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.

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.

An exposure scale for marine shores in western Norway

1978 ◽  
Vol 58 (4) ◽  
pp. 975-996 ◽  
Author(s):  
D. H. Dalby ◽  
E. B. Cowell ◽  
W. J. Syratt ◽  
J. H. Crothers
Keyword(s):  
Species Abundance ◽  
Shell Shape ◽  
Rocky Shores ◽  
Shape Variation ◽  
Nucella Lapillus ◽  
Extended Form ◽  
Independent Evidence ◽  
The North ◽  
Western Norway ◽  
The North Sea

A rocky shore exposure scale, intended primarily for use in the Fensfjord area, Western Norway, has been prepared. This scale is developed from an earlier scale devised by Ballantine for Milford Haven, Wales, making use of species abundance curves along the wave exposure gradient. Independent evidence for the validity of the scale is provided by shell shape variation in Nucella lapillus and by the height of the black lichen zone in the supralittoral fringe. The successive steps in the preparation of the scale are outlined, definitions of the exposure grades are given in tabular form for the restricted set of species analysed numerically and descriptions are provided in an extended form to provide a fuller picture for users of the scale. It is believed that the scale will prove applicable to other rocky shores around the North Sea.

scholarly journals Adaptive divergence in shell morphology in an ongoing gastropod radiation from Lake Malawi

2020 ◽  
Vol 20 (1) ◽  
Author(s):  
Bert Van Bocxlaer ◽  
Claudia M. Ortiz-Sepulveda ◽  
Pieter R. Gurdebeke ◽  
Xavier Vekemans
Keyword(s):  
Common Garden ◽  
Shell Morphology ◽  
Model Systems ◽  
Shell Shape ◽  
Adaptive Divergence ◽  
Nominal Species ◽  
Shape Variation ◽  
In The Wild ◽  
Evolutionary Radiations ◽  
Contrasting Habitats

Abstract Background Ecological speciation is a prominent mechanism of diversification but in many evolutionary radiations, particularly in invertebrates, it remains unclear whether supposedly critical ecological traits drove or facilitated diversification. As a result, we lack accurate knowledge on the drivers of diversification for most evolutionary radiations along the tree of life. Freshwater mollusks present an enigmatic example: Putatively adaptive radiations are being described in various families, typically from long-lived lakes, whereas other taxa represent celebrated model systems in the study of ecophenotypic plasticity. Here we examine determinants of shell-shape variation in three nominal species of an ongoing ampullariid radiation in the Malawi Basin (Lanistes nyassanus, L. solidus and Lanistes sp. (ovum-like)) with a common garden experiment and semi-landmark morphometrics. Results We found significant differences in survival and fecundity among these species in contrasting habitats. Morphological differences observed in the wild persisted in our experiments for L. nyassanus versus L. solidus and L. sp. (ovum-like), but differences between L. solidus and L. sp. (ovum-like) disappeared and re-emerged in the F1 and F2 generations, respectively. These results indicate that plasticity occurred, but that it is not solely responsible for the observed differences. Our experiments provide the first unambiguous evidence for genetic divergence in shell morphology in an ongoing freshwater gastropod radiation in association with marked fitness differences among species under controlled habitat conditions. Conclusions Our results indicate that differences in shell morphology among Lanistes species occupying different habitats have an adaptive value. These results also facilitate an accurate reinterpretation of morphological variation in fossil Lanistes radiations, and thus macroevolutionary dynamics. Finally, our work testifies that the shells of freshwater gastropods may retain signatures of adaptation at low taxonomic levels, beyond representing an evolutionary novelty responsible for much of the diversity and disparity in mollusks altogether.

scholarly journals Morphological shell variation of Zidona dufresnei (Caenogastropoda: Volutidae) from the Southwestern Atlantic Ocean

2020 ◽  
Vol 33 (1) ◽  
pp. 53-68
Author(s):  
Alonso I. Medina ◽  
María Alejandra Romero ◽  
Augusto Crespi-Abril ◽  
Maite A. Narvarte
Keyword(s):  
Atlantic Ocean ◽  
San Antonio ◽  
Maximum Size ◽  
Shell Morphology ◽  
Shell Shape ◽  
Southwestern Atlantic ◽  
Shape Variation ◽  
Fishery Resource ◽  
Southwestern Atlantic Ocean ◽  
Shape And Size

The volutid gastropod Zidona dufresnei is an important fishery resource from the Southwestern Atlantic Ocean. This species exhibits strong interpopulation differences in life history features, which lead to postulate the existence of two morphotype ('normal' and 'dwarf'). In this study, we combine and compare traditional and geometric morphometrics to capture shell shape variation of Z. dufresnei among three populations from Mar del Plata (37° S) to San Matías Gulf (42° S) to test the hypothesis that the phenotypic variation already described in the life cycle and size is also expressed in the shell shape. Significant differences in the shell morphology among these three populations were detected, mainly associated to the maximum size of individuals and shell shape. The Bahía San Antonio morphotype had shells with higher general roundness and weight compared to San Matías Gulf and Mar del Plata morphotypes, which were not differentiated. Our results support the hypothesis of Lahille (1895) who distinguished the morphotype of Bahía San Antonio ('dwarf' morphotype) as Voluta angulata affinis. The functional significance of the variability found is discussed in terms of the ecological and genetic effects on shape and size.

Shell morphometry of the deep sea protobranch bivalve Ledella pustulosa in the Rockall Trough, north-east Atlantic

1999 ◽  
Vol 79 (4) ◽  
pp. 661-671 ◽  
Author(s):  
Lee A. Fuiman ◽  
John D. Gage ◽  
Peter A. Lamont
Keyword(s):  
Discriminant Function ◽  
Deep Sea ◽  
Environmental Control ◽  
Shell Morphology ◽  
Shell Shape ◽  
Gradual Transition ◽  
North East ◽  
Training Samples ◽  
Wide Range ◽  
Rockall Trough

The deep sea protobranch bivalve species Ledella pustulosa recently has been described as comprised of four subspecies, differentiated on subtle and qualitative differences in shell morphology. Two of these, L. p. pustulosa and L. p. marshalli, possess overlapping geographic distributions, L. p. pustulosa occurring on the continental slope, and L. p. marshalli occurring on the continental rise and at upper abyssal depths. Principal components analysis was applied to six samples of Ledella pustulosa from the Rockall Trough in order to explore patterns of variation in shell shape and to test whether the variability follows a depth-related cline which might be under environmental control. Two of these samples had previously been identified as L. p. pustulosa and L. p. marshalli, respectively. The distributions of shapes at every depth overlapped broadly with the distributions from other depths and none of the depths had uniformly distinct shells. However, the mean shapes of the six samples divided into two clusters: a shallow cluster characterized by a lower dorsal profile (smaller ‘shoulders’) and a deep cluster with larger ‘shoulders’. No bathymetric cline in shape was found within these clusters. A discriminant function based on training samples of L. p. pustulosa and L. p. marshalli correctly identified 84% of the shells in the training samples and was applicable over a wide range in shell size. It showed that the subspecies differed primarily in the dorsal profile. The discriminant function was applied to 598 shells from depths of 1632–2900 m in the Rockall Trough in order to test the hypothesis of depth-related segregation of the subspecies. Although individual variability was high, the results indicated a gradual transition from L. p. pustulosa dominance at ∼2000 m to L. p. marshalli dominance at 3000 m depth, but not marked segregation. A sample from 1632 m depth with large proportions of both subspecies disrupted the bathymetric trend and suggested a latitudinal gradient in distribution. Possible environmental factors, including bottom currents, acting on a common genotype to cause the observed pattern of differentiation, are also discussed.

Effect of geographic location and sexual dimorphism on shield shape of the Red Sea hermit crab Clibanarius signatus using the geometric morphometric approach

2018 ◽  
Vol 96 (7) ◽  
pp. 667-679 ◽  
Author(s):  
Tarek G. Ismail
Keyword(s):  
Sexual Dimorphism ◽  
Red Sea ◽  
Salt Marshes ◽  
Hermit Crab ◽  
Size Variation ◽  
Procrustes Analysis ◽  
Shell Shape ◽  
Rocky Shores ◽  
Shape Variation ◽  
Geometric Morphometric

The hermit crab Clibanarius signatus Heller, 1861 inhabits varied intertidal habitats of the Red Sea coast, such as rocky shores and mangrove littoral salt marshes. Shield-shape variation among three populations of C. signatus was analyzed with geometric morphometric methods. Shape variation was studied through multivariate analyses using configurations aligned by the generalized Procrustes analysis. Shape variation was explored through principal component analysis. The ordination of the populations and the sexes was investigated using discriminant analysis of canonical variables. Centroid size, as a measure of overall size, was used to estimate size variation among the three populations and the sexes. The results revealed the presence of shield-size variation among the three populations and confirmed the size sexual dimorphism in two populations. Moreover, the analysis revealed the occurrence of two morphotypes based on a covariation between shield shape and shape of occupied shells. The geographic distance was not a good predictor of shield shape. Cross-validation analyses correctly reclassified more than 70% of individuals and 66% of sexes to their correct group. It was suggested that association in shield-shell shape could be the result of the phenotypic plasticity of this species.

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