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.     

A non‐invasive geometric morphometrics method for exploring variation in dorsal head shape in urodeles: sexual dimorphism and geographic variation in Salamandra salamandra

The study of morphological variation among and within taxa can shed light on the evolution of phenotypic diversification. In the case of urodeles, the dorso‐ventral view of the head captures most of the ontogenetic and evolutionary variation of the entire head, which is a structure with a high potential for being a target of selection due to its relevance in ecological and social functions. Here, we describe a non‐invasive procedure of geometric morphometrics for exploring morphological variation in the external dorso‐ventral view of urodeles' head. To explore the accuracy of the method and its potential for describing morphological patterns we applied it to two populations of Salamandra salamandra gallaica from NW Iberia. Using landmark‐based geometric morphometrics, we detected differences in head shape between populations and sexes, and an allometric relationship between shape and size. We also determined that not all differences in head shape are due to size variation, suggesting intrinsic shape differences across sexes and populations. These morphological patterns had not been previously explored in S. salamandra , despite the high levels of intraspecific diversity within this species. The methodological procedure presented here allows to detect shape variation at a very fine scale, and solves the drawbacks of using cranial samples, thus increasing the possibilities of using collection specimens and alive animals for exploring dorsal head shape variation and its evolutionary and ecological implications in urodeles. J. Morphol. 278:475–485, 2017. © 2017 Wiley Periodicals, Inc.     

Species coherence in the face of karyotype diversification in holocentric organisms: the case of a cytogenetically variable sedge (Carex scoparia,Cyperaceae)

Background and Aims

The sedge genus Carex, the most diversified angiosperm genus of the northern temperate zone, is renowned for its holocentric chromosomes and karyotype variability. The genus exhibits high variation in chromosome numbers both among and within species. Despite the possibility that this chromosome evolution may play a role in the high species diversity of Carex, population-level patterns of molecular and cytogenetic differentiation in the genus have not been extensively studied.

Methods

Microsatellite variation (11 loci, 461 individuals) and chromosomal diversity (82 individuals) were investigated in 22 Midwestern populations of the North American sedge Carex scoparia and two Northeastern populations.

Key Results

Among Midwestern populations, geographic distance is the most important predictor of genetic differentiation. Within populations, inbreeding is high and chromosome variation explains a significant component of genetic differentiation. Infrequent dispersal among populations separated by >100 km explains an important component of molecular genetic and cytogenetic diversity within populations. However, karyotype variation and correlation between genetic and chromosomal variation persist within populations even when putative migrants based on genetic data are excluded.

Conclusions

These findings demonstrate dispersal and genetic connectivity among widespread populations that differ in chromosome numbers, explaining the phenomenon of genetic coherence in this karyotypically diverse sedge species. More generally, the study suggests that traditional sedge taxonomic boundaries demarcate good species even when those species encompass a high range of chromosomal diversity. This finding is important evidence as we work to document the limits and drivers of biodiversity in one of the world''s largest angiosperm genera.     

Geometric craniometric analysis of sexual dimorphism and ontogenetic variation: A case study based on two geographically disparate species, Aethomys ineptus from southern Africa and Arvicanthis niloticus from Sudan (Rodentia: Muridae)

Non-geographic morphometric variation, particularly at the level of sexual dimorphism and ontogenetic (age-related) variation, has been documented in rodents, and useful for establishing whether to analyse sexes separately or together, and for selecting adult specimens for subsequent data recording and analysis. However, such studies have largely been based on traditional morphometric analyses of linear measurements that mainly focus on overall size, rather than shape-related morphometric variation. Unit-free, landmark/outline-based geometric morphometric analyses are considered to offer a more appropriate tool for assessing shape-related morphometric variation. In this study, we used geometric cranial morphometric analysis to assess the nature and extent of sexual dimorphism and age variation within the Tete veld rat, Aethomys ineptus (Thomas and Wroughton, 1908) from southern Africa and the African Nile rat, Arvicanthis niloticus (Desmarest, 1822) from Sudan. The results obtained were in turn compared with previously published results based on independent geometric and traditional cranial morphometric data from the same sampled populations examined in the present study. While our geometric morphometric results detected statistically significant sexual dimorphism in cranial shape within Ar. niloticus only, previously published results based on traditional morphometric data failed to detect significant sexual dimorphism within this species. However, similar to previously published traditional morphometric data, our geometric morphometric results detected statistically significant age-related variation in cranial shape and size within both Ae. ineptus and Ar. niloticus, with individuals of age classes 5 and 6 being considered to represent adult specimens. Our results highlight the importance of carefully evaluating both size- and shape-related non-geographic morphometric variation prior to the analysis of geographic variation and the delineation of species. Erroneous conclusions of non-geographic variation may have implications in the interpretation of geographic and evolutionary processes that may be responsible for morphological differences at both the inter- and intra-specific levels.     

Geographical variations in freshwater populations of the three-spined stickleback,Gasterosteus aculeatus,in Japan

This paper describes an investigation of morphological variation among six freshwater populations (dominantly low-plated morph) of the three-spined stickleback,Gasterosteus aculeatus, in Japan. Such populations are mainly distributed in restricted water areas within a band from Ise to Wakasa Bays, the most constricted part of Honshu Island. According to some differences in morphological variation, i.e. plate morph, number of lateral plates, body size, body shape and body colour, they were classified into two types corresponding to occurrence in the Ibi River and Lake Biwa water systems. The former type was monomorphic dominated by lowplated morphs in spring-fed water, whereas the latter was a dimorphic population consisting of low- and partially-plated morphs. My results suggest that the plate morph type is not correlated with climate nor predation but is related to geological isolation patterns during the course of the landlocking process. Conversely, variations in meristic (number of dorsal and anal fin rays and gill rakers) and morphometric (body shape and body colour) characteristics may have been related to different environmental conditions. This study also provides supporting evidence that the freshwater three-spined stickleback is a distinct species from the anadromous stickleback,G. aculeatus.     

Geographical variation in the cranial and external characters of the little tube-nosed bat,Murina silvatica in the Japanese archipelago

The distribution ofMurina silvatica (Yoshiyuki, 1983) in the Japanese archipelago extends over about 2000 km from north to south. Specimens were obtained from populations in Hokkaido and Yakushima, which are at the northern and southern ends of the range, and from two intermediate locations in Honshu. Measurements of cranial and external morphology were examined for evidence of geographical variation. The results of both multivariate analysis of variance and cluster analysis showed that there was no distinct cline in skull morphology among the Hokkaido, Tohoku and Chubu populations. However, the results of multivariate analysis of variance showed that all measures were significantly greater for the Yakushima population than for the others. Similarly, in a dendrogram of cluster analysis, the Yakushima population formed a cluster that was distinct from the other populations. However, as the difference between the Yakushima population and the other populations was less than the variation found within the Hokkaido, Tohoku and Chubu populations, morphological divergence of the Yakushima population was attributable to intraspecific variation. The island of Yakushima is the most isolated of the four locations and the morphological divergence of this population may be associated with its relative geographic isolation.     

An ontogenetic perspective on the study of sexual dimorphism, phylogenetic variability, and allometry of the skull of European ground squirrel, Spermophilus citellus (Linnaeus, 1766)

Most studies of morphological variability in or among species are performed on adult specimens. However, it has been proven that knowledge of the patterns of size and shape changes and their covariation during ontogeny is of great value for the understanding of the processes that produce morphological variation. In this study, we investigated the patterns of sexual dimorphism, phylogenetic variability, and ontogenetic allometry in the Spermophilus citellus with geometric morphometrics applied to cross-sectional ontogenetic data of 189 skulls from three populations (originating from Burgenland, Banat, and Dojran) belonging to two phylogenetic lineages (the Northern and Southern). Our results indicate that sexual dimorphism in the ventral cranium of S. citellus is expressed only in skull size and becomes apparent just before or after the first hibernation because of accelerated growth in juvenile males. Sexes had the same pattern of ontogenetic allometry. Populations from Banat and Dojran, belonging to different phylogroups, were the most different in size but had the most similar adult skull shape. Phylogenetic relations among populations, therefore, did not reflect skull morphology, which is probably under a significant influence of ecological factors. Populations had parallel allometric trajectories, indicating that alterations in development probably occur prenatally. The species’ allometric relations during cranial growth showed characteristic nonlinear trajectories in the two northern populations, with accelerated shape changes in juveniles and continued but almost isometric growth in adults. The adult cranial shape was reached before sexual maturity of both sexes and adult size after sexual maturity. The majority of shape changes during growth are probably correlated with the shift from a liquid to a solid diet and to a lesser degree due to allometric scaling, which explained only 20 % of total shape variation. As expected, viscerocranial components grew with positive and neurocranial with negative allometry.     

Intraspecific epigenetic polymorphism of the East European vole (Microtus levis Miller, 1908) in South-eastern Europe and Turkey

This study aims to represent the first report on population variation of 20 non-metric skull characters in East European vole (Microtus levis) from the Balkan (populations from Northern Dobruja; Southern Dobruja; East part of the Danube Plain; North-east Trace; Sofia field; South-east Trace) and Anatolian peninsulas (populations from North-west Anatolia region and Central Anatolia region), on the basis of which to determine its epigenetic variability and to analyse their mutual geographical epigenetic relations through comparison of the epigenetic divergence among them. Estimation of epigenetic variation of the studied populations of M. levis showed similar pattern of variation, but it is mostly higher than the other rodent species with a similar range of distribution, such as Microtus arvalis, Mus musculus, Apodemus sylvaticus, Apodemus flavicollis and Clethrionomys glareolus. Each one of the studied traits manifested some polymorphism. Moreover, all the calculated epigenetic distances (MMD) were statistically insignificant (P < 0.05) and epigenetic cranial uniqueness (MU) of any studied population was not found. These results reveal lack of expressed geographic relationship of population epigenetic variability in East European vole. The revealed populations epigenetic polymorphism of M. levis gives an opportunity for more complete assessment of variability and biological diversity of this species, but further research is necessary to elucidate its population epigenetics, especially as the data obtained in recent investigations of cranial morphology of the sibling species from the group the M. arvalis (sensu lato) added new locations to the distribution map of the East European vole in Eurasia.     

Protein synthesis in dorsal and ventral regions of Xenopus laevis embryos in relation to dorsal and ventral differentiation

Two-dimensional gel electrophoresis has been used to analyze protein synthesis in dorsal and ventral regions in embryonic stages of Xenopus laevis. Proteins specific either to dorsal or to ventral regions are synthesized for the first time at gastrulation, concomitant with morphological differentiation. The reliability of these proteins as markers of dorsal and ventral differentiation was tested by examining their synthesis in Uv-irradiated embryos, which have severely reduced capacity for dorsal development, reflected in reduced levels of the neuromuscular-specific enzyme acetylcholinesterase, but which continue to synthesize the great majority of proteins at normal rates. Synthesis of dorsal indicator proteins should be reduced or absent in these embryos, whereas ventral indicators should be synthesized at least to the same extent as in control embryos. Some of the putative dorsal and ventral indicators failed this test, but the majority were confirmed as reliable markers of dorsal and ventral differentiation, thus providing a connection between morphology and gene expression in the establishment of the dorsal-ventral axis in X. laevis.     

Morphological Comparison of Meloidogyne Female Head Structures,Perineal Patterns,and Stylets

The external morphology of female heads of three populations of each of two cytological races of Meloidogyne hapla (race A-meiotic, race B-mitotic) and single populations of M. arenaria, M. incognita, and M. javanica was compared by light (LM) and scanning electron microscopy (SEM). Perineal patterns of all nine populations were observed with a LM and then examined with a SEM. In addition, female stylets of each population were excised, viewed with a SEM, and compared with observations made with a LM. Head morphology of the females, including shape of medial and lateral lips, expression of sensilla, and head annulation, was distinct for each species, each race of M. hapla, and each population of M. hapla race A. The morphology of a given perineal pattern appeared similar with the SEM and the LM. The SEM emphasized surface details, whereas the LM revealed subcuticular structure as well. Stylet morphology was unique for each species but similar in all populations of M. hapla. There were differences between species in the shape of the cone, shaft, and knobs and in the distance of the dorsal esophageal gland orifice from the stylet knob base. Several of the morphological characters first detected in the SEM were seen subsequently with the LM and are helpful in species identification.     

Phylogeography and genetic structure of disjunct Salix arbutifolia populations in Japan

Disjunct geographic distributions of boreal plant species at the southern edges of their ranges are expected to result in low genetic diversity and high genetic differentiation in the disjunct populations. This prediction was tested in a riparian willow, Salix arbutifolia, distributed in the northeastern Eurasian continent and the Sakhalin, Hokkaido, and Honshu Islands, using chloroplast DNA haplotypes and nuclear microsatellite genotypes. Hokkaido and Honshu populations shared a chloroplast haplotype identical to a closely related species, S. cardiophylla. This haplotype was divergent from haplotypes in the Eurasian continent (Primorsky) and the Sakhalin Island. In the nuclear microsatellites, most Hokkaido populations were genetically closer to Primorsky populations than to Sakhalin populations in spite of the geographical vicinity between Sakhalin and Hokkaido. The unexpected genetic divergence between Sakhalin and Hokkaido implies a complicated history of migration and colonization. The most peripheral populations in Honshu had the lowest genetic diversity and were most differentiated from the others. Thus, low genetic diversity and high genetic differentiation at the range periphery suggest substantial effects of genetic drift on genetic structure in the disjunct populations of Salix arbutifolia at the southern edge of its range.     

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.     

Quantitative analysis strengthens qualitative assessment: a case study of Devonian brachiopod species

Species recognition attributed to the brachiopod family Atrypidae is evaluated based on qualitative and quantified morphological characters. I identified two brachiopod species—Pseudoatrypa lineata and Pseudoatrypa devoniana—from a rich assemblage of brachiopods recovered from the middle Devonian Genshaw Formation of the Traverse Group. Qualitative examination suggested that the former had fine-medium-sized ribbing, a narrow hinge line, widened anterior, moderately steep mid-anterior fold, domal shaped dorsal valve, and an inflated ventral valve in contrast to the coarse ribbing, widened hinge line, narrow anterior, gentle mid-anterior fold, arched-shape dorsal valve, and flat ventral valve of the latter. The shell outline appears rounded for P. lineata and elongated for P. devoniana. Quantitative assessment of the morphological characters on the dorsal, ventral, anterior, and posterior regions of the valves of the two species using geometric morphometric and statistical analyses suggests that the morphologies of the two species are considerably different (P  $ \ll $  0.01). Thus, qualitative differences between the two atrypid species were further corroborated by quantitative results. This emphasizes the fact that these two species of Pseudoatrypa were indeed different from each other. This study highlights the necessity of incorporating quantified morphological characters to successfully investigate the taxonomic distinctness of fossil invertebrates to the species level.     

Morphological divergence of lake and stream Phoxinus of Northern Italy and the Danube basin based on geometric morphometric analysis

Minnows of the genus Phoxinus are promising candidates to investigate adaptive divergence, as they inhabit both still and running waters of a variety of altitudes and climatic zones in Europe. We used landmark‐based geometric morphometric methods to quantify the level of morphological variability in Phoxinus populations from streams and lakes of Northern Italy and the Danube basin. We analyzed body shape differences of populations in the dorsal, lateral, and ventral planes, using a large array of landmarks and semilandmarks. As the species identification of Phoxinus on morphological characters is ambiguous, we used two mitochondrial genes to determine the genetic background of the samples and to ensure we are comparing homogenous groups. We have found significant body shape differences between habitats: Minnow populations inhabiting streams had a deeper body and caudal peduncle and more laterally inserted pectoral fins than minnows inhabiting lakes. We have also found significant body shape differences between genetic groups: Italian minnows had deeper bodies, deeper and shorter caudal peduncles, and a shorter and wider gape than both groups from the Danube. Our results show that the morphology of Phoxinus is highly influenced by habitat and that body shape variation between habitats was within the same range as between genetic groups. These morphological differences are possibly linked to different modes of swimming and foraging in the respective habitats and are likely results of phenotypic plasticity. However, differences in shape and interlandmark distances between the groups suggest that some (though few) morphometric characters might be useful for separating Phoxinus species.     

Cranial morphological variation in Peromyscus maniculatus over nearly a century of environmental change in three areas of California

Determining how species respond to prolonged environmental change is critical to understanding both their evolutionary biology and their conservation needs. In general, organisms can respond to changing environmental conditions by moving, by adapting in situ, or by going locally or globally extinct. Morphological changes, whether plastic or adaptive, are one way that species may respond in situ to local environmental change. Because cranial morphology is influenced by selective pressures arising from an organism's abiotic and biotic environments, including aspects of thermal physiology, diet, and sensory ecology, studies of cranial morphology may generate important insights into how species are responding to environmental change. To assess potential response of deer mice (Peromyscus maniculatus) to changing conditions in the Sierra Nevada Mountains of California, we quantified cranial variation in museum specimens of this species collected approximately 100 years apart. Specifically, we examined how cranial morphology varies in three populations of this geographically widespread, ecological generalist over elevation and time. Our analyses indicate that cranial morphology does not differ with elevation within either modern or historical samples but does vary between time periods, suggesting that in situ responses to environmental change have occurred. Contrary to predictions based on Bergmann's rule, we found no consistent relationship between body size and either elevation or time, suggesting that morphological differences detected between historic and modern specimens are specific to factors influencing cranial structure. Collectively, these analyses demonstrate the potential importance of in situ changes in morphology as a response to changing environmental conditions. J. Morphol. 277:96–106, 2016. © 2016 Wiley Periodicals, Inc.     

Correlation between Hox code and vertebral morphology in archosaurs

The relationship between developmental genes and phenotypic variation is of central interest in evolutionary biology. An excellent example is the role of Hox genes in the anteroposterior regionalization of the vertebral column in vertebrates. Archosaurs (crocodiles, dinosaurs including birds) are highly variable both in vertebral morphology and number. Nevertheless, functionally equivalent Hox genes are active in the axial skeleton during embryonic development, indicating that the morphological variation across taxa is likely owing to modifications in the pattern of Hox gene expression. By using geometric morphometrics, we demonstrate a correlation between vertebral Hox code and quantifiable vertebral morphology in modern archosaurs, in which the boundaries between morphological subgroups of vertebrae can be linked to anterior Hox gene expression boundaries. Our findings reveal homologous units of cervical vertebrae in modern archosaurs, each with their specific Hox gene pattern, enabling us to trace these homologies in the extinct sauropodomorph dinosaurs, a group with highly variable vertebral counts. Based on the quantifiable vertebral morphology, this allows us to infer the underlying genetic mechanisms in vertebral evolution in fossils, which represents not only an important case study, but will lead to a better understanding of the origin of morphological disparity in recent archosaur vertebral columns.     

Population Genetic Structure of a Centipede Species with High Levels of Developmental Instability

European populations of the geophilomorph centipede Haplophilus subterraneus show a high proportion of individuals with morphological anomalies, suggesting high levels of developmental instability. The broad geographic distribution of this phenomenon seems to exclude local environmental causes, but the source of instability is still to be identified. The goal of the present study was to collect quantitative data on the occurrence of phenodeviants in different populations, along with data on the patterns of genetic variation within and between populations, in order to investigate possible association between developmental instability and genetic features. In a sample of 11 populations of H. subterraneus, distributed in western and central Europe, we looked for phenodeviants, in particular with respect to trunk morphology, and studied genetic variation through the genotyping of microsatellite loci. Overall, no support was found to the idea that developmental instability in H. subterraneus is related to a specific patterns of genetic variation, including inbreeding estimates. We identified a major genetic partition that subdivides French populations from the others, and a low divergence among northwestern areas, which are possibly related to the post-glacial recolonization from southern refugia and/or to recent anthropogenic soil displacements. A weak correlation between individual number of leg bearing segments and the occurrence of trunk anomalies seems to support a trade-off between these two developmental traits. These results, complemented by preliminary data on developmental stability in two related species, suggest that the phenomenon has not a simple taxonomic distribution, while it exhibits an apparent localization in central and eastern Europe.