Effects of substrate and phylogeny on quadrupedal gait in free‐ranging platyrrhines

Abstract

Objectives: Primate diagonal sequence (DS) gaits are often argued to be an adaptation for moving and foraging in the fine-branch niche; however, existing data have come predominantly from laboratory studies that are limited in taxonomic breadth and fail to account for the structural and ecological variation of natural substrates.We test the extent to which substrate diameter and orientation influence gait sequence type and limb phase in free-ranging primates, as well as how phylogenetic relatedness might condition response patterns. Materials and methods:We filmed quadrupedal locomotion in 11 platyrrhine species at field sites in Ecuador and Costa Rica and measured the diameter and orientation of locomotor substrates using remote sensors. We quantified limb phase values and classified strides by gait sequence type (N = 988 strides). Results:Our results show that most of the species in our sample consistently used DS gaits, regardless of substrate diameter or orientation; however, all taxa also used asymmetrical and/or lateral sequence gaits. By incorporating phylogenetic eigenvectors into our models, we found significant differences in gait sequence patterns and limb phase values among the major platyrrhine clades, suggesting that phylogeny may be a better predictor of gait than substrate diameter or orientation.Discussion: Our field data generally corroborate locomotor patterns from laboratory studies but capture additional aspects of gait variability and flexibility in response to the complexity of natural environments. Overall, our results suggest that DS gaits are not exclusively tailored to narrow or oblique substrates but are used on arboreal substrates in general. K E Y W O R D Sarboreal quadrupedalism, locomotion, phylogenetic eigenvector, platyrrhine

Asymmetrical gait kinematics of free-ranging callitrichines in response to changes in substrate diameter and orientation

“…The increased affordability and durability of high-speed cameras and remote sensors now allow researchers to record animals moving in their natural habitats, which ultimately provides more relevant tests of locomotor adaptation (Dunham et al, 2018(Dunham et al, , 2019aMcNamara et al, 2019). Even though the small body sizes characteristic of callitrichines are the result of phyletic dwarfism rather than a retention of a primitive ancestral state (Montgomery and Mundy, 2013), extant callitrichines represent valuable biomechanical analogs for early stages of primate evolution because of their small body size and reduced grasping ability (Nyakatura, 2019).…”

“…values ranging from −1 to 1) to test for substrate angles ranging from −90 to 90 deg, thus differentiating declines versus inclines, and (2) cosine of substrate orientation angle (i.e. values ranging from 0 to 1 and back to 0) for substrate angles ranging from −90 deg to 0 deg to 90 deg, thus differentiating oblique supports from horizontal supports, but ignoring the distinction between declines and inclines (Dunham et al, 2019a). Though the resulting transformations of substrate angles were not normally distributed themselves, residual error was normally distributed (in all but two of our models), a condition necessary to satisfy the assumptions of linear mixed-effects regression (Harrison et al, 2018).…”

“…right (R) or left (L) hindlimb (H) touchdown is followed by a contralateral forelimb (F) touchdown; e.g. LH, RF, RH, LF] and their potential adaptive significance in primates (Cartmill et al, 2007a,b;Dunham et al, 2019a;Granatosky et al, 2019;Hildebrand, 1967;Raichlen, 2005, 2007;Stevens, 2008;Usherwood and Smith, 2018;Wallace and Demes, 2008).…”

“…As part of our previous research on the gait kinematics of 11 species of free-ranging platyrrhines, we observed that goldenmantled tamarins (Saguinus tripartitus) used primarily asymmetrical gaits and pygmy marmosets (Cebuella pygmaea) used exclusively asymmetrical gaits (Dunham et al, 2019a). These species were excluded from our initial statistical analyses because the study focused on symmetrical gait kinematics.…”

Diagonal‐couplet gaits on discontinuous supports in Japanese macaques and implications for the adaptive significance of the diagonal‐sequence, diagonal‐couplet gait of primates

“…To extend our argument, we require extensive data on the gaits of other quadrupeds on discontinuous supports. By filming the gaits of 11 species of free‐ranging platyrrhine primates, Dunham et al (2019) investigated factors that affect gait selection, such as quadrupedal walking speed, substrate diameter and orientation, and phylogeny. They found that phylogeny had a more substantial impact on the footfall sequence than substrate diameter (lack of influence) and orientation (relatively weak influence) through their logistic regression analysis, which used the footfall sequence (LS or DS) as the response variable and the independent factors.…”