Vision does not impact walking performance in Argentine ants

AbstractMany walking insects use vision for long-distance navigation, but the influence of vision in detecting close-range obstacles and directing the limbs to maintain stability remains largely untested. We compared Argentine ant workers in light versus darkness while traversing flat and uneven terrain. In darkness, ants reduced flat-ground walking speeds by only 5%. Similarly, neither the approach speed nor the time to cross a step obstacle was affected by lighting. To determine if tactile sensing might compensate for vision loss, we tracked antennal motion and observed shifts in spatiotemporal activity due to terrain structure but not illumination. Together, these findings suggest that vision does not impact walking performance in Argentine ant workers. Our results help contextualize eye variation across ants, including subterranean, nocturnal, and eyeless species that walk in complete darkness. More broadly, our findings highlight the importance of integrating vision, proprioception, and tactile sensing for robust locomotion in unstructured environments.</jats:p

Rough substrates constrain walking speed in ants through modulation of stride frequency and not stride length

AbstractNatural terrain is rarely flat. Substrate irregularities challenge walking animals to maintain stability, yet we lack quantitative assessments of walking performance and limb kinematics on naturally rough ground. We measured how continually rough 3D-printed substrates influence walking performance of Argentine ants by measuring walking speeds of workers from lab colonies and by testing colony-wide substrate preference in field experiments. Tracking limb motion in over 8,000 videos, we used statistical models that associate walking speed with limb kinematic parameters to compare movement over flat versus rough ground. We found that rough substrates reduced preferred and peak walking speeds by up to 42% and that ants actively avoided rough terrain in the field. Observed speed reductions were modulated primarily by shifts in stride frequency and not stride length, a pattern consistent across flat and rough substrates. Modeling revealed that walking speeds on rough substrates were accurately predicted based on flat walking data for over 89% of strides. Those strides that were not well modeled primarily involved limb perturbations, including missteps, active foot repositioning, and slipping. Together these findings relate kinematic mechanisms underlying walking performance on rough terrain to ecologically-relevant measures under field conditions.</jats:p

Uneven substrates constrain walking speed in ants through modulation of stride frequency more than stride length

Natural terrain is rarely flat. Substrate irregularities challenge walking animals to maintain stability, yet we lack quantitative assessments of walking performance and limb kinematics on naturally uneven ground. We measured how continually uneven 3D-printed substrates influence walking performance of Argentine ants by measuring walking speeds of workers from laboratory colonies and by testing colony-wide substrate preference in field experiments. Tracking limb motion in over 8000 videos, we used statistical models that associate walking speed with limb kinematic parameters to compare movement over flat versus uneven ground of controlled dimensions. We found that uneven substrates reduced preferred and peak walking speeds by up to 42% and that ants actively avoided uneven terrain in the field. Observed speed reductions were modulated primarily by shifts in stride frequency instead of stride length (flatR2: 0.91 versus 0.50), a pattern consistent across flat and uneven substrates. Mixed effect modelling revealed that walking speeds on uneven substrates were accurately predicted based on flat walking data for over 89% of strides. Those strides that were not well modelled primarily involved limb perturbations, including missteps, active foot repositioning and slipping. Together these findings relate kinematic mechanisms underlying walking performance on uneven terrain to ecologically relevant measures under field conditions.</jats:p

SI Movie 2: Post-processing of limb tracking for an ant walking on a 3 mm substrate. from Uneven substrates constrain walking speed in ants through modulation of stride frequency more than stride length

Post-processing of limb tracking for an ant walking on a 3 mm substrate. (Left) Limb, antennal, and body landmarks generated from the deep-learning based tracker are projected onto a background-subtracted cropped view. A large white dot represents the approximate ant body location from the “Automated full-body tracking” workflow. The smaller dots represent LEAP tracked landmarks, with color representing the output confidence. (Center) Post-processed tracking of body (white), left tarsi (blue), and right tarsi (magenta) points. White circles represents a trusted touchdown. Trusted strides have a white line connecting the tarsus with its prior touchdown location. (Right above) The full recorded frame. (Right below) Time-varying total velocity of each tarsus. Dots represent trusted touchdowns

SI Movie 1: Wild ants walking over smooth or rough substrates to reach a food source. from Uneven substrates constrain walking speed in ants through modulation of stride frequency more than stride length

Wild ants walking over smooth or uneven substrates to reach a food source. (Left) Raw footage of the outdoor preference set-up with ants identified in red (1 mm bridge), green (3 mm bridge), and blue (5 mm bridge). (Center) Isolated regions of the bridges were background subtracted using the neighboring frames. Non-touching blobs were identified as ants. (Right) The number of ant-pixels identified on the flat or uneven substrate for each bridge

Supplementary methods, figures, and table from Uneven substrates constrain walking speed in ants through modulation of stride frequency more than stride length

This file includes 8 supplemental appendices on methods, 13 supplemental figures, one supplemental table, and the captions for two supplemental movies

A virtuous cycle between invertebrate and robotics research: perspective on a decade of Living Machines research

Many invertebrates are ideal model systems on which to base robot design principles due to their success in solving seemingly complex tasks across domains while possessing smaller nervous systems than vertebrates. Three areas are particularly relevant for robot designers: Research on flying and crawling invertebrates has inspired new materials and geometries from which robot bodies (their morphologies) can be constructed, enabling a new generation of softer, smaller, and lighter robots. Research on walking insects has informed the design of new systems for controlling robot bodies (their motion control) and adapting their motion to their environment without costly computational methods. And research combining wet and computational neuroscience with robotic validation methods has revealed the structure and function of core circuits in the insect brain responsible for the navigation and swarming capabilities (their mental faculties) displayed by foraging insects. The last decade has seen significant progress in the application of principles extracted from invertebrates, as well as the application of biomimetic robots to model and better understand how animals function. This Perspectives paper on the past 10 years of the Living Machines conference outlines some of the most exciting recent advances in each of these fields before outlining lessons gleaned and the outlook for the next decade of invertebrate robotic research