The biomechanics of foraging determines face length among kangaroos and their relatives

Mitchell, D. Rex; Sherratt, Emma; Ledogar, Justin A.; Wroe, Stephen

doi:10.1098/rspb.2018.0845

Cited by 33 publications

(72 citation statements)

References 42 publications

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“…This posits that closely related mammals tend to have longer rostra and narrower zygomatic arches as they increase in size [49,50], in a pattern that closely resembles what we found in wombats without allometry. CREA was suggested for kangaroo crania [18], but contested in a slightly different sample and landmarking protocol of kangaroos [23,24]. Instead, the authors postulated that a CREA-like pattern is not allometric and instead purely due to biomechanics.…”

Section: Discussionmentioning

confidence: 99%

“…Suggestions of a constraint on marsupial skull shape through static allometry are at odds with several geometric morphometric studies that show only low or moderate levels of static allometry in marsupial crania [15,[20][21][22]. Two recent studies on kangaroos even suggested that allometry plays a lesser role in shaping cranial variation in this group, instead positing fast adaptation or individual developmental plasticity of the masticatory apparatus as the main driver [23,24]. This is consistent with suggestions that masticatory biomechanics may impact individual cranial shape to such a degree that developmental constraints either do not contribute much to within-species shape variation, or can be obscured by individual differences in mastication due to the bone's plastic response to mastication stresses [6,[25][26][27].…”

Section: Introductionmentioning

confidence: 98%

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Individual variation of the masticatory system dominates 3D skull shape in the herbivory-adapted marsupial wombats

et al. 2019

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Background: Within-species skull shape variation of marsupial mammals is widely considered low and strongly size-dependent (allometric), possibly due to developmental constraints arising from the altricial birth of marsupials. However, species whose skulls are impacted by strong muscular stressesparticularly those produced through mastication of tough food itemsmay not display such intrinsic patterns very clearly because of the known plastic response of bone to muscle activity of the individual. In such cases, allometry may not dominate within-species shape variation, even if it is a driver of evolutionary shape divergence; ordination of shape in a geometric morphometric context through principal component analysis (PCA) should reveal main variation in areas under masticatory stress (incisor region/zygomatic arches/mandibular ramus); but this main variation should emerge from high individual variability and thus have low eigenvalues. Results: We assessed the evidence for high individual variation through 3D geometric morphometric shape analysis of crania and mandibles of three species of grazing-specialized wombats, whose diet of tough grasses puts considerable strain on their masticatory system. As expected, we found little allometry and low Principal Component 1 (PC1) eigenvalues within crania and mandibles of all three species. Also as expected, the main variation was in the muzzle, zygomatic arches, and masticatory muscle attachments of the mandibular ramus. We then implemented a new test to ask if the landmark variation reflected on PC1 was reflected in individuals with opposite PC1 scores and with opposite shapes in Procrustes space. This showed that correspondence between individual and ordinated shape variation was limited, indicating high levels of individual variability in the masticatory apparatus. Discussion: Our results are inconsistent with hypotheses that skull shape variation within marsupial species reflects a constraint pattern. Rather, they support suggestions that individual plasticity can be an important determinant of within-species shape variation in marsupials (and possibly other mammals) with high masticatory stresses, making it difficult to understand the degree to which intrinsic constraints act on shape variation at the within-species level. We conclude that studies that link micro-and macroevolutionary patterns of shape variation might benefit from a focus on species with low-impact mastication, such as carnivorous or frugivorous species.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Individual variation of the masticatory system dominates 3D skull shape in the herbivory-adapted marsupial wombats

et al. 2019

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“…Though it has been suggested that this approach may bias studies toward recovery of the CREA pattern (Linde-Medina 2016), we use centroid size here in accordance with Tamagnini et al (2017) and Cardini (2019), who find it to correspond well with other methods of measurement. This also allows for more direct comparability with previous mammalian studies (Cardini and Polly 2013;Cardini et al 2015;Tamagnini et al 2017;Mitchell et al 2018;Cardini 2019). To investigate whether nonmammalian synapsid groups share a common allometric pattern, we performed a phylogenetic generalized leastsquares (PGLS) regression with a Brownian motion model of evolution using the geomorph function procD.pgls on a data set including all species in our study and using our concatenated supertree.…”

Section: Analysis Of Allometrymentioning

confidence: 99%

The many faces of synapsid cranial allometry

2019

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Previous studies of cranial shape have established a consistent interspecific allometric pattern relating the relative lengths of the face and braincase regions of the skull within multiple families of mammals. In this interspecific allometry, the facial region of the skull is proportionally longer than the braincase in larger species. The regularity and broad taxonomic occurrence of this allometric pattern suggests that it may have an origin near the base of crown Mammalia, or even deeper in the synapsid or amniote forerunners of mammals. To investigate the possible origins of this allometric pattern, we used geometric morphometric techniques to analyze cranial shape in 194 species of nonmammalian synapsids, which constitute a set of successive outgroups to Mammalia. We recovered a much greater diversity of allometric patterns within nonmammalian synapsids than has been observed in mammals, including several instances similar to the mammalian pattern. However, we found no evidence of the mammalian pattern within Therocephalia and nonmammalian Cynodontia, the synapsids most closely related to mammals. This suggests that the mammalian allometric pattern arose somewhere within Mammaliaformes, rather than within nonmammalian synapsids. Further investigation using an ontogenetic series of the anomodont Diictodon feliceps shows that the pattern of interspecific allometry within anomodonts parallels the ontogenetic trajectory of Diictodon. This indicates that in at least some synapsids, allometric patterns associated with ontogeny may provide a “path of least resistance” for interspecific variation, a mechanism that we suggest produces the interspecific allometric pattern observed in mammals.

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“…This posits that closely related mammals tend to have longer rostra and narrower zygomatic arches as they increase in size [59], in a pattern that is highly similar to the one we found within wombats but without allometry. CREA was suggested for kangaroo crania [18], but contested in a slightly different sample and landmarking protocol of kangaroos [23,24].…”

Section: Discussionmentioning

confidence: 99%

“…Suggestions of a constraint on marsupial skull shape through static allometry are at odds with several geometric morphometric studies that show only low or moderate levels of static allometry in marsupial crania [15,[20][21][22]. Two recent studies on kangaroos even suggested that allometry plays a lesser role in shaping cranial variation in this group, instead positing fast adaptation or individual developmental plasticity of the masticatory apparatus as the main driver [23,24]. This is consistent with suggestions that masticatory biomechanics may impact individual cranial shape to such a degree that developmental constraints either do not contribute much to within-species shape variation, or can 5 be obscured by individual differences in mastication due to the bone's plastic response to mastication stresses [6,[25][26][27].…”

Section: Introductionmentioning

confidence: 98%

Individual variation of the masticatory system dominates 3D skull shape in the herbivory-adapted marsupial wombats

Weisbecker

Guillerme

Speck

et al. 2019

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Background: Within-species skull shape variation of marsupial mammals is widely considered low and strongly size-dependent (allometric), possibly due to developmental constraints arising from the altricial birth of marsupials. However, species whose skulls are impacted by strong muscular stresses -particularly those produced through mastication of tough food items -may not display such intrinsic patterns very clearly because of the known plastic response of bone to muscle activity of the individual. In such cases, shape variation should not be dominated by allometry; ordination of shape in a geometric morphometric context through principal component analysis (PCA) should reveal main variation in areas under masticatory stress (incisor region/zygomatic arches/mandibular ramus); but this main variation should emerge from high individual variability and thus have low eigenvalues. Results:We assessed the evidence for high individual variation through 3D geometric morphometric shape analysis of crania and mandibles of thre species of grazing-specialized wombats, whose diet of tough grasses puts considerable strain on their masticatory system. As expected, we found little allometry and low Principal Component 1 (PC1) eigenvalues within crania and mandibles of all three species. Also as expected, the main variation was in the muzzle, zygomatic arches, and masticatory muscle attachments of the mandibular ramus. We then implemented a new test to ask if the landmark variation reflected on PC1 was reflected in individuals with opposite PC1 scores and with opposite shapes in Procrustes space. This showed that correspondence between individual and ordinated shape variation was limited, indicating high levels of individual variability in the masticatory apparatus. Discussion:Our results are inconsistent with hypotheses that skull shape variation within marsupial species reflects a constraint pattern. Rather, they support suggestions that individual plasticity can be an important determinant of within-species shape variation in marsupials (and possibly other mammals) with high masticatory stresses, making it difficult to understand the degree to which intrinsic constraint act on shape variation at the within-species level. We conclude that studies that link micro-and macroevolutionary patterns of shape variation might benefit from a focus on species with low-impact mastication, such as carnivorous or frugivorous species.3

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The biomechanics of foraging determines face length among kangaroos and their relatives

Cited by 33 publications

References 42 publications

Individual variation of the masticatory system dominates 3D skull shape in the herbivory-adapted marsupial wombats

Individual variation of the masticatory system dominates 3D skull shape in the herbivory-adapted marsupial wombats

The many faces of synapsid cranial allometry

Individual variation of the masticatory system dominates 3D skull shape in the herbivory-adapted marsupial wombats

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