DOI: 10.6075/j0rr1wm2
title: Uneven substrates constrain walking speed in ants through modulation of stride frequency more than stride length

description: 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
 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 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 (flat R2: 0.91 vs.
 0.50), a pattern consistent across flat and uneven substrates.
 Mixed-effect modeling 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 modeled 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.
description: All files are saved as .pickle and can be read into python using
 the pandas package and function pandas.read_pickle All
 distance variables are in pixels. 31.992 pixels per mm
 Data was tracked from videos filmed at 240 fps
   GENERAL INFO FOR EACH TRACKWAY
 'ID' - identifier for the ant (number of trackway found
 in given video)<br> 'colony' - date of the colony
 collected<br> 'date' - date of recording<br>
 'datetime' - date and time of recording<br>
 'substrate' - what substrate 0 = flat, 1/3/5 = checkerboards of
 mm dimension<br> 'time' - time of recording<br>
 'video' - full path of video associated with trackway
     FULL BODY TRACKING AND
 ASSOCIATING OUTPUT 'x_kal' - raw x-position
 output of body centroid from OpenCV contour fit, associated across frames
 using kalman filter<br> 'y_kal' - raw y-position output of
 body centroid from OpenCV contour fit, associated across frames using
 kalman filter<br> 'angle' - raw angle of body from OpenCV
 contour fit, associated across frames using kalman filter, +y axis = 0
 radians<br> 'frames' - frames associated with x_kal,
 y_kal, x_raw, y_raw, angle, and all LEAP output<br> 'area'
 - area of the tracked contour from OpenCV contour fit<br>
 'xy_cov_matrix' - output from kalman filter associating across
 frames<br> 'error' - norm of covariance output from kalman
 filter associating across frames<br> 'measurements' -
 xhat, P, and K measurements from kalman filter associating across
 frames<br> 'LA' - previous version of tracking left
 antennal tip, should be empty<br> 'RA' - previous version
 of tracking right antennal tip, should be empty
     POST-PROCESSING
 OUTPUT 'x_raw' - lowpass butterworth filtered
 x_kal<br> 'y_raw' - lowpass butterworth filtered
 y_kal<br> 'vfilt' - instantaneous speed of ant using
 x_raw, y_raw<br> 'vxfilt' - instantaneous speed of ant in
 x-axis using x_raw<br> 'vyfilt' - instantaneous speed of
 ant in y-axis using y_raw<br> 'movave_v' - moving average
 of vfilt across 24 frames = 0.1 s<br> 'movave_fr' - frames
 associated with movave_v<br> <br> 'dist_90fr' -
 moving calculation of distance traveled over 90 frames = 375 ms<br>
 'x' - removed x_raw data where ant is close to frame edge and
 when ant is stopped/moving slowly<br> 'y' - removed y_raw
 data where ant is close to frame edge and when ant is stopped/moving
 slowly<br> 'v' - instantaneous speed of ant using x,
 y<br> 'vx' - instantaneous speed of ant in x-axis using
 x<br> 'vy' - instantaneous speed of ant in y-axis using
 y<br> 'median_v' - median velocity of
 'v'<br> 'median_vx' - median velocity of
 'vx'<br> 'median_vy' - median velocity of
 'vy'<br> 'sinuosity' - sinuosity calculation of
 trackway using x, y<br> <br> 'angle_improved' - raw
 OpenCV contour angle output does not factor in facing. this uses antennae
 and comparisons across a tracked trailway to correct the angle to be the
 ant facing. it is then interpolated and smoothed<br>
 'frames_final' - frame number associated with x, y
     LEAP TRACKING
 OUTPUT  'thorax_conf' - body center
 confidence<br>  'thorax_x' - body center x
 position<br>  'thorax_y' - body center y
 position  'neck_conf' - neck
 confidence<br>  'neck_x' - neck x position<br>
  'neck_y' - neck y position
  'antenna0_conf' - left antenna confidence <br>
  'antenna0_x' - left antenna tip x-position<br>
  'antenna0_y' - left antenna tip y-position<br>
  'antenna1_conf' - right antenna confidence<br>
  'antenna1_x' - right antenna tip x-position<br>
  'antenna1_y' - right antenna tip y-position
  'joint0_conf' - left hindlimb<br>
  'joint0_x',<br>  'joint0_y',<br>
  'joint1_conf' - left midlimb<br>
  'joint1_x',<br>  'joint1_y',<br>
  'joint2_conf' - left forelimb<br>
  'joint2_x',<br>  'joint2_y',<br>
  'joint3_conf' - right hindlimb<br>
  'joint3_x',<br>  'joint3_y',<br>
  'joint4_conf' - right midlimb<br>
  'joint4_x',<br>  'joint4_y',<br>
  'joint5_conf' - right forelimb<br>
  'joint5_x',<br>  'joint5_y',