Shape variation in the mole dentary (Talpidae: Mammalia)

The clade Talpidae consists of specialized fossorial forms, shrew‐like moles and semi‐aquatic desmans. As with all higher jawed vertebrates, different functional, phylogenetic and developmental constraints act on different parts of dentary influencing its shape. In order to determine whether morphological variation in the dentary was unified or dispersed into an integrated complex of structural–functional components, a morphometric analysis of the mole dentary was undertaken. The dentary was subdivided into component parts – horizonal ramus; coronoid, condylar, angular processes of the ascending ramus – and outline‐based geometric morphometric methods used to quantify, compare and contrast modes of shape variation within the clade. These were successful in revealing subtle differences and aspects of shape important in distinguishing between mole genera. Closer examination of shape variation within the two fully fossorial mole clades (Talpini and Scalopini) revealed several similarities in ascending ramus shapes between genera from each clade. For example, the broad, truncated appearance of the coronoid process in the talpine genera Talpa and Parascalops was shared with the scalopine genus Scapanus. Also, the more slender, hook‐shaped coronoid process of Euroscaptor and Parascaptor (Talpini) closely resembles that of Scalopus (Scalopini). Interestingly, subspecies (one from each clade) more closely resembled genera other than their own in coronoid process shape. Important distinctions in horizontal ramus shape were found to exist between the two clades, such as the extent of curvature of the ventral margin and relative depth of the horizontal ramus. Results show shape variation in this region is correlated with dental formulae and the relative sizes of the teeth. The taxonomically important dentition differences characteristic of mammals are also reflected in the horizontal ramus results. Moreover, these results suggest size may be affecting shape and the extent of variation in, for example, the coronoid and condylar processes between the semi‐aquatic moles Desmana and Galemys. It is likely that the effects of morphological integration seen at this level of analysis – covariation between shapes of dentary components – may exist because interacting traits are evolving together. Horizontal ramus and coronoid process shape, for example, are similar across Scapanus and Parascalops, but both these shapes have diverged in Scalopus. © 2008 Trustees of the Natural History Museum (London). Journal compilation © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 153 , 187–211.     

Cranial shape variation and molecular phylogenetic structure of crested newts (Triturus cristatus superspecies: Caudata,Salamandridae) in the Balkans

In the present study, we investigated the degree of congruence between phylogeny, as inferred from mitochondrial (mt)DNA sequences, and cranium shape variation of crested newts (Triturus cristatus superspecies) in the Balkans. These newts belong to four phylogenetic clades defined by mtDNA analysis, and significantly differed in cranial shape. Allometry explained a high percentage of shape variation in crested newts. The clade‐specific allometric slopes significantly diverged for both the ventral cranium and dorsal cranium, indicating that differences in shape between clades could not be a simple consequence of their difference in size. The analysis of hierarchical and spatial variation showed similarity in the patterns of global and spatially localized hierarchical variation of cranial shape. We also found significant congruence between the pattern of cranial shape variation and molecular phylogeny. The differences in morphology of Triturus dobrogicus in comparison to other crested newt clades, including marked differences in cranium shape, is discussed in the context of the evolution and ecology of crested newts. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 348–360.     

Mandible shape in marsupial and placental carnivorous mammals: a morphological comparative study using geometric morphometrics

We analysed mandible shape of the orders Dasyuromorpha, Didelphimorphia, and Carnivora using two‐dimensional geometric morphometrics, in order to explore the relationship between shape, size, and phylogeny. We studied 541 specimens, covering most of the genera of the terrestrial Carnivora (115 species) and a wide sample of marsupials (36 species). The observed shape variation had an ecological component. As an example, omnivorous carnivores have thick mandibles and large talonids in the carnassials, while hypercarnivores possess short mandibles and reduced talonids. There is also a discrimination between different taxonomic groups (i.e. marsupials and Carnivora), indicating some kind of constraint. Size explains a large percentage of total variance (large species had shorter and stronger mandibles, with anteriorly displaced carnassials), was significant when phylogeny was taken into account with a comparative method, but not when size and shape were optimized on the phylogeny. Carnivora presents a larger disparity and variation in body size, which could be related to the difference in teeth replacement. The optimization of mandible shape on the phylogenetic tree indicates that functional aspects, such as diet, are a key factor in the evolution of the carnivore mandible, but also that there is a phylogenetic pattern that cannot be explained by differences in diet alone. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 164 , 836–855.     

Ecological and phylogenetic dimensions of cranial shape diversification in South American caviomorph rodents (Rodentia: Hystricomorpha)

Caviomorph rodents represent an excellent model to explore morphological diversification on a macroevolutionary scale, as they are ecologically and morphologically diverse. We analysed cranial shape variation using geometric morphometrics and phylogenetic comparative methods. Most variation involved the shape of the rostrum, basicranium, and cranial vault, and clearly matched the phylogenetic structure. At the same time, a strong allometric pattern was associated with the length of the rostrum and cranial vault, size of the auditory bulla, and depth of the zygomatic arch. After accounting for size influence, and taking phylogenetic structure into account, shape variation was significantly associated with habitat. Our results highlight the presence of complex relationships between morphological, phylogenetic, and ecological dimensions in the diversification of the caviomorph cranium. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 898–913.     

Phenetic relationships among four Apodemus species (Rodentia, Muridae) inferred from skull variation

Phenetic relationships among four Apodemus species (A. agrarius, A. epimelas, A. flavicollis and A. sylvaticus) inferred from skull (mandible and cranium) variation were explored using landmark-based geometric morphometrics. Analysis of size variation revealed that mandibles and crania of A. epimelas were the largest, followed by those of A. flavicollis, while A. agrarius and A. sylvaticus had the smallest ones. Phenetic relationships inferred from mandible shape variation better reflected phylogenetic relationships among the analyzed Apodemus species than those inferred from cranial differences. Concerning cranial shape variation, the most differentiated species was A. epimelas, whose ecology clearly differs from the other three species. Thus, differentiation of the mandible provided a pattern fully concordant with the phylogeny, while the cranium differentiation was in agreement with ecology expectations. The most evident shape changes of mandible and cranium involved the angular process and facial region, respectively. We also found that allometry had a significant influence on shape variation and that size-dependent shape variation differed among the analyzed species. Moreover, mandible and cranium are differently influenced by allometric changes. Different phenetic relationships inferred from mandible and cranium shape variation imply that phylogeny, ecology, together with factors related to size differences are all involved in the observed morphological divergence among the analyzed Apodemus species.     

Morphological evolution in the mandible of spiny rats, genus Trinomys (Rodentia: Echimyidae)

The development and evolution of the rodent mandible have been studied in depth in recent years. The mandible is a complex structure because it consists of six morphogenetic components formed by different condensations of mesenchymal cells. Using recent techniques for the geometric analysis of shape, we have combined developmental information with a powerful quantification of shape variation and an independent estimate of phylogeny (molecular data) to assess the evolutionary patterns of shape change in mandibles of the rodent genus Trinomys . In general, the major trends in shape variation did not agree with the expected phylogenetic pattern. However, for small-scale morphological differences, one species ( T. yonenagae ) was responsible for the lack of association between morphology and molecular divergence. This species is genetically similar to but morphologically different from other Trinomys . The coronoid process was considered to be the most conservative morphogenetic component in the mandible.     

Ecological and evolutionary factors in the morphological diversification of South American spiny rats

Understanding the processes underlying morphological diversification is a central goal in ecology and evolutionary biology and requires the integration of information about phylogenetic divergence and ecological niche diversity. In the present study, we use geometric morphometrics and comparative methods to investigate morphological diversification in Neotropical spiny rats of the family Echimyidae. Morphological diversification is studied as shape variation in the skull, comprising a structure composed of four distinct units: vault, base, orognathofacial complex, and mandible. We demonstrate association among patterns of variation in shape in different cranial units, levels of phylogenetic divergence, and ecological niche diversification. At the lower level of phylogenetic divergence, there is significant and positive concordance between patterns of phylogenetic divergence and cranial shape variation in all cranial units. This concordance may be attributable to the phylogenetic and shape distances being calculated between species that occupy the same niche. At higher phylogenetic levels of divergence and with ecological niche diversity, there is significant concordance between shape variation in all four cranial units and the ecological niches. In particular, the orognathofacial complex revealed the most significant association between shape variation and ecological niche diversity. This association may be explained by the great functional importance of the orognathofacial complex.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 646–660.     

Evolution of the zygomasseteric construction in Rodentia,as revealed by a geometric morphometric analysis of the mandible of Graphiurus (Rodentia,Gliridae)

Graphiurus is a peculiar taxon among the monophyletic Gliridae (order Rodentia) in showing hystricomorphy of the zygomasseteric architecture of the skull [large infraorbital foramen (IOF), and correlative muscular arrangements). We analysed 34 extant genera taken from two groups of sciurognath rodents that share a large IOF (hystricomorph and myomorph) using elliptical Fourier transform in order to appraise whether this feature of cranial morphology was also accompanied by similar changes in mandible shape. The mandible of Graphiurus is distinct from those of all other hystricomorph sciurognath rodents in showing a more elongated coronoid process and a shorter angular process. Thus, two distinct zygomasseteric organizations (i.e. myomorphy and hystricomorphy of graphiurines) are associated with a similar mandible shape characterized by a well‐developed coronoid process. Results show that hystricomorphy of graphiurines was achieved convergently with other hystricomorph rodents. Protrogomorphy is the plesiomorphic condition in Gliridae and hystricomorphy is an autapomorphic feature of Graphiurus. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 154 , 807–821.     

Two- Versus Three-Dimensional Morphometric Approaches in Macroevolution: Insight from the Mandible of Caviomorph Rodents

Morphological variation is one of the most studied dimensions of evolutionary biology, given its close relationship with the ecological aspects of biological diversification. In this work we examine the differences between the use of two- and three-dimensional morphometric techniques for the analysis of macroevolutionary patterns of morphological variation in the mandible of the South American caviomorph rodents, which displays varying degrees of hystricognathy. The variation patterns were similar for 2D and 3D coordinate datasets. However, phylogenetic comparative statistical analyses showed widely different results for mandible variation. Both the phylogenetic signal values and the results of phylogenetic regressions were markedly different between the two macroevolutionary mandible datasets. This suggests that the inclusion of the third coordinate to characterize a hystricognathous mandible may lead to completely different interpretations concerning the processes that could be regulating the morphological diversification of the caviomorph mandible. We also compare these results with the 2D and 3D macroevolutionary patterns of variation in cranial shape and the intra-specific mandible variation. The variation patterns were similar for 2D and 3D coordinate for all these comparative datasets. The differing results obtained at different evolutionary scales, give strength to the statement about careful selection of data not only in studies of morphological variation in caviomorphs but also for other groups of organisms.     

Morphological diversity of Old World rats and mice (Rodentia, Muridae) mandible in relation with phylogeny and adaptation

The respective roles of the phylogenetic and ecological components in an adaptive radiation are tested on a sample of Old World rats and mice (Muridae, Murinae). Phylogeny was established on nuclear and mitochondrial genes and reconstructed by maximum likelihood and Bayesian methods. This phylogeny is congruent with previous larger scale ones recently published, but includes some new results: Bandicota and Nesokia are sister taxa and Micromys would be closely related to the Rattus group. The ecological diversification is investigated through one factor, the diet, and the mandible outline provides the morphological marker. Elliptic and radial Fourier transforms are used for quantifying size and shape differences among species. Univariate size and shape parameters indicate that phylogeny is more influential on size than diet, and the reverse occurs for shape and robust patterns are recognized by multivariate analyses of the data sets provided by the Fourier methods. Omnivorous and herbivorous groups are well separated despite some overlapping, as well as are other Murinae with a specialized diet (insects, seeds). Phylogeny is also influential as shown by the segregation of several groups (Praomys, Arvicanthini, Rattus, Apodemus). Allometric shape variation was investigated, and although present it does not overwhelm effects of either phylogeny or diet. Massive mandibles characterize herbivorous Murinae and slender mandibles, the insectivorous ones. A strong angular process relative to the coronoid process characterizes seedeaters, and the reverse characterized Murinae with a diet based largely on animal matter. Such changes in morphology are clearly in relation with the functioning of the mandible, and with the forces required by the nature of the food: the need of a stronger occlusal force in herbivorous species would explain massive mandibles, and an increase of the grasping and piercing function of incisors in insectivorous species would explain slender mandibles.     

Modularity in attachment organs of African Cichlidogyrus (Platyhelminthes: Monogenea: Ancyrocephalidae) reflects phylogeny rather than host specificity or geographic distribution

Cichlidogyrus spp. (Monogenea, Ancyrocephalidae) are common parasites of cichlid fishes from Africa and the Levant. They display important morphological variation in their attachment apparatus and infect a broad host spectrum throughout a wide geographic range. Thus, they offer an interesting model to investigate to what extent the phenotypic variability of the attachment organ among congeners is related to host specificity, geographic/environmental components, or phylogeny. A geometric morphometric approach was carried out to analyse the shape variation of sclerotized structures of the attachment organ within 66 African species of the genus Cichlidogyrus. The interspecific shape comparison supports the presence of three main morphological configurations, each consisting of a given combination of particular sclerite shapes. Moreover, data emphasize strong coordination and integration (shape co‐variation) among the different sclerites jointly forming the attachment organ. Although attachment apparatuses are usually considered to be the result of adaptive processes and must be adapted to the hosts and local environmental conditions, we found no relationship between these clusters and host specificity or geographical distribution. Nevertheless, groups are partially congruent with those obtained with the molecular phylogeny of a subset of species, suggesting a phylogenetic constraint rather than an adaptation to either hosts or environment. Because of the necessity to form a functional entity, modularity within attachment organ imposes important evolutionary constraint. This provides new insights into the evolvability of attachment organs, as well as into the morphological basis of host specificity and host–parasite co‐evolutionary interaction in helminth parasites. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 694–706.     

Chewing on the trees: Constraints and adaptation in the evolution of the primate mandible

Chewing on different food types is a demanding biological function. The classic assumption in studying the shape of feeding apparatuses is that animals are what they eat, meaning that adaptation to different food items accounts for most of their interspecific variation. Yet, a growing body of evidence points against this concept. We use the primate mandible as a model structure to investigate the complex interplay among shape, size, diet, and phylogeny. We find a weak but significant impact of diet on mandible shape variation in primates as a whole but not in anthropoids and catarrhines as tested in isolation. These clades mainly exhibit allometric shape changes, which are unrelated to diet. Diet is an important factor in the diversification of strepsirrhines and platyrrhines and a phylogenetic signal is detected in all primate clades. Peaks in morphological disparity occur during the Oligocene (between 37 and 25 Ma) supporting the notion that an adaptive radiation characterized the evolution of South American monkeys. In all primate clades, the evolution of mandible size is faster than its shape pointing to a strong effect of allometry on ecomorphological diversification in this group.     

THE SHAPE OF CONTENTION: ADAPTATION,HISTORY, AND CONTINGENCY IN UNGULATE MANDIBLES

Mandibles and teeth of ungulates have been extensively studied to discern the functional significance of their design. Grazing ungulates have deeper mandibles, longer coronoid processes, flatter incisor arcades, and more hypsodont molars in comparison to browsers. If the functional significance of both mandible and teeth shapes is well‐established, it remains uncertain to what extent mandible shapes are really adapted to grazing, meaning that they evolved either to serve their current biological function or just as a structural requirement to accommodate higher crowned molars. Here, we address this question by studying the contribution of phylogeny, hypsodonty, and body size to mandibular shape variation. The mandible shape appeared to be significantly influenced by hypsodonty but not by body size. Interestingly, hypsodonty‐related changes influenced the tooth row in artiodactyls and perissodactyls significantly but in the opposite directions, which is ultimately related to their different digestive strategies. Yet, we obtained a strong phylogenetic effect in perissodactyls, suggesting that their mandible shape should be strongly inherited. The strength of this effect was not significant within artiodactyls (where hypsodonty explained much more variance in mandible shape). Digestive strategy is deemed to interplay with hypsodonty to produce different paths of adaptation to particular diets in ungulates.     

Morphological traits as predictors of diet and microhabitat use in a diverse beetle assemblage

We explored how morphological traits can complement phylogenetic information to extend our predictions of the ecology of a diverse beetle assemblage. We analysed ten morphological traits from an assemblage of 239 species from 35 families, and identified three axes of morphological variation that were independent of body length: (1) relative robustness; (2) relative appendage length; and (3) relative abdomen length. The trait associations defining these axes of morphological variation did not change after adjusting for family‐level phylogeny. We detected significant differences in morphological variation across the beetle assemblage according to diet and microhabitat use, and these patterns were only partially influenced by family membership. Further analysis within dominant families showed that species of Carabidae, Curculionidae, Scarabaeidae and Staphylinidae had greater body length in open versus tree litter microhabitat, and species of Carabidae and Curculionidae had greater relative robustness, but shorter relative appendage length, in open versus tree litter microhabitat. Although it is clear that family‐level phylogeny and morphology share some explanatory power for predicting the diet and microhabitat use by beetles, we demonstrate that body length, robustness and appendage length are correlated significantly with microhabitat use when comparing members of the same family. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 301–310.     

Phylogenetic signal in the evolution of body colour and spicule skeleton in calcareous sponges

Some of the morphological characters used in Porifera taxonomy have often been shown to be inconsistent. In the present study, we tested the phylogenetic coherence of currently used taxonomic characters of the calcarean genus Clathrina. For this, 20 species of Clathrina and three other calcinean genera (Ascandra, Guancha, and Leucetta) were sequenced for the ITS and D2 region of the 28S ribosomal DNA. Maximum‐likelihood and maximum‐parsimony algorithms were used to reconstruct phylogenetic trees. Deep divergences were observed in our tree and Clathrina was shown to be paraphyletic. The major split in our topology showed a clear‐cut distinction between sponges with and without tetractine spicules. Moreover, a group of yellow‐coloured Clathrina was clearly separated from the remaining white‐coloured species. Our results show that the presence of diactines, water‐collecting tubes, the degree of cormus anastomosis, and actine shapes do not correlate with the major clades of the calcinean phylogeny. On the other hand, the presence of tripods, the absence of tetractines, and the presence of spines in the apical actine of tetractines seem to be good synapomorphies for clades in our tree. Our results demonstrate that skeleton characters can be reliably used in higher level taxonomy in Clathrinida. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 163 , 1026–1034.     

Disentangling the effects of intraspecies variability,phylogeny, space,and climate on the evolution of shell morphology in endemic Greek land snails of the genus Codringtonia

Extensive variation in land snail shell morphology has been widely documented, although few studies have attempted to investigate the ecological and evolutionary drivers of this variation. Within a comparative phylogenetic framework, we investigated the temporal and spatial evolution of the shell morphology of the Greek endemic land snail genus Codringtonia. The contribution of both inter‐ and intraspecies shell differentiation in the overall shell variability is assessed. The effect of climate, space, and evolutionary history on the shell variability was inferred using a variance partitioning framework. For Codringtonia species, intraspecies divergence of shell traits contributes substantially to the overall shell variability. By decomposing this variability, it was shown that the overall shell size of Codringtonia clades is phylogenetically constrained, related to early speciation events, and strongly affected by large‐scale spatial variability (latitudinal gradient). The effect of climate on shell size cannot be disentangled from phylogeny and space. Shell and, to a larger extent, aperture shape are not phylogenetically constrained, and appear to be mostly related to conspecific populations divergence events. Shell shape is substantially explained by both climate and space that greatly overlap. Aperture shape is mainly interpreted by medium to small‐scale spatial variables. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 796–813.     

Conservatism and Adaptability during Squirrel Radiation: What Is Mandible Shape Telling Us?

Both functional adaptation and phylogeny shape the morphology of taxa within clades. Herein we explore these two factors in an integrated way by analyzing shape and size variation in the mandible of extant squirrels using landmark-based geometric morphometrics in combination with a comparative phylogenetic analysis. Dietary specialization and locomotion were found to be reliable predictors of mandible shape, with the prediction by locomotion probably reflecting the underlying diet. In addition a weak but significant allometric effect could be demonstrated. Our results found a strong phylogenetic signal in the family as a whole as well as in the main clades, which is in agreement with the general notion of squirrels being a conservative group. This fact does not preclude functional explanations for mandible shape, but rather indicates that ancient adaptations kept a prominent role, with most genera having diverged little from their ancestral clade morphologies. Nevertheless, certain groups have evolved conspicuous adaptations that allow them to specialize on unique dietary resources. Such adaptations mostly occurred in the Callosciurinae and probably reflect their radiation into the numerous ecological niches of the tropical and subtropical forests of Southeastern Asia. Our dietary reconstruction for the oldest known fossil squirrels (Eocene, 36 million years ago) show a specialization on nuts and seeds, implying that the development from protrogomorphous to sciuromorphous skulls was not necessarily related to a change in diet.     

Extensive genetic divergence in the East Asian natricine snake,Rhabdophis tigrinus (Serpentes: Colubridae), with special reference to prominent geographical differentiation of the mitochondrial cytochrome b gene in Japanese populations

We investigated intraspecific phylogenetic relationships in the natricine snake, Rhabdophis tigrinus. A partial sequence of mitochondrial cytochrome b gene (990 bp) was sequenced for 220 individuals from 112 populations. The phylogeny indicated monophyly of the Japanese populations against the continental and Taiwanese populations, sister relationships of the Japanese and continental populations, and monophyly of the whole species. The results strongly suggested substantial genetic divergences among population assemblages from those three regions. We thus consider both lateralis from the continent, which is often synonymized to R. tigrinus, and formosanus from Taiwan, which is usually regarded as a subspecies of the latter, as distinct full species based on the evolutionary species concept. In the Japanese populations, haplotypes were classified to in two major clades (I and II) that were parapatric to each other. Clade I consisted of three distinct subclades (I‐A, I‐B, and I‐C), of which the former two were parapatric with each other, whereas the latter was sympatric with each of the former two subclades. The geographical haplotype structure exhibited by the Japanese populations is likely to have resulted from a series of allopatric differentiations with rapid range extensions of resultant lineages, leading to secondary contact or further admixture of mitochondrial haplotype clades and subclades. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 395–408.