Transneuronal induction of muscle atrophy in grasshoppers

Limb Loss and Specialized Leg Dynamics in Tiny Water-Walking Insects

The air-water interface of the planet's water bodies, such as ponds, lakes, and streams, presents an uncertain ecological niche with predatory threats from above and below. As Microvelia americana move across the water surface in small ponds, they face potential injury from attacks by birds, fish, and underwater invertebrates. Thus, our study investigates the effects of losing individual or pairs of tarsi on M. americana's ability to walk on water. Removal of both hind tarsi causes M. americana to rock their bodies (yaw) while running across the water surface at $\pm 19^{\circ }$, compared to $\pm 7^{\circ }$ in nonablated specimens. This increase in yaw, resulting from the removal of hind tarsi, indicates that M. americana use their hind legs as "rudders" to regulate yaw, originating from the contralateral middle legs' strokes on the water's surface through an alternating tripod gait. Ablation of the ipsilateral middle and hind tarsi disrupts directionality, making M. americana turn in the direction of their intact limbs. This loss of directionality does not occur with the removal of contralateral middle and hind tarsi. However, M. americana lose their ability to use the alternating tripod gait to walk on water on the day of contralateral ablation. Remarkably, by the next day, M. americana adapt and regain the ability to walk on water using the alternating tripod gait. Our findings elucidate the specialized leg dynamics within the alternating tripod gait of M. americana, and their adaptability to tarsal loss. This research could guide the development and design strategies of small, adaptive, and resilient micro-robots that can adapt to controller malfunction or actuator damage for walking on water and terrestrial surfaces.

Limb loss and specialized leg dynamics in tiny water-walking insects

The air-water of the planet's water bodies, such as ponds, lakes and streams, presents an uncertain ecological niche with predatory threats from above and below. As Microvelia move across the water surface in small ponds, they face potential injury from attacks by birds, fish, and underwater invertebrates. Thus, our study investigates the effects of losing individual or pairs of tarsi on the Microvelia's ability to walk on water. Removal of both hind tarsi causes Microvelia spp. to rock their bodies (yaw) while running across the water surface at ±19°, compared to ±7° in non-ablated specimens. This increase in yaw, resulting from the removal of hind tarsi, indicates that Microvelia use their hind legs as 'rudders' to regulate yaw, originating from the contralateral middle legs' strokes on the water's surface through an alternating tripod gait. Ablation of the ipsilateral middle and hind tarsi disrupts directionality, making Microvelia turn in the direction of their intact limbs. This loss of directionality does not occur with the removal of contralateral middle and hind tarsi. However, Microvelia lose their ability to use the alternating tripod gait to walk for water walking on the day of contralateral ablation. Remarkably, by the next day Microvelia adapt and regain the ability to walk on water using the alternating tripod gait. Our findings elucidate the specialized leg dynamics within the alternating tripod gait of Microvelia spp., and their adaptability to tarsal loss. This research could guide the development and design strategies of small, adaptive, and resilient micro-robots that can adapt to controller malfunction or actuator damage for walking on water and terrestrial surfaces.

Ontogenetic effects on aerobic and anaerobic metabolism during jumping in the American locust, Schistocerca americana

Developing vertebrates increase both their locomotory power output and endurance due to ontogenetic improvements in anaerobic and aerobic metabolic capacities. Do similar patterns hold for insect locomotion, or do longer tracheal lengths create problems for oxygen delivery in older animals? We forced developing American locust grasshoppers (Schistocerca americana) to jump repeatedly and examined the effect of development on power output, endurance, lactate concentration, oxygen consumption and the oxygen sensitivity of jump performance. As previously shown, power outputs, relative leg lengths and leg cuticular content increased with age. A key finding of this study is that both lactate concentration and aerobic metabolic rate of the jumping muscle increase with age, explaining how the increased leg cuticular stiffness can result in increased power output. After two minutes of jumping, grasshoppers rely completely on aerobic ATP production. The rise in mass-specific, active aerobic metabolic rates with age indicates that problems with longer tracheae can be overcome; however, the reduced endurance, higher lactate concentrations and increased oxygen sensitivity of locomotory performance in older animals indicate that larger/older grasshoppers have smaller safety margins for oxygen delivery during hopping.

Control of muscle degeneration following autotomy of a hindleg in the grasshopper, Barytettix humphreysii

When the grasshopper, Barrytettix humphreysii, sheds a hindlimb during autotomy, certain thoracic muscles degenerate although they are neither directly damaged nor denervated. Muscle degeneration is induced when a leg nerve (N5) that does not innervate the thoracic muscles is severed. Together these results suggest that transneuronal mechanisms influence muscle survival. To further characterize this autotomy-induced process, we studied the degeneration of a thoracic tergotrochanteral muscle (M#133b,c) following autotomy or experimental manipulation in adult animals. Its degeneration is correlated with reduced activity of its neural input and occurs by programmed cell death (PCD). PCD onset is variable between individual muscle fibers, indicating that the trigger of degeneration is fiber specific. Muscle degeneration appears to be triggered by the loss of proprioceptive input from the autotomized limb, since severing of axons from proprioceptive organs, but not exteroceptive chemo- or mechanoreceptors, leads to muscle degeneration. Muscle disuse, neuronal degeneration, or changes in juvenile hormone titer do not appear to play a role in autotomy-induced degeneration. We propose that the loss of proprioceptive input from proximal campaniform sensilla on the tibia deafferents the thoracic muscle motor neurons and leads to a decrease in their activity. Muscle degeneration is ultimately triggered by the loss of normal neural activity.