Geometric morphometrics of mandibles for dietary differentiation of Bovidae (Mammalia: Artiodactyla)

The mammalian family Bovidae has been widely studied in ecomorphological research, with important applications to paleoecological and paleohabitat reconstructions. Most studies of bovid craniomandibular features in relation to diet have used linear measurements. In this study, we conduct landmark-based geometric-morphometric analyses to evaluate whether different dietary groups can be distinguished by mandibular morphology. Our analysis includes data for 100 species of extant bovids, covering all bovid tribes and 2 dietary classifications. For the first classification with 3 feeding categories, we found that browsers (including frugivores), mixed feeders, and grazers are moderately well separated using mandibular shape. A finer dietary classification (frugivore, browser, browser–grazer intermediate, generalist, variable grazer, and obligate grazer) proved to be more useful for differentiating dietary extremes (frugivores and obligate grazers) but performed equally or less well for other groups. Notably, frugivorous bovids, which belong in tribe Cephalophini, have a distinct mandibular shape that is readily distinguished from all other dietary groups, yielding a 100% correct classification rate from jackknife cross-validation. The main differences in mandibular shape found among dietary groups are related to the functional needs of species during forage prehension and mastication. Compared with browsers, both frugivores and grazers have mandibles that are adapted for higher biomechanical demand of chewing. Additionally, frugivore mandibles are adapted for selective cropping. Our results call for more work on the feeding ecology and functional morphology of frugivores and offer an approach for reconstructing the diet of extinct bovids.     

Geometric morphometrics in entomology: Basics and applications

The recent expansion of a variety of morphometric tools has brought about a revolution in the comparison of morphology in the context of the size and shape in various fields including entomology. First, an overview of the theoretical issues of geometric morphometrics is presented with a caution about the usage of traditional morphometric measurements. Second, focus is then placed on two broad approaches as tools for geometric morphometrics; that is, the landmark‐based and the outline‐based approaches. A brief outline of the two methodologies is provided with some important cautions. The increasing trend of entomological studies in using the procedures of geometric morphometrics is then summarized. Finally, information is provided on useful toolkits such as computer software as well as codes and packages of the R statistical software that could be used in geometric morphometrics.     

Geometric morphometrics: Current and future in China

Although there were many ancient Chinese mathematicians contributed a lot on geometry,Geometric morphometrics (GM) in modern concept was not firstly proposed by Chinese.The super capability of geometric morphometrics in scientific computing and problem solving has gained a lot of attentions in the world.Until early of 21 centuries,geometric morphometrics was introduced into China.Since then,GM was rapidly applied in many research fields.However,it is a pity that GM is still not well-known in China as many works are published out of China.Thus,the special issue "Geometric morphometrics:Current shape and future directions" is organized.The present issue presents a series of contributions in this scientific field.In future,there will be many considerable new developing fields on GM needed to pay more attentions,for instances,3D geometric morphometrics,4D analysis,visualization of amber,new machine developing,new software developing,automatic identification system,etc.Once these technical bottle-necks on 3D data collecting and merging geometric morphometric data from multiple characters could be solved,the automatic identification system and other fields based on Big Data would come true.     

Geometric morphometrics for the taxonomy of 11 species of Anopheles (Nyssorhynchus) mosquitoes

The subgenus Anopheles (Nyssorhynchus) (Diptera: Culicidae) includes the primary vectors of Plasmodium spp. in Colombia. Most adult females of this subgenus are difficult to identify in the field using the available keys. With the objective of further investigating the discriminatory power of modern morphometrics, both landmark‐based and outline‐based approaches were explored using the wing venation geometry of 11 Anopheles (Nyssorhynchus) species. Wing shape was able to separate the closest species of the subgenus. When the 11 species were analysed together, validated classification scores on average 5.3–8.6 times higher than those expected by chance were observed. These scores computed from the total sample of 11 species were not satisfactory for the recognition of Anopheles benarrochi B, Anopheles oswaldoi s.l. and Anopheles strodei. These sibling species were captured in sympatry. To improve the identification power of the morphometric tool, it was necessary to analyse these species separately from the remaining species. The best classification scores were obtained using a combination of 12 landmarks collected not only on the intersections of wing veins, but also on spots. An outline approach also gave excellent reclassification scores. Another pair of sibling species, collected in allopatry, Anopheles nuneztovari and Anopheles rangeli, also showed high classification scores.     

Geometric morphometrics and ecological niche modelling for delimitation of near-sibling triatomine species

Identifying morphologically similar triatomine species is key to Chagas' disease vector control and surveillance, but remains challenging when only qualitative phenotypic data are available. We investigated whether morphometric and ecological variation can provide additional criteria for species delimitation by combining geometric morphometrics and ecological niche modelling to characterize two near-sibling triatomine species, Triatoma sordida and Triatoma garciabesi (Reduviidae: Triatominae). We analysed size and shape variation in 231 wings and 123 heads from one T. garciabesi and three T. sordida populations. Predicted distribution maps (21 climatic variables, 324 vector occurrence points) were produced using the Maxent method. Multivariate analyses summarized morphological and ecological variation. Wings and heads of T. sordida were significantly larger and more elongated than those of T. garciabesi. Discriminant analyses separated the species, with a partial overlap between Argentinean populations. The predicted distribution of T. garciabesi included northwest Argentina (mainly arid Chaco), whereas that of T. sordida included northeast Argentina (humid Chaco) and the Brazilian Cerrado and Caatinga ecoregions. Clear ecological niche differences were observed, with T. garciabesi occupying colder and drier areas than T. sordida. Our results show how morphometric variation and niche divergence can be used to enhance operational criteria for the delimitation of phenotypically similar triatomine species.     

Geometric morphometrics and paleoneurology: brain shape evolution in the genus Homo

Paleoneurology concerns the study and analysis of fossil endocasts. Together with cranial capacity and discrete anatomical features, shape can be analysed to consider the spatial relationships between structures and to investigate the endocranial structural system. A sample of endocasts from fossil specimens of the genus Homo has been analysed using traditional metrics and 2D geometric morphometrics based on lateral projections of endocranial shape. The maximum and frontal widths show a size-related pattern of variation shared by all the taxa considered. Furthermore, as cranial capacity increases in the non-modern morphotypes there is a general endocranial vertical stretching (mainly centred at the anterior ascending circumvolution) with flattening and relative shortening of the parietal areas. This pattern could have involved some structural stress between brain development and vault bones at the parietal midsagittal profile in the heavy encephalised Neandertals. In contrast, modern humans show a species-specific neomorphic hypertrophy of the parietal volumes, leading to a dorsal growth and ventral flexion (convolution) and consequent globularity of the whole structure. Brain tensors such as the falx cerebri have been hypothesised to represent one of the main physical constraints on morphogenetic trajectories, with additional influences from cranial base structures. The neurofunctional inferences discussed here stress the role of the parietal areas in the visuo-spatial coordination and integration, which can be involved in higher cerebral functions and related to conceptual thinking.     

Geometric morphometrics of corpus callosum and subcortical structures in the fetal-alcohol-affected brain.

BACKGROUND: Although experienced clinicians have been diagnosing fetal alcohol syndrome (FAS) for nearly 30 years, the rest of the spectrum of fetal alcohol damage is not being classified effectively. This article describes a quantification of neuroanatomical structure that may supply a useful discriminator of prenatal brain damage from alcohol. It is demonstrated in a data set of adults of both sexes. METHODS: Ninety adults (45 males) were examined by magnetic resonance imaging (MRI). These subjects were group-matched for age and ethnicity across three diagnoses: FAS, fetal alcohol effects (FAE), and normals. All FAS and FAE were heavily alcohol-exposed in utero; normals were not. From T(1)-weighted MR brain images, we extracted 3D morphometric representations of shape for 33-landmark point configurations and 40-point outlines of the corpus callosum along its midline (a slightly nonplanar structure). RESULTS: There are striking differences between exposed and unexposed in the statistical distributions of these two shapes. The differences are better characterized by excess variance in the exposed group than by any change in average landmark or outline shape. For each sex, combining the callosal outline data with the landmark data leads to a powerful quadratic discriminator of exposed from unexposed. The discriminating features include the relationship of brain stem to diencephalon, and localized variabilities of callosal outline shape, but not diagnosis (FAS vs. FAE). CONCLUSIONS: Statistical analysis of brain shape is a powerful new source of information relevant to fetal alcohol spectrum nosology and etiology. Patients with FAS and FAE do not differ in these brain shape features, but both differ from the unexposed. The aspects of brain shape that are especially variable may be entailed in the underlying neuroteratogenetic mechanisms.     

横断山区高山姬鼠（Apdoemus chevrieri）头骨几何形态分析

研究对分布于横断山区（从北到南：巴塘、中甸、宁蒗、景东）的高山姬鼠头骨背面、腹面、侧面及下颌侧面的形态特征进行主成分分析、判别分析、薄片样条分析和多维尺度分析,以进一步探讨高山姬鼠头骨形态变异与环境之间的关系。研究结果表明,高山姬鼠头骨的背面和腹面在研究多种群头骨形态时更适宜,更有参考价值;经过薄片样条法分析显示形变集中在鼻骨、眼眶和臼齿,这可能与高山姬鼠生存的横断山从北到南的气候和地理环境变化相关;经多维尺度分析显示横断山地区的高山姬鼠的头骨发生了变异,这可能与高山姬鼠生活环境的经度和纬度有关。综上,横断山区的高山姬鼠种群的头骨形态有一定的变异,这可能反映了其对横断山不同生态环境的形态适应性变异．     

Geometric morphometrics of the skull of Tinamidae (Aves, Palaeognathae)

The Tinamidae comprise exclusively Neotropical palaegnathous birds, with homogeneous body morphology and no sexual dimorphism. The goal of this work was to explore the variation in skull morphology between taxa and its possible correspondence with features such as diet or gender using geometric morphometric tools. Eleven landmarks were analyzed in 53 skulls of 4 genera that inhabit grasslands: Nothoprocta, Eudromia, Nothura and Rhynchotus. Intrageneric and intergeneric variability was analyzed. The genera studied here can be distinguished based on the geometric shape of their skull, with prenarial region length and neurocranium shape as the most outstanding features. In the genus Eudromia, males and females could be differentiated, while in the genus Nothoprocta, the species differentiated according to their trophic habits. This study allows establishing that genera and, in some cases, the gender of the Tinamidae can be differentiated based on cranial shape.     

蜣螂后胸叉骨的几何形态学分析及其适应进化研究

【目的】甲虫的后胸叉骨是基部位于后足基节关节处,端部游离在胸腔内的几丁质构成的内骨骼。后胸叉骨作为胸腹部运动肌肉的联结点,在甲虫运动过程中扮演了重要角色,同时也承载了分类和系统发育信息。蜣螂根据其习性可分为滚粪球和直接掘洞两类行为类型。通过传统的比较形态学方法,我们无法得知滚粪球或直接掘洞的行为对后胸叉骨形态的影响。本研究旨在利用定量的几何形态学方法探究蜣螂后胸叉骨形态对不同行为选择压力的响应关系。【方法】对76种蜣螂后胸叉骨的形态多样性进行二维几何形态学定量评估;利用显微CT和计算机三维重建方法,对直接掘洞类蜣螂和滚粪球类蜣螂的代表种西班牙粪蜣螂Copris hispanus和忠诚泽蜣螂Kheper devotus的后胸叉骨进行三维重建,用于比较两者的三维形态差异。【结果】经过几何形态学分析可知,两类蜣螂后胸叉骨背面观和侧面观的马氏距离和普氏距离的p值均低于0.0001,表明两类蜣螂的后胸叉骨的形态存在显著性差异;通过对C.hispanus和K.devotus后胸叉骨3D模型的比较发现,两类蜣螂后胸叉骨的最大区别在于后胸叉骨的端半部(叉臂和中突)。前者的叉臂细长,中突面积大,背立脊呈窄条状且不发达;后者的叉臂宽扁,叉臂基半部十分宽大,中突面积小,背立脊呈鳍状且十分发达。【结论】滚粪球或直接掘洞的行为会对蜣螂后胸叉骨的形态有显著性影响,蜣螂后胸叉骨形态与滚粪球和直接掘洞两种行为的选择压力显著相关,这与后胸叉骨所附着的胸部肌肉参与相关运动关系密切。本研究为探索昆虫形态与功能关系提供了一个有益范例。     

Geometric morphometrics: recent applications to the study of evolution and development

The field of morphometrics is developing quickly and recent advances allow for geometric techniques to be applied easily to many zoological problems. This paper briefly introduces geometric morphometric techniques and then reviews selected areas where those techniques have been applied to questions of general interest. This paper is relevant to non-specialists looking for an entry into geometric morphometric methods and for ideas of how to incorporate them into the study of variation within and between species, the measurement of developmental stability, the role of development in shaping evolution and the special problem of measuring the shape of fossil specimens that are deformed from their original shape.     

Geometric morphometrics as a tool for understanding Dactylorhiza (Orchidaceae) diversity in European Russia

Geometric morphometric techniques were employed to assess the diversity of lip shapes (305 samples from 83 populations) in flowers of European Russian Dactylorhiza (Orchidaceae: Orchidinae). We found significant agreement between the results from geometric morphometrics, classic morphometrics and the distribution of certain nuclear DNA markers. The lip shapes from Arctic Dactylorhiza samples occupied an intermediate position between D. maculata and D. fuchsii samples from Central Russia, supporting a hybrid origin of 'northern tetraploids'. Lip shapes of the taxonomically controversial allotetraploid D. baltica were found to form a distinct group, with members having definite relationships with diploid D. incarnata samples from the same localities, indicating either their local origin or introgression with D. incarnata . In addition to demonstrating the value of geometric morphometric methods in studies of plant taxonomy and hybridization, we suggest future applications designed to explore pollinator-driven directional selection, developmental constraints and fluctuating asymmetry.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 1–12.     

Geometric morphometrics as a tool for identifying emperor fish (Lethrinidae) larvae and juveniles

The aim of this study was to evaluate the efficiency of geometric morphometrics for describing the body shape of fish larvae and juveniles, and identifying them to species, in comparison with traditional linear measurements. Species of emperor fishes (Perciformes: Lethrinidae, genus Lethrinus) were chosen as the model group, as the late larval and early juvenile stages in this genus are particularly difficult to identify. Forty‐five individuals of different species of Lethrinus were collected from the south‐western lagoon of New Caledonia between May 2005 and March 2006. The individuals were first identified to species by their partial cytochrome‐b gene sequence. They were then morphologically characterized using eight linear measurements and 23 landmarks recorded on digital photographs. Except for a small proportion of individuals, geometric morphometrics gave better results to distinguish the different species than linear measurements. A ‘leave one out’ approach confirmed the nearly total discrimination of recently settled Lethrinus genivittatus and Lethrinus nebulosus, whereas traditional identification keys failed to distinguish them. Therefore, geometric morphometrics is a promising tool for identifying fish larvae and juveniles to species. An effective approach would require building image databases of voucher specimens associated with their DNA barcodes. These images could be downloaded by the operator and processed with the specimens to be identified.     

Geometric morphometrics as a tool for interpreting evolutionary transitions in the black fly wing (Diptera: Simuliidae)

A geometric morphometric analysis was conducted on wing‐vein landmarks on exemplar species of the family Simuliidae of the following genera: Parasimulium, Gymnopais, Twinnia, Helodon, Prosimulium, Greniera, Stegopterna, Tlalocomyia, Cnephia, Ectemnia, Metacnephia, Austrosimulium, and Simulium. Generalized least squares superimposition was performed on landmarks, followed by a principal component analysis on resulting Procrustes distances. Patterns of shape change along the principal component axes were visualized using the thin‐plate spline. The analysis revealed wing shape diversity through (1) the insertion points of the subcosta and R₁, resulting in the terminus of the costa exhibiting a trend towards a more apical position on the wing, and (2) the insertion point of the humeral cross vein, resulting in the anterior branch of the media exhibiting a trend toward a more basal position on the wing. Canonical variates analysis of Procrustes distances successfully assigned all exemplar species into their a priori taxonomic groupings. The diversity in wing shape reveals a trend towards decreased length of basal radial cell and increased costalization of anterior wing veins in the evolutionary transition from plesiomorphic prosimuliines to more derived simuliines. The functional significance of these evolutionary transitions is discussed. © 2013 The Linnean Society of London     

Craniometric differentiation within wild-living cats in Scotland using 3D morphometrics

Due to the unknown effects of long-term sympatry and interbreeding with the domestic cat, there is an ongoing debate about the characterization and taxonomic status of the wildcat Felis silvestris in Europe. Recent results on the morphology of wild-living cats in Scotland had revealed two morphological groups, T1 and T2, defined from a discriminant function (based on intestine length and limb bone size). We compared wild-living cats of each of these types from Scotland, together with known domestic cats, using a new technique: geometric analysis of 3D landmarks, with the goal of formalizing a definition of wildcats that would assist with their conservation. Eighty-five landmarks were digitized on a set of 85 skulls and subjected to superimposition techniques and univariate and multivariate analyses. Results showed that T1 cats generally clustered together while, despite showing their own morphological characteristics, T2 cats seemed closer to domestic cats. T1 cats had the largest skulls, the lowest braincase capacity index and demonstrated the greatest sexual dimorphism. Domestic cats were more heterogeneous, exhibiting a wide overlap between males and females. Analysing individual landmarks, females showed more differences between the groups, particularly in the orbito-nasal region. Our results not only provide a completely independent verification of the T1/T2 categorization, but also show that, as a practical tool, skulls can be identified as T1 using six linear skull characters selected from the 85 landmarks. From current evidence it is not logically possible to state conclusively that T1 cats are wildcats, but our results firmly support the hypothesis that they are furthest from domestic cats. Thus, the distribution of T1 cats in Scotland provides a possible basis for wildcat conservation through protection by area.     

Geometric morphometrics meets metacommunity ecology: environment and lineage distribution affects spatial variation in shape

Patterns of univariate trait variation across metacommunities are widely explored, as are searches for their underlying causes. Surprisingly, patterns of multivariate shape remain unknown, and the search for drivers of functional traits of communities often neglect the biogeographical distribution of phylogenetic clades. Our aim was to investigate multivariate shape distribution across metacommunities and to determine the main environmental drivers of shape beyond/taking into account the phylogenetic distribution of lineages. We obtained mean skull and mandible shape for 228 species of Neotropical sigmodontine rodents through geometric morphometrics (GM), and then calculated mean shapes for 1° × 1° cells across the Neotropics based on the incidence of sigmodontines. We investigated the effects of lineage distribution on mean trait variation by using phylogenetic fuzzy weighting to calculate principal coordinates of phylogenetic structure (PCPS). Effects of environmental variables on shape variation incorporating phylogenetic composition were realized through redundancy analysis. We found that the different distributions of major lineages throughout the Neotropics were responsible for much of the mean shape variation. The association of landscape features with tribal groupings (Oryzomyini with Amazonia and Phyllotini and Abrotrichini with the Andes) were standouts. Environmental variables and lineage distribution explain the same (i.e. shared) portion of shape variation, suggesting phylogenetic niche conservatism at the metacommunity level. Seasonality in temperature and land cover were the best environmental predictors of mean shape: larger tympanic bullae, incisive foramina, and check teeth are all associated with highly seasonal and less vegetated areas. Our new approach of using GM shape across metacommunities was demonstrably useful in understanding large‐scale biogeographical patterns of shape variation and identifying its underlying causes. The overlap between environmental variables and phylogenetic lineage distribution suggests that a process of niche conservatism is likely: the phenotype–environment correlation is mediated by the differential biogeographical distribution of the main clades.     

Geometric morphometrics applied to viscerocranial bones in three populations of the Lake Tanganyika cichlid fish Tropheus moorii

Lake Tanganyika comprises the oldest and most diverse species flock of cichlid fishes. Many species are subdivided into numerous populations, often classified as geographical races, colour morphs or sister species. Unlike younger species flocks, in which speciation is accompanied by eco-morphological diversification that of Lake Tanganyika is at a mature stage with little further morphological change, most probably caused by stabilizing selection. This study addresses body shape differences among three genetically distinct but morphologically similar populations of Tropheus  moorii , by focusing on bony structures of the cichlid head. We test by means of geometric morphological methods whether shape changes in the cichlid head are based on particular osteological differences. Specimens were disarticulated enzymatically, and standardized digital images of the disarticulated bony elements were taken. A landmark system was established for the dentary, articular, premaxilla, quadrate and the preopercle. Only the dentary shows significant differentiation among the three populations. Since all three populations live in similar cobble habitats and occupy the same trophic niche, the observed difference in the shape of the dentary can either be explained by different directional selection due to subtle habitat differences, or by neutral drift constrained by borders enforced through stabilizing selection. Lack of difference might indicate stabilizing selection on bone shape.     

How females become complex: cell differentiation in the gametophyte

In contrast to animals, gametes in plants form a separate haploid generation, the gametophyte. The female gametophyte of flowering plants consists of just four different cell types that play distinct roles in the reproductive process. Differentiation of the distinct cell fates is tightly controlled and appears to follow regional cues that are arranged along a polar axis. Mutant analysis suggests that important aspects of gametophyte patterning are gametophytically regulated. Additionally, structural and molecular changes following misspecification indicate that the female gametophyte is a remarkably versatile structure with enormous respecification potential. Recently, new tools have been developed that open fascinating possibilities to access and analyze those processes that ultimately ensure successful fertilization.