Quantification of cranial convergences in arvicolids (Rodentia)

Cranial convergence in nine species of arvicolids is quantified phenetically using geometric morphometry. In a preliminary step, a hypothesis about phyletic relationships is proposed as a framework against which to examine morphological comparisons. The cranial morphology is then depicted in three series of 37, 20 and 13 landmarks characterizing the lower, upper and lateral sides of the skull respectively. Superimposition (Procrustes) methods are used to quantify shape differences and establish phenograms for the three sides of the skull. The phenogram obtained for lateral sides reveals a strong connection between skull profile and mode of life: surface dwelling forms have elongated skulls whereas burrowers have angular skulls. The phenogram of the lower sides show no clear correlation between shape and mode of life. Analysis of the upper cranial sides revealed a substantial difference between hard-substrate burrowers and other ecological groups. The results of the morphological analyses are compared with the phyletic hypothesis and with ecological data to explore how convergences take place in the evolution of arvicolids. Analyses pointed out three instances of morphological convergence: one between Synaptomys cooperi and voles, one between Lagurus lagurus and lemmings, and one between Myopus schisticolor and some voles. Four main ecological events are discussed.     

Quantitative-genetic analysis of wing form and bilateral asymmetry in isochromosomal lines ofDrosophila subobscura using Procrustes methods

Fluctuating asymmetry (FA) is often used as a measure of underlying developmental instability (DI), motivated by the idea that morphological variance is maladaptive. Whether or not DI has evolutionary potential is a highly disputed topic, marred by methodological problems and fuzzy prejudices. We report here some results from an ongoing study of the effects of karyotype, homozygosity and temperature on wing form and bilateral asymmetry using isochromosomal lines ofDrosophila subobscura. Our approach uses the recently developed methodologies in geometric morphometrics to analyse shape configurations of landmarks within the standard statistical framework employed in studies of bilateral asymmetries, and we have extended these methods to partition the individual variation and the variation in asymmetries into genetic and environmental causal components. The analyses revealed temperaturedependent expression of genetic variation for wing size and wing shape, directional asymmetry (DA) of wing size, increased asymmetries at suboptimal temperature, and a transition from FA to DA in males as a result of increase in the rearing temperature. No genetic variation was generally detected for FA in our samples, but these are preliminary results because no crosses between lines were carried out and, therefore, the contribution of dominance was not taken into account. In addition, only a subset of the standing genetic variation was represented in the experiments.     

Exploring artificial cranial deformation using elliptic Fourier analysis of Procrustes aligned outlines

The anatomical effects of artificial cranial deformation on the face and the base have been subject to various metric approaches, including standard linear as well as finite element techniques, and have produced controversial results (Antón [1989] Am. J. Phys. Anthropol. 79:253-267; Kohn et al. [1993] Am. J. Phys. Anthropol. 90:147-158). It can be argued that diverging observations partly result from methodological constraints. The present study compares samples of intentionally deformed and undeformed human crania, using elliptic Fourier analysis (EFA), a morphometric approach which has been shown to be particularly appropriate for characterizing the shape of two-dimensional outlines and associated shape changes. We improve the standard EFA approach by adding a preliminary orientation of the outlines following the rotation parameters of a Procrustes superimposition, using multiple homologous landmarks called control points. The results confirm that circumferentially deformed skulls exhibit modifications of the basioccipital region, together with increased anterior and inferior facial projection. However, the degree to which basioccipital flattening is modified in circumferentially deformed Peruvians was found to be less marked than changes observed in the face. Some of the modifications observed here can be related to morphological trends existing in the population from which our sample was taken. The observation of other modifications may be subject to methodological constraints of standard morphometric approaches.     

Concordance of Species Composition Patterns among Microcrustaceans,Rotifers and Testate Amoebae in a Shallow Pond

In this study, spatial concordance among microcrustaceans, rotifers and testate amoebae was examined in a small pond in Central Brazil. The main goal was to test how consistently different taxonomic groups ordinate 9 sites distributed along the pond's main axis. Microcrustaceans were more abundant during the dry season, characterized by waters with high transparency and dissolved oxygen concentration. An increase in species richness and densities of rotifers and testate amoebae was detected during rainy season, with low values of Secchi disk and concentrations of dissolved oxygen. However, the ordination patterns generated by these groups were different. Concordant patterns across sites were found only between cladocerans and copepods. These results suggest that great care should be taken when ordination patterns based on some taxonomic groups are extrapolated to other groups for detecting environmental changes. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mean Figures and Mean Shapes Applied to Biological Figure and Shape Distributions in the Plane

Fundamental propositions for mean figures and mean shapes in the plane are proved by using complex numbers. A test of equality of two figure or shape distributions is introduced and applied to data from larvae of mussels and from saurian heads.     

Morphometric analysis of variation in the sternum with sex and age

Age and sex‐related variations in sternum morphology may affect the thoracic injury tolerance. Male and female sternum size and shape variation was characterized for ages 0–100 from landmarks collected from 330 computed tomography scans. Homologous landmarks were analyzed using Procrustes superimposition to produce age and sex‐specific functions of 3D‐sternum morphology representing the combined size and shape variation and the isolated shape variation. Significant changes in the combined size and shape variation and isolated shape variation of the sternum were found to occur with age in both sexes. Sternal size increased from birth through age 30 and retained a similar size for ages 30–100. The manubrium expanded laterally from birth through age 30, becoming wider in relation to the sternal body. In infancy, the manubrium was 1.1–1.2 times the width of the sternal body and this width ratio increased to 1.6–1.8 for adults. The manubrium transformed from a circular shape in infancy to an oval shape in early childhood. The distal sternal body became wider in relation to the proximal sternal body from birth through age 30 and retained this characteristic throughout adulthood. The most dramatic changes in sternum morphology occur in childhood and young adulthood when the sternum is undergoing ossification. The lesser degree of ossification in the pediatric sternum may be partly responsible for the prevalence of thoracic organ injuries as opposed to thoracic skeletal injuries in pediatrics. Sternum fractures make up a larger portion of thoracic injury patterns in adults with fully ossified sternums. The lack of substantial size or shape changes in the sternum from age 30–100 suggests that the increased incidence of sternal fracture seen in the elderly may be due to cortical thickness or bone mineral density changes in the sternum as opposed to morphological changes. J. Morphol. 275:1284–1299, 2014. © 2014 Wiley Periodicals, Inc.     

Wing shape versus asymmetry as an indicator of changing environmental conditions in insects

Abstract In insects, the fluctuating asymmetry of bilaterally symmetrical traits has been suggested as an indicator of environmental stress because asymmetry is expected to increase when stressful conditions disturb the normal development of organisms. However, the extensive literature on asymmetry–stress associations is indeterminate. Here we contrast changes in asymmetry with changes in an alternate stress indicator, the shape of insect wings. The development of wing shape involves numerous genes that act throughout egg-to-adult development, so stresses that act at a specific time could alter shape in specific ways. Shape changes, as measured by the Procrustes technique, were considered in five data sets: exposure of Drosophila melanogaster (Meigen) to multiple stresses involving ethanol, low nutrition and cold shocks; exposure of a chironomid ( Chironomus tepperi (Skuse)), a blowfly ( Lucilia cuprina (Wiedemann)), and lightbrown apple moth ( Epiphyas postvittana (Walker)) to pesticides; and development of C. tepperi under saline conditions. All these conditions influenced viability and development time. In none of these cases was a change in symmetry of wing size or wing shape detected. In contrast, in four of the five data sets there was a change in wing shape. These results suggest that wing shape may be altered more commonly by stress than trait asymmetry. Wing-shape monitoring may be useful in detecting stressful environmental conditions during development, at least under controlled conditions.     

GENETIC ANALYSIS OF SKULL SHAPE VARIATION AND MORPHOLOGICAL INTEGRATION IN THE MOUSE USING INTERSPECIFIC RECOMBINANT CONGENIC STRAINS BETWEEN C57BL/6 AND MICE OF THE MUS SPRETUS SPECIES

To assess the genetic basis of the skull shape variation and morphological integration in mice, we have used a tool based on the cross between the distantly related mouse species Mus spretus (SEG/Pas strain) and the laboratory strain C57BL/6 called interspecific recombinant congenic strains (IRCSs). The genome of each IRCS consists on average of 1.3% of SEG/Pas derived sequences, located on multiple chromosomes as small-sized, DNA segments. Quantitative trait loci (QTL) on the skull shape, separated into dorsal and ventral sides, were analyzed in 17 IRCSs by a Procrustes superimposition method using 3D landmarks. The shapes of 16 strains differed significantly from C57BL/6. Discrepancy in the QTLs effects was found between the dorsal side and the anterior region of the ventral side due to a differential effect of the SEG/Pas alleles on the skull shape. A comprehensive analysis of all allelic combinations of the BCG-66H strain showed strong epistatic interactions between SEG/Pas segment acting on both skull sides. Epistatic pleiotropy and covariation between sides were dependent in SEG/Pas alleles direction and contributed to the strong morphological integration between sides. Introduction of Mus spretus alleles in a C57BL/6 background induced strong morphological changes mostly in SEG/Pas alleles direction and provided evidence for high level of morphological integration.