Morphological analyses of the neurocranium of a group of rock-dwelling cichlid fishes (Cichlidae: Perciformes) from Lake Malawi,Africa

Variation in the size and the shape of neurocrania of a group of rock-dwelling cichlid fishes (mbuna; from Lake Malawi, Africa was analysed using principal components and regression analyses on a set of 24 neurocranial measurements of 86 individuals from 11 species. The results reveal effective morphological discrimination between species. Most of the structural variation between species demonstrates positive allometry and represents size-dependent species differences. Thus, morphological differentiation in these fish may be largely the result of heterochronic changes in relative growth rates. The vomerine region, however, exhibited shape differentiation. Distinct groupings, based on vomer shape, are identified. Foraging behaviour and diet are found to be correlated with this region of the neurocrania. The correlation of the shape of the vomer and fine-scale resource partitioning suggests that this structure may be important in the evolutionary success of the group. Also, most structural shape variation in neurocranial morphology is associated with structural variation in buccal jaws.     

Geographic Variation in the Skull Morphometry of Four Populations of Batrachuperus karlschmidti(Urodela: Hynobiidae)

Geographic variation of morphology is an important topic of evolutionary biology, and research on geographic variation can provide insights on the formation, evolution, and adaptation of species and subspecies. The vertebrate skull is a developmentally and functionally complex morphological structure with multiple functions, that is susceptible to vary according to selection pressure. In this study, geographic variations in skull morphology of Batrachuperus karlschmidti from four different geographic populations(Shade, Gexi,Shangluokema, and Xinduqiao) were examined via geometric morphometrics. No significant differences were found among these populations with regard to skull size; however, significant variation was found in skull shape. The most notable shape changes are the relative sizes and positions of the frontal, maxilla,pterygoid, and vomer. Skull shape changes were not related to allometry. However, due to limitation of sample populations and size, the results of this study need to be further verified by more sample populations and individuals in the future. The results of this study contribute to our knowledge about these aspects of morphological variability in this species as well as in hynobiid salamanders.     

Linking stream ecology with morphological variability in a native freshwater fish from semi‐arid Australia

Environmental variation is a potent force affecting phenotypic expression. While freshwater fishes have provided a compelling example of the link between the environment and phenotypic diversity, few studies have been conducted with arid‐zone fishes, particularly those that occur in geographically isolated regions where species typically inhabit intermittent and ephemeral creeks. We investigated morphological variation of a freshwater fish (the western rainbowfish, Melanotaenia australis) inhabiting creeks in the Pilbara region of northwest Australia to determine whether body shape variation correlated with local environmental characteristics, including water velocity, habitat complexity, predator presence, and food availability. We expected that the geographic isolation of creeks within this arid region would result in habitat‐specific morphological specializations. We used landmark‐based geometric morphometrics to quantify the level of morphological variability in fish captured from 14 locations within three distinct subcatchments of a major river system. Western rainbowfish exhibited a range of morphologies, with variation in body depth accounting for a significant proportion (>42%) of the total variance in shape. Sexual dimorphism was also apparent, with males displaying deeper bodies than females. While the measured local habitat characteristics explained little of the observed morphological variation, fish displayed significant morphological differentiation at the level of the subcatchment. Local adaptation may partly explain the geographic patterns of body shape variation, but fine‐scale genetic studies are required to disentangle the effects of genetic differentiation from environmentally determined phenotypic plasticity in body shape. Developing a better understanding of environment–phenotype relationships in species from arid regions will provide important insights into ecological and evolutionary processes in these unique and understudied habitats.     

Variation in Body Shape across Species and Populations in a Radiation of Diaptomid Copepods

Inter and intra-population variation in morphological traits, such as body size and shape, provides important insights into the ecological importance of individual natural populations. The radiation of Diaptomid species (~400 species) has apparently produced little morphological differentiation other than those in secondary sexual characteristics, suggesting sexual, rather than ecological, selection has driven speciation. This evolutionary history suggests that species, and conspecific populations, would be ecologically redundant but recent work found contrasting ecosystem effects among both species and populations. This study provides the first quantification of shape variation among species, populations, and/or sexes (beyond taxonomic illustrations and body size measurements) to gain insight into the ecological differentiation of Diaptomids. Here we quantify the shape of five Diaptomid species (family Diaptomidae) from four populations each, using morphometric landmarks on the prosome, urosome, and antennae. We partition morphological variation among species, populations, and sexes, and test for phenotype-by-environment correlations to reveal possible functional consequences of shape variation. We found that intraspecific variation was 18-35% as large as interspecific variation across all measured traits. Interspecific variation in body size and relative antennae length, the two traits showing significant sexual dimorphism, were correlated with lake size and geographic location suggesting some niche differentiation between species. Observed relationships between intraspecific morphological variation and the environment suggest that divergent selection in contrasting lakes might contribute to shape differences among local populations, but confirming this requires further analyses. Our results show that although Diaptomid species differ in their reproductive traits, they also differ in other morphological traits that might indicate ecological differences among species and populations.     

Effects of fronto-occipital cranial reshaping on mandibular form.

Cultural reshaping (artificial deformation or modification) of the neurocranial vault provides an artificially increased range of morphological variability within which the relationship between the growing neurocranium and face can be investigated. We analyze crania which have been fronto-occipitally compressed to ascertain possible morphological effects on the mandible. We collected measures of mandibular breadth, length, and height from 82 modified (N = 48) and unmodified (N = 34) crania from a Peruvian Ancon series. Angle classification was also scored in order to investigate whether or not occlusal relationships were affected by neurocranial reshaping. Only intercondylar distance (posterior mandibular breadth) exhibited significant differences between unmodified and modified groups, though this difference was relatively small compared with vault deformation. The modified crania had a higher frequency of normal occlusion (Class I) than the unmodified crania. Increased intercondylar breadth in modified skulls is due to a cascade of effects which begin with a direct effect of the fronto-occipital deforming device on neurocranial shape (increased neurocranial width). The increase in mandibular breadth may be a compensatory response to increased cranial base breadth and maintains articulation between the cranial base and mandible. The increased posterior breadth, coupled with a slight decrease in mandibular depth, may contribute to the change in occlusal relationships suggested for this sample.     

Evaluation of the fossil fish‐specific diversity in a chadian continental assemblage: Exploration of morphological continuous variation in Synodontis (Ostariophysi,Siluriformes)

In the fossil record, the quantification of continuous morphological variation has become a central issue when dealing with species identification and speciation. In this context, fossil taxa with living representatives hold great promise, because of the potential to characterise patterns of intraspecific morphological variation in extant species prior to any interpretation in the fossil record. The vast majority of catfish families fulfil this prerequisite, as most of them are represented by extant genera. However, although they constitute a major fish group in terms of distribution, and ecological and taxonomic diversity, the quantitative study of their past morphological variation has been neglected, as fossil specimens are generally identified based on the scarcest remains, that is, complete neurocrania that bear discrete characters. Consequently, a part of freshwater catfish history is unprospected and unknown. In this study, we explored the morphological continuous variation of the humeral plate shape in Synodontis catfishes using Elliptic Fourier Analysis (EFA), and compared extant members and fossil counterparts. We analysed 153 extant specimens of 11 Synodontis species present in the Chad basin, in addition to 23 fossil specimens from the Chadian fossiliferous area of Toros Menalla which is dated around 7 Ma. This highly speciose genus, which is one of the most diversified in Africa, exhibits a rich fossil record with several hundred remains mostly identified as Synodontis sp. The analysis of the outline of the humeral plate reveals that some living morphological types were already represented in the Chad Basin 7 My ago, and allows for the discovery of extinct species. Beside illuminating the complex Neogene evolutionary history of Synodontis, these results underline the interest in the ability of isolated remains to reconstruct a past dynamic history and to validate the relevance of EFA as a tool to explore specific diversity through time. J. Morphol. 277:1486–1496, 2016. © 2016 Wiley Periodicals, Inc.     

Developmental and Genetic Constraints on Neurocranial Globularity: Insights from Analyses of Deformed Skulls and Quantitative Genetics

Neurocranial globularity is one of the few derived traits defining anatomically modern humans. Variations in this trait derive from multiple and complex interactions between portions of the brain and the size and shape of the cranial base, among other factors. Given their evolutionary and functional importance, neurocranial globularity is expected to present high genetic and developmental constraints on their phenotypic expression. Here we applied two independent approaches to investigate both types of constraints. First, we assessed if patterns of morphological integration are conserved or else disrupted on a series of artificially deformed skulls in comparison to non-deformed (ND) ones. Second, after the estimation of the genetic covariance matrix for human skull shape, we explored how neurocranial globularity would respond to putative selective events disrupting the normal morphological patterns. Simulations on these deviations were explicitly set to replicate the artificial deformation patterns in order to compare developmental and genetic constraints under the same biomechanical conditions. In general terms, our results indicate that putative developmental constraints help to preserve some aspects of normal morphological integration even in the deformed skulls. Moreover, we find that the response to selection in neurocranial globularity is pervasive. In other words, induced changes in the vault generate a global response, indicating that departures from normal patterns of neurocranial globularity are genetically constrained. In summary, our combined results suggest that neurocranial globularity behaves as a highly genetic and developmental constrained trait. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Neus Martínez-Abadías and Rolando González-José contributed equally to this work.     

Intra- and interspecific morphological variation in the field mouse species Apodemus argenteus and A. speciosus in the Japanese archipelago: the role of insular isolation and biogeographic gradients

Two species of field mice, Apodemus argenteus and A. speciosus, occur in sympatry across the Japanese archipelago. The inter- and intraspecific patterns of morphological differentiation have been evaluated, using a Fourier analysis of the mandible outline. The relative importance of the effect of insular isolation and latitudinal climatic gradient on the size and shape of the two species was assessed by a comparison of the populations from the large island of Honshu and the surrounding small-island populations. The size variation in A. argenteus is correlated with the climatic gradient whilst the shape variation corresponds mainly to a random differentiation of the small-island populations from a Honshu-like basic morphological pattern. A. speciosus displays increased size on small islands, and its shape variation is related to both the climatic gradient and insularity. Finally, the two species are differentiated by both the size and shape of the mandible across the Japanese archipelago, suggesting that interspecific competition between both species is reduced via niche partitioning. Our results emphasize the importance of insular isolation on shape differentiation, but a part of the morphological differentiation is also related to the latitudinal climatic gradient. Isolation on small islands could have favoured such a response to environmental factors by lowering the gene flow that prevents almost any significant differentiation within Honshu populations.     

Morphological constraints in the digging apparatus of pocket gophers (Mammalia: Geomyidae)

The digging apparatus of pocket gophers offers a unique opportunity to examine morphological constraints within a historical context because relationships among extant taxa are well resolved and the features enhancing digging performance are relatively well understood. Structural and functional considerations suggest that the muscles associated with tooth- and claw-digging in pocket gophers are subjected to contrasting levels of morphological constraints. To assess this hypothesis, we analysed the bones and muscles of the jaws and forelimbs in four genera comprising five species of pocket gophers. Morphometric analyses were performed on 12 osteological measurements selected to reflect overall skull size, variation in rostral shape and procumbency, differences in overall length of the forelimbs and processes relating to the function of lever systems used in claw-digging. In addition, dissections were made of the jaw, hyoid, neck and all of the forelimb muscles excluding the intrinsic muscles of the manus. Results of our morphometric analyses corroborate the recent suggestion that pocket gophers encompass a wide range of morphological variation extending from claw-diggers to tooth-diggers. Myologically, however, we found structural variation only in the forelimb muscles, some of which may be advantageous for digging. No changes in jaw, neck and hyoid muscles, other than differences in muscle mass or those concordant with differences in rostral shape, were noted. These results support our hypothesis that constrasting levels of morphological constraint exist between the jaw and forelimb muscles of pocket gophers. We present a discussion of the structural and functional constraints on jaws and forelimbs in gophers as well as an analysis of historical constraints acting on this group, and perhaps on mammals in general.     

Morphology of the Podarcis wall lizards (Squamata: Lacertidae) from the Iberian Peninsula and North Africa: patterns of variation in a putative cryptic species complex

Cryptic species complexes represent groups that have been classified as a single species, because of the difficulty in distinguishing its members morphologically. Morphological investigation following the discovery of cryptic diversity is crucial for describing and conserving biodiversity. Here we present a detailed account of morphological variation in a group of Iberian and North African Podarcis wall lizards of the family Lacertidae, trying to elucidate the morphological patterns observed between known mitochondrial lineages. Our results reveal very high morphological variation within lineages, considering both biometric and pholidotic traits, but also indicate that lineages are significantly different from each other. The main sources of variation, both globally and between lineages, arise from body size, head dimensions, and limb length, possibly pointing to underlying ecological mechanisms. A combination of body size, body shape, and continuous pholidotic traits allows a relatively good discrimination between groups, especially when comparing one group with the rest or pairs of groups. However, ranges of variation greatly overlap between groups, thereby not allowing the establishment of diagnostic traits. The high morphological variation observed indicates that external morphology is not particularly useful for species delimitation in this group of lizards, as local adaptation seems to play a major role in within‐ and between‐group differentiation. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 164 , 173–193.     

Variation in morphology and functional performance across distinct evolutionary lineages of the Moorish gecko (Tarentola mauritanica) from the Iberian Peninsula

Deciphering the mechanisms that underlie morphological and functional diversity is essential for understanding how organisms adapt to their environment. Interestingly, phenotypic divergence does not necessarily correspond to the geographic and genetic separation between populations. Here, we explored the morphological and functional divergence among populations of two genetically differentiated clades of the Moorish gecko, Tarentola mauritanica. We used linear and geometric morphometrics to quantify morphological variation and investigated how it translates into biting and CLIMBING PERFORMANCE, to better understand the mechanisms potentially underlying population and lineage divergence. We found marked morphological differences between clades, both in body size and head shape. However, much of this differentiation is more strongly related to local variation between populations of the same clade, suggesting that recent ecological events may be more influential than deep evolutionary history in shaping diversity patterns in this group. Despite a lack of association between morphology and functional diversification in the locomotor system of the Moorish gecko, straightforward links are observed between head morphology and biting performance, providing more hints on the possible underlying causes. Indeed, variation in bite force is mostly determined by size variation and sexual dimorphism, and differences between the two clades concern how sexual variation is expressed, reinforcing the idea that both social and ecological factors contribute in shaping differentiation. Interestingly, the individuals from the islets off the coast of Murcia exhibit particular morphological and functional traits, which suggests that the ecological conditions related to insularity may drive the phenotypic differentiation of this population.     

A phylogenetic view on skull size and shape variation in the smooth newt (Lissotriton vulgaris,Caudata, Salamandridae)

In this study, we explore skull size and shape variation in the smooth newt, a taxon with substantial morphological differentiation and complex phylogeographic relations. By projecting phylogenies into the morphospace of the skull shape, we explore the variation in and differentiation of this complex morphological structure within a phylogenetic framework. For these analyses, we used a dataset that covers the most southern part of the species’ distribution range, including all conventionally recognized subspecies. The study revealed different patterns of divergence in skull shape between sexes, which is paralleled by intraspecific differentiation. The divergence in dorsal skull shape is concordant with the phylogenetic divergence, as the most diverged clades of the smooth newt (Lissotriton vulgaris kosswigi and Lissotriton vulgaris lantzi) exhibit a skull shape that significantly diverges from the smooth newt’s mean shape configuration. The results of this study also indicate that ventral skull portion, which is more directly related to feeding and foraging, shows higher variation between populations than dorsal skull portion, which appears to be less variable and phylogenetically informative.     

Cranial evolution in sakis (Pithecia, Platyrrhini). II: Evolutionary processes and morphological integration

Patterns of interspecific differentiation in saki monkeys (Pithecia) are quantitatively described and possible evolutionary processes producing them are examined. The comparison of species correlation matrices to expected patterns of morphological integration reveal significant and similar patterns of development-based cranial integration among species. Aspects of the facial region are more heavily influenced by general size variation than features of the neural region. The comparison of pooled within- and between-groups V/CV matrices suggests that genetic drift might be a sufficient explanation for saki cranial evolution. Differential natural selection gradients are also reconstructed because selection may also have caused population differentiation through evolutionary time. These gradients illustrate the inherent multivariate nature of selection, being a consequence of the interaction between existing morphological integration (correlation) among traits and the action of natural selection. Yet, our attempt to interpret selection gradients in terms of their functional significance did not result in any clear association between selection and function. Perhaps this is also an indication that morphological evolution in sakis was mostly neutral.     

Morphological variation in house mice from the Robertsonian polymorphism area of Barcelona

Morphometric variation in the Robertsonian polymorphism zone of Barcelona of Mus musculus domesticus was studied by geometric morphometrics. This system is characterized by populations of reduced diploid number (2 n  = 27–39) surrounded by standard populations (2 n  = 40). We investigated the morphological variation in mice from this area, as well as the effect of geographical distance and karyotype on this variation. We also investigated the degree of co-variation between the two functional units of the mandible to explore the origin of this system (primary intergradation or secondary contact). The size and shape of the cranium, mandible and scapula were analysed for 226 specimens grouped by population, chromosome number and structural heterozygosity. Size was estimated as the centroid size, and shape was estimated after Procrustes superimposition. No significant differences in size between populations or chromosomal groups were detected. Diploid number, structural heterozygosity and local geographical isolation contributed to the differentiation in shape. Morphological differentiation between standard mice and Robertsonian specimens was observed, suggesting genetic isolation between these groups. Co-variation between the ascending ramus and alveolar region of the mandible was quantified by the trace correlation between landmark subsets of these modules. The trace values showed an ascending trend, correlated with the distance from the centre of the polymorphism area, a pattern consistent with a primary intergradation scenario.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 555–570.     

Morphometric testing of structural hypotheses of the supraorbital region in modern humans

Our understanding of the functional morphology of the primate supraorbital region is based largely on previous morphometric and in vivo mechanical tests of hypotheses in non-human anthropoids. Prior tests of two structural hypotheses explaining morphological variation in the supraorbital region, the craniofacial size hypothesis and the spatial hypothesis, did not fully consider modern humans. We extend these previous findings to include modern humans by conducting morphometric tests of these two hypotheses in a sample of adult Melanesian crania. Morphometric correlates of structural predictions for the craniofacial size and spatial hypotheses were developed and compared to measurements of the supraorbital region via bivariate product-moment correlations. Measurements of the supraorbital region are significantly correlated with a craniofacial size estimate across individuals from this Melanesian sample. This result supports the prediction of the craniofacial size hypothesis that the magnitude of the supraorbital region is proportional to craniofacial size. The predicted link between the degree of neural-orbital disjunction and the magnitude of the supraorbital region, explicated in the spatial hypothesis, receives mixed support in the correlation analysis. These two results agree with previous research indicating that support for the craniofacial size and spatial hypotheses can be found across and within anthropoid primate species, including modern humans. Correlational support for both the craniofacial size and spatial hypotheses suggests multiple factors influence variation in the modern human supraorbital region. Thus, a single hypothesis cannot fully account for modern human variation in this region. The low bivariate correlation coefficients in this study further question whether existing hypotheses can adequately explain morphological variation in the supraorbital region in a primate population sample. Novel functional, structural, behavioral and developmental ideas must be explored if we are to better understand morphological variation in the modern human supraorbital region.     

Cranial morphological variation of Dromiciops gliroides (Microbiotheria) along its geographical distribution in south-central Chile: A three-dimensional analysis

We analyzed the variation in cranial morphology of the marsupial Dromiciops gliroides along its distribution in south-central Chile. We evaluated whether the cranial morphological variation is congruent with the phylogeographic structure previously observed in this species. We built three-dimensional models of 69 crania on which we digitized 30 landmarks. We used standard geometric morphometric methods to extract and analyze the shape and size components of the crania. Our data showed a subtle but consistent cranial size and shape variation along the studied distributional range, suggesting a geographic variation pattern rather than a phylogeographic structuring. Indeed, our multivariate analyses recovered a subtle morphological differentiation between island and mainland populations, contrary to what is suggested by a former phylogeographic study. We detected that either the cranial size variation, as well as the insularity and the latitude could be important factors underlying the cranial shape changes. We suggest that an interplay of historical and contemporary processes could be shaping the morphological pattern observed in this marsupial.     

Geographical variation and diversification in the flightless leaf beetles of the Chrysolina angusticollis species complex (Chrysomelidae, Coleoptera) in northern Japan

Geographical variation and differentiation of flightless leaf beetles of the Chrysolina angusticollis species complex were analysed. Nine morphological groups were recognized on the basis of metric characters relating to body size, shape of hind wing and shape of male genitalia, and binary characters relating to females' elytral surface and larval pubescence. The nine groups were essentially parapatric or allopatric to each other. Five groups occupied a continuous geographical range each, whereas another four groups were disjunctively distributed. Morphometric distance and geographical distance between populations were significantly correlated. Analyses based on 13 allozyme loci demonstrated that six out of the nine morphological groups were further divided into more than one genetically distinct group each. Genetic similarity between populations was significantly correlated with morphometric similarity and geographical closeness. Disjunctively distributed populations of a single morphological group more often resembled geographically adjacent populations of different morphological groups than geographically remote populations of the same group. In a morphological group that occupied a wide continuous range, remote populations substantially differed genetically from each other. The results suggest that there exist at least 19 morphologically and/or genetically differentiated units in the C. angusticollis complex in northern Japan. The C. angusticollis complex is likely a superspecies composed of a number of semispecies. We postulate that the diversification of this species complex might have resulted from the repeated range contraction and expansion during the ice ages. Movement of tension zones that separate two adjacent forms might contribute to enhance their geographical differentiation.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 557–578.     

中国鲨类脑颅的研究

本文解剖观察了我国有代表性的鲨类脑颅共32种,分隶于8目14科24属。研究结果认为鲨类的脑颅共可分为9个式型和12个亚型。现存虎鲨目、须鲨目的鲸鲨科和扁鲨目吻软骨缺如,六鳃鲨目、须鲨目、角鲨目和锯鲨目均具一吻软骨,它们是一些古老和一些特化的类群。现存大多数种类均具3根吻软骨。在各不同分类阶元常有其不同的形态特征,可作为分类依据之一,亦可显示其亲缘关系。     

Relationships between head morphology, bite performance and ecology in two species of Podarcis wall lizards

Understanding the relationship between form and function is central to our comprehension of how phenotypic diversity evolves. Traits involved in multiple activities, such as social interactions and ecological resource use, are under the influence of different evolutionary forces potentially acting in opposite directions. Such systems provide the opportunity of understanding how potential constraints on morphological variation may influence whole-organism performance. In this study we examined morphology and bite performance in two closely related species of Podarcis wall lizards with divergent microhabitat preferences, to investigate how natural and sexual selection interact to shape the evolution of head traits. Our results show that although head morphology is markedly different between species and sexes, only sexes differ in bite force, indicating that the ecological differentiation between species is reflected in their morphology but does not constrain performance. Rather, the modification of the relative size of head components between species and a shift in the form-function relationship provide a potential explanation of how equal performance is attained by different morphological configurations. Geometric morphometrics provide a clear, biomechanically meaningful image of how this is achieved and show a bisexual pattern of head shape-bite force association in both species. This, together with a strong allometry of head size on body size and head shape on head size, provides indirect morphological evidence for the importance of sexual selection in shaping morphological and functional patterns. Finally, our findings suggest that the differences observed between species and sexes in head traits and bite performance are not reflected in their dietary ecology, implying that if trophic niche segregation between groups occurs, the reasons behind it are not primarily related to head morphology and functional variation.