Patterns of integration in the canine skull: an inside view into the relationship of the skull modules of domestic dogs and wolves.
TL;DR: It is shown that the higher skull shape diversity in dogs is not explained by less integrated skull modules, and the pattern of their covariation in the dog skull can be traced back to similar patterns in the wolf.
About: This article is published in Zoology.The article was published on 2017-08-18. It has received 29 citations till now. The article focuses on the topics: Skull.
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TL;DR: This is the first study that combines different skeletal features for the description and comparison of shape changes in all living equid groups using geometric morphometrics and supports Darwin’s hypothesis that the shape variation in the skull of domesticated horses is similar to theshape variation of all wild equid species existing today.
Abstract: In horses, the morphological changes induced by the process of domestication are reportedly less pronounced than in other species, such as dogs or pigs – although the horses’ disparity has rarely been empirically tested. We investigated shape differences and modularity of domesticated horses, Przewalski’s horses, donkeys and zebras. Mandibular and tooth shape have been shown to be valuable features for differentiating wild and domesticated forms in some mammals. Both mandible and teeth, show a pattern of shape space occupation analogous to that of the cranium, with domesticated horses occupying a similar extension in shape space to that of wild equids. Only cranial shape data exhibit a tendency to separate domesticated horses and Przewalski’s horses from donkeys and zebras. Maximum likelihood model-based tests confirm the horse cranium is composed of six developmental modules, as reported for placental mammals in general. The magnitude of integration in domesticated horse skull was lower than in wild equids across all six cranial modules, and lower values of integration were associated with higher disparity values across all modules. This is the first study that combines different skeletal features for the description and comparison of shape changes in all living equid groups using geometric morphometrics. We support Darwin’s hypothesis that the shape variation in the skull of domesticated horses is similar to the shape variation of all wild equid species existing today. Lower magnitudes of module integration are recovered in domesticated horses compared to their wild relatives.
43 citations
Cites result from "Patterns of integration in the cani..."
...There exist few empirical tests of this hypothesis and results on dogs are inconclusive, with reports that patterns of integration have remained stable despite the morphological diversification associated with domestication [9, 44], but also that high module disparity is associated with greater cranial shape variation in dogs compared to wolves [45]....
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TL;DR: The first high-precision 3D in vivo hindlimb kinematic data to be recorded in normal dogs of four different breeds using biplanar, high-frequency fluoroscopy combined with a 3D optoelectric system followed by a markerless XROMM analysis reveal an unprecedented degree of precision and substantial limitations to the use of skin marker-based data.
Abstract: The first high-precision 3D in vivo hindlimb kinematic data to be recorded in normal dogs of four different breeds (Beagle, French bulldog, Malinois, Whippet) using biplanar, high-frequency fluoroscopy combined with a 3D optoelectric system followed by a markerless XROMM analysis (Scientific Rotoscoping, SR or 3D-2D registration process) reveal a) 3D hindlimb kinematics to an unprecedented degree of precision and b) substantial limitations to the use of skin marker-based data. We expected hindlimb kinematics to differ in relation to body shape. But, a comparison of the four breeds sets the French bulldog aside from the others in terms of trajectories in the frontal plane (abduction/adduction) and long axis rotation of the femur. French bulldogs translate extensive femoral long axis rotation (>30°) into a strong lateral displacement and rotations about the craniocaudal (roll) and the distal-proximal (yaw) axes of the pelvis in order to compensate for a highly abducted hindlimb position from the beginning of stance. We assume that breeds which exhibit unusual kinematics, especially high femoral abduction, might be susceptible to a higher long-term loading of the cruciate ligaments.
30 citations
TL;DR: It is shown that urban and rural populations of red foxes (Vulpes vulpes) from London and surrounding boroughs are divergent in skull traits, suggesting that occurrences of phenotypic divergence in relation to human activity, while interesting themselves, also have the potential to inform us of the conditions and mechanisms that could initiate domestication.
Abstract: Human activity is drastically altering the habitat use of natural populations. This has been documented as a driver of phenotypic divergence in a number of wild animal populations. Here, we show th...
30 citations
Cites background from "Patterns of integration in the cani..."
...In fact, the dog skull (both domesticated and wild), and that of other canids is known to be modular with the anterior snout region forming a separate variational module from the brain case [12,14]....
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TL;DR: There is no single, universal and global pattern of paedomorphosis or any other kind of heterochrony behind the morphological diversification that accompanies domestication, as shown in a taxonomically broad study.
Abstract: As shown in a taxonomically broad study, domestication modifies postnatal growth. Skull shape across 1128 individuals was characterized by 14 linear measurements, comparing 13 pairs of wild versus domesticated forms. Among wild forms, the boar, the rabbit and the wolf have the highest proportion of allometric growth, explaining in part the great morphological diversity of the domesticated forms of these species. Wild forms exhibit more isometric growth than their domesticated counterparts. Multivariate comparisons show that dogs and llamas exhibit the greatest amount of differences in trajectories with their wild counterparts. The least amount is recorded in the pig-boar, and camel and horse pairs. Bivariate analyses reveal that most domesticated forms have growth trajectories different from their respective wild counterparts with regard to the slopes. In pigs and camels slopes are shared and intercepts are different. There is a trajectory extension in most domesticated herbivores and the contrary pattern in carnivorous forms. However, there is no single, universal and global pattern of paedomorphosis or any other kind of heterochrony behind the morphological diversification that accompanies domestication.
28 citations
Cites background from "Patterns of integration in the cani..."
...Recently, the subject of modularity as it relates to dog domestication has been examined [56], and recent work on pig skull growth looked at modules of the skull and their differential growth [49]....
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TL;DR: Accumulated evidence does not definitively show that the dingo was ever domesticated and additional focused research is required, but it is suggested that incorporating ancient DNA data into the debate concerning dingo origins will be pivotal to understanding the evolutionary history of the canid.
Abstract: The Australian dingo continues to cause debate amongst Aboriginal people, pastoralists, scientists and the government in Australia. A lingering controversy is whether the dingo has been tamed and has now reverted to its ancestral wild state or whether its ancestors were domesticated and it now resides on the continent as a feral dog. The goal of this article is to place the discussion onto a theoretical framework, highlight what is currently known about dingo origins and taxonomy and then make a series of experimentally testable organismal, cellular and biochemical predictions that we propose can focus future research. We consider a canid that has been unconsciously selected as a tamed animal and the endpoint of methodical or what we now call artificial selection as a domesticated animal. We consider wild animals that were formerly tamed as untamed and those wild animals that were formerly domesticated as feralized. Untamed canids are predicted to be marked by a signature of unconscious selection whereas feral animals are hypothesized to be marked by signatures of both unconscious and artificial selection. First, we review the movement of dingo ancestors into Australia. We then discuss how differences between taming and domestication may influence the organismal traits of skull morphometrics, brain and size, seasonal breeding, and sociability. Finally, we consider cellular and molecular level traits including hypotheses concerning the phylogenetic position of dingoes, metabolic genes that appear to be under positive selection and the potential for micronutrient compensation by the gut microbiome. Western Australian Government policy is currently being revised to allow the widespread killing of the Australian dingo. These policies are based on an incomplete understanding of the evolutionary history of the canid and assume the dingo is feralized. However, accumulated evidence does not definitively show that the dingo was ever domesticated and additional focused research is required. We suggest that incorporating ancient DNA data into the debate concerning dingo origins will be pivotal to understanding the evolutionary history of the canid. Further, we advocate that future morphological, behavioural and genetic studies should focus on including genetically pure Alpine and Desert dingoes and not dingo-dog hybrids. Finally, we propose that future studies critically examine genes under selection in the dingo and employ the genome from a wild canid for comparison.
23 citations
Cites background from "Patterns of integration in the cani..."
...question of how shape variation in the skull of wolves, dingoes and domesticated dogs is organized [84]....
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References
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TL;DR: The MorphoJ software offers an integrated and user‐friendly environment for standard multivariate analyses such as principal components, discriminant analysis and multivariate regression as well as specialized applications including phylogenetics, quantitative genetics and analyses of modularity in shape data.
Abstract: Increasingly, data on shape are analysed in combination with molecular genetic or ecological information, so that tools for geometric morphometric analysis are required. Morphometric studies most often use the arrangements of morphological landmarks as the data source and extract shape information from them by Procrustes superimposition. The MorphoJ software combines this approach with a wide range of methods for shape analysis in different biological contexts. The program offers an integrated and user-friendly environment for standard multivariate analyses such as principal components, discriminant analysis and multivariate regression as well as specialized applications including phylogenetics, quantitative genetics and analyses of modularity in shape data. MorphoJ is written in Java and versions for the Windows, Macintosh and Unix/Linux platforms are freely available from http://www.flywings.org.uk/MorphoJ_page.htm.
3,122 citations
TL;DR: A method for partitioning the total shape variation of landmark configurations with object symmetry into components of asymmetric variation among individuals and asymmetry is explained and some general recommendations for morphometric studies of symmetric shapes are provided.
Abstract: Morphometric studies often consider parts with internal left-right symmetry, for instance, the vertebrate skull. This type of symmetry is called object symmetry and is distinguished from matching symmetry, in which two separate structures exist as mirror images of each other, one on each body side. We explain a method for partitioning the total shape variation of landmark configurations with object symmetry into components of symmetric variation among individuals and asymmetry. This method is based on the Procrustes superimposition of the original and a reflected copy of each landmark configuration and is compatible with the two-factor ANOVA model customary in studies of fluctuating asymmetry. We show a fully multivariate framework for testing the effects in the two-factor model with MANOVA statistics, which also applies to shapes with matching symmetry. We apply the new methods in a small case study of pharyngeal jaws of the Neotropical cichlid fish Amphilophus citrinellus. The analysis revealed that the symmetric component of variation in the pharyngeal jaws is dominated by the contrast between two alternative trophic morphs in this species and that there is subtle but statistically significant directional asymmetry. Finally, we provide some general recommendations for morphometric studies of symmetric shapes.
889 citations
TL;DR: There is no evidence that special developmental processes control fluctuating asymmetry, and some of the morphometric patterns are related to processes known to be involved in the development of fly wings.
Abstract: Although fluctuating asymmetry has become popular as a measure of developmental instability, few studies have examined its developmental basis. We propose an approach to investigate the role of development for morphological asymmetry by means of morphometric methods. Our approach combines geometric morphometrics with the two-way ANOVA customary for conventional analyses of fluctuating asymmetry and can discover localized features of shape variation by examining the patterns of covariance among landmarks. This approach extends the notion of form used in studies of fluctuating asymmetry from collections of distances between morphological landmarks to an explicitly geometric concept of shape characterized by the configuration of landmarks. We demonstrate this approach with a study of asymmetry in the wings of tsetse flies (Glossina palpalis gambiensis). The analysis revealed significant fluctuating and directional asymmetry for shape as well as ample shape variation among individuals and between the offspring of young and old females. The morphological landmarks differed markedly in their degree of variability but multivariate patterns of landmark covariation identified by principal component analysis were generally similar between fluctuating asymmetry (within-individual variability) and variation among individuals. Therefore there is no evidence that special developmental processes control fluctuating asymmetry. We relate some of the morphometric patterns to processes known to be involved in the development of fly wings.
816 citations
TL;DR: The relatively new two-block partial least-squares method for analyzing the covariance between two sets of variables is described and contrasted with the well-known method of canonical correlation analysis.
Abstract: The relatively new two-block partial least-squares method for analyzing the covariance between two sets of variables is described and contrasted with the well-known method of canonical correlation analysis. Their statistical properties, types of answers, and visualization techniques are discussed. Examples are given to show its usefulness in comparing two sets of variables—especially when one or both of the sets of variables are shape variables from a geometric morphometric study. (Canonical correlation; covariance; morphometrics; Mus musculus domesticus; partial least squares; Plethodon; visualization.)
757 citations
TL;DR: How development produces covariation between traits can have substantial implications for understanding genetic variation and the potential for evolutionary change, but research in this area has only begun and many questions remain unanswered.
Abstract: Biological systems, from molecular complexes to whole organisms and ecological interactions, tend to have a modular organization. Modules are sets of traits that are internally integrated by interactions among traits, but are relatively independent from other modules. The interactions within modules rely on different mechanisms, depending on the context of a study. For morphological traits, modularity occurs in developmental, genetic, functional, and evolutionary contexts. A range of methods for quantifying integration and modularity in morphological data is available, and a number of comparative and experimental designs can be used to compare the different contexts. How development produces covariation between traits can have substantial implications for understanding genetic variation and the potential for evolutionary change, but research in this area has only begun and many questions remain unanswered.
678 citations