Geometric Morphometric Data Research Articles

Head Shape Heritability in the Hungarian Meadow Viper Vipera ursinii rakosiensis.

Understanding heritability patterns in functionally relevant traits is a cornerstone for evaluating their evolutionary potential and their role in local adaptation. In this study, we investigated patterns of heritability in the head shape of the Hungarian meadow viper (Vipera ursinii rakosiensis). To this end, we used geometric morphometric data from 12 families composed of 8 mothers, 6 fathers and 221 offspring, bred in captivity at the Hungarian Meadow Viper Conservation Centre (Hungary). We separately evaluated maternal and paternal contributions to the offspring phenotype, in addition to additive genetic effects, all determined using a mixed animal model. Our results indicate a strong genetic and maternal contribution to head shape variations. In contrast, the paternal effects-which are rarely evaluated in wild-ranging species-as well as residual environmental variance, were minimal. Overall, our results indicate a high evolutionary potential for head shape in the Hungarian meadow viper, which suggests a strong contribution of this ecologically important trait in shaping the ability of this endangered species to adapt to changing conditions and/or habitats. Furthermore, our results suggest that maternal phenotypes should be carefully considered when designing captive breeding parental pairs for reinforcing the adaptive capacity of threatened populations, whereas the paternal phenotypes seem less relevant.

Evolutionary Patterns of Modularity in the Linkage Systems of the Skull in Wrasses and Parrotfish.

The concept of modularity is fundamental to understanding the evolvability of morphological structures and is considered a central framework for the exploration of functionally and developmentally related subsets of anatomical traits. In this study, we explored evolutionary patterns of modularity and integration in the 4-bar linkage biomechanical system of the skull in the fish family Labridae (wrasses and parrotfish). We measured evolutionary modularity and rates of shape diversification of the skull partitions of three biomechanical 4-bar linkage systems using 205 species of wrasses (family: Labridae) and a three-dimensional geometric morphometrics data set of 200 coordinates. We found support for a two-module hypothesis on the family level that identifies the bones associated with the three linkages as being a module independent from a module formed by the remainder of the skull (neurocranium, nasals, premaxilla, and pharyngeal jaws). We tested the patterns of skull modularity for four tribes in wrasses: hypsigenyines, julidines, cheilines, and scarines. The hypsigenyine and julidine groups showed the same two-module hypothesis for Labridae, whereas cheilines supported a four-module hypothesis with the three linkages as independent modules relative to the remainder of the skull. Scarines showed increased modularization of skull elements, where each bone is its own module. Diversification rates of modules show that linkage modules have evolved at a faster net rate of shape change than the remainder of the skull, with cheilines and scarines exhibiting the highest rate of evolutionary shape change. We developed a metric of linkage planarity and found the oral jaw linkage system to exhibit high planarity, while the rest position of the hyoid linkage system exhibited increased three dimensionality. This study shows a strong link between phenotypic evolution and biomechanical systems, with modularity influencing rates of shape change in the evolution of the wrasse skull.

Digital Morphology: The Final Frontier

Morphology is central to biological anthropology and its allied fields of anatomical sciences, forensics, and other related disciplines. Many biological anthropology students have their first real foray into the discipline after completing a course in osteology, craniometry, or vertebrate morphology. Unfortunately, the natural history collections that support this type of research and training have not grown. Many countries have strict rules about natural history specimen collections, and these collections seem to be concentrated in a few developed countries, regardless of where the specimens had been collected. Thus, access to comparative material can be problematic where such collections are not readily available. Even if collections are available, accessing them can be severely restricted due to external circumstances, as the prolonged pandemic has shown. Luckily, digital morphology has emerged over the last decade as a new field that stands to change the landscape of specimenbased research and training. Concerted 2D and 3D digitization efforts, the emergence of online aggregate specimen repositories, and availability of comprehensive open-source software tools (such as 3D Slicer) for utilizing these resources has conveniently transformed the field of quantitative and comparative morphology. In this brief review, I will focus explicitly on the 3D Slicer ecosystem and how it can be leveraged as part of a curriculum or research program on digital morphology. In a nutshell, the primary differentiator of the 3D Slicer is not that it is just free but that it is open-source and extensible, making access to digital data more equitable for everyone. I will particularly focus on the 3D Slicer’s SlicerMorph extension, which facilitates 3D geometric morphometric data collection and analysis within the Slicer ecosystem, so all the steps in the digital morphology workflow from import, visualization, and data collection to visualizing the morpho-space can be achieved in a single, well-documented environment.

Machine Learning interspecific identification of mouse first lower molars (genus Mus Linnaeus, 1758) and application to fossil remains from the Estrecho Cave (Spain)

One of the first steps to address palaeontological studies is the taxonomic identification of fossils according to their morphology. Geometric Morphometric techniques together with multivariate statistical analysis are known to be precise tools to achieve this goal. More recent alternative techniques such as Machine Learning are still rarely used in Palaeontology, although it has been shown in various examples that they can offer powerful alternative statistical approaches to analyse quantitative morphometric data. Here we show how Machine Learning applied to two-dimensional geometric morphometric data from the outline shape of the lower first molars of Mus spp. has proven useful to overcome taxonomic problems. We collated a photographic database of 303 lower first molars from modern populations of Mus musculus domesticus and Mus spretus from southwestern Europe and North Africa to compare the performance between classic multivariate statistics and Machine Learning algorithms in identifying the two species from their dental morphology. We also include Late Holocene Mus specimens from the Estrecho Cave (east-central Spain) to predict their specific status. Our results suggest that Machine Learning is more efficient than classical statistical analyses in taxonomic identification of Mus molars, reaching 100% of correct classification. The application of such techniques to fossil material showed that ensemble/stacking algorithms provided robust identification of both M. m. domesticus and M. spretus in the Estrecho Cave assemblage and confirmed that both species colonised the Iberian Peninsula at a time prior to the formation of the site.

Update: Assessing the evolutionary trajectory of the Apaporis caiman (Caiman crocodilus apaporiensis, Medem 1955) via mitochondrial molecular markers

Abstract The spectacled caiman (Caiman crocodilus) is currently considered to be a species complex due to the relatively high morphological and molecular diversity expressed across its range. One of the populations of interest, inhabiting the Apaporis River (Colombia), was described based on skull features as an incipient species (C. c. apaporiensis) and has been treated by some authors as a full species. Recent molecular work challenged this hypothesis, because relatively low mitochondrial molecular differentiation was found between the morphologically described Apaporis caiman and C. crocodilus (s.s.) Amazonian populations. Here, we present an update on the topic based on a larger molecular sample size and on analysis of expanded geometric morphometric data that include six newly collected skulls. Morphometric data support the existence of previously recognized morphotypes within the complex in Colombia and demonstrate that the newly collected material can be assigned to the classic Apaporis caiman morphotype. However, our expanded genetic analysis fails to find appreciable mitochondrial molecular divergence of the Apaporis caiman population from the C. c. crocodilus population (COI-CytB: Amazon Peru 0.17 ± 0.06%, CytB-only: Caquetá River Colombia 0.08 ± 0.07%). The Apaporis caiman is interpreted to be a phenotypically distinct member of the cis-Andean C. crocodilus metapopulation that has not yet achieved (or may not be undergoing at all) appreciable genetic differentiation. Thus, it should not be considered a fully independent evolutionary lineage, nor given full species rank.

Testing inter-observer error under a collaborative research framework for studying lithic shape variability

Evaluating error that arises through the aggregation of data recorded by multiple observers is a key consideration in many metric and geometric morphometric analyses of stone tool shape. One of the most common approaches involves the convergence of observers for repeat trails on the same set of artefacts: however, this is logistically and financially challenging when collaborating internationally and/or at a large scale. We present and evaluate a unique alternative for testing inter-observer error, involving the development of 3D printed copies of a lithic reference collection for distribution among observers. With the aim of reducing error, clear protocols were developed for photographing and measuring the replicas, and inter-observer variability was assessed on the replicas in comparison with a corresponding data set recorded by a single observer. Our results demonstrate that, when the photography procedure is standardized and dimensions are clearly defined, the resulting metric and geometric morphometric data are minimally affected by inter-observer error, supporting this method as an effective solution for assessing error under collaborative research frameworks. Collaboration is becoming increasingly important within archaeological and anthropological sciences in order to increase the accessibility of samples, encourage dual-project development between foreign and local researchers and reduce the carbon footprint of collection-based research. This study offers a promising validation of a collaborative research design whereby researchers remotely work together to produce comparable data capturing lithic shape variability.

Evolutionary convergence in body shape obscures taxonomic diversity in species of the African Labeo forskalii group: Case study of L. parvus Boulenger 1902 and L. ogunensis Boulenger 1910.

Labeo is the third most diverse genus of African cyprinids and is widely distributed across the continent. Labeo parvus, a small species originally described from the Congo basin, has been considered the only species of the L. forskalii group distributed across five African ichthyofaunal provinces (Nilo-Sudan, Congo, Cuanza, and Upper and Lower Guinea). However, morphological similarity between L. parvus and numerous congeners remains a central cause of taxonomic confusion within the genus. Here we employed a phylogenetic comparative approach to assess phenotypic convergence among species of the L. forskalii group, investigate the taxonomic status of L. parvus sensu lato (sl) in west Africa, and reevaluate the composition and distribution of L. parvus sensu stricto (ss). Our phylogenetic analysis provides no support for a sister relationship between L. parvus ss and any of the west African Labeo parvus-like species. Geometric morphometric and molecular phylogenetic data indicate that L. parvus ss is a Congo basin endemic, and seemingly ecologically equivalent species found in west Africa are L. ogunensis, L. obscurus and other undescribed or previously synonymized species. We discuss our findings in terms of convergent evolution using phylomorphospace and tests for phylogenetic signal.

The homogenization of avian morphological and phylogenetic diversity under the global extinction crisis

Biodiversity is facing a global extinction crisis that will reduce ecological trait diversity, evolutionary history, and ultimately ecosystem functioning and services.1-4 A key challenge is understanding how species losses will impact morphological and phylogenetic diversity at global scales.5,6 Here, we test whether the loss of species threatened with extinction according to the International Union for Conservation of Nature (IUCN) leads to morphological and phylogenetic homogenization7,8 across both the whole avian class and within each biome and ecoregion globally. We use a comprehensive set of continuous morphological traits extracted from museum collections of 8,455 bird species, including geometric morphometric beak shape data,9 and sequentially remove species from those at most to least threat of extinction. We find evidence of morphological, but not phylogenetic, homogenization across the avian class, with species becoming more alike in terms of their morphology. We find that most biome and ecoregions are expected to lose morphological diversity at a greater rate than predicted by species loss alone, with the most imperiled regions found in East Asia and the Himalayan uplands and foothills. Only a small proportion of assemblages are threatened with phylogenetic homogenization, in particular parts of Indochina. Species extinctions will lead to a major loss of avian ecological strategies, but not a comparable loss of phylogenetic diversity. As the decline of species with unique traits and their replacement with more widespread generalist species continues, the protection of assemblages at most risk of morphological and phylogenetic homogenization should be a key conservation priority.

A case of integrative taxonomy based on traditional morphology, molecular systematics and geometric morphometrics in the taxonomy of Torrenticolidae (Acari, Hydrachnidiae)

An integrative taxonomy based on traditional morphological method, molecular systematics and geometric morphometrics was tested to identify two species of torrenticolid mites, which are similar in morphology. A new species of the water mite genus Torrenticola from China, T. nipponicella Gu & Guo sp. nov., was described and illustrated in this paper. The descriptions included morphological features, molecular data, geometric morphometric data, and a discussion of their taxonomic status and integrative taxonomy. Meanwhile, some potential taxonomic characters of those species were analyzed by canonical variate analysis and principal component analysis. Those analyses of two landmark configurations revealed important taxonomical characters in dorsal (dorsoglandularia 1–3) and ventral shields (coxoglandularia 2, 4, ventroglandularia 3).

Distribution and Morphological Variation of Xeronycteris vieirai Gregorin and Ditchfield, 2005 (Chiroptera, Phyllostomidae)

Xeronycteris Gregorin and Ditchfield, 2005 is a rare monotypic genus of Lonchophyllinae bats endemic to Brazil, with Xeronycteris vieirai Gregorin and Ditchfield, 2005 as the type and sole species. We updated the geographical distribution of the species, including new records from the Cerrado and the Caatinga. Using traditional and geometric morphometric data obtained from 49 museum specimens, including the type series and those representing new records, we describe and discuss the morphological variation of skull shape found in the most comprehensive sample of X. vieirai to date. We also compare similar species and the geographic distribution of X. vieirai and highlight diagnostic traits useful for field identification. Xeronycteris vieirai is now known to occur in 14 localities confirmed by 54 museum specimens housed in Brazilian scientific collections. Records of this species are sparse, as even 15 years after its discovery the knowledge on this species is based on specimens from only a few localities. Specimens of this species show considerable morphological variation in different regions of the skull, especially for a highly specialized nectar-feeding bat, demonstrating variations in the snout and temporomandibular articulation. We discuss endemism issues related to the different biomes where it occurs (in the South American dry diagonal). We also compare these aspects to other bat species with similar geographic distributions, identifying important elements for future research on this species.

Ontogenetic drivers of morphological evolution in monitor lizards and allies (Squamata: Paleoanguimorpha), a clade with extreme body size disparity

BackgroundHeterochrony, change in the rate or timing of development, is thought to be one of the main drivers of morphological evolution, and allometry, trait scaling patterns imposed by size, is traditionally thought to represent an evolutionary constraint. However, recent studies suggest that the ontogenetic allometric trajectories describing how organisms change as they grow may be labile and adaptive. Here we investigated the role of postnatal ontogenetic development in the morphological diversification of Paleoanguimorpha, the monitor lizards and allies, a clade with extreme body size disparity. We obtained linear and geometric morphometric data for more than 1,600 specimens belonging to three families and 60 species, representing ~ 72% of extant paleoanguimorph diversity. We used these data to undertake one of the largest comparative studies of ontogenetic allometry to date.ResultsHeterochrony is likely dictating morphological divergence at shallow evolutionary scales, while changes in the magnitude and direction of ontogenetic change are found mainly between major clades. Some patterns of ontogenetic variation and morphological disparity appear to reflect ontogenetic transitions in habitat use. Generally, juveniles are more similar to each other than adults, possibly because species that differ in ecology as adults are arboreal as juveniles. The magnitude of ontogenetic change follows evolutionary models where variation is constrained around an optimal value. Conversely, the direction of ontogenetic change may follow models with different adaptive optima per habitat use category or models where interspecific interactions influence its evolution. Finally, we found that the evolutionary rates of the ontogenetic allometric trajectories are phylogenetically variable.ConclusionsThe attributes of ontogenetic allometric trajectories and their evolutionary rates are phylogenetically heterogeneous in Paleoanguimorpha. Both allometric constraints and ecological factors have shaped ontogeny in the group. Our study highlights the evolutionary lability and adaptability of postnatal ontogeny, and teases apart how different evolutionary shifts in ontogeny contribute to the generation of morphological diversity at different evolutionary scales.

The Level of Pollination Specialization Affects the Relationship between the Shape of Flowers and the Bills of Their Hummingbird Pollinators in Antillean Gesneriaceae

Premise of research. Pollinators are known to impose strong selection on floral shape. Particularly well studied is the relationship between the flowers of hummingbird-pollinated plant species and the bills of their pollinators. However, no studies to date have evaluated whether these relationships vary according to the level of pollination specialization. Here, we quantify the relationship between the corolla shape of Antillean Gesneriaceae and the bills of their hummingbird pollinators for species with a specialist (one functional group of pollinators: hummingbirds) and a generalist (more than one functional group of pollinators: hummingbirds, bats, and insects) pollination strategy.Methodology. We used phylogenetic generalized least squares analyses on linear measurements and phylogenetic two blocks partial least squares on multivariate geometric morphometrics data to test whether and how the variation in the corolla shape of the Antillean Gesneriaceae is correlated to the shape of the bills of their hummingbird pollinators.Pivotal results. We found that corolla shape is correlated with the bill shape of the hummingbird pollinators but that the nature of this relationship differed between pollination specialists and generalists. For example, corolla curvature was positively correlated with bill curvature for specialists but not for generalists.Conclusions. Our study suggests that pollinators affect the evolution of flower shape but that the nature and strength of the selective pressures are affected by the pollinator guild of the pollinators in the Antillean Gesneriaceae.

Morphological diversity within the Ozark minnow (Notropis nubilus: Leuciscidae).

The Ozark minnow, Notropis nubilus, is a small stream fish that has a disjunct distribution in the Ozark Plateau and upper Mississippi River basin. Three reciprocally monophyletic and deeply divergent lineages have been hypothesized within the species based on molecular data. These lineages are allopatric and isolated from each other. The objective of this study was to test the hypothesis that these lineages and the disjunct population in the upper Mississippi River basin are morphologically distinct. Meristic and geometric morphometric data were used to identify and quantify morphological diversity within the Ozark minnow. Analyses of the meristic data and a principal component analysis of the morphometric data were unable to find any noticeable differences in morphology among groups. However, canonical variates analyses of the morphometric data and linear models were able to define statistically significant differences in shape. Analyses of all-individuals were able to identify shape differences between all groups. Males-only analyses were less conclusive, but there was some indication that males may be diverging more quickly than all-individuals. The detection of subtle variation in shape implies selection is not a strong factor in morphological divergence and observed differences are most likely due to morphological drift. This indicates that the lineages within the Ozark minnow are likely on the trajectory for speciation. The allopatric nature of these clades makes the Ozark minnow an interesting model for the study of morphological drift and speciation.

Developmental instability in domesticated mammals.

Measures of fluctuating asymmetry (FA) have been adopted widely as an estimate of developmental instability. Arising from various sources of stress, developmental instability is associated with an organism's capacity to maintain fitness. The process of domestication has been framed as an environmental stress with human-specified parameters, suggesting that FA may manifest to a larger degree among domesticates compared to their wild relatives. This study used three-dimensional geometric morphometric landmark data to (a) quantify the amount of FA in the cranium of six domestic mammal species and their wild relatives and, (b) provide novel assessment of the commonalities and differences across domestic/wild pairs concerning the extent to which random variation arising from the developmental system assimilates into within-population variation. The majority of domestic mammals showed greater disparity for asymmetric shape, however, only two forms (Pig, Dog) showed significantly higher disparity as well as a higher degree of asymmetry compared to their wild counterparts (Wild Boar, Wolf). Contra to predictions, most domestic and wild forms did not show a statistically significant correspondence between symmetric shape variation and FA, however, a moderate correlation value was recorded for most pairs (r-partial least squares >0.5). Within pairs, domestic and wild forms showed similar correlation magnitudes for the relationship between the asymmetric and symmetric components. In domesticates, new variation may therefore retain a general, conserved pattern in the gross structuring of the cranium, whilst also being a source for response to selection on specific features.

Sexual dimorphism in the first rib of Homo sapiens.

This work aimed to study sexual dimorphism in the first rib of modern humans, with a special focus on whether differences in shape are due to divergent allometric growth in males and females. Also, we compare the accuracy of sex classification using different approaches based on two methodologies, traditional morphometry based on linear measurements and geometric morphometric analysis based on 2D landmark coordinates. The sample studied here comprised 121 right and left first ribs from 65 female and male adult recent Euro-American Homo sapiens individuals. For traditional morphometrics, 12metric variables were collected from each rib using a digital caliper, and for geometric morphometrics, six landmarks and 31semilandmarks were captured from photographs using digital software. Both geometric morphometric and metric data were analyzed to calculate the index of sexual dimorphism, variation related to lateral asymmetry, variation in size and shape, and allometric trends between males and females. Finally, a linear discriminant analysis (LDA) was performed comparing both methodologies to test the best approach for sex classification. Results indicated that there are significant sex differences in the size and shape of the first ribs of recent Euro-American Homo sapiens. Regression analysis revealed different allometric patterns for males and females, and this could partially explain shape differences between sexes. Additionally, traditional morphometrics showed that all characteristics analyzed are significantly dimorphic, with the midshaft minimum craniocaudal diameter, the sternal end minimum diameter, and the neck minimum craniocaudal diameter displaying the most dimorphic scores. Similarly, geometric morphometrics results indicated that males have more curved and interno-exteriorly wider first ribs. Finally, analysis of sex classification using LDA yielded slightly better accuracy for traditional morphometry (83.8%) than the geometric morphometrics approach (81.3%) based on form Procrustes coordinates. This study demonstrates the usefulness of applying two different morphometric approaches to obtain more comprehensive results.

On Information Rank Deficiency in Phenotypic Covariance Matrices.

This article investigates a form of rank deficiency in phenotypic covariance matrices derived from geometric morphometric data, and its impact on measures of phenotypic integration. We first define a type of rank deficiency based on information theory then demonstrate that this deficiency impairs the performance of phenotypic integration metrics in a model system. Lastly, we propose methods to treat for this information rank deficiency. Our first goal is to establish how the rank of a typical geometric morphometric covariance matrix relates to the information entropy of its eigenvalue spectrum. This requires clear definitions of matrix rank, of which we define three: the full matrix rank (equal to the number of input variables), the mathematical rank (the number of nonzero eigenvalues), and the information rank or “effective rank” (equal to the number of nonredundant eigenvalues). We demonstrate that effective rank deficiency arises from a combination of methodological factors—Generalized Procrustes analysis, use of the correlation matrix, and insufficient sample size—as well as phenotypic covariance. Secondly, we use dire wolf jaws to document how differences in effective rank deficiency bias two metrics used to measure phenotypic integration. The eigenvalue variance characterizes the integration change incorrectly, and the standardized generalized variance lacks the sensitivity needed to detect subtle changes in integration. Both metrics are impacted by the inclusion of many small, but nonzero, eigenvalues arising from a lack of information in the covariance matrix, a problem that usually becomes more pronounced as the number of landmarks increases. We propose a new metric for phenotypic integration that combines the standardized generalized variance with information entropy. This metric is equivalent to the standardized generalized variance but calculated only from those eigenvalues that carry nonredundant information. It is the standardized generalized variance scaled to the effective rank of the eigenvalue spectrum. We demonstrate that this metric successfully detects the shift of integration in our dire wolf sample. Our third goal is to generalize the new metric to compare data sets with different sample sizes and numbers of variables. We develop a standardization for matrix information based on data permutation then demonstrate that Smilodon jaws are more integrated than dire wolf jaws. Finally, we describe how our information entropy-based measure allows phenotypic integration to be compared in dense semilandmark data sets without bias, allowing characterization of the information content of any given shape, a quantity we term “latent dispersion”. [Canis dirus; Dire wolf; effective dispersion; effective rank; geometric morphometrics; information entropy; latent dispersion; modularity and integration; phenotypic integration; relative dispersion.]

ALPACA: A fast and accurate computer vision approach for automated landmarking of three-dimensional biological structures.

Landmark‐based geometric morphometrics has emerged as an essential discipline for the quantitative analysis of size and shape in ecology and evolution. With the ever‐increasing density of digitized landmarks, the possible development of a fully automated method of landmark placement has attracted considerable attention. Despite the recent progress in image registration techniques, which could provide a pathway to automation, three‐dimensional (3D) morphometric data are still mainly gathered by trained experts. For the most part, the large infrastructure requirements necessary to perform image‐based registration, together with its system specificity and its overall speed, have prevented its wide dissemination.Here, we propose and implement a general and lightweight point cloud‐based approach to automatically collect high‐dimensional landmark data in 3D surfaces (Automated Landmarking through Point cloud Alignment and Correspondence Analysis). Our framework possesses several advantages compared with image‐based approaches. First, it presents comparable landmarking accuracy, despite relying on a single, random reference specimen and much sparser sampling of the structure's surface. Second, it can be efficiently run on consumer‐grade personal computers. Finally, it is general and can be applied at the intraspecific level to any biological structure of interest, regardless of whether anatomical atlases are available.Our validation procedures indicate that the method can recover intraspecific patterns of morphological variation that are largely comparable to those obtained by manual digitization, indicating that the use of an automated landmarking approach should not result in different conclusions regarding the nature of multivariate patterns of morphological variation.The proposed point cloud‐based approach has the potential to increase the scale and reproducibility of morphometrics research. To allow ALPACA to be used out‐of‐the‐box by users with no prior programming experience, we implemented it as a SlicerMorph module. SlicerMorph is an extension that enables geometric morphometrics data collection and 3D specimen analysis within the open‐source 3D Slicer biomedical visualization ecosystem. We expect that convenient access to this platform will make ALPACA broadly applicable within ecology and evolution.

Microsatellites and petal morphology reveal new patterns of admixture in Orchis hybrid zones.

The genetic structure of hybrid zones provides insight into the potential for gene flow to occur between plant taxa. Four closely related European orchid species (Orchis anthropophora, O. militaris, O. purpurea, and O. simia) hybridize when they co-occur. We aimed to characterize patterns of hybridization in O. militaris-O. purpurea, O. purpurea-O. simia, and O. anthropophora-O. simia hybrid zones using molecular and morphological data. We used 11 newly isolated nuclear microsatellites to genotype 695 individuals collected from seven hybrid zones and six allopatric parental populations in France. Geometric morphometric analysis was conducted using 15 labellum landmarks to capture the main aspects of petal shape. Backcrossing was asymmetric toward O. militaris in multiple O. militaris-O. purpurea hybrid zones. Hybrids in O. purpurea-O. simia and O. anthropophora-O. simia hybrid zones were largely limited to F1 and F2 generations, but further admixture had occurred. These patterns were reflected in labellum geometric morphometric data, which correlated strongly with nuclear microsatellite data in all three species combinations. The coexistence of parental and admixed individuals in these Orchis hybrid zones implies they are likely to be tension zones being maintained by a balance between gene flow into the hybrid zone and selection acting against admixed individuals. The pattern of admixture in the three species combinations suggests intrinsic selection acting on the hybrids is weaker in more closely related taxa.

Shell-specific differentiation: how geometric morphometrics can add to knowledge of Macominae species (Tellinidae, Bivalvia)

Tellinidae is one of the most diverse families in Brazilian coastal areas, comprising nine subfamilies, one of which is Macominae. These species are known for their morphological similarities, which make their identification difficult. To minimize such difficulties, taxonomists have sought methods or tools, such as the use of geometric morphometric data, to study the continuous characteristics which are often observed subjectively and are not measurable. Almost thirty right valves were chosen from five of the most representative Macominae species: Austromacoma biota Arruda & Domaneschi, 2005, Austromacoma constricta (Bruguiere, 1792), Psammotreta brevifrons (Say, 1834 in Say 1830–1834), Psammotreta cleryana (d’ Orbigny, 1846 in d’ Orbigny 1834–1847), Macoploma tenta (Say, 1834 in Say 1830–1834). The geometric morphometric data were based on the fourteen landmarks of each internal valve, performed by TPSDig, and the morphometric and statistical analyses, carried out with MorphoJ, were Procrustes analysis, Procrustes Anova, principal components analysis, discriminant function analysis, and regression analysis. Permutations and Goodall’s F test with bootstrap were performed in the R software package. All the analyses divided the studied species into two groups based on the external shape of their shells: oval-trigonal or elongated. The variation of the external shape of the shell is related to the life habits of the bivalve, with the elongated shells lying inclined in the substrata, and the oval-trigonal shells lying horizontally, facilitating deposit-feeding habits. The pallial sinus shape and position of the adductor muscle scar also helped differentiate species of each group, relating them to the bivalve anatomy. Psammotreta cleryana and P. brevifrons exhibited remarkably similar shapes, and a broader population study is needed to differentiate between these two species.

A model of developmental canalization, applied to human cranial form.

Developmental mechanisms that canalize or compensate perturbations of organismal development (targeted or compensatory growth) are widely considered a prerequisite of individual health and the evolution of complex life, but little is known about the nature of these mechanisms. It is even unclear if and how a “target trajectory” of individual development is encoded in the organism’s genetic-developmental system or, instead, emerges as an epiphenomenon. Here we develop a statistical model of developmental canalization based on an extended autoregressive model. We show that under certain assumptions the strength of canalization and the amount of canalized variance in a population can be estimated, or at least approximated, from longitudinal phenotypic measurements, even if the target trajectories are unobserved. We extend this model to multivariate measures and discuss reifications of the ensuing parameter matrix. We apply these approaches to longitudinal geometric morphometric data on human postnatal craniofacial size and shape as well as to the size of the frontal sinuses. Craniofacial size showed strong developmental canalization during the first 5 years of life, leading to a 50% reduction of cross-sectional size variance, followed by a continual increase in variance during puberty. Frontal sinus size, by contrast, did not show any signs of canalization. Total variance of craniofacial shape decreased slightly until about 5 years of age and increased thereafter. However, different features of craniofacial shape showed very different developmental dynamics. Whereas the relative dimensions of the nasopharynx showed strong canalization and a reduction of variance throughout postnatal development, facial orientation continually increased in variance. Some of the signals of canalization may owe to independent variation in developmental timing of cranial components, but our results indicate evolved, partly mechanically induced mechanisms of canalization that ensure properly sized upper airways and facial dimensions.