimulation simulating those recorded
during horizontal crawling (see below). Stress values were based upon muscle
cross-sectional areas calculated using a relationship determined from imaging
of individual muscle fibers in a separate set of preparations, as described by
Dorfmann et al. (Dorfmann et al.,
2007). Data were analyzed in Aurora DMA, SigmaPlot 2000 (SAS
Institute Inc., Cary, NC, USA) and Systat 10.0 (Systat Software Inc.,
Richmond, CA, USA).
Kinematic and EMG measurements
Second or third day fifth instar animals were anaesthetized on ice. Small
drops of ultraviolet-fluorescing dye served as external markers for kinematics
recordings; these were applied with a small insect pin to the head, terminal
and abdominal prolegs, and points to which the attachment points of the VIL
muscles of abdominal segments 3 to 6 (A3–A6) had been mapped to the
exterior.
Animals were then re-anaesthetized and prepared for EMG recordings. An electrode was prepared by twisting a pair of 25 µm insulated nichrome wires into a tight double helix, then cleaning and cutting the tip at a 45° angle. Using a fine insect pin, a small hole was made into the center of the posterior margin of A3. The electrode was dipped into orange fluorescent powder (Risk Reactor, Huntington Beach, CA, USA) and inserted 0.1–0.2 mm into the hole, then sealed with Vetbond (3M, St Paul, MN, USA). 1–2 mm of the dorsal horn was cut off, and a fine silver grounding wire was inserted into the horn and sealed with Vetbond.
Upon recovery from anaesthesia, the animal was placed upon a horizontal 7 mm diameter wooden dowel secured in a flat black-lined open-fronted enclosure that served as a videography studio. The EMG signal was amplified 10 000x and filtered below 10 Hz and above 10 kHz with a differential AC amplifier (model 1700, A-M Systems, Sequim, WA, USA), digitized with a DI1720 A-D converter and recorded using Windaq software (both from Dataq Instruments, Inc., Akron, OH, USA). Two digital video cameras (Canon ZR 10, Canon USA, Lake Success, NY, USA) were mounted at the front corners of the apparatus, facing the center of the dowel at 45° angles. The cameras simultaneously monitored crawling, with each sending data to a separate computer where it was recorded in VideoWave. During each crawling cycle, an LED placed within the cameras' fields was flashed, while, simultaneously, a voltage signal was sent to a dedicated channel of the EMG file in Windaq; these allowed data to be synchronized for analysis.
When recordings of an individual were complete, the electrode leads were cut near the point of insertion and the animal was dissected to confirm electrode placement. If the fluorescent dye was not visible, the terminus of the electrode remaining within the muscle was located.
The strain cycle of VIL during crawling was represented by the time course of the distance between the beads applied to the external markers of the attachment points. It was assumed that the muscle remained linear throughout its strain cycle; we based this assumption on preliminary experiments that showed that the hemolymph that surrounds the gut of the animal accounts for about 40% of its body mass. Video data were analyzed in APAS (Ariel Performance Analysis System, Ariel Dynamics Inc., San Diego CA, USA) and synchronized with EMG recordings.
Elicitation of excitatory junction potentials
Preliminary analysis of EMG data from in vivo crawling experiments
consisted of demeaning, rectifying and integrating the signal to yield an
integrated activation index. However, variations in waveform amplitude made it
difficult to distinguish the onset and duration of the crawl-associated burst.
Therefore, the waveform characteristics of the excitatory junction potentials
(EJPs) were determined from evoked EMG recordings in a separate set of reduced
preparations. These characteristics could then be used to define the
relationship of EMG bursts to motoneuron spike activity. Using `flatterpillar'
preparations as described earlier, a suction electrode was applied to the
posterior branch of the A3 dorsal nerve. A double-helical nichrome electrode
was placed in the central posterior margin of the A3 VIL, and a silver
grounding wire was secured beneath the animal. Action potentials were evoked
using 0.1 ms voltage pulses in trains 1.2 s long with frequencies varied from
10 to 70 Hz. The motoneuron of VIL, the largest ventral muscle, had the lowest
activation threshold and could therefore be activated in isolation.
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RESULTS |
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Sinusoidal strain cycling of stimulated and unstimulated muscle
During sinusoidal strain cycling, VIL displays considerable hysteresis in
the relationship between force and length
(Fig. 4). VIL also showed
distinct pseudoelasticity; that is, the force–length relationship is
different during lengthening than during shortening. In addition, varying
cycling frequency alters the force–length relationship, so VIL can also
be said to display viscoelasticity (Fig.
4). The passive contribution to force during lengthening was
comparatively high, about 20–30% at cycling frequencies (0.5–2 Hz)
yielding stretch rates comparable to crawling movements, about 60% during
cycling frequencies (8–10 Hz) equivalent (M. Simon, personal
communication) to the rapid strike response
(Walters et al., 2001), and
exceeding 80% at 16 Hz (Fig.
5).
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Comparatively little of the energy input during stretching of the muscle in each oscillation was recovered elastically during shortening. Resilience (R), the fraction of energy required to lengthen the muscle that is recovered when the muscle is shortened to its initial length, was calculated as the area under the lower limb of the work loop divided by the area under the upper limb. The value of R at 0.5 Hz (mean scalar velocity 0.4 lengths s–1) for active muscle was only 0.20 (Fig. 6), with R increasing exponentially toward a maximum of 0.37 by the relationship R=0.138+0.223 (1–e–0.689F), where F is cycling frequency in Hz.
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There was considerable variation in stimulus timing and duration relative to the shortening of VIL, even between individual steps in the same crawl. In some cases, though not all, the stimulus began after the muscle had begun to shorten. The mean stimulus duration was 0.68 s, with the onset of stimulation occurring 0.19 s after the muscle began shortening and ceasing 0.11 s before shortening was complete. The muscle was thus stimulated beginning when shortening was 19% complete and ending when shortening was 91% complete.
In vitro work loops during simulated crawling
To produce consistent `crawling work loops', the in vivo strain
cycles were reduced to a simple representation in which the muscle was
shortened and lengthened at two constant velocities for 45% of the crawling
cycle duration and held at resting length for the remainder
(Fig. 11A). Administering a
0.68 s stimulus beginning 0.19 s after the beginning of muscle shortening
yielded a figure-eight-shaped work loop, with VIL performing work during the
shortest 45–65% of the strain cycle but dissipating work for the
remainder of it (Fig.
11B).
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Net work during a simulated crawling cycle varied between preparations, from positive (counterclockwise) to negative. During the positive portions of the work loop, VIL did 0.22±0.09 J kg–1 (mean ± s.e.m.) work per cycle. At natural crawling cycling frequency, the muscle produced power at 0.18±0.08 W kg–1 during the positive work loop portions.
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DISCUSSION |
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TOPSummaryINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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) suggest that the
dynamic properties of not only active but also of passive muscle are
particularly important components of caterpillar locomotion. Most of the
dynamic properties we report have counterparts in muscles of other organisms
and indeed in animal soft tissues in general, and can be described in
elastomeric terms (Fung, 1993;
Fung, 1980). However, the
contribution of the passive, as compared to active, properties of A3 VIL to
forces developed during strain cycling (Figs
4,
5) is far greater than it is
for vertebrate skeletal muscle (e.g. Brown
et al., 1996; Herzog and
Leonard, 2005; James et al.,
2004) (Layland et al.,
1995; Stevens and Faulkner,
2000) or insect flight muscle
(Josephson, 1997). Whereas
passive contributions within muscle–tendon systems can be substantial
(Biewener and Roberts, 2000),
their function is often to store elastic energy and thereby to contribute to
the energetic efficiency of locomotion
(Bennett et al., 1986;
Biewener and Baudinette, 1995;
Biewener and Roberts, 2000;
Biewener et al., 2004;
Dickinson and Lighton, 1995;
Gosline et al., 2002). A3 VIL,
in contrast, dissipates most of the energy used to extend it, whether in
sinusoidal strain cycling (Figs
4,
6) or during simulated natural
crawling (Figs 11,
12), a property associated in
locomotory structures of other organisms with maintenance of stability
(Biewener and Roberts, 2000;
Dudek and Full, 2006;
Hof, 2003;
Jindrich and Full, 2002;
Marsh, 1999), by means of
preflex rather than CNS-dependent reflex
(Campbell and Kirkpatrick,
2001; Cham et al.,
2000; Chen et al.,
2006; Dickinson et al.,
2000; Seipel et al.,
2004). Although muscles of like mechanical qualities in
vitro can have markedly different mechanical outputs in vivo
(Ahn et al., 2006), the visual
similarity of fibers in all M. sexta larval muscles at least raises
the possibility that this low resilience may be a general characteristic of
caterpillar muscles. Efficiency of caterpillar locomotion is very low
(Casey, 1991), but given the
growth-oriented role of the larval stage, locomotory efficiency may be
unimportant; caterpillars allocate far more of their energy uptake to tissue
production than to activity (Schowalter et
al., 1977; Scriber,
1977). With a comparatively simple CNS
(Levine and Truman, 1985) and
without a jointed skeleton to limit mechanical degrees of freedom, maintenance
of stability via preflex may be critical to caterpillar locomotion,
and the low-resilience yet consistent elastomeric properties of caterpillar
muscle may make an important contribution.
Force development and length–tension relationship
Caterpillar muscle develops force over an unusually large strain range.
Whereas skeletal muscle of a wide range of vertebrates can generate 60% of
peak force (force developed at optimal length; Lo) at
strain ranges from about 70–85% to 110–130% of
Lo (Abbott and Aubert,
1952; Heerkens et al.,
1987; Lutz and Rome,
1996a), M. sexta larval muscle does so from about 65% to
over 160% of Lo (Fig.
3), a range similar to that of Guinea pig taenia coli,
Mytilus byssal retractor, and Calliphora body wall muscles
(Hardie, 1976). This range is
considerably greater than the 80–120% of Lo over
which the obliquely striated dorsal longitudinal muscles of the leech develop
60% of peak force (Miller,
1975), and greater than the working strain range of the
fundamentally similar (Mill and Knapp,
1970) muscles of earthworms during crawling
(Quillin, 1999). Although
obliquely striated muscles are not found in insects, supercontracting muscles
are (Carnevali, 1978;
Hardie, 1976;
Rice, 1970); for example, in
tsetse flies some visceral muscles are supercontracting whereas others are
not, and the supercontracting muscles are capable of contractions of
70–80%, or about twice the operating strain range of their
non-supercontracting counterparts (Rice,
1970). The muscles of M. sexta larvae have been described
as striated, but with much longer sarcomeres than in adult M. sexta
wing muscle, and with irregularly arranged and poorly defined Z-bands
(Rheuben and Kammer, 1980).
Whether they are actually supercontracting muscles, with perforated Z-bands
that allow myosin filaments to engage thin filaments of adjacent sarcomeres
(Herrel et al., 2002), is not
known. Although large working strain ranges are found in non-supercontracting
insect muscle – adult tsetse fly external visceral muscles have complete
Z-bands and yet undergo normal contractions of about 40%
(Rice, 1970), roughly the
range over which VIL produces substantial force
(Fig. 3) – the larvae of
at least two lepidopteran species have supercontracting body wall muscles
(Carnevali, 1978).
Force development during tetanic stimulation is comparatively slow,
requiring more than 2 s to reach peak value and more than 0.5 s to reach 80%
of maximum value. The peak force rise time is up to 90 times the values for
vertebrate striated muscle (Ashley-Ross,
2002; Ellerby et al.,
2001; Gordon et al.,
1966; Herzog and Leonard,
2005; Lutz and Rome,
1996b; Stevens and Faulkner,
2000), 40 times the values for obliquely striated earthworm muscle
(Tashiro, 1971), and about
four to seven times the values for earthworm circular muscles
(Tashiro, 1971) and for insect
flight muscle, whether synchronous or asynchronous
(Josephson, 1997;
Rheuben and Kammer, 1980), and
twice that for a vertebrate smooth muscle
(Gordon and Siegman, 1971).
During crawling, when VIL is stimulated for a duration of 0.68 s while
shortening, it (Fig. 11), it
develops only a small fraction of the force developed under tetanic
stimulation (Fig. 2).
Crawling strain on the ascending portion of the length–tension curve
During horizontal crawling, the length of VIL does not exceed resting
values (Figs 11,
12), with the consequence that
strain cycling occurs entirely within the ascending limb of its
length–tension curve (Fig.
3), a characteristic it shares with the wing depressor muscles of
adult Manduca (Tu and Daniel,
2004) as well as with hydrostatic skeletal muscle of the hermit
crab (Chapple, 1983),
mammalian cardiac muscle (Layland et al.,
1995), the soleus and plantaris muscles of cats
(Herzog et al., 1992) and the
gastrocnemius muscles of cats (Herzog et
al., 1992) and humans (Herzog
and Read, 1993). In the case of cardiac muscle, this means that
increases in ventricular filling are met with increases in the muscle's force
production (Layland et al.,
1995) without extrinsic computation, amounting to an embedded
control system. Chapple (Chapple,
1983) suggests a similar role for a hydrostatic skeletal muscle of
the hermit crab. In the case of Manduca adults, Tu and Daniel
(Tu and Daniel, 2004) reason
that the strong dependence of force generation on length amount to intrinsic
regulation without neural intervention; firing patterns of wing depressor
muscles change little during maneuvering but wing stroke amplitude does, most
probably because of changing contributions from the direct wing muscles
(Kammer, 1971;
Rheuben and Kammer, 1980). It
should be pointed out that in contrast to the cardiac
(Layland et al., 1995) and
Manduca flight muscle (Tu and
Daniel, 2004) studies, the data in
Fig. 3 are for tetanically
stimulated muscle. Because subtetantically stimulated force–length
relationships shift at lower stimulation levels so that optimal length values
are greater (Rack and Westbury,
1969), the comparison is arguably not a direct one. However, if
the same is true for larval muscle, then tetanic stimulation would be expected
to shift the curve in Fig. 3 to
the left of where it would be for subtetanic stimulation, thus providing a
more demanding test of whether the strain cycle falls within the ascending
limb of the force-length relationship.
In caterpillars such embedded control may be important in maintaining the body wall tension against which actuating muscles act, as it appears they do: if a three-segment `flatterpillar' preparation is made, stretched to in vivo resting length, and all muscles in the middle segment cut, the tension in the other segments will stretch the middle segment by about 50% of its resting length; if instead the cuticle is cut and the muscles left intact, the middle segment in stretched by only about 4% (unpublished observation). Furthermore, when caterpillars are anesthetized by cooling or CO2 they become flaccid. Hence resting tension in muscles must provide a substantial amount of pressurization and body stiffness. By operating on the ascending portion of the force–length relationship, Manduca muscles might increase tension in response to applied forces with no need for neural intervention.
Elastomeric properties
Elastomeric characteristics are nearly universal in soft tissues
(Fung, 1980). VIL, like other
muscle, shows pseudoelasticity, a characteristic in which a material behaves
as one kind of elastic when being lengthened and another when being shortened.
It also shows a Mullins effect, or stress-softening under repeated
constant-velocity strain cycling (Dorfmann
et al., 2007). With respect to these characteristics, VIL's
dynamic properties are qualitatively similar to those of synthetic elastomers
(Dorfmann and Ogden, 2003;
Dorfmann and Ogden, 2004) and
have been described using a constitutive modeling approach
(Dorfmann et al., 2007).
Additionally, these characteristics are dependent upon strain rate (Figs
4,
5,
6,
8,
9), indicating viscoelasticity
(Fung, 1993;
Wineman and Rajagopal, 2000).
What appears to distinguish VIL from well-described skeletal locomotory
muscles is the relative importance of these characteristics in the passive, as
compared with the stimulated, state. Passive muscle forces are often reported
to be comparatively unimportant under normal strain cycling
(Brown et al., 1996;
James et al., 2004;
Stevens and Faulkner, 2000),
though force values can become significant when the muscle is extended beyond
optimal length (Heerkens et al.,
1987; Josephson,
1997; Stokes and Josephson,
1994). By contrast, in the case of VIL, passive forces are
significant even at resting length during crawling, with peak force reached
when the unstimulated muscle is re-lengthened to resting length, about 93% of
Lo (Fig.
11).
One characteristic of VIL that is not found in synthetic elastomers or in
soft biological tissues other than muscle is the transition from a higher to a
lower rate of force increase during stretching
(Fig. 7), a phenomenon first
described in detail by Hill (Hill,
1968). For VIL, the transition occurs when the muscle has been
stretched by about 4%, far higher than the 0.2% Hill found
(Hill, 1968). The occurrence
of the transition at strain values of 1–3% of resting length in slowly
stretched vertebrate skeletal muscles
(Mutungi and Ranatunga, 1996;
Proske and Morgan, 1999) has
been attributed to previous contraction history or to the contribution of
tendons (Proske and Morgan,
1999). However, our stretch-and-hold measurements were made on
muscles that had not been stimulated in vitro, and caterpillar
muscles lack discrete tendons. Other explanations may become apparent as
information about caterpillar muscle ultrastructure advances beyond the work
of Carnevali (Carnevali, 1978)
and Rheuben and Kammer (Rheuben and
Kammer, 1980) The linear relationship between muscle tension
during the transition and the stretch velocity
(Fig. 9) is similar to that
reported previously for vertebrate skeletal muscle
(Mutungi and Ranatunga, 1996),
as is the exponential relationship between peak force and stretch velocity
(Fig. 8A)
(Hill, 1968;
Mutungi and Ranatunga, 1996).
These similarities suggest that the stress–strain relationship of
passive VIL is due to characteristic properties of muscle arising from stable
cross-bridges, gap filaments composed of titin-like proteins, or both
(Kellermayer et al., 1997;
Mutungi and Ranatunga, 1996;
Proske and Morgan, 1999;
Tskhovrebova and Trinick,
2002; Wang et al.,
1991). By contrast, collagen shows a characteristic J-shaped
stress–strain curve (Fung,
1993; Gosline et al.,
2002).
Resilience
In muscle–tendon systems, elastic storage during locomotion can be
considerable, and can provide a large savings of energy expenditure that would
be required from muscle alone (Biewener et
al., 1998; Biewener and
Roberts, 2000; Roberts et al.,
1997); over 90% of the work expended lengthening tendon collagen
is returned during shortening (Gosline et
al., 2002). Passive skeletal muscle too dissipates comparatively
little work under strain cycling (James et
al., 2004; Josephson,
1997; Layland et al.,
1995; Stevens and Faulkner,
2000). By contrast, the resilience (R) of VIL is
comparatively low; most of the work done on the muscle during lengthening is
dissipated during shortening. During sinusoidal cycling, the forces are
slightly negative for most of the shortening limb. This could not be
characterized as compression (Josephson
and Ellington, 1997) or buckling, since the muscle fibers were
simply bending freely, arguably in a manner not representative of in
vivo activity. Values of R for the passive muscle would
therefore have questionable meaning. However, even under tetanic stimulus,
R values are low (Fig.
6). As strain cycling frequency increased from 0.5 to 2 Hz,
corresponding to crawling strain rates, values of R increased from
about 20% to 30%, and at higher cycling frequencies R plateaus at
under 40%. These values are far lower than those for passive insect
(bumblebee) wing muscle, which exceed 90%
(Josephson and Ellington,
1997), or passive rat gastrocnemius medialis muscle, for which
elastic energy storage and release is about eightfold higher than energy
dissipation (Heerkens et al.,
1987). In studies that recorded work loops for passive or
tetanically stimulated muscle without reporting values for R, work
loops have small ratios of area to length, showing low work dissipation
(James et al., 2004;
Stevens and Faulkner, 2000).
Lower values of R are found in other structures: 60–75% for
cockroach hindlegs (Dudek and Full,
2006), 77% for cuttlefish mantle
(Curtin et al., 2000) and 58%
for jellyfish mesoglea (Demont and
Gosline, 1988). In the case of cockroach hindlegs, it has been
proposed that the presence of damping associated with lower conservation of
elastic energy may be critical in maintaining stability without feedback
(Alexander, 1988;
Dudek and Full, 2006;
Full and Koditschek,
1999).
In the case of caterpillars, conservation of elastic energy may not be
particularly important. More than half of the energy a caterpillar acquires
from feeding is dedicated to body mass production – Manduca
larvae increase in body mass by about four orders of magnitude in about 3
weeks – and only about 15% to maintenance, including locomotion
(Schowalter et al., 1977;
Scriber, 1977). Caterpillar
locomotion is so inefficient – nearly five times as energetically costly
as for an animal with a skeleton –
(Casey, 1991) that recovering
more of the energy expended during muscle lengthening may not be important to
the overall energy budget.
Embedded computation?
It is not yet possible to state whether the high damping, together with the
velocity dependence of peak force and of force decay during stretching of
passive muscle, might play a critical role in maintaining stability in the
face of perturbations during caterpillar locomotion, thereby amounting to
information processing embedded in the dynamic properties of the muscle. The
models and robots in which this principle has been demonstrated have as little
as one degree of freedom, whereas a caterpillar's hydrostatic skeleton would
appear to have virtually limitless degrees of freedom. We raise the
possibility that degrees of freedom in caterpillars and other soft-bodied
animals may be reduced by means other than simple mechanical constraints on
movement. The presence of a central pattern generator thought to drive
crawling behavior in Manduca
(Johnston and Levine, 1996)
and the highly stereotyped activity of Manduca planta retractor
muscles (Belanger and Trimmer,
2000) may serve to constrain motion options during common
activities. Often material properties and morphology can substitute for
computation and thereby simplify control
(Pfeifer, 2000), and
caterpillar muscle may be an example of this.
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Acknowledgments |
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TOPSummaryINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
|---|
Abbott, B. and Aubert, X. (1952). The force
exerted by active striated muscle during and after change of length.
J. Physiol. 117,77
-86.
Ahn, A., Meijer, K. and Full, R. (2006). In
situ muscle power differs without varying in vitro mechanical
properties in two insect leg muscles innervated by the same motor neuron.
J. Exp. Biol. 209,3370
-3382.
Alexander, R. M. (1988). Elastic Mechanisms in Animal Movement. Cambridge: Cambridge University Press.
Ashley-Ross, M. A. (2002). Mechanical properties of the dorsal fin muscle of seahorse (Hippocampus) and pipefish (Syngnathus). J. Exp. Zool. 293,561 -577.[CrossRef][Medline]
Barth, R. (1937). Muskulatur und Bewegungsart der Raupen. Zool. Jb. Physiol. 62,507 -566.
Beckel, W. E. (1958). The morphology, histology and physiology of the spiracular regulatory apparatus of Hyalophora cecropia. Proc. 10th Int. Congr. Entomol. 2, 87-115.
Belanger, J. H. and Trimmer, B. A. (2000). Combined kinematic and electromyographic analyses of proleg function during crawling by the caterpillar Manduca sexta. J. Comp. Physiol. A 186,1031 -1039.[CrossRef][Medline]
Bell, R. A. and Joachim, F. A. (1978). Techniques for rearing laboratory colonies of tobacco hornworms and pink bollworms. Ann. Entomol. Soc. Am. 69,365 -373.
Bennett, M., Ker, R., Dimery, N. and Alexander, R. (1986). Mechanical properties of various mammalian tendons. J. Zool. Lond. A 209,537 -548.
Biewener, A. and Baudinette, R. (1995). In vivo muscle force and elastic energy storage during steady-speed hopping of tammar wallabies (Macropus eugenii). J. Exp. Biol. 198,1841 .
Biewener, A. and Roberts, T. (2000). Muscle and tendon contributions to force, work, and elastic energy savings: a comparative perspective. Exerc. Sport Sci. Rev. 28, 99-107.[Medline]
Biewener, A., Corning, W. and Tobalske, B. (1998). In vivo pectoralis muscle force-length behavior during level flight in pigeons (Columba livia). J. Exp. Biol. 201,3293 -3307.[Abstract]
Biewener, A. A., McGowan, C., Card, G. M. and Baudinette, R.
V. (2004). Dynamics of leg muscle function in tammar
wallabies (M. eugenii) during level versus incline hopping.
J. Exp. Biol. 207,211
-223.
Brackenbury, J. (1996). Novel locomotory mechanism in caterpillars: life-line climbing in Epinotia abbreviana (Tortricidae) and Yponomeuta padella (Ypononmeutidae). Physiol. Entomol. 21,7 -14.[CrossRef]
Brackenbury, J. (1997). Caterpillar kinematics. Nature 390,453 .[CrossRef]
Brackenbury, J. (1999). Fast locomotion in caterpillars. J. Insect Physiol. 45,525 -533.[CrossRef][Medline]
Brackenbury, J. (2000). Locomotory modes in the larva and pupa of Chironomus plumosus (Diptera, Chironomidae). J. Insect Physiol. 46,1517 -1527.[CrossRef][Medline]
Brown, I., Liinamaa, T. and Loeb, G. (1996). Relationships between range of motion, Lo, and passive force in five strap-like muscles of the feline hind limb. J. Morphol. 230,69 -77.[CrossRef][Medline]
Cacciatore, T. W., Rozenshteyn, R. and Kristan, W. B., Jr
(2000). Kinematics and modeling of leech crawling: evidence for
an oscillatory behavior produced by propagating waves of excitation.
J. Neurosci. 20,1643
-1655.
Campbell, K. and Kirkpatrick, R. (2001). Mechanical preflexes and neuromuscular function. Proc. ASME 50,591 -592.
Carnevali, M. (1978). Z-line and supercontraction in the hydraulic muscular systems of insect larvae. J. Exp. Zool. 203,15 -30.[CrossRef]
Casey, T. M. (1991). Energetics of caterpillar
locomotion: biomechanical constraints of a hydraulic skeleton.
Science 252,112
-114.
Cham, J., Bailey, S. and Cutkosky, M. (2000). Robust dynamic locomotion through feedforward-preflex interaction. ASME IMECE Proceedings, Orlando, Florida, November,5 -10.
Chapple, W. (1983). Mechanical responses of a
crustacean slow muscle. J. Exp. Biol.
107,367
-383.
Chen, J., Peattie, A., Autumn, K. and Full, R.
(2006). Differential leg function in a sprawled-posture
quadrupedal trotter. J. Exp. Biol.
209,249
-259.
Curtin, N., Woledge, R. and Bone, Q. (2000). Energy storage by passive elastic structures in the mantle of Sepia officinalis. J. Exp. Biol. 203,869 -878.[Abstract]
Demont, M. and Gosline, J. (1988). Mechanics of
jet propulsion in the hydromedusan jellyfish, Polyorchis
penicillatus. II. Energetics of the jet cycle. J. Exp.
Biol. 134,333
-345.
Dickinson, M. and Lighton, J. (1995). Muscle
efficiency and elastic storage in the flight motor of Drosophila.
Science 268,87
-90.
Dickinson, M. H., Farley, C. T., Full, R. J., Koehl, M. A.,
Kram, R. and Lehman, S. (2000). How animals move: an
integrative view. Science
288,100
-106.
Dorfmann, A. and Ogden, R. (2003). A pseudo-elastic model for loading, partial unloading and reloading of particle-reinforced rubber. Int. J. Solids Struct. 40,2699 -2714.[CrossRef]
Dorfmann, A. and Ogden, R. (2004). A constitutive model for the Mullins effect with permanent set in particle-reinforced rubber. Int. J. Solids Struct. 41,1855 -1878.[CrossRef]
Dorfmann, A., Trimmer, B. A. and Woods, W. A., Jr (2007). A constitutive model for muscle properties in a soft-bodied arthropod. J. R. Soc. Interface 4, 257-269.[CrossRef][Medline]
Dudek, D. and Full, R. (2006). Passive
mechanical properties of legs from running insects. J. Exp.
Biol. 209,1502
-1515.
Ellerby, D., Spierts, I. and Altringham, J.
(2001). Fast muscle function in the European eel (Anguilla
anguilla L.) during aquatic and terrestrial locomotion. J.
Exp. Biol. 204,2231
-2238.
Full, R. J. and Koditschek, D. E. (1999). Templates and anchors: neuromechanical hypotheses of legged locomotion on land. J. Exp. Biol. 202,3325 -3332.[Abstract]
Fung, Y. (1993). Biomechanics: Mechanical Properties of Living Tissues. New York: Springer-Verlag.
Fung, Y. C. (1980). On pseudo-elasticity of living tissues. In Mechanics Today. Vol.5 (ed. S. Nemat-Nasser), pp.49 -66. Oxford: Pergamon Press.
Gordon, A. and Siegman, M. (1971).Mechanical properties of smooth muscle. II. Active state . 221,1250 -1254.
Gordon, A., Huxley, A. and Julian, F. (1966).
The variation in isometric tension with sarcomere length in vertebrate muscle
fibres. J. Physiol. 184,170
-192.
Gosline, J., Lillie, M., Carrington, E., Guerette, P., Ortlepp,
C. and Savage, K. (2002). Elastic proteins: biological roles
and mechanical properties. Philos. Trans. R. Soc. Lond. B Biol.
Sci. 357,121
-132.
Hardie, J. (1976). The tension/length relationship of an insect (Calliphora erythrocephala) supercontracting muscle. Experientia 32,714 -716.[CrossRef]
Heerkens, Y. F., Woittiez, R. D., Kiela, J., Huijing, P. A., Huson, A., van Ingen Schenau, G. J. and Rozendal, R. H. (1987). Mechanical properties of passive rat muscle during sinusoidal stretching. Pflügers Arch. 409,438 -447.[CrossRef][Medline]
Herrel, A., Meyers, J. J., Timmermans, J. P. and Nishikawa, K.
C. (2002). Supercontracting muscle: producing tension over
extreme muscle lengths. J. Exp. Biol.
205,2167
-2173.
Herzog, W. and Leonard, T. (2005). The role of passive structures in force enhancement of skeletal muscles following active stretch. J. Biomech. 38,409 -415.[CrossRef][Medline]
Herzog, W. and Read, L. (1993). Lines of action and moment arms of the major force-carrying structures crossing the human knee joint. J. Anat. 182,213 -230.[Medline]
Herzog, W., Leonard, T., Renaud, J., Wallace, J., Chaki, G. and Bornemisza, S. (1992). Force-length properties and functional demands of cat gastrocnemius, soleus and plantaris muscles. J. Biomech. 25,1329 -1335.[CrossRef][Medline]
Hill, D. (1968). Tension due to interaction
between the sliding filaments in resting striated muscle. The effect of
stimulation. J. Physiol.
199,637
-384.
Hof, A. (2003). Muscle mechanics and neuromuscular control. J. Biomech. 36,1031 -1038.[CrossRef][Medline]
James, R. S., Wilson, R. S. and Askew, G. N.
(2004). Effects of caffeine on mouse skeletal muscle power output
during recovery from fatigue. J. Appl. Physiol.
96,545
-552.
Jindrich, D. and Full, R. (2002). Dynamic
stabilization of rapid hexapedal locomotion. J. Exp.
Biol. 205,2803
-2823.
Johnston, R. M. and Levine, R. B. (1996).
Crawling motor patterns induced by pilocarpine in isolated larval nerve cords
of Manduca sexta. J. Neurophysiol.
76,3178
-3195.
Josephson, R. (1997). Power output from a flight muscle of the bumblebee Bombus terrestris. II. Characterization of the parameters affecting power output. J. Exp. Biol. 200,1227 -1239.[Abstract]
Josephson, R. and Ellington, C. (1997). Power output from a flight muscle of the bumblebee Bombus terrestris. I. Some features of the dorso-ventral flight muscle. J. Exp. Biol. 200,1215 -1226.[Abstract]
Kammer, A. E. (1971). The motor output during turning flight in a hawkmoth, Manduca sexta. J. Insect Physiol. 17,1073 -1086.[CrossRef]
Kellermayer, M. S., Smith, S. B., Granzier, H. L. and
Bustamante, C. (1997). Folding-unfolding transitions in
single titin molecules characterized with laser tweezers.
Science 276,1112
-1116.
Layland, J., Young, I. and Altringham, J. (1995). The length dependence of work production in rat papillary muscles in vitro. J. Exp. Biol. 198,2491 -2499.[Medline]
Levine, R. B. and Truman, J. W. (1985). Dendritic reorganization of abdominal motoneurons during metamorphosis of the moth, Manduca sexta. J. Neurosci. 5,2424 -2431.[Abstract]
Lutz, G. J. and Rome, L. C. (1996a). Muscle function during jumping in frogs. I. Sarcomere length change, EMG pattern, and jumping performance. Am. J. Physiol. 271,C563 -C570.[Medline]
Lutz, G. J. and Rome, L. C. (1996b). Muscle function during jumping in frogs. II. Mechanical properties of muscle: implications for system design. Am J. Physiol. 271,C571 -C578.[Medline]
Marsh, R. L. (1999). How muscles deal with real-world loads: the influence of length trajectory on muscle performance. J. Exp. Biol. 202,3377 -3385.[Abstract]
Mill, P. and Knapp, M. (1970). The fine
structure of obliquely striated body wall muscles in the earthworm,
Lumbricus terrestris LINN. J. Cell Sci.
7, 233-261.
Miller, J. (1975). The length-tension
relationship of the dorsal longitudinal muscle of a leech. J. Exp.
Biol. 62,43
-53.
Mutungi, G. and Ranatunga, K. W. (1996). The
viscous, viscoelastic and elastic characteristics of resting fast and slow
mammalian (rat) muscle fibres. J. Physiol.
496,827
-836.
O'Reilly, J., Ritter, D. and Carrier, D. (1997). Hydrostatic locomotion in a limbless tetrapod. Nature 386,269 -272.[CrossRef]
Pfeifer, R. (2000). On the role of morphology and materials in adaptive behavior. From Animals to Animats 6,23 -32.
Proske, U. and Morgan, D. L. (1999). Do cross-bridges contribute to the tension during stretch of passive muscle? J. Muscle Res. Cell Motil. 20,433 -442.[CrossRef][Medline]
Quillin, K. J. (1998). Ontogenetic scaling of
hydrostatic skeletons: geometric, static stress and dynamic stress scaling of
the earthworm Lumbricus terrestris. J. Exp. Biol.
201,1871
-1883.
Quillin, K. J. (1999). Kinematic scaling of locomotion by hydrostatic animals: ontogeny of peristaltic crawling by the earthworm Lumbricus terrestris. J. Exp. Biol. 202,661 -674.[Abstract]
Quillin, K. J. (2000). Ontogenetic scaling of burrowing forces in the earthworm Lumbricus terrestris. J. Exp. Biol. 203,2757 -2770.[Abstract]
Rack, P. and Westbury, D. (1969). The effects
of length and stimulus rate on tension in the isometric cat soleus muscle.
J. Physiol. 204,443
-460.
Rheuben, M. B. and Kammer, A. E. (1980).
Comparison of slow larval and fast adult muscle innervated by the same motor
neurone. J. Exp. Biol.
84,103
-118.
Rice, M. J. (1970). Supercontracting and non-supercontracting visceral muscles in the tsetse fly, Glossina austeni.J. Insect Physiol. 16,1109 -1122.[CrossRef][Medline]
Roberts, T. J., Marsh, R. L., Weyand, P. G. and Taylor, C.
R. (1997). Muscular force in running turkeys: the economy of
minimizing work. Science
275,1113
-1115.
Schowalter, T., Whitford, W. and Turner, R. (1977). Bioenergetics of the range caterpillar, Hemileuca oliviae (Ckll.). Oecologia 28,153 -161.[CrossRef]
Scriber, J. (1977). Limiting effects of low leaf-water content on the nitrogen utilization, energy budget, and larval growth of Hyalophora cecropia (Lepidoptera: Saturniidae). Oecologia 28,269 -287.[CrossRef]
Seipel, J., Holmes, P. and Full, R. (2004). Dynamics and stability of insect locomotion: a hexapedal model for horizontal plane motions. Biol. Cybern. 91, 76-90.[Medline]
Stevens, E. D. and Faulkner, J. A. (2000). The
capacity of mdx mouse diaphragm muscle to do oscillatory work. J.
Physiol. 522,457
-466.
Stevenson, R. and Josephson, R. (1990). Effects
of operating frequency and temperature on mechanical power output from moth
flight muscle. J. Exp. Biol.
149, 61-78.
Stokes, D. and Josephson, R. (1994). Contractile properties of a high-frequency muscle from a crustacean – contraction kinetics. J. Exp. Biol. 187,275 -293.[Abstract]
Tashiro, N. (1971). Mechanical properties of
the longitudinal and circular muscle in the earthworm. J. Exp.
Biol. 55,101
-110.
Trueman, E. R. (1975). The Locomotion of Soft-bodied Animals. London: Edward Arnold.
Tskhovrebova, L. and Trinick, J. (2002). Role
of titin in vertebrate striated muscle. Philos. Trans. R. Soc.
Lond. B Biol. Sci. 357,199
-206.
Tu, M. S. and Daniel, T. L. (2004).
Cardiac-like behavior of an insect flight muscle. J. Exp.
Biol. 207,2455
-2464.
Vogel, S. (2003). Comparative Biomechanics: Life's Physical World. Princeton, NJ: Princeton University Press.
Wainwright, S. A. (1988). Axis and Circumference. Cambridge, MA: Harvard University Press.
Walters, E., Illich, P., Weeks, J. and Lewin, M. (2001). Defensive responses of larval Manduca sexta and their sensitization by noxious stimuli in the laboratory and field. J. Exp. Biol. 204,457 -469.[Abstract]
Wang, K., McCarter, R., Wright, J., Beverly, J. and
Ramirez-Mitchell, R. (1991). Regulation of skeletal muscle
stiffness and elasticity by titin isoforms: a test of the segmental extension
model of resting tension. Proc. Natl. Acad. Sci. USA
88,7101
-7105.
Weeks, J. C. and Truman, J. W. (1984). Neural organization of peptide-activated ecdysis behaviors during the metamorphosis of Manduca sexta. 1. Conservation of the peristalsis motor pattern at the larval-pupal transformation. J. Comp. Physiol. 155,407 -422.[CrossRef]
Wineman, A. and Rajagopal, K. (2000). Mechanical Response of Polymers: An Introduction. Cambridge: Cambridge University Press.
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) of force decay from the peak values shown in A with the muscle held at
110% of resting length was associated with stretch velocity (v) by
the relationship 
