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Convergent evolution of slow arboreality in mammals The seven independent acquisitions of the slow arboreal lifestyle (red sections), reconstructed with Stochastic Character Mapping, are shown on the time-calibrated tree of the taxa for which morphological data were obtained (see Supplementary Fig. 1 for an extended version). Timescale unit: million years ago (Mya). See Supplementary Note 4 for credits and copyright licenses for slow arboreal mammal images used in the figure.
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Eco-morphological convergence, i.e., similar phenotypes evolved in ecologically convergent taxa, naturally reproduces a common-garden experiment since it allows researchers to keep ecological factors constant, studying intrinsic evolutionary drivers. The latter may result in differential evolvability that, among individual anatomical parts, causes...
Citations
... This type of digging involves a combination of humeral retraction, elbow extension, and extension of the claws, leading us to expect relevant bone developmental adaptation in the humerus and ulna of wild-caught P. polionotus (Martin et al., 2019). Previous work has examined how locomotor habits inform bone evolution, which is called phylogenetic or functional morphology (Alfieri et al., 2023). Locomotor habits also affect bone development within the lifetime of an individual, which is called ontogenetic adaptation or mechanoadaptation. ...
We compare the effects of burrowing behavior on appendicular bone structure in two Peromyscus (deer mouse) species. P. polionotus creates complex burrows in their territories, while P. eremicus is a non‐burrowing nesting mouse. We examined museum specimens' bones of wild‐caught mice of the two species and lab‐reared P. polionotus not given the opportunity to burrow. Bones were scanned using micro‐computed tomography, and cortical and trabecular bone structural properties were quantified. Wild P. polionotus mice had a larger moment of area in the ulnar and tibial cortical bone compared with their lab‐reared counterparts, suggesting developmental adaptation to bending resistance. Wild P. polionotus had a larger normalized second moment of area and cross‐sectional area in the tibia compared with P. eremicus. Tibial trabecular analysis showed lower trabecular thickness and spacing in wild P. polionotus than in P. eremicus and femoral analysis showed wild P. polionotus had lower thickness than P. eremicus and lower spacing than lab‐reared P. polionotus, suggesting adaptation to high loads from digging. Results lay the groundwork for future exploration of the ontogenetic and evolutionary basis of mechanoadaptation in Peromyscus.
The fibula, despite being traditionally overlooked compared to the femur and the tibia, has recently received attention in primate functional morphology due to its correlation with the degree of arboreality (DOA). Highlighting further fibular features that are associated with arboreal habits would be key to improving palaeobiological inferences in fossil specimens. Here we present the first investigation on the trabecular bone structure of the primate fibula, focusing on the distal epiphysis, across a vast array of species. We collected μCT data on the distal fibula for 21 species of primates, with representatives from most of the orders, and we employed a recently developed approach implemented in the R package ‘indianaBones’ to isolate the entire trabecular bone underlying an epiphysis or articular facet. After extracting both traditional trabecular parameters and novel topological indices, we tested for the posited relationship between trabecular bone and DOA. To disentangle this effect from others related to body size and phylogenetic relationship, we included a body mass proxy as covariate and employed phylogenetic comparative methods. We ran univariate/multivariate and exploratory/inferential statistical analyses. The trabecular structure of the fibular distal epiphysis in primates does not appear to be associated with the DOA. Instead, it is strongly affected by body mass and phylogenetic relationships. Although we identified some minor trends related to human bipedalism, our findings overall discourage, at this stage, the study of distal fibula trabecular bone to infer arboreal behaviors in extinct primates. We further found that body size distribution is strongly related to phylogeny, an issue preventing us from unravelling the influence of the two factors and that we believe can potentially affect future comparative analyses of primates. Overall, our results add to previous evidence of how trabecular traits show variable correlation with locomotor aspects, size and phylogenetic history across the primate skeleton, thus outlining a complex scenario in which a network of interconnected factors affects the morphological evolution of primates. This work may represent a starting point for future studies, for example, focusing on the effect of human bipedalism on distal fibula trabecular bone, or aiming to better understand the effects of body size and phylogenetic history on primate morphological evolution.
