scholarly journals A developmentally descriptive method for quantifying shape in gastropod shells

2020 ◽  
Vol 17 (163) ◽  
pp. 20190721
Author(s):  
J. Larsson ◽  
A. M. Westram ◽  
S. Bengmark ◽  
T. Lundh ◽  
R. K. Butlin
Keyword(s):  
Empirical Studies ◽  
Three Dimensional ◽  
Shell Shape ◽  
Large Set ◽  
Littorina Saxatilis ◽  
Shape Variation ◽  
Gastropod Shell ◽  
Geometric Morphometric ◽  
Wide Range ◽  
Descriptive Method

The growth of snail shells can be described by simple mathematical rules. Variation in a few parameters can explain much of the diversity of shell shapes seen in nature. However, empirical studies of gastropod shell shape variation typically use geometric morphometric approaches, which do not capture this growth pattern. We have developed a way to infer a set of developmentally descriptive shape parameters based on three-dimensional logarithmic helicospiral growth and using landmarks from two-dimensional shell images as input. We demonstrate the utility of this approach, and compare it to the geometric morphometric approach, using a large set of Littorina saxatilis shells in which locally adapted populations differ in shape. Our method can be modified easily to make it applicable to a wide range of shell forms, which would allow for investigations of the similarities and differences between and within many different species of gastropods.

scholarly journals Shell Shape Variation in Littorina Saxatilis and L. Arcana: A Case of Character Displacement?

1989 ◽  
Vol 69 (4) ◽  
pp. 837-855 ◽  
Author(s):  
J. Grahame ◽  
P.J. Mill
Keyword(s):  
Character Displacement ◽  
Shell Morphology ◽  
Shell Shape ◽  
Rocky Shores ◽  
Littorina Saxatilis ◽  
Shape Variation ◽  
Separate Species ◽  
Wide Range ◽  
Littorina Arcana ◽  
Variable Species

It is now well established that there are several species in the group of rough periwinkles inhabiting European rocky shores. The usual consensus agrees on four, namely Littorina saxatilis (Olivi), Littorina arcana Ellis, Littorina nigrolineata Gray and Littorina neglecta Bean. The first two species are particularly difficult to distinguish in the field and have received much attention. Recent work indicates that the ovoviviparous L.saxatilis is a very variable species living in a wide range of habitats (e.g. Janson, 1985) and that, although it is close to the oviparous L. arcana in shell morphology and in genotype, the two are separate species (Ward & Warwick, 1980; Ward & Janson, 1985), and not reproductive morphs of the same species.

Phenotypic variation of south-western Atlantic clam Mactra isabelleana (Bivalvia: Mactridae)

2012 ◽  
Vol 93 (2) ◽  
pp. 511-517 ◽  
Author(s):  
Javier H. Signorelli ◽  
Federico Márquez ◽  
Guido Pastorino
Keyword(s):  
Principal Component ◽  
Shell Shape ◽  
Physical Parameters ◽  
Buenos Aires Province ◽  
Shape Variation ◽  
Geometric Morphometric ◽  
Western Atlantic ◽  
Canonical Variates Analysis ◽  
Canonical Variates ◽  
Geometric Morphometric Method

The phenotypic shell shape variation of Mactra isabelleana was tested using the geometric morphometric method. Four localities were sampled along the Río de la Plata estuary and the coast of Buenos Aires province. Principal component analysis and canonical variates analysis of the first principal components were performed to reveal the shell variation and differences among localities, respectively. The specimens from different microhabitats mostly overlapped, although differences in shape were observed in the development of the umbo, the enlargement of the dorsoventral axes and the elongation of the posterior end. The ecological and physical parameters that could influence shell shape variation are discussed.

Virtual Environments for Assessing and Rehabilitating Cognitive/Functional Performance A Review of Projects at the USC Integrated Media Systems Center

2001 ◽  
Vol 10 (4) ◽  
pp. 359-374 ◽  
Author(s):  
Albert A. Rizzo ◽  
J. Galen Buckwalter ◽  
Jocelyn S. McGee ◽  
Todd Bowerly ◽  
Cheryl van der Zaag ◽  
...  
Keyword(s):  
Virtual Environments ◽  
Functional Performance ◽  
Empirical Studies ◽  
Three Dimensional ◽  
Head Mounted Display ◽  
Wide Range ◽  
Visuospatial Skills ◽  
Media Systems ◽  
Integrated Media ◽  
Future Work

Virtual reality (VR) technology offers new options for the creation of sophisticated tools that could be applied in the areas of assessment and rehabilitation of cognitive and functional processes. VR systems allow for the precise presentation and control of dynamic, multisensory, three-dimensional (3-D) stimulus environments, as well as the recording of all behavioral responses that occur within them. Assessment and rehabilitation scenarios that would be difficult if not impossible to deliver using conventional neuropsychological methods are now being developed that take advantage of these VR assets. If empirical studies demonstrate effectiveness, virtual environments (VEs) could be of considerable value for better understanding, measuring, and treating persons with impairments due to traumatic brain injury, neurological disorders, and learning disabilities. This article describes the progress of a VR research program at the USC Integrated Media Systems Center and Information Sciences Institute that has developed and investigated the use of a series of VEs designed to target (i) molecular visuospatial skills using a 3-D, projection-based ImmersaDesk system, and (ii) attention (and soon memory and executive functioning) processes within ecologically valid functional scenarios utilizing a head-mounted display (HMD). Results from completed research, rationales and methodology of works in progress, and our plan for future work is presented. Our primary vision has been to develop VR systems that target cognitive processes and functional skills that are of relevance to a wide range of patient populations with central nervous system (CNS) dysfunction, as well as for the assessment of unimpaired performance. We have also sought to select cognitive/functional targets that intuitively appear well matched to the specific assets available with currently available VR technology.

scholarly journals Phylogeny and adaptation shape the teeth of insular mice

2016 ◽  
Vol 283 (1824) ◽  
pp. 20152820 ◽  
Author(s):  
Ronan Ledevin ◽  
Pascale Chevret ◽  
Guila Ganem ◽  
Janice Britton-Davidian ◽  
Emilie A. Hardouin ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Size Variation ◽  
Wood Mouse ◽  
Relative Role ◽  
Resource Exploitation ◽  
Shape Variation ◽  
Geometric Morphometric ◽  
Competition Level ◽  
History Of

By accompanying human travels since prehistorical times, the house mouse dispersed widely throughout the world, and colonized many islands. The origin of the travellers determined the phylogenetic source of the insular mice, which encountered diverse ecological and environmental conditions on the various islands. Insular mice are thus an exceptional model to disentangle the relative role of phylogeny, ecology and climate in evolution. Molar shape is known to vary according to phylogeny and to respond to adaptation. Using for the first time a three-dimensional geometric morphometric approach, compared with a classical two-dimensional quantification, the relative effects of size variation, phylogeny, climate and ecology were investigated on molar shape diversity across a variety of islands. Phylogeny emerged as the factor of prime importance in shaping the molar. Changes in competition level, mostly driven by the presence or absence of the wood mouse on the different islands, appeared as the second most important effect. Climate and size differences accounted for slight shape variation. This evidences a balanced role of random differentiation related to history of colonization, and of adaptation possibly related to resource exploitation.

scholarly journals Assessing species boundaries in the open sea: an integrative taxonomic approach to the pteropod genus Diacavolinia

2019 ◽  
Vol 187 (4) ◽  
pp. 1016-1040 ◽  
Author(s):  
Alice K Burridge ◽  
Remy Van Der Hulst ◽  
Erica Goetze ◽  
Katja T C A Peijnenburg
Keyword(s):  
Integrative Taxonomy ◽  
Species Boundaries ◽  
Shell Shape ◽  
Shape Variation ◽  
Geometric Morphometric ◽  
Integrative Framework ◽  
Rdna Sequences ◽  
Biogeographic Provinces ◽  
Taxonomic Approach ◽  
Species Specific

Abstract To track changes in pelagic biodiversity in response to climate change, it is essential to accurately define species boundaries. Shelled pteropods are a group of holoplanktonic gastropods that have been proposed as bio-indicators because of their vulnerability to ocean acidification. A particularly suitable, yet challenging group for integrative taxonomy is the pteropod genus Diacavolinia, which has a circumglobal distribution and is the most species-rich pteropod genus, with 24 described species. We assessed species boundaries in this genus, with inferences based on geometric morphometric analyses of shell-shape variation, genetic (cytochrome c oxidase subunit I, 28S rDNA sequences) and geographic data. We found support for a total of 13 species worldwide, with observations of 706 museum and 263 freshly collected specimens across a global collection of material, including holo‐ and paratype specimens for 14 species. In the Atlantic Ocean, two species are well supported, in contrast to the eight currently described, and in the Indo‐Pacific we found a maximum of 11 species, partially merging 13 of the described species. Distributions of these revised species are congruent with well-known biogeographic provinces. Combining varied datasets in an integrative framework may be suitable for many diverse taxa and is an important first step to predicting species-specific responses to global change.

A three-dimensional geometric morphometric analysis of variation in cranial size and shape in tammar wallaby (Macropus eugenii) populations

2009 ◽  
Vol 57 (5) ◽  
pp. 337 ◽  
Author(s):  
Claire Hadley ◽  
Nick Milne ◽  
Lincoln H. Schmitt
Keyword(s):  
Three Dimensional ◽  
Tammar Wallaby ◽  
Shape Variation ◽  
Isolated Populations ◽  
Geometric Morphometric ◽  
Island Populations ◽  
Macropus Eugenii ◽  
Size And Shape ◽  
Geographic Separation ◽  
Analysis Of Variation

This study uses geometric morphometric techniques to examine cranial size and shape variation in nine isolated populations of the tammar wallaby (Macropus eugenii). A set of 36 three-dimensional landmarks were digitised on 143 tammar crania from two mainland and seven island populations. While there was no evidence of island dwarfism or gigantism, cranial size increased with both increasing island size and increasing latitude. As latitude increased, the palate narrowed relative to the nasal bones, cranial flexion and nasal height increased, and the zygomatic arches spread out laterally from the cranium. Overall, the anterior nasal aperture (nares) narrowed with increasing latitude. Mean shapes were calculated for each population, and pair-wise comparisons were made; most of these were significantly different. There was a clear tendency for island populations and those with greater geographic separation to show greater shape differentiation. Thus, regional and population differences in the cranial size and shape of tammar wallabies provide examples of selection, founder effect and random genetic drift.

scholarly journals Cranial integration in the ring-necked parakeet, Psittacula krameri (Psittaciformes: Psittaculidae)

2021 ◽  
Vol 133 (1) ◽  
pp. 47-56
Author(s):  
Matthew J Mitchell ◽  
Anjali Goswami ◽  
Ryan N Felice
Keyword(s):  
Invasive Species ◽  
Significant Influence ◽  
Three Dimensional ◽  
Shape Variation ◽  
Geometric Morphometric ◽  
Functional Relationships ◽  
Psittacula Krameri ◽  
Beak Shape ◽  
Native Populations ◽  
Parrot Species

Abstract The study of integration and modularity aims to describe the organization of components that make up organisms, and the evolutionary, developmental and functional relationships among them. Both have been studied at the interspecific (evolutionary) and intraspecific (phenotypic and ontogenetic) levels to different degrees across various clades. Although evolutionary modularity and integration are well-characterized across birds, knowledge of intraspecific patterns is lacking. Here, we use a high-density, three-dimensional geometric morphometric approach to investigate patterns of integration and modularity in Psittacula krameri, a highly successful invasive parrot species that exhibits the derived vertical palate and cranio-facial hinge of the Psittaciformes. Showing a pattern of nine distinct cranial modules, our results support findings from recent research that uses similar methods to investigate interspecific integration in birds. Allometry is not a significant influence on cranial shape variation within this species; however, within-module integration is significantly negatively correlated with disparity, with high variation concentrated in the weakly integrated rostrum, palate and vault modules. As previous studies have demonstrated differences in beak shape between invasive and native populations, variation in the weakly integrated palate and rostrum may have facilitated evolutionary change in these parts of the skull, contributing to the ring-necked parakeet’s success as an invasive species.

scholarly journals Three-dimensional geometric morphometric studies of modern human occipital variation

PLoS ONE ◽  
2021 ◽  
Vol 16 (1) ◽  
pp. e0245445
Author(s):  
Yameng Zhang ◽  
Lynne A. Schepartz
Keyword(s):  
Three Dimensional ◽  
Principal Component ◽  
Modern Human ◽  
Foramen Magnum ◽  
European Ancestry ◽  
Shape Variation ◽  
Geometric Morphometric ◽  
Phylogenetic Studies ◽  
Males And Females ◽  
Ct Data

Objectives To investigate three-dimensional morphological variation of the occipital bone between sexes and among populations, to determine how ancestry, sex and size account for occipital shape variation and to describe the exact forms by which the differences are expressed. Methods CT data for 214 modern crania of Asian, African and European ancestry were compared using 3D geometric morphometrics and multivariate statistics, including principal component analysis, Hotelling’s T2 test, multivariate regression, ANOVA, and MANCOVA. Results Sex differences in average occipital morphology are only observed in Europeans, with males exhibiting a pronounced inion. Significant ancestral differences are observed among all samples and are shared by males and females. Asian and African crania have smaller biasterionic breadths and flatter clivus angles compared to Europeans. Asian and European crania are similar in their nuchal and occipital plane proportions, nuchal and occipital angles, and lower inion positions compared to Africans. Centroid size significantly differs between sexes and among populations. The overall allometry, while significant, explains little of the shape variation. Larger occipital bones were associated with a more curved occipital plane, a pronounced inion, a narrower biasterionic breadth, a more flexed clivus, and a lower and relatively smaller foramen magnum. Conclusions Although significant shape differences were observed among populations, it is not recommended to use occipital morphology in sex or population estimation as both factors explained little of the observed variance. Other factors, relating to function and the environment, are suggested to be greater contributors to occipital variation. For the same reason, it is also not recommended to use the occiput in phylogenetic studies.

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