Cranial size and shape variation in mainland and island populations of the quokka

Dawson, Rebekah; Milne, Nick

doi:10.1111/j.1469-7998.2012.00952.x

Cited by 18 publications

(14 citation statements)

References 29 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Instead, the authors postulated that a CREA-like pattern is not allometric and instead purely due to biomechanics. CREA-like shape variation is also found in other kangaroo species, and is allometric in tammar wallabies [51] and quokkas [20], but only partially so among the rock wallabies [15]. By contrast, geometric morphometric analyses of two marsupial species with a comparatively soft dietthe insectivorous Dromiciops gliroides and two species of the omnivorous Caluromysshow little cranial variation of zygomatic arch or rostrum shape, but strong within-species allometry [21,22].…”

Section: Discussionmentioning

confidence: 91%

“…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].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

et al. 2019

View full text Add to dashboard Cite

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.

show abstract

Section: Discussionmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

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

et al. 2019

View full text Add to dashboard Cite

show abstract

“…Instead, the authors postulated that a CREA-like pattern is not allometric and instead purely due to biomechanics. CREA-like shape variation is also found in other kangaroo species, and is allometric in tammar wallabies [60] and quokkas [20], but only partially so among the rock wallabies [15]. By contrast, geometric morphometric analyses of two marsupial species with a comparatively soft dietthe insectivorous Dromiciops gliroides and two species of the omnivorous Caluromys -show little cranial variation of zygomatic arch or rostrum shape, but strong-species allometry [21,22].…”

Section: Discussionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

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

Weisbecker

Guillerme

Speck

et al. 2019

Preprint

View full text Add to dashboard Cite

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

show abstract

“…Instead, relative age of each individual was determined through measurement of their molar index (MI) – the number of molars in front of the anterior zygomatic arch of the skull (Kirkpatrick, ). The MI value increases steadily with age and can be used as a proxy for age within macropodid species (Hadley, Milne & Schmitt, ; Dawson & Milne, ). Specimens under MI of two were judged to be juvenile (Jackson, ) and were removed from the sample.…”

Section: Methodsmentioning

confidence: 99%

Strong arm tactics: sexual dimorphism in macropodid limb proportions

2015

Self Cite

View full text Add to dashboard Cite

Macropodid (kangaroo and wallaby) males use their forelimbs as weaponry in fights for dominance and access to females. The choreography and intensity of these fights varies with species body size. It has been established that the largest species show stronger dimorphism in upper limb muscularity as a product of sexual selection via increased intermale competition. However, beyond muscularity, and across the other macropodid species, limb dimorphism is poorly understood. Here, we examine dimorphism in the relative proportions of the bones within the forelimb and between the fore-and hindlimbs. We used a large sample of bones from 15 promiscuous macropodid species to confirm that absolute dimorphism in the forelimb becomes greater with body size (indexed by cranial length), and to further explore whether dimorphism in relative forelimb proportions increases also. As macropodids are obligate bipedal hoppers, no dimorphism was expected in the lower limb. Phylogenetic generalized least-square regression was used to resolve phylogenetic non-independence of the data. Greater upper limb dimorphism was significantly correlated with longer crania, confirming established patterns, but we found it was the relative length of the male humerus that became increasingly exaggerated with species' body size, not the radius as previously suggested. Enlarged proximal limb segments are indicative of adaptations for powerful movements. This aligns with higher intensity and ritualization of male agonistic behaviour, and reflects an increased selection for strong male forelimbs in the larger promiscuous species. Contrary to our hypothesis, relative male pes length decreased with body size, possibly indicating selection for a stronger and sturdier pes required for powerful kicks. This study clarifies the patterns of sexual dimorphism in Macropodidae limbs and illustrates the power of sexual selection to influence anatomy that is fundamental to locomotion in both sexes.

show abstract

Cranial size and shape variation in mainland and island populations of the quokka

Cited by 18 publications

References 29 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

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

Strong arm tactics: sexual dimorphism in macropodid limb proportions

Contact Info

Product

Resources

About