Quadrupedal gaits in hexapod animals - inter-leg coordination in free-walking adult stick insects

SUMMARYIn its natural habitat, Carausius morosus climbs on the branches of bushes and trees. Previous work suggested that stick insects perform targeting movements with their hindlegs to find support more easily. It has been assumed that the animals use position information from the anterior legs to control the touchdown position of the ipsilateral posterior legs. Here we addressed the question of whether not only the hindleg but also the middle leg performs targeting, and whether targeting is still present in a walking animal when influences of mechanical coupling through the ground are removed. If this were the case, it would emphasize the role of underlying neuronal mechanisms. We studied whether targeting occurred in both legs, when the rostral neighboring leg, i.e. either the middle or the front leg, was placed at defined positions relative to the body, and analyzed targeting precision for dependency on the targeted position. Under these conditions, the touchdown positions of the hindlegs show correlation to the position of the middle leg parallel and perpendicular to the body axis, while only weak correlation exists between the middle and front legs, and only in parallel to the body axis. In continuously walking tethered animals, targeting accuracy of the hindlegs and middle legs parallel to the body axis barely differed. However, targeting became significantly more accurate perpendicular to the body axis. Our results suggest that a neural mechanism exists for controlling the touchdown position of the posterior leg but that the strength of this mechanism is segment specific and dependent on the behavioral context in which it is used. Supplementary material available online at

Section: Targeting Accuracy Changes Between Standing and Moving Targesupporting

confidence: 84%

Segment-specific and state-dependent targeting accuracy of the stick insect

Wosnitza

Engelen

Gruhn

2013

“…Previous studies reported stump oscillations or muscle activity in otherwise intact walking insects (Hughes, 1957;Delcomyn, 1988Delcomyn, , 1991avon Buddenbrock, 1921;Wendler, 1966;Graham, 1977;Bässler et al, 1987;Grabowska et al, 2012). These studies report multiple stump oscillations during single steps in intact legs but were often only qualitative and focused on effects of amputations on the remaining intact legs.…”

Section: New Insights and Open Questionsmentioning

confidence: 99%

Speed-dependent interplay between local pattern-generating activity and sensory signals during walking inDrosophila

Berendes

Zill

Büschges

et al. 2016

In insects, the coordinated motor output required for walking is based on the interaction between local pattern-generating networks providing basic rhythmicity and leg sensory signals, which modulate this output on a cycle-to-cycle basis. How this interplay changes speed-dependently and thereby gives rise to the different coordination patterns observed at different speeds is not sufficiently understood. Here, we used amputation to reduce sensory signals in single legs and decouple them mechanically during walking in Drosophila. This allowed for the dissociation between locally generated motor output in the stump and coordinating influences from intact legs. Leg stumps were still rhythmically active during walking. Although the oscillatory frequency in intact legs was dependent on walking speed, stumps showed a high and relatively constant oscillation frequency at all walking speeds. At low walking speeds we found no strict cycle-to-cycle coupling between stumps and intact legs. In contrast, at high walking speeds stump oscillations were strongly coupled to the movement of intact legs on a one-to-one basis. Although during slow walking there was no preferred phase between stumps and intact legs, we nevertheless found a preferred time interval between touch-down or lift-off events in intact legs and levation or depression of stumps. Based on these findings, we hypothesize that, as in other insects, walking speed in Drosophila is predominantly controlled by indirect mechanisms and that direct modulation of basic pattern-generating circuits plays a subsidiary role. Furthermore, interleg coordination strength seems to be speed-dependent and greater coordination is evident at higher walking speeds.

“…In other challenging walking situations, such as forward walks on an inclined surface, a particular modification of common stepping patterns is revealed. In stick insects, the front legs become uncoupled from normal locomotion, showing multiple stepping, while the middle and hind leg coordination remains regular (Grabowska et al, 2012).…”

Section: Specializations Of Leg Pairsmentioning

confidence: 99%

“…It should be noted that this kind of classification represents idealized forms of coordination patterns, but walking insects produce also intermediate versions to avoid jerky movements (Grabowska et al, 2012). The different gait patterns described show a transition into each other, forming a continuum (Schilling et al, 2013;Wilson, 1966).…”

Section: Introductionmentioning

confidence: 96%

How to find home backwards? Locomotion and inter-leg coordination during rearward walking ofCataglyphis fortisdesert ants

Pfeffer

Wahl

Wittlinger

2016

For insects, flexibility in the performance of terrestrial locomotion is a vital part of facing the challenges of their often unpredictable environment. Arthropods such as scorpions and crustaceans can switch readily from forward to backward locomotion, but in insects this behaviour seems to be less common and, therefore, is only poorly understood. Here we present an example of spontaneous and persistent backward walking in Cataglyphis desert ants that allows us to investigate rearward locomotion within a natural context. When ants find a food item that is too large to be lifted up and to be carried in a normal forward-faced orientation, they will drag the load walking backwards to their home nest. A detailed examination of this behaviour reveals a surprising flexibility of the locomotor output. Compared with forward walks with regular tripod coordination, no main coordination pattern can be assigned to rearward walks. However, we often observed leg-pair-specific stepping patterns. The front legs frequently step with small stride lengths, while the middle and the hind legs are characterized by less numerous but larger strides. But still, these specializations show no rigidly fixed leg coupling, nor are they strictly embedded within a temporal context; therefore, they do not result in a repetitive coordination pattern. The individual legs act as separate units, most likely to better maintain stability during backward dragging.