Geometric Morphometrics of Bilateral Asymmetry in Eunotia bilunaris (Eunotiales, Bacillariophyceae) as a Tool for the Quantitative Assessment of Teratogenic Deviations in Frustule Shapes

A number of pennate diatom genera typically have teratogenic deformations of their siliceous frustules due to the effects of environmental stress, such as high concentrations of heavy metals and low pH. However, the quantitative assessment of these deformations has rarely been applied. One species in which aberrations have frequently been reported is Eunotia bilunaris, which typically has bilaterally symmetric frustules with dorso-ventral differentiation. In this study, we aimed to illustrate the geometric morphometric analysis of symmetry as a tool for assessing the severity of teratogenic deformations. These were quantified by Procrustes superimposition of equidistant points placed along the valvar outlines in pairs of configurations based on their bilateral reflection symmetry. The shape deformations were mostly confined to central parts of the ventral outlines and were captured both by the symmetric and asymmetric subspaces of the variation. The amount of bilateral asymmetry in individual cells was negatively related to frustule size via the allometric power law relationship, illustrating that asymmetry increased in the asexual diminution series. The presented analysis provides a framework for the quantitative assessment of frustule deformations in eunotioid diatoms that can be used for the comparative scoring of teratogenic deviations among cells, populations, or species.

Incisor Occlusion Affects Profile Shape Variation in Middle-Aged Adults

Background: The aim of this study was to assess the effect of overjet and overbite on profile shape in middle–aged individuals. Methods: The study population comprised 1754 46-year-old individuals, members of the 1966 Northern Finland Birth Cohort. Their profile images were digitized using 48 landmarks and semi-landmarks. The subsequent landmark coordinates were then transformed to shape coordinates through Procrustes Superimposition, and final data were reduced into Principal Components (PCs) of shape. Overjet and overbite values were measured manually, during a clinical examination. A multivariate regression model was developed to evaluate the effect of overjet and overbite on profile shape. Results: The first nine PCs described more than 90% of profile shape variation in the sample and were used as the shape variables in all subsequent analyses. Overjet predicted 21.3% of profile shape in the entire sample (η2overjet = 0.213; p < 0.001), while the effect of overbite was weaker (η2overbite = 0.138; p < 0.001). In males, the equivalent effects were 22.6% for overjet and 14% for overbite, and in females, 25.5% and 13.5%, respectively. Conclusion: Incisor occlusion has a noteworthy effect on profile shape in middle-aged adults. Its impact becomes more significant taking into consideration the large variety of genetic and environmental factors affecting soft tissue profile.

How Exactly Did the Nose Get That Long? A Critical Rethinking of the Pinocchio Effect and How Shape Changes Relate to Landmarks

The Pinocchio effect has long been discussed in the literature on geometric morphometrics. It denotes the observation that Procrustes superimposition tends to distribute shape changes over many landmarks, even though a different superimposition may exist for the same landmark configurations that concentrates changes in just one or a few landmarks. This is widely seen as a flaw of Procrustes methods. Visualizations illustrating the Pinocchio effect use a comparison of the same pair of shapes superimposed in two different ways: in a resistant-fit superimposition that concentrates the shape difference in just one or a few landmarks, and in Procrustes superimposition, which distributes differences over most or all landmarks. Because these superimpositions differ only in the non-shape aspects of size, position and orientation, they are equivalent from the perspective of shape analysis. Simulation studies of the Pinocchio effect usually generate data, either single pairs or larger samples of landmark configurations, in a particular superimposition so that differences occur mostly or exclusively at just one or a few landmarks, but no steps are taken to remove variation from size, position and orientation. When these configurations are then compared with Procrustes-superimposed data, differences appear and are attributed to the Pinocchio effect. Overall, it is ironic that all manifestations of the Pinocchio effect in one way or another rely on differences in the non-shape properties of position and orientation. Rigorous thinking about shape variation and careful choice of visualization methods can prevent confusion over this issue.

Sexual dimorphism in Belostoma angustum Lauck (Insecta: Heteroptera: Belostomatidae) may be related to paternal care

The structures involved in parental care are often dimorphic. Female Belostoma angustum water bugs lay eggs on the hemelytra of their mates, where the eggs are brooded until hatching. Males use their hind legs to carry, aerate and protect the eggs. After controlling for covariance between variables, we fitted a series of structural equation models (SEMs) and evaluated the existence of sexual dimorphism in the size of the body and hind legs, in the shape and centroid size of the hemelytrum, and among the static allometry slopes of the size-related differences. Landmarks were used to capture phenotypic variation, by eliminating all non-shape variations with a Procrustes superimposition. Neither the shape of the hemelytrum nor its centroid size was related significantly to the aforementioned linear body measurements. Instead, the differences in the size of the hind legs were mediated by body dimensions only in males. We also found that males were wider and had longer heads than females, according to the SEM intercept values. Our findings suggest that sexual dimorphism in B. angustum may be related to a balance between sexual role reversal and viability costs.

Extraocular muscle positions in anterior plagiocephaly: V-pattern strabismus explained using geometric mophometrics

IntroductionOphthalmological involvement in anterior plagiocephaly (AP) due to unicoronal synostosis (UCS) raises management challenges. Two abnormalities of the extraocular muscles (EOM) are commonly reported in UCS without objective quantification: (1) excyclorotation of the eye and (2) malposition of the trochlea of the superior oblique muscle. Here we aimed to assess the positions of the EOM in AP, using geometric morphometrics based on MRI data.Materials and methodsPatient files were listed using Dr WareHouse, a dedicated big data search engine. We included all patients with AP managed between 2013 and 2018, with an available digital preoperative MRI. MRIs from age-matched controls without craniofacial conditions were also included. We defined 13 orbital and skull base landmarks in order to model the 3D position of the EOM. Cephalometric analyses and geometric morphometrics with Procrustes superimposition and principal component analysis were used with the aim of defining specific EOM anomalies in UCS.ResultsWe included 15 preoperative and 7 postoperative MRIs from patients with UCS and 24 MRIs from age-matched controls. Cephalometric analyses, Procrustes superimposition and distance computations showed a significant shape difference for the position of the trochlea of the superior oblique muscle and an excyclorotation of the EOM.ConclusionsOur results confirm that UCS-associated anomalies of the superior oblique muscle function are associated with malposition of its trochlea in the roof of the orbit. This clinical anomaly supports the importance of MRI imaging in the surgical management of strabismus in patients with UCS.

High-Density Morphometric Analysis of Shape and Integration: The Good, the Bad, and the Not-Really-a-Problem

The field of comparative morphology has entered a new phase with the rapid generation of high-resolution three-dimensional (3D) data. With freely available 3D data of thousands of species, methods for quantifying morphology that harness this rich phenotypic information are quickly emerging. Among these techniques, high-density geometric morphometric approaches provide a powerful and versatile framework to robustly characterize shape and phenotypic integration, the covariances among morphological traits. These methods are particularly useful for analyses of complex structures and across disparate taxa, which may share few landmarks of unambiguous homology. However, high-density geometric morphometrics also brings challenges, for example, with statistical, but not biological, covariances imposed by placement and sliding of semilandmarks and registration methods such as Procrustes superimposition. Here, we present simulations and case studies of high-density datasets for squamates, birds, and caecilians that exemplify the promise and challenges of high-dimensional analyses of phenotypic integration and modularity. We assess: (1) the relative merits of “big” high-density geometric morphometrics data over traditional shape data; (2) the impact of Procrustes superimposition on analyses of integration and modularity; and (3) differences in patterns of integration between analyses using high-density geometric morphometrics and those using discrete landmarks. We demonstrate that for many skull regions, 20–30 landmarks and/or semilandmarks are needed to accurately characterize their shape variation, and landmark-only analyses do a particularly poor job of capturing shape variation in vault and rostrum bones. Procrustes superimposition can mask modularity, especially when landmarks covary in parallel directions, but this effect decreases with more biologically complex covariance patterns. The directional effect of landmark variation on the position of the centroid affects recovery of covariance patterns more than landmark number does. Landmark-only and landmark-plus-sliding-semilandmark analyses of integration are generally congruent in overall pattern of integration, but landmark-only analyses tend to show higher integration between adjacent bones, especially when landmarks placed on the sutures between bones introduces a boundary bias. Allometry may be a stronger influence on patterns of integration in landmark-only analyses, which show stronger integration prior to removal of allometric effects compared to analyses including semilandmarks. High-density geometric morphometrics has its challenges and drawbacks, but our analyses of simulated and empirical datasets demonstrate that these potential issues are unlikely to obscure genuine biological signal. Rather, high-density geometric morphometric data exceed traditional landmark-based methods in characterization of morphology and allow more nuanced comparisons across disparate taxa. Combined with the rapid increases in 3D data availability, high-density morphometric approaches have immense potential to propel a new class of studies of comparative morphology and phenotypic integration.

Preliminary Study to Determine the Reference Plane of Patients with a Unilateral Cleft Lip and Palate

Objective The objective of this study was to determine the three-dimensional midsagittal reference planes for unilateral cleft lip and palate (UCLP) patients that can be easily applied in a clinical setting. Design This was a retrospective analysis. Patients There were 35 UCLP patients (25 men, 10 women; 28.1 ± 6.9 years old) in this study. Methods With landmark's three-dimensional coordinates obtained from cone-beam computed tomography, the symmetric midsagittal reference planes were calculated by applying the ordinary Procrustes superimposition method using the original and mirror images. Procrustes analysis was also used to find the closest landmarks to the calculated symmetric midsagittal reference plane and test its compatibility with the symmetrical midsagittal reference plane. Main Outcome Measure The three nearest landmarks to the symmetric midsagittal reference plane were Opisthion, Basion, and Nasion. Results The averages of the sums of the squared Euclidean distance and squared Procrustes distance differences between the two configurations and shapes fabricated by the symmetrical and landmark-based midsagittal reference planes, respectively, were calculated as 1.836 ± 3.295 and 1.519 × 10–5 ± 2.351 × 10–5. Conclusion It was confirmed that the midsagittal reference planes from these selected landmarks for UCLP patients were compatible with symmetric midsagittal reference planes from the Procrustes analysis and the asymmetric measurements.