Effects of Substrate Size and Orientation on Quadrupedal Gait Kinematics in Mouse Lemurs (Microcebus murinus)

Abstract

As the smallest living primate, the mouse lemur is a suitable model for reconstructing the locomotor mechanisms by which primate ancestors might have responded to the challenges of an arboreal environment. In this study, we tested the effects of substrate diameter and orientation on quadrupedal gait kinematics in mouse lemurs (Microcebus murinus). Mouse lemurs highly preferred asymmetrical to symmetrical gaits as they moved across a flat board and poles of three diameters (2.5, 1.0, and 0.5 cm), set at horizontal, 30°inclined, and 30°declined orientations. During symmetrical gaits, mouse lemurs used diagonal sequence walking and ambling gaits on the same substrates and at the same duty factors for which some similarly sized nonprimate mammals use lateral sequence gaits, suggesting that reliance on diagonal sequence walking in primates may not be explicitly a response to body size relative to substrate diameter. When using asymmetrical gaits, kinematic adjustments to small diameter and/or nonhorizontal substrates included a preference for transverse gallops over other gaits, the avoidance of whole-body suspensions, increases in limb contact duration, and increases in the time interval between the landing of trailing and leading limbs. All of these adjustments are consistent with increasing locomotor stability by dampening center of mass movements and reducing the forces imparted to the substrate. Like mouse lemurs, small-bodied ancestral primates likely used symmetrical gaits occasionally, but more frequently used asymmetrical gaits that were adjusted in response to challenging substrates. Therefore, asymmetrical gait dynamics should be incorporated into hypotheses addressing early primate locomotor evolution.

Effects of support diameter and compliance on common marmoset (Callithrix jacchus) gait kinematics

“…Similar kinematic adjustments have been documented in studies of squirrels (Schmidt, 2011) and mouse lemurs (Shapiro et al, 2016) using asymmetrical gaits on flat versus narrow substrates, and several studies have found a general tendency to increase substrate contact duration on cylindrical supports (Schmitt, 1999;Lemelin and Cartmill, 2010;Schmidt and Fischer, 2010;Shapiro and Young, 2012;Shapiro et al, 2014;Karantanis et al, 2015;Hsieh, 2016). In contrast, differences in gait kinematics among variably sized cylindrical substrates are generally subtler (Schmitt, 2003a;Shapiro and Young, 2010;Hyams et al, 2012;Hsieh, 2016) -as was observed in the current study.…”

“…2). Studies of other small-bodied arboreal mammals, including red squirrels (Schmidt, 2011) and mouse lemurs (Shapiro et al, 2016), have also shown a decrease in bounding gaits, and a corresponding increase in gallops, associated with narrow-perch locomotion. In an analysis of high-speed locomotion in 12 arboreal primates, Schmitt and colleagues (2006) found that primates generally avoided whole-body aerial phases during fast travel, most frequently using 'ambles' (symmetrical running gaits in which at least one limb is always in contact with the substrate throughout the stride) or 'canters' (their term for galloping gaits that lack an aerial phase; see also Howell, 1944).…”

Arboreality in acacia rats (Thallomys paedulcus; Rodentia, Muridae): gaits and gait metrics

“…Ascents may be faster than horizontal locomotion, as in the agile European red squirrels, as they help achieve dynamic stability (Schmidt & Fischer, ), but can also be slower, as in the more generalized rats (Schmidt & Fischer, , ) and larger primates (Nakano, ). On the other hand, some smaller arboreal primates do not adjust velocity relative to their direction of movement (Nyakatura et al ., ; Shapiro et al ., ).…”

“…On the other hand, asymmetrical gaits allow reaching higher speeds of locomotion (Hildebrand, 1977;Pridmore, 1994;Gasc, 2001;Young, 2009;Shapiro, Kemp & Young, 2016), and may provide advantages over symmetrical gaits, such as a reduction in metabolic costs (Hoyt & Taylor, 1981). Moreover, although in general asymmetrical gaits produce higher reaction forces that those of symmetrical gaits, the transition from trotting (symmetrical) to galloping (asymmetrical) has been shown to reduce peak forces on the muscles, tendons and bones (Farley & Taylor, 1991).…”

“…In small mammals, asymmetrical gaits may also provide an energetic input to locomotion through the sagittal movements of their flexible spine and related muscles (Schilling & Hackert, 2006). In an arboreal setting, asymmetrical gaits also confer advantages in stability by reducing peak vertical forces, limiting centre of mass movements, and resulting in shorter and more frequent strides (Young, 2009;Schmidt & Fischer, 2010;Shapiro et al, 2016).…”