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

2019 ◽  
Vol 16 (1) ◽  
Author(s):  
Vera Weisbecker ◽  
Thomas Guillerme ◽  
Cruise Speck ◽  
Emma Sherratt ◽  
Hyab Mehari Abraha ◽  
...  
Keyword(s):  
Individual Variation ◽  
Principal Component ◽  
Individual Variability ◽  
Shape Variation ◽  
Mandibular Ramus ◽  
Geometric Morphometric ◽  
Skull Shape ◽  
Marsupial Species ◽  
Masticatory System ◽  
The Individual

Abstract 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, 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.

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

2019 ◽  
Author(s):  
Vera Weisbecker ◽  
Thomas Guillerme ◽  
Cruise Speck ◽  
Emma Sherratt ◽  
Hyab Mehari Abraha ◽  
...  
Keyword(s):  
Individual Variation ◽  
Principal Component ◽  
Individual Variability ◽  
Shape Variation ◽  
Mandibular Ramus ◽  
Geometric Morphometric ◽  
Skull Shape ◽  
Marsupial Species ◽  
Masticatory System ◽  
The Individual

AbstractBackgroundWithin-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.ResultsWe 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.DiscussionOur 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.

Phenotypic variation of south-western Atlantic clam Mactra isabelleana (Bivalvia: Mactridae)

2012 ◽  
Vol 93 (2) ◽  
pp. 511-517 ◽  
Author(s):  
Javier H. Signorelli ◽  
Federico Márquez ◽  
Guido Pastorino
Keyword(s):  
Principal Component ◽  
Shell Shape ◽  
Physical Parameters ◽  
Buenos Aires Province ◽  
Shape Variation ◽  
Geometric Morphometric ◽  
Western Atlantic ◽  
Canonical Variates Analysis ◽  
Canonical Variates ◽  
Geometric Morphometric Method

The phenotypic shell shape variation of Mactra isabelleana was tested using the geometric morphometric method. Four localities were sampled along the Río de la Plata estuary and the coast of Buenos Aires province. Principal component analysis and canonical variates analysis of the first principal components were performed to reveal the shell variation and differences among localities, respectively. The specimens from different microhabitats mostly overlapped, although differences in shape were observed in the development of the umbo, the enlargement of the dorsoventral axes and the elongation of the posterior end. The ecological and physical parameters that could influence shell shape variation are discussed.

scholarly journals Beyond the carapace: skull shape variation and morphological systematics of long-nosed armadillos (genus Dasypus)

2017 ◽  
Author(s):  
Lionel Hautier ◽  
Guillaume Billet ◽  
Benoit De Thoisy ◽  
Frédéric Delsuc
Keyword(s):  
Morphological Variation ◽  
Distinct Species ◽  
Morphological Characters ◽  
Molecular Data ◽  
Guiana Shield ◽  
Shape Variation ◽  
Skull Morphology ◽  
Geometric Morphometric ◽  
Skull Shape ◽  
Shape And Size

Background. The systematics of long-nosed armadillos (genus Dasypus) has been mainly based on a handful of external morphological characters and classical measurements. Here, we studied the pattern of morphological variation in the skull of long-nosed armadillos species, with a focus on the systematics of the widely distributed nine-banded armadillo (D. novemcinctus). Methods. We present the first exhaustive 3D comparison of the skull morphology within the genus Dasypus, based on µCT-scans. We used geometric morphometric approaches to explore the patterns of the intra- and interspecific morphological variation of the skull with regard to several factors such as taxonomy, geography, allometry, and sexual dimorphism. Results. We show that the shape and size of the skull vary greatly between Dasypus species, with D. pilosus representing a clear outlier compared to other long-nosed armadillos. The study of the cranial intraspecific variation in D. novemcinctus evidences clear links to the geographic distribution and argue in favour of a revision of past taxonomic delimitations. Our detailed morphometric comparisons detected previously overlooked morphotypes of nine-banded armadillo, especially a very distinctive unit circumscribed to the Guiana Shield. Discussion. As our results are congruent with recent molecular data and analyses of the structure of paranasal sinuses, we propose that D. novemcinctus should be regarded either as a polytypic species (with three to four subspecies) or as a complex of several distinct species.

scholarly journals The importance of individual variation in the dynamics of animal collective movements

2018 ◽  
Vol 373 (1746) ◽  
pp. 20170008 ◽  
Author(s):  
Maria del Mar Delgado ◽  
Maria Miranda ◽  
Silvia J. Alvarez ◽  
Eliezer Gurarie ◽  
William F. Fagan ◽  
...  
Keyword(s):  
Individual Variation ◽  
Decision Rules ◽  
Movement Ecology ◽  
Individual Variability ◽  
Collective Movement ◽  
Individual Based Models ◽  
Theoretical Investigations ◽  
Group Heterogeneity ◽  
Collective Movements ◽  
The Individual

Animal collective movements are a key example of a system that links two clearly defined levels of organization: the individual and the group. Most models investigating collective movements have generated coherent collective behaviours without the inclusion of individual variability. However, new individual-based models, together with emerging empirical information, emphasize that within-group heterogeneity may strongly influence collective movement behaviour. Here we (i) review the empirical evidence for individual variation in animal collective movements, (ii) explore how theoretical investigations have represented individual heterogeneity when modelling collective movements and (iii) present a model to show how within-group heterogeneity influences the collective properties of a group. Our review underscores the need to consider variability at the level of the individual to improve our understanding of how individual decision rules lead to emergent movement patterns, and also to yield better quantitative predictions of collective behaviour. This article is part of the theme issue ‘Collective movement ecology’.

scholarly journals The use of the geometric morphometric method to illustrate shape difference in the skulls of different-aged horses

2020 ◽  
Vol 44 (3-4) ◽  
pp. 137-145
Author(s):  
Tiziana Liuti ◽  
Padraic M. Dixon
Keyword(s):  
Age Groups ◽  
Nasal Bone ◽  
Principal Component ◽  
Age Group ◽  
Shape Variation ◽  
Geometric Morphometric ◽  
Biological Studies ◽  
Potential Applications ◽  
Variation Explained ◽  
Ethmoid Sinuses

Abstract The geometric morphometrics method (GMM) is a technique to study scale and shape relationships of structures using Cartesian geometric coordinates rather than linear, areal (of area), or volumetric variables. GMM has been of great value in many biological studies, but does not appear to have been used to examine equine skulls. In this exploratory study, twenty-nine normal equine heads of three different age groups: <5 years old (N = 9), 6–15 years old (N = 10) and > 16 years old (N = 10) were examined. Computed tomography (CT) bone window DICOM images were reconstructed into isosurfaces (3-dimensional contoured surfaces), onto which landmarks were added using Stratovan Checkpoint® software. Data from 29 landmarks were analysed using MorphoJ analysis, which applies a Procrustes fit, prior to reducing data dimensionality through principal component (PC) analysis. PCs with and without allometry were considered. Allometric shape described by PC1 accounted for 27% of variance. Loading pertaining to: the pterygoid process, bilaterally; caudal aspect of hard palate; tip of nasal bone; ethmoid sinuses, bilaterally; caudal aspect of the ventral conchal bulla, bilaterally and caudal aspect of the vomer bone suggest that these anatomical structures are predictive of age group. When allometric effects (shape variation explained by size) were removed, PC1 was unable to distinguish horses by age group. Allometric shape differences could distinguish the youngest versus the two older age groups. The potential applications of GMM in equine diagnostic imaging are wide ranging and include the investigation of changes in the equine skull with respect to genetics and characterisation of conformation-related diseases affecting the teeth, jaws and sinonasal compartments.

Averaging v. outlier removal. Decrypting variance among cryptic Lejeunea species (Lejeuneaceae: Jungermanniopsida) using geometric morphometrics

2013 ◽  
Vol 26 (1) ◽  
pp. 13 ◽  
Author(s):  
Matt A. M. Renner ◽  
Elizabeth A. Brown ◽  
Glenda M. Wardle
Keyword(s):  
Cryptic Species ◽  
Individual Variation ◽  
Species Difference ◽  
Molecular Data ◽  
Species Variation ◽  
Shape Variation ◽  
Outlier Removal ◽  
Geometric Morphometric ◽  
Size And Shape ◽  
Developmental Capacity

Molecular data have revealed many morphologically cryptic species. More surprising than lack of difference, however, is that morphological variation and complex patterns of overlapping features can mask cryptic species. We employ geometric morphometric methods (GMM) to explore patterns of variation within four liverwort species, three of which were previously attributed to Lejeunea tumida Mitt. Each species exhibited considerable variation within, and overlap among, species in size and shape, independent of degree of relatedness. Most variation was expressed within individuals, suggesting that the observed breadth of variation was within the developmental capacity of single genotypes. Size and shape variation within, and consequently overlap among, individuals resulted primarily from variance in growth of shoots. Inter-specific differences were swamped by intra- and inter-individual variation. We coupled GMM with multivariate methods for outlier removal, and simple averaging of individuals to explore whether intra-individual variation could be reconciled to maximise the inter-species difference, facilitating resolution of cryptic species despite extensive morphological continuity and overlap. Unfortunately, outlier removal did not achieve separation among species, because removing extremes failed to eliminate overlap resulting from within-species variation. Individual averaging was partially successful in extracting L. tumida as a discrete entity but did not segregate the remaining three species. Although the challenges for morphology-based identification of cryptic species are significant, GMM provide one of the best sets of methods for identifying and communicating any subtle morphological differences that may exist.

scholarly journals Geographic variation in the skull morphology of the lesser grison (Galictis cuja: Carnivora, Mustelidae) from two Brazilian ecoregions

PeerJ ◽  
2020 ◽  
Vol 8 ◽  
pp. e9388
Author(s):  
Raissa Prior Migliorini ◽  
Rodrigo Fornel ◽  
Carlos Benhur Kasper
Keyword(s):  
Atlantic Forest ◽  
Size Variation ◽  
Neotropical Region ◽  
Shape Variation ◽  
Skull Morphology ◽  
Geometric Morphometric ◽  
Morphological Variations ◽  
Skull Shape ◽  
Temperature And Precipitation ◽  
Forest Region

Background The lesser grison (Galictis cuja) is one of the least known carnivores in the Neotropical region. Its wide geographical occurrence and range of habitats could lead to morphological variations along its distribution. So, this study aimed to investigate the variation in skull shape and size of this species, by testing the existence of ecotypes adapted to their respective environments (Uruguayan savanna and Atlantic Forest), as well as its relationship with selected abiotic variables. Methods The skulls of 52 museum specimens were photographed in the ventral, dorsal, and lateral views, and were analyzed using geometric morphometric techniques. Results We found sexual size dimorphism, with males being larger than females. The shape variation between sexes, as well as between ecoregions, is mostly explained by the effect of allometry. The specimens from Uruguayan savanna are larger than the ones from the Atlantic Forest. Size variation was also significantly correlated to latitude, temperature and precipitation patterns. No correlation between skull shape with geographical distance was detected. Discussion Morphometric measurements and diet data of lesser grison in regions from higher latitudes than our sampling show a tendency to heavier individuals, and the consumption of bigger prey compared to Uruguayan savanna. The results indicated the smaller specimens associated to low variability in annual temperature, congruent to Atlantic Forest region. An explanation for observed variation may be related to the “resource rule” but, due the minimal natural history information regards this species, we can just speculate about this.

scholarly journals Geometric morphometry of pupae to identify four medically important flies (Order: Diptera) in Thailand

2019 ◽  
Vol 20 (6) ◽  
Author(s):  
TANAWAT CHAIPHONGPACHARA ◽  
PATCHARAPRON TUBSAMUT
Keyword(s):  
Fourier Coefficients ◽  
Principal Component ◽  
Future Application ◽  
Size Analysis ◽  
Size Estimation ◽  
Shape Variation ◽  
Elliptic Fourier Analysis ◽  
Geometric Morphometric ◽  
Significance Level ◽  
Geometric Morphometry

Abstract. Chaiphongpachara T, Tubsamut P. 2019. Geometric morphometry of pupae to identify four medically important flies (Order: Diptera) in Thailand. Biodiversitas 20: 1504-1509. In this study, we evaluated an outline-based geometric morphometric (GM) approach for species identification from pupae of four common flies medically important in Thailand, Chrysomya megacephala, Lucilia cuprina, Musca domestica, and Boettcherisca nathani. For size estimation, mean perimeter length was used. For shape analysis, Elliptic Fourier Analysis was performed to produce the contour shape variables, which was calculated as Normalised Elliptic Fourier coefficients. Then, principal component analysis was performed on the Normalized Fourier coefficients for discriminant analysis, and used to estimate pupal shape variation among the species. The difference in size and shape between the fly species was analyzed using a non-parametric test based on 1000 permutations after Bonferroni correction for the significance level (p < 0.05). In the size analysis, the mean perimeter length for pupae of B. nathani was the largest (20.35 mm) followed by C. megacephala (14.73 mm), while that for M. domestica was the smallest (11.82 mm). The size differences were statistically significant between all species (p < 0.05). The contour shapes of all pupae were significantly different among all species. The results of this study can be used as a basis for the future application of GM to identify other types of flies via their pupae.

scholarly journals Geometric morphometric analysis of the skull of Podocnemis spp. (Pleurodira, Podocnemididae) and its implications on the taxonomic status of Podocnemis bassleri Williams, 1956

2015 ◽  
Author(s):  
Pedro S. R. Romano ◽  
Sergio A. K. Azevedo ◽  
Alexander W. A. Kellner ◽  
Gustavo R. Oliveira
Keyword(s):  
Multivariate Regression ◽  
Phylogenetic Signal ◽  
Ventral View ◽  
Taxonomic Status ◽  
Shape Variation ◽  
Diagnostic Features ◽  
Geometric Morphometric ◽  
Geometric Morphometric Analysis ◽  
Independent Variable ◽  
The Individual

Background. Podocnemis bassleri Williams, 1956 is the oldest definite record for Podocnemis, dating back to the Miocene of South America. However, the diagnosis of P. ba. is fragile, as assumed by Williams himself. Here we evaluated the hypothesis of P. ba. as a synonym of P. expansa by exploring the shape variation of the skull among Podocnemis spp. Methods. We collected 19 landmarks on the left side of the skull in ventral view from 33 Podocnemis spp. skulls. We included in the sample a new specimen of P. ba. from the Miocene of Acre, Brazil (MCT/RJ unnumbered) and the holotype (AMNH 1662) from the Miocene of Peru, along with: P. erythrocephala (n=3), P. ex. (n=9), P. lewyana (n=1), P. sextuberculata (n=9), P. unifilis (n=6), and P. vogli (n=3). The data was then Procrustes superimposed and a Relative Warps Analysis (RW) was performed to evaluate shape variation. Also, a multivariate regression of the Partial Warps (i.e.: the eigenvectors of the “bending energy” matrix) versus the log-transformed centroid size (the independent variable) was computed in order to evaluate the allometry in the data. All analyses were fulfilled using Rohlf’s TPS softwares. Results. The two first RWs accumulated ~52% of shape variation. The individual projection of the specimens in RW1 and RW2 showed a structure partially explained by a phylogenetic signal. P. ex. and P. se., previously considered as sister-groups, were projected in the negative scores of RW1. Also, these two species were projected, respectively, in the positive and negative scores of the RW2. The two specimens of P. ba. were nested among P. ex. specimens. Furthermore, the multivariate regression revealed an effect of the size in the shape variation: larger skulls have wider maxillae and posterior region laterally extended. Discussion. According to the literature, P. ex. and P. ba. are nearly indistinguishable (besides the larger size of the second), and Williams seems to have used the Miocene age of the second as a criterion for differentiating the two taxa. Indeed, one of the diagnostic features pointed out by Williams – slightly shorter relative distance from snout tip to posterior borders of the orbits – seems to be a taphonomic outcome. Moreover, the second diagnostic character – internal palatal processes of the maxillae abruptly dorsally projected – is extended anteroposteriorly in the MCT/RJ P. ba. specimen, as in all recent taxa. So, this character is polymorphic or also results of a taphonomic outcome. As consequence, P. ba. lacks a suitable diagnosis. Our preliminary results revealed little differences in shape of P. ex. and P. ba. and a clear allometric effect in the shape variation. In conclusion, it seems reasonable to suggest that P. ba. is a junior synonym of P. ex., although we will wait to claim it after additional analyses.

scholarly journals Geometric morphometric analysis of the skull of Podocnemis spp. (Pleurodira, Podocnemididae) and its implications on the taxonomic status of Podocnemis bassleri Williams, 1956

2015 ◽  
Author(s):  
Pedro S. R. Romano ◽  
Sergio A. K. Azevedo ◽  
Alexander W. A. Kellner ◽  
Gustavo R. Oliveira
Keyword(s):  
Multivariate Regression ◽  
Phylogenetic Signal ◽  
Ventral View ◽  
Taxonomic Status ◽  
Shape Variation ◽  
Diagnostic Features ◽  
Geometric Morphometric ◽  
Geometric Morphometric Analysis ◽  
Independent Variable ◽  
The Individual

Background. Podocnemis bassleri Williams, 1956 is the oldest definite record for Podocnemis, dating back to the Miocene of South America. However, the diagnosis of P. ba. is fragile, as assumed by Williams himself. Here we evaluated the hypothesis of P. ba. as a synonym of P. expansa by exploring the shape variation of the skull among Podocnemis spp. Methods. We collected 19 landmarks on the left side of the skull in ventral view from 33 Podocnemis spp. skulls. We included in the sample a new specimen of P. ba. from the Miocene of Acre, Brazil (MCT/RJ unnumbered) and the holotype (AMNH 1662) from the Miocene of Peru, along with: P. erythrocephala (n=3), P. ex. (n=9), P. lewyana (n=1), P. sextuberculata (n=9), P. unifilis (n=6), and P. vogli (n=3). The data was then Procrustes superimposed and a Relative Warps Analysis (RW) was performed to evaluate shape variation. Also, a multivariate regression of the Partial Warps (i.e.: the eigenvectors of the “bending energy” matrix) versus the log-transformed centroid size (the independent variable) was computed in order to evaluate the allometry in the data. All analyses were fulfilled using Rohlf’s TPS softwares. Results. The two first RWs accumulated ~52% of shape variation. The individual projection of the specimens in RW1 and RW2 showed a structure partially explained by a phylogenetic signal. P. ex. and P. se., previously considered as sister-groups, were projected in the negative scores of RW1. Also, these two species were projected, respectively, in the positive and negative scores of the RW2. The two specimens of P. ba. were nested among P. ex. specimens. Furthermore, the multivariate regression revealed an effect of the size in the shape variation: larger skulls have wider maxillae and posterior region laterally extended. Discussion. According to the literature, P. ex. and P. ba. are nearly indistinguishable (besides the larger size of the second), and Williams seems to have used the Miocene age of the second as a criterion for differentiating the two taxa. Indeed, one of the diagnostic features pointed out by Williams – slightly shorter relative distance from snout tip to posterior borders of the orbits – seems to be a taphonomic outcome. Moreover, the second diagnostic character – internal palatal processes of the maxillae abruptly dorsally projected – is extended anteroposteriorly in the MCT/RJ P. ba. specimen, as in all recent taxa. So, this character is polymorphic or also results of a taphonomic outcome. As consequence, P. ba. lacks a suitable diagnosis. Our preliminary results revealed little differences in shape of P. ex. and P. ba. and a clear allometric effect in the shape variation. In conclusion, it seems reasonable to suggest that P. ba. is a junior synonym of P. ex., although we will wait to claim it after additional analyses.

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