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Stills from the videos used for data collection. From left to right, the striped field mouse (Apodemus agrarius), the yellow-necked mouse (Apodemus flavicollis), and the bank vole (Myodes glareolus). The images are on the same scale. In the stills, the animals are traversing a horizontal substrate of 10 mm diameter, and the distance between two vertical lines on the substrate is 1 cm.
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Vertical stratification of the arboreal habitat allows the coexistence of several species in a given area, because the complex arboreal strata can be used in different ways by arboreal and scansorial mammals. The present report experimentally investigated the gait metrics on different arboreal substrates, of three sympatric rodents living in a deci...
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... the purposes of the current study, we tested one wild-caught adult male and one wild-caught adult female of each of three sym- patric rodent species: Apodemus agrarius and Apodemus flavicollis (Murinae, Muridae, Rodentia), and Myodes glareolus (Arvicolinae, Cricetidae, Rodentia) ( Fig. 1). All individuals were trapped in a deciduous forest around Lake Moraskie, close to the Morasko cam- pus of the Adam Mickiewicz University (AMU) in Pozná n, during June 2013. The trapped individuals were subsequently transported to laboratory facilities at the School of Biology of AMU. The animals were housed for 20 days in glass ...
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... a single, specially con- figured, filming glass terrarium (L: 90 cm × H: 40 cm × W: 40 cm), topped by a wooden cover. Inside the terrarium, we used poles of 80 cm long, composed of cylindrical semi-hardwood rods, which were supported by wooden frames on each end. All poles were marked with vertical blue lines every 1 cm for scaling purposes ( Fig. 1). During the recordings, the visible length of the rod was 30-40 cm. Diameter and direction of movement accounted for the classification of the different substrate categories. Thus, we con- sidered four different diameters (2 mm, 5 mm, 10 mm, 25 mm) and three different movement directions (45 • descent, horizontal, 45 • ascent) ...
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... < 0.001; M. glareolus, N = 54, F (2,53) = 12.93, p < 0.001, controlling for gait type and substrate orientation). Stride frequency tended to increase with substrate size in A. agrarius (N = 93, F (2,92) = 8.13, p = 0.001) and A. flavicollis (N = 123, F (3,122) = 17.42, p < 0.001), but not in M. glareolus (N = 54, F (2,53) = 2.76, p = 0.073). ...
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... found no significant covariance between stride length and direction of movement ( Fig. 5; A. agrarius, F (1,92) = 2.18, p = 0.143; A. flavicollis, N = 123, F (2,122) = 2.57, p = 0.081; M. glareolus, N = 54, F (1,53) = 3.73, p = 0.059; controlling for gait type and sub- strate size). Controlling for gait type and substrate size, A. agrarius and M. glareolus used higher stride frequencies in descents than in horizontal locomotion (N = 93, F (1,92) = 5.99, p = 0.003; and N = 54, Fig. 5. Boxplots of the distribution of dimensionless velocity (top), dimensionless stride length (middle) and dimensionless stride frequency (bottom) in the substrate size categories examined, split into three graphs for each direction of movement. The top and bottom sides of the box denote the upper and lower quartiles, the line within the box is the median, while the top and bottom whiskers represent the maximum and minimum values obtained. ...
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... 1. On arboreal substrates, speed will be lower, stance phase will be longer, and gait patterns that maximize the portion of the stride where the limbs are positioned as a wide polygon of support will be preferred 2. Velocity will be regulated by stride frequency on terrestrial substrates and by stride length on arboreal supports 3. Humeral and femoral protraction and excursion will increase as substrate size decreases 4. Wrist and ankle excursion will be smaller than in true arboreal chameleons, regardless of substrate As has been found in previous studies from a host of tetrapods moving on arboreal substrates (Delciellos & Vieira, 2007;Granatosky et al., 2021;Hanna et al., 2022;Karantanis et al., 2017aKarantanis et al., , 2017b, we anticipate that Brookesia will move more slowly with significantly longer stance phases on arboreal substrates to maximize stability (Hypothesis 1). They will adopt gait patterns that maximize the portion of the stride where the limbs are positioned as a wide polygon of support on thin substrates, such as lateral-sequence diagonal couplet (LSDC) gaits (Cartmill et al., 2002(Cartmill et al., , 2020Wimberly et al., 2021). ...
... Source: Table 1 adapted from Hanna et al. (2022) and functional hypotheses derived from Schmidt and Fischer (2010), Karantanis et al. (2015Karantanis et al. ( , 2017a2017b), Granatosky et al. (2019Granatosky et al. ( , 2021, Granatosky and McElroy (2022), and Hanna et al. (2022). ...
... Differentiating these strategies is difficult and requires experiments in more a more naturalistic environment. Similar to other small animals such as rodents and marsupials (Granatosky & McElroy, 2022;Granatosky et al., 2021;Karantanis et al., 2015Karantanis et al., , 2017aKarantanis et al., , 2017b, speed in Brookesia is mainly driven by stride frequency rather than stride length. In contrast, larger arboreal animals, including lorises, which resemble chameleons in using slow arboreal quadrupedalism, often use stride length to regulate speed (Demes et al., 1990;Granatosky & McElroy, 2022). ...
Understanding the locomotor characteristics of early diverging ground-walking chameleons (members of the genera Brookesia, Rhampholeon, Palleon, and Rieppeleon) can help to explain how their unique morphology is adapted to fit their environment and mode of life. However, nearly all quantitative studies of chameleon locomotion thus far have focused on the larger “true arboreal” chameleons. We investigated kinematics and spatiotemporal gait characteristics of the Brown Leaf Chameleon (Brookesia superciliaris) on different substrates and compared them with true arboreal chameleons, nonchameleon lizards, and other small arboreal animals. Brookesia exhibits a combination of locomotor traits, some of which are traditionally arboreal, others more terrestrial, and a few that are very unusual. Like other chameleons, Brookesia moved more slowly on narrow dowels than on broad planks (simulating arboreal and terrestrial substrates, respectively), and its speed was primarily regulated by stride frequency rather than stride length. While Brookesia exhibits the traditionally arboreal trait of a high degree of humeral protraction at the beginning of stance, unlike most arboreal tetrapods, it uses smaller shoulder and hip excursions on narrower substrates, possibly reflecting its more terrestrial habits. When moving at very slow speeds, Brookesia often adopts an unusual footfall pattern, lateral-sequence lateral-couplets. Because Brookesia is a member of one of the earliest-diverging groups of chameleons, its locomotion may provide a good model for an intermediate stage in the evolution of arboreal chameleons. Thus, the transition to a fully arboreal way of life in “true arboreal” chameleons may have involved changes in spatiotemporal and kinematic characteristics as well as morphology.
... Increased speed also increases the probability of improper limb placements and other locomotor "accidents" (Wheatley et al., 2015;Wynn et al., 2015;Amir Abdul Nasir et al., 2017). Accordingly, performance testing across a range of tetrapods (including anurans, squamates, marsupials, rodents, carnivores, and primates), has shown average speed is directly correlated with support diameter, such that the fastest speeds are observed on flat supports and speed progressively decreases with decreases in support size on cylindrical perches (Losos & Sinervo, 1989;Sinervo & Losos, 1991;Lammers & Biknevicius, 2004;Renous et al., 2010;Gálvez-López et al., 2011;Herrel et al., 2013a;Shapiro et al., 2014;Karantanis et al., 2015Karantanis et al., , 2017aClemente et al., 2019;Gaschk et al., 2019;Young & Chadwell, 2020;Granatosky et al., 2021;Wölfer et al., 2021). Although most of this research has been conducted in controlled laboratory environments, similar reductions in speed with decreasing support diameters have also been observed in field-based studies of Anolis lizards, tree squirrels, and primates (Mattingly & Jayne, 2004;Dunham et al., 2019bDunham et al., , 2020. ...
... Several studies have indicated increased use of compliant gait kinematics on narrow supports in a wide variety of animals. For instance, studies of animals as diverse as lizards, rodents, marsupials, and primates broadly reveal that there is an inverse correlation between mean duty factor and support size, even after controlling for variation in speed (which is important, given the broadly negative correlation between speed and duty factor) (Lemelin & Cartmill, 2010;Schmidt & Fischer, 2010;Shapiro & Young, 2010, 2012Foster & Higham, 2012;Shapiro et al., 2014Shapiro et al., , 2016bKarantanis et al., 2015Karantanis et al., , 2017aYoung et al., 2016;Clemente et al., 2019;Dunham et al., 2019bDunham et al., , 2020Gaschk et al., 2019;Young & Chadwell, 2020;Wölfer et al., 2021). Typically, increases in duty factor are accompanied by changes in gait selection, shifting from footfall patterns characterized by simultaneous footfalls (i.e., symmetrical trots and asymmetrical bounds/ half-bounds) to gaits with more distributed contacts (i.e., symmetrical walks or ambles and asymmetrical canters and gallops) (Young, 2009;Gálvez-López et al., 2011;Shapiro et al., 2016b;Young et al., 2016;Dunham et al., 2019bDunham et al., , 2020Wölfer et al., 2021). ...
Arboreal supports impose a set of locomotor challenges not typically encountered in other terrestrial ecosystems. Because all arboreal animals must negotiate this common set of physical challenges in an environment where clumsy mistakes can lead to tragedy (or at least to the increased energetic burden of having to fight gravity to regain a lost position), it is of little surprise that we see widespread convergence of locomotor morphology and behavior among arboreal amphibians, lizards, and mammals. In this chapter I consider the biomechanical challenges imposed by moving on narrow and compliant arboreal supports, and survey existing data on how arboreal amphibians, lizards, and mammals have arrived at morphological and behavioral solutions to these problems. I focus on the biomechanical problems of negotiating narrow and compliant supports given that these challenges are, to some degree, uniquely characteristic of the arboreal environment. Narrow supports potentially compromise locomotor performance in two ways: (1) by increasing the probability that the animal may tangentially slip from the support and, (2) by challenging mediolateral (i.e., transverse/rolling plane) stability. Compliant supports, by contrast, have the potential to reduce locomotor performance by absorbing some of the mechanical energy that the animal could use to accelerate and redirect its center of mass, and then unpredictably returning this energy at random times and in random directions (at least with respect to the animal’s desired movement dynamics). Widespread morphological solutions to the biomechanical problems of moving on narrow and compliant supports include small body size, appendicular joints with enhanced mobility, grasping extremities, and long tails. Convergent behavioral solutions for increasing stability on precarious arboreal supports include reducing speed, increased limb joint flexion, the use of “compliant” gait kinematics marked by elongated limb contact durations (i.e., duty factors), a switch to gaits that facilitate more continuous contact with the substrate (and fewer ballistic aerial phases), and a decrease overall limb stiffness typically accomplished via exaggerated limb joint excursions during the stance phase. Future research on arboreal locomotion in tetrapods should focus on integrating quantitative laboratory data on locomotor kinematics and kinetics with holistic ecological data on substrate use and support morphology gleaned in the field. Such integrated datasets will be critical for furthering our understanding of how locomotor anatomy and behavior are shaped by the rigors of the natural arboreal environment.
... Most animal species use a characteristic primary mode of locomotion for the majority of their daily activities, but several species were shown to be capable of expanding their locomotion mode in order to access atypical habitats or substrates, such as some European terrestrial rodents when climbing vegetation [31]. Even if rarely used, this ability to adjust the movement type to access otherwise inaccessible areas may confer those individuals important or even critical advantages in particular situations such as during dispersal, when facing stressful To aid data visualisation, we have excluded four datapoints for PRF height greater than or equal to 13.5m (3 for woodlice and 1 for snails). ...
Terrestrial anurans, with their typically short limbs, heavy-set bodies and absent claws or toe pads are incongruous tree climbers, but even occasional arboreal locomotion could offer substantial advantages for evading predators or accessing new shelter or food resources. Despite recent interest, arboreal behaviour remains rarely and unsystematically described for terrestrial amphibians in Europe, likely due to fundamental differences in survey methods and therefore a lack of field data. However, other taxa surveys specifically target trees and tree cavities. We undertook collaborations and large-scale data searches with two major citizen science projects surveying for arboreal mammals in Britain to investigate potential tree climbing by amphibians at a national scale. Remarkably, we found widespread arboreal usage by amphibians in England and Wales, with occupancy of hazel dormouse (Muscardinus avellenarius) nest boxes, tree cavities investigated as potential bat roosts and even a bird nest, by common toads (Bufo bufo), but few additional records of frogs or newts. Of the 277-400 sites surveyed annually for dormice since 2009 at least 18 sites had amphibians recorded in nest boxes while of the 1388 trees surveyed for bats a total 1.4% (19 trees) had toads present. Common toads were found using cavities in seven tree species and especially goat willow (Salix caprea). Toads are potentially attracted to tree cavities and arboreal nests because they provide safe and damp microenvironments which can support an abundance of invertebrate prey but the importance of such tree microhabitats for toad conservation remains unknown and our results should be interpreted cautiously. We encourage expanding and linking of unrelated biodiversity monitoring surveys and citizen science initiatives as valuable tools for investigating ecological traits and interactions.
... Evenly spaced markers on the runways were used to calibrate videos. As many spatiotemporal gait characteristics are size-dependent, we followed Karantanis et al., 2015Karantanis et al., , 2017aKarantanis et al., , 2017bKarantanis et al., , 2017cKarantanis et al., , 2017d and used effective hindlimb length to derive dimensionless variables (see Table 1). Effective hindlimb length was collected at mid-stance and corresponds to the distance between the hip joint and the substrate, parallel to the axis of gravity. ...
... As stated in prediction (3), the northern treeshrews in this study demonstrated considerable variation in gait type. Consistent with other non-primate small-bodied mammals, asymmetrical gaits were most common on large-diameter substrates at high speeds Karantanis et al., 2017aKarantanis et al., , 2017b. On largediameter substrates, where balance is no longer a biomechanical concern, switching to asymmetrical gaits confers a reduction in intercycle variability (Diedrich & Warren, 1995;Granatosky et al., 2018) and energetic expenditure (Hoyt & Taylor, 1981;Reilly et al., 2007). ...
... Recent work on a host of arboreal mammals Karantanis et al., 2017aKarantanis et al., , 2017bShapiro & Young, 2010) highlight that primate-like gait characteristics are not necessary for effective movement in the trees. Our hope is that the data provided on northern treeshrews adds to the growing body of literature on this subject and helps spark new investigations on the mechanical necessities of arboreal movement. ...
The locomotor behaviors of treeshrews are often reported as scurrying "squirrel-like" movements. As such, treeshrews have received little attention beyond passing remarks in regard to primate locomotor evolution. However, scandentians vary considerably in habitat and substrate use, thus categorizing all treeshrew locomotion based on data collected from a single species is inappropriate. This study presents data on gait characteristics, positional, and grasping behavior of the northern treeshrew (Tupaia belangeri) and compares these findings to the fat-tailed dwarf lemur (Cheirogaleus medius) to assess the role of treeshrews as a model for understanding the origins of primate locomotor and grasping evolution. We found that northern treeshrews were primarily arboreal and shared their activities between quadrupedalism, climbing and leaping in rates similar to fat-tailed dwarf lemurs. During quadrupedal locomotion, they exhibited a mixture of gait characteristics consistent with primates and other small-bodied non-primate mammals and demonstrated a hallucal grasping mode consistent with primates. These data reveal that northern treeshrews show a mosaic of primitive mammalian locomotor characteristics paired with derived primate features. Further, this study raises the possibility that many of the locomotor and grasping characteristics considered to be "uniquely" primate may ultimately be features consistent with Euarchonta.
... The outstandingly large IMMA optimum at the extension angle of 40°(1.5 times larger than that of the terrestrial species) suggests an importance of powerful torques at early stance. This coincides with the fact that scansorial species typically exploit symmetrical gaits with small extension angles during early stance (e.g., Biknevicious et al., 2013;Hesse et al., 2015;Karantanis et al., 2017). Additionally, independent of gait, it might compromise the crouched posture that is usually utilized during climbing on narrow substrates to bring the center of mass closer to the substrate and thus avoid large fatal toppling moment (Nakano, 2002;Schmidt and Fischer, 2011). ...
Vertebrate musculoskeletal locomotion is realized through lever-arm systems. The instantaneous muscle moment arm (IMMA), which is expected to be under selective pressure and thus of interest for ecomorphological studies, is a key aspect of these systems. The IMMA changes with joint motion. It’s length change is technically difficult to acquire and has not been compared in a larger phylogenetic ecomorphological framework, yet. Usually, proxies such as osteological in-levers are used instead. We used 18 species of the ecologically diverse clade of caviomorph rodents to test whether its diversity is reflected in the IMMA of the hip extensor M. gluteus medius. A large IMMA is beneficial for torque generation; a small IMMA facilitates fast joint excursion. We expected large IMMAs in scansorial species, small IMMAs in fossorial species, and somewhat intermediate IMMAs in cursorial species, depending on the relative importance of acceleration and joint angular velocity. We modeled the IMMA over the entire range of possible hip extensions and applied macroevolutionary model comparison to selected joint poses. We also obtained the osteological in-lever of the M. gluteus medius to compare it to the IMMA. At little hip extension, the IMMA was largest on average in scansorial species, while the other two lifestyles were similar. We interpret this as an emphasized need for increased hip joint torque when climbing on inclines, especially in a crouched posture. Cursorial species might benefit from fast joint excursion, but their similarity with the fossorial species is difficult to interpret and could hint at ecological similarities. At larger extension angles, cursorial species displayed the second-largest IMMAs after scansorial species. The larger IMMA optimum results in powerful hip extension which coincides with forward acceleration at late stance beneficial for climbing, jumping, and escaping predators. This might be less relevant for a fossorial lifestyle. The results of the in-lever only matched the IMMA results of larger hip extension angles, suggesting that the modeling of the IMMA provides more nuanced insights into adaptations of musculoskeletal lever-arm systems than this osteological proxy.
... While the 'uniqueness' of primate gait characteristics has been noted in a number of studies (Larson et al., 2000(Larson et al., , 2001Schmitt, 1999), it seems that the strategy for increasing speed primarily through stride length should extend to other arboreal species. The results have been equivocal, and studies of arboreal gait mechanics across a number of primate and non-primate species reveal the reliance on stride length to increase speed may not be ubiquitous (Clemente et al., 2013;Granatosky et al., 2019bGranatosky et al., , 2021Karantanis et al., 2017). ...
... With these considerations in mind, we explored the interrelationships between stride length, stride frequency and locomotor speed across a broad phylogenetic sample of tetrapods. We used this sample to assess whether patterns of these three variables are primarily driven by mechanical (Heglund and Taylor, 1988;Reilly et al., 2007;Strang and Steudel, 1990), allometric (Reilly et al., 2007), phylogenetic (Buchwitz et al., 2021;Larson et al., 2001) or ecological factors (Granatosky et al., 2019b;Karantanis et al., 2017;Nyakatura et al., 2008). ...
... The resulting R 2 ratio was then log-transformed such that species with a negative R 2 ratio primarily regulated speed via stride length and any species with a positive R 2 ratio primarily regulated speed via stride frequency. Increased velocity during locomotion can be achieved by: increasing primarily stride frequency and, at a lesser rate, stride length (a positive R 2 ratio; Granatosky et al., 2021;Karantanis et al., 2017;Nyakatura et al., 2008;Pfau et al., 2011); by increasing primarily stride length and, at a lesser rate, stride frequency (a negative R 2 ratio; Granatosky et al., 2019b;Strang and Steudel, 1990); or by increasing stride frequency and stride length simultaneously (and R 2 ratio equal to 0). It should be noted that, although an animal may consistently modulate either stride frequency (a positive R 2 ratio) or stride length (a negative R 2 ratio) to influence speed, this does not necessarily imply that consistent modulation results in the greatest effect on speed. ...
Speed regulation in animals involves stride frequency and stride length. While the relationship between these variables has been well documented, it remains unresolved whether animals primarily modify stride frequency or stride length to increase speed. In this study, we explored the interrelationships between these three variables across a sample of 103 tetrapods and assessed whether speed regulation strategy is influenced by mechanical, allometric, phylogenetic or ecological factors. We observed that crouched terrestrial species tend to regulate speed through stride frequency. Such a strategy is energetically costly, but results in greater locomotor maneuverability and greater stability. In contrast, regulating speed through stride length is closely tied to larger arboreal animals with relatively extended limbs. Such movements reduce substrate oscillations on thin arboreal supports and/or helps to reduce swing phase costs. The slope of speed on frequency is lower in small crouched animals than in large-bodied erect species. As a result, substantially more rapid limb movements are matched with only small speed increases in crouched, small-bodied animals. Furthermore, the slope of speed on stride length was inversely proportional to body mass. As such, small changes in stride length can result in relatively rapid speed increases for small-bodied species. These results are somewhat counterintuitive, in that larger species, which have longer limbs and take longer strides, do not appear to gain as much speed increase out of lengthening their stride. Conversely, smaller species that cycle their limbs rapidly do not gain as much speed out of increasing stride frequency as do larger species.
... Studies of animals as diverse as lizards, rodents, marsupials, and primates have broadly shown an inverse correlation between duty factor and support size, such that animals increase duty factor as support diameters become more narrow-even after controlling for variation in speed (Chadwell & Young, 2015;Clemente et al., 2019;Dunham et al., 2019Dunham et al., , 2020Foster & Higham, 2012;Gaschk et al., 2019;Karantanis et al., 2017aKarantanis et al., , 2017bKarantanis et al., , 2017cKarantanis et al., , 2017dKarantanis et al., , 2015Lemelin & Cartmill, 2010;A. Schmidt & Fischer, 2010;Shapiro et al., 2016Shapiro et al., , 2014Shapiro & Young, 2010Wölfer et al., 2021;Young & Chadwell, 2020;Young et al., 2016). ...
Arboreal environments require overcoming navigational challenges not typically encountered in other terrestrial habitats. Supports are unevenly distributed and vary in diameter, orientation, and compliance. To better understand the strategies that arboreal animals use to maintain stability in this environment, laboratory researchers must endeavor to mimic those conditions. Here, we evaluate how squirrel monkeys (Saimiri boliviensis) adjust their locomotor mechanics in response to variation in support diameter and compliance. We used high-speed cameras to film two juvenile female monkeys as they walked across poles of varying diameters (5, 2.5, and 1.25 cm). Poles were mounted on either a stiff wooden base ("stable" condition) or foam blocks ("compliant" condition). Six force transducers embedded within the pole trackway recorded substrate reaction forces during locomotion. We predicted that squirrel monkeys would walk more slowly on narrow and compliant supports and adopt more "compliant" gait mechanics, increasing stride lengths, duty factors, and an average number of limbs gripping the support, while the decreasing center of mass height, stride frequencies, and peak forces. We observed few significant adjustments to squirrel monkey locomotor kinematics in response to changes in either support diameter or compliance, and the changes we did observe were often tempered by interactions with locomotor speed. These results differ from a similar study of common marmosets (i.e., Callithrix jacchus, with relatively poor grasping abilities), where variation in diameter and compliance substantially impacted gait kinematics. Squirrel monkeys' strong grasping apparatus, long and mobile tails, and other adaptations for arboreal travel likely facilitate robust locomotor performance despite substrate precarity.
... This is well known for the European bank vole (Myodes glareolus Schreber 1780), which has repeatedly been caught in traps set on trees (Holisova, 1969;Montgomery, 1980;Tattersall and Whitbread, 1994;Buesching et al., 2008;Bobretsov et al., 2019) and has been found in artificial nests and nests of birds (Formozov, 1948;Juškaitis, 1999). In a number of works, the ability of this species to climb was investigated experimentally (Trebatická et al., 2008;Karantanis et al., 2017). The ability to climb is also known for other representatives of this genus, for example, Gupper voles (M. ...
... In Europe, comparative studies have shown that forest (Apodemus uralensis Pallas 1811) and, especially, yellow-throated mice (A. flavicollis Melchior 1834) use trees more often (Holisova, 1969;Montgomery, 1980;Buesching et al., 2008) and are better adapted to climbing (Karantanis et al., 2017). In North America, the white-footed hamster (Peromyscus leucopus Rafinesque 1818) (Getz and Ginsberg, 1968) climbs trees. ...
... It has been argued that, in addition to the variability resulting from genetic variation, the ability to produce innovations, whether functional, behavioral or by modifying other phenotypic traits, might be an important source of variation on which selection can operate. Although, in general, animals have a characteristic primary locomotor mode, which is performed during their current activities, it is known that several species may be able to move in more than one way through habitats or substrates that are not the usual ones (Karantanis et al., 2017). Whereas there are many anecdotal reports on this issue the ability to move through non-typical habitats has been scarcely assessed in the scientific literature (Dagg & Windsor, 1972;Hyams et al., 2012;Pizzatto et al., 2017). ...
Several studies of arboreal anuran species show morphological specializations for clinging onto narrow substrates. However, little is known about these capacities in non-specialized anurans, which is crucial to understand the initial phases of adaptation to a new niche. To assess the functional requirements related to the evolution of arboreality in anurans we analyzed climbing performance, and correlated anatomical traits, in the terrestrial toad Rhinella arenarum, a species choose as a proxy for the ancestral condition regarding the evolution of this specialized niche. We studied the impact of a substrate of wooden rods with different diameters, arrangements, and slopes on locomotion, grasping, and climbing with a comparative framework. Animals were confronted with climbing tests, video recording their behaviors. Preserved specimens were dissected to assess limb myology, osteology, and tendons’ characteristics. Our results show that how terrestrial toad R. arenarum climbs is different from those displayed by specialized tree
frogs. Animals flexed their fingers and toes, grasping the substrate displaying hookings and partial graspings. The palm was scarcely involved in the grip, as in specialized anurans. These actions were performed although flexor and extensor muscles of the digits are highly conserved and generalized. Further, we formally assess the evolutionary history of ecological and anatomical traits related to climbing among Rhinella species to improving the comprehension of the relation between morphofunctional patterns and behavioral climbing skills. Our experiments revealed that this terrestrial toad possesses
unexpected climbing capacities, suggesting a way in which evolution of new niches could have developed in the evolution of anurans.
... The retention of asymmetrical gaits on the pole is also likely to be determined by the relation between body size and substrate size as found in other rodents (e.g., Karantanis et al., 2017a,b). A narrower pole diameter somewhere below 13 mm might have forced the squirrels in our study to switch to symmetrical gaits as observed for species used in these two studies by Karantanis et al. (2017c). Nevertheless, narrower substrates come with increased compliance, a confounding factor when comparing pole to trackway that was not of interest in this study. ...
... But strikingly, all available data for such potential modern analogs documents ubiquitous occurrence of asymmetrical gaits. This includes the small scandentian Dendrogale murina (Youlatos et al., 2017), the small primate Microcebus murinus (Shapiro et al., 2016;Herbin et al., 2018), and small arboreal rodents such as Apodemus flavicollis (Karantanis et al., 2017c) and Tamiops swinhoei (our study). The lagomorphs are usually larger and only nonarboreal pikas can be smaller than 100 g. ...
Differences between arboreal and terrestrial supports likely pose less contrasting functional demands on the locomotor system at a small body size. For arboreal mammals of small body size, asymmetrical gaits have been demonstrated to be advantageous to increase dynamic stability. Many of the extant arboreal squirrel-related rodents display a small body size, claws on all digits, and limited prehensility, a combination that was proposed to have characterized the earliest Euarchontoglires. Thus, motion analysis of such a modern analog could shed light onto the early locomotor evolution of eurarchontoglirans. In this study, we investigated how Swinhoe’s striped squirrels (Tamiops swinhoei; Scuiromorpha) adjust their locomotion when faced with different orientations on broad supports and simulated small branches. We simultaneously recorded high-Hz videos (501 trials) and support reaction forces (451 trials) of squirrels running on two types of instrumented trackways installed at either a 45° incline (we recorded locomotion on inclines and declines) or with a horizontal orientation. The striped squirrels almost exclusively used asymmetrical gaits with a preference for full bounds. Locomotion on simulated branches did not differ substantially from locomotion on the flat trackway. We interpreted several of the quantified adjustments on declines and inclines (in comparison to horizontal supports) as mechanisms to increase stability (e.g., by minimizing toppling moments) and as adjustments to the differential loading of fore- and hind limbs on inclined supports. Our data, in addition to published comparative data and similarities to the locomotion of other small arboreal rodents, tree shrews, and primates as well as a likely small body size at the crown-group node of Euarchontoglires, render a preference for asymmetrical gaits in early members of the clade plausible. This contributes to our understanding of the ancestral lifestyle of this mammalian ‘superclade’.
