Vertical Locomotion in Micromys minutus (Rodentia: Muridae): Insights into the Evolution of Eutherian Climbing
Climbing is integral to scansorial and arboreal lifestyles as it enables access to and vertical ranging within the arboreal strata. As early eutherian mammals exhibit osteological correlates for arboreality, it is important to assess the behavioral mechanisms that are related to competent vertical climbing. In this context, we examined climbing gaits in one of the smallest extant rodents, the Eurasian harvest mouse. For these purposes, we filmed six adult Micromys minutus at 240 fps moving on four different substrate sizes (2 mm, 5 mm, 10 mm, 25 mm), during both vertical ascents and descents. All climbing cycles were lateral sequence slow gaits. Upward climbing was characterized by a higher contribution of the hind limbs, longer swing phases, and a significant involvement of stride frequency in velocity modulation. On the other hand, downward climbing was promoted by employing gaits of even lower diagonality, an increased contact with the substrate, enhanced role of the forelimbs, and a subtler modulation of velocity by stride frequency. Eurasian harvest mice effectively negotiate the finest substrates, but their effectiveness decreased significantly on the largest ones. The morphofunctional similarities of M. minutus to Juramaia sinensis and Eomaia scansoria imply analogous behaviors in early eutherians, which apparently contributed to the successful access and exploitation of the fine-branch arboreal milieu. In this way, extant small arboreal mammals can constitute good models for elucidating and comprehending the adaptive significance of behavioral mechanisms that are related to the evolution of arboreality in early mammals.
KeywordsGaits Eutherian evolution Arboreality Gait Small body size Rodent
All authors wish to express their gratitude to all the people who helped throughout this project: the staff of the Nowe Zoo of Poznan for granting permission and providing the specimens, as well as their invaluable help and patience throughout the experimental procedures, Peter Klimant for his extensive assistance in the experiments, and Doug Brown for essential modifications to the Tracker software that made data analysis possible. Two anonymous reviewers and the editor-in-chief, Dr. John Wible, provided feedback that greatly improved an earlier version of this manuscript. Financial support was provided through funds by the Erasmus studies scholarships to NEK, the School of Biology of the Aristotle University of Thessaloniki, and the Department of Systematic Zoology, Adam Mickiewicz University, Poznan.
Compliance with Ethical Standards
Conflict of Interest
The authors declare that they have no conflict of interest.
Research Involving Animals
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. The present research strictly adhered to the guidelines for the treatment of animals in behavioral research and teaching (ASAB/ABS 2012) and complied with relevant regulations and legislations of the Nowe Zoo and the Adam Mickiewicz University in Poznan and the relevant legislation of the Aristotle University of Thessaloniki. Handling, housing of animals and behavioral tests were carried out with permission by the Local Ethical Commission for the Animal Experiments in Poznan.
No human subjects participated in the experiments of this study.
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