The grasping capabilities and gait kinematics characteristic of primates are often argued to be adaptations for safely moving on small terminal branches. The goal of this study was to identify whether Eastern gray squirrels (
- Award ID(s):
- 1930744
- NSF-PAR ID:
- 10206550
- Date Published:
- Journal Name:
- Integrative and Comparative Biology
- Volume:
- 60
- Issue:
- 4
- ISSN:
- 1540-7063
- Page Range / eLocation ID:
- 829 to 839
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Sciurus carolinensis )—arboreal rodents that frequently move and forage on small branches, lack primate‐like grasping and gait patterns, and arguably represent extant analogs of a stem primate ancestor—adjust gait kinematics to narrow and nonhorizontal branches. We studied locomotor kinematics of free‐ranging and laboratory‐housed squirrels moving over various substrates. We used high‐speed video to film (a) a population of free‐ranging squirrels moving on natural substrates and (b) laboratory‐housed squirrels moving on horizontal poles. Substrates were coded as small, medium, or large relative to squirrel trunk diameter, and as inclined, declined, or horizontal. Free‐ranging squirrels used more gallops and half‐bounds on small‐ and medium‐sized substrates, and more high‐impact bounds, with reduced limb‐lead durations, on declined substrates. Laboratory squirrels moved at higher speeds than free‐ranging squirrels and responded to decreasing diameter by using more gallops and half‐bounds, lowering speed, and—controlling for speed—increasing mean duty factor, mean number of supporting limbs, and relative forelimb lead duration. Our inability to detect substantial diameter or orientation‐related gait adjustments in the wild may be due to a limited accounting of confounding influences (e.g., substrate compliance). Ultimately, studies assessing stability measures (e.g., center of mass fluctuations and peak vertical force) are required to assess whether primates' enhanced grasping and gait patterns engender performance advantages on narrow or oblique substrates. -
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Abstract Objectives Laboratory studies have yielded important insights into primate locomotor mechanics. Nevertheless, laboratory studies fail to capture the range of ecological and structural variation encountered by free‐ranging primates. We present techniques for collecting kinematic data on wild primates using consumer grade high‐speed cameras and demonstrate novel methods for quantifying metric variation in arboreal substrates.
Materials and methods These methods were developed and applied to our research examining platyrrhine substrate use and locomotion at the Tiputini Biodiversity Station, Ecuador. Modified GoPro cameras equipped with varifocal zoom lenses provided high‐resolution footage (1080 p.; 120 fps) suitable for digitizing gait events. We tested two methods for remotely measuring branch diameter: the parallel laser method and the distance meter photogrammetric method. A forestry‐grade laser rangefinder was used to quantify substrate angle and a force gauge was used to measure substrate compliance. We also introduce GaitKeeper, a graphical user interface for MATLAB, designed for coding quadrupedal gait.
Results Parallel laser and distance meter methods provided accurate estimations of substrate diameter (percent error: 3.1–4.5%). The laser rangefinder yielded accurate estimations of substrate orientation (mean error = 2.5°). Compliance values varied tremendously among substrates but were largely explained by substrate diameter, substrate length, and distance of measurement point from trunk. On average, larger primates used relatively small substrates and traveled higher in the canopy.
Discussion Ultimately, these methods will help researchers identify more precisely how primate gait kinematics respond to the complexity of arboreal habitats, furthering our understanding of the adaptive context in which primate quadrupedalism evolved.
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/icb/icaa078
