Running of the feathertail glider (Acrobates pygmaeus) on level ground: Gaits

Abstract

Gliding is a crucial adaptation to arboreal habitats in several groups of mammals.Along with certain advantages it imposes limitations on the quadrupedal running since it affects the locomotor apparatus. To estimate the impact on quadrupedal running in gliders, the feathertail glider (Acrobates pygmaeus) was chosen considering that the small size allows minor morphological modifications for aerial locomotion.The gaits were studied on horizontal flat substrate which made it possible to compare running technique of the glider with that of terrestrial mammals. In all analyzed plots the footfall sequence was found to be asymmetrical; in most cases the bound was used, in contrast, the gallop occurred only occasionally. The half-bound with the fore lead, the most usual asymmetrical gait in quadrupedal marsupials, was much less common in A. pygmaeus than the bound; the rare among mammals half-bound with the hind lead was also found. The bound was not only the most common gait but also the steadiest one; therefore we can conclude that A. pygmaeus uses all other asymmetrical gaits as transitional forms associated with changes in speed, direction, etc. The bound with extended suspension is probably preferred by A. pygmaeus because it most closely resembles gliding by posture. | INTRODUCTIONGliding is an efficient way of locomotion for inhabitants of the complex three-dimensional arboreal environment. It allows the cost of transport to be reduced compared to terrestrial locomotion (Alexander, 1982;Scholey, 1986) and besides, increases the chance to avoid predators (Byrnes & Spence, 2011;Emmons & Gentry, 1983). However, gliding entails a loss of altitude and the need to compensate for this by climbing tree trunks (Panyutina, 2020;Scholey, 1986). Thus, the quadrupedal performance (at least climbing) has a crucial influence on total energy expenditures for locomotion (Dial, 2003) and either promotes the survival and positive selection of relevant forms, or, conversely, leaves no chance to win in the evolutionary race.The proportions of the locomotor apparatus of gliding mammals differ from those of their nonaerial relatives (Essner, 2007;Peterka, 1936;Thorington & Heaney, 1981). There are no clear biomechanical explanations as to the negative impact of changes in the skeletal proportions and the locomotor muscles design in gliders on the efficiency of their quadrupedal running, whereas, direct energy measurements show the existence of such an impact.Gliders spend more energy on quadrupedal running than nongliders (Flaherty et al., 2010;Shaw, 2004). However, studies on this subject are still fragmentary, and little is known about how the acquisition of gliding affects running technique. Of interest is not only the structural modification of the locomotor apparatus in gliders, but also a degree of modification of their type of quadrupedal locomotion, in case it in fact differs.In this context, it is especially intriguing to study such alterations in the smallest gliders, in which the development of aerial locomotion can be achie...

Running of the feathertail glider (Acrobates pygmaeus) on level ground: Kinematics

“…It can be noted that specific gliding adaptations of Acrobates have affected the kinematics of the limbs during quadrupedal running to a much greater extent than they have influenced gaits (Makarov & Panyutina, 2022). The main specific feature of gaits of Acrobates on flat horizontal substrate is the predominance of the bound with extended suspension, which can be interpreted as a trace of the gliding posture in terrestrial locomotion.…”

“…In the true gallop, the delay in limb protraction results in a quite equal increase in the duration of both the extended and gathered suspension stages with increasing speed. In Acrobates, the first option is obviously observed-with a long stage of extended suspension, the gathered suspension is absent and appears only in the case of a significant shortening of the former (figure 3 in Makarov & Panyutina, 2022 ). Thus, it can be argued that asymmetrical gaits of Acrobates refer to the primitive ricochet category in terms of Gambaryan (1974).…”

“…We used video footage of three animals, for a detailed description of the experiment see Makarov and Panyutina (2022). We performed a kinematic analysis for 13 plots, including a total of 25 complete and 13 incomplete 1 strides for which video recording was obtained from two angles: from the side and from above.…”

“…In modern biota, the smallest glider among mammals is the feathertail glider. Previous studies of its quadrupedal locomotion have shown that this animal employs predominantly symmetrical gaits on thin supports (Karantanis et al, 2015; Youlatos et al, 2018), but exclusively asymmetrical gaits on a horizontal surface (Makarov & Panyutina, 2022). The prevalent asymmetrical gait on the ground was the bound with extended suspension.…”

“…In our study Acrobates used exclusively asymmetrical gaits, two thirds of strides were represented by bound (Makarov & Panyutina, 2022).…”