On growth and form of irregular coiled-shell of a terrestrial snail: Plectostoma concinnum (Fulton, 1901) (Mollusca: Caenogastropoda: Diplommatinidae) (original) (raw)
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The rampant convergent and parallel evolution in shell form in the Gastropoda is well known. Many studies focus on the functional drivers which have been regarded as a major force in shell evolution. There is, however, a scarcity in studies that aim at understanding shell form evolution with respect to their ontogeny. Hence, we investigated the evolution of shell form in the micro-landsnail genus Plectostoma (Diplommatinidae) from the viewpoint of shell ontogeny. We examined the aperture ontogeny profiles that describe how aperture form and growth trajectory change along the shell ontogeny, and how the aperture ontogeny profiles relate to the observed shell forms. We also estimated the phylogeny of Plectostoma species, and examined patterns of character evolution for shell form. Our study revealed a general issue in the characterisation of shell shape and demonstrated how shell shape differences can be expressed as differences in the ontogeny of morphospace. It is clear that in Plectostoma the phylogenetic history does not prevent the course of shell ontogeny, and the resultant form. Finally, each species has a unique aperture ontogeny profile that determines its shell shape while retaining a conserved developmental program that maintains shell size.
PeerJ, 2014
Predator-prey interactions are among the main ecological interactions that shape the diversity of biological form. In many cases, the evolution of the mollusc shell form is presumably driven by predation. However, the adaptive significance of several uncommon, yet striking, shell traits of land snails are still poorly known. These include the distorted coiled "tuba" and the protruded radial ribs that can be found in micro-landsnails of the genus Plectostoma. Here, we experimentally tested whether these shell traits may act as defensive adaptations against predators. We characterised and quantified the possible anti-predation behaviour and shell traits of Plectostoma snails both in terms of their properties and efficiencies in defending against the Atopos slug predatory strategies, namely, shell-apertural entry and shell-drilling. The results showed that Atopos slugs would first attack the snail by shell-apertural entry, and, should this fail, shift to the energetically mor...
PeerJ, 2014
Predator-prey interactions are among the main ecological interactions that shape the diversity of biological form. In many cases, the evolution of the mollusc shell form is presumably driven by predation. However, the adaptive significance of several uncommon, yet striking, shell traits of land snails are still poorly known. These include the distorted coiled "tuba" and the protruded radial ribs that can be found in micro-landsnails of the genus Plectostoma. Here, we experimentally tested whether these shell traits may act as defensive adaptations against predators. We characterised and quantified the possible anti-predation behaviour and shell traits of Plectostoma snails both in terms of their properties and efficiencies in defending against the Atopos slug predatory strategies, namely, shell-apertural entry and shell-drilling. The results showed that Atopos slugs would first attack the snail by shell-apertural entry, and, should this fail, shift to the energetically more costly shell-drilling strategy. We found that the shell tuba of Plectostoma snails is an effective defensive trait against shell-apertural entry attack. None of the snail traits, such as resting behaviour, shell thickness, shell tuba shape, shell rib density and intensity can fully protect the snail from the slug's shell-drilling attack. However, these traits could increase the predation costs to the slug. Further analysis on the shell traits revealed that the lack of effectiveness in these anti-predation shell traits may be caused by a functional trade-off between shell traits under selection of two different predatory strategies.
Dietary effects on shell growth and shape in an intertidal marine snail, Littorina saxatilis
Journal of Molluscan Studies, 2012
In the marine gastropod Littorina saxatilis differences in relative shell apertural form between two ecotypes from NW Spain have been associated with an environmental cline related to the degree of wave exposure. Such differences have been claimed to have a strong genetic basis, with little influence of phenotypic plasticity. However, dietary changes are expected to affect the growth rate and, potentially, the shell shape, and could thus challenge the adaptive interpretation of the polymorphism. To address this issue we performed a laboratory experiment to grow one of these ecotypes under different food treatments with the aim of testing differences in shell growth. We then investigated the correlation of shell size and shape to quantify the impact of growth on shell aperture. Our results reveal significant dietary effects, an increase in growth rate leading to larger relative apertural size. However, this change occurs in the opposite direction to that expected from the differences between the two ecotypes in nature. This is in line with the low contribution of phenotypic plasticity to the polymorphism observed in previous studies.
Adaptive responses and invasion: the role of plasticity and evolution in snail shell morphology
Ecology and evolution, 2013
Invasive species often exhibit either evolved or plastic adaptations in response to spatially varying environmental conditions. We investigated whether evolved or plastic adaptation was driving variation in shell morphology among invasive populations of the New Zealand mud snail (Potamopyrgus antipodarum) in the western United States. We found that invasive populations exhibit considerable shell shape variation and inhabit a variety of flow velocity habitats. We investigated the importance of evolution and plasticity by examining variation in shell morphological traits 1) between the parental and F1 generations for each population and 2) among populations of the first lab generation (F1) in a common garden, full-sib design using Canonical Variate Analyses (CVA). We compared the F1 generation to the parental lineages and found significant differences in overall shell shape indicating a plastic response. However, when examining differences among the F1 populations, we found that they ...
The ecology of shell shape difference in chirally dimorphic snails
2012
The Southeast-Asian tree snail subgenus Amphidromus s. str. (Gastropoda Pulmonata: Camaenidae) is unusual among all gastropods for its genetic antisymmetry: populations consist of stable mixtures of individuals with clockwise (dextral) and counterclockwise (sinistral) coiling directions. Although previous studies in A. inversus suggest that this genetic dimorphism is maintained by sexual selection, it cannot be ruled out that environmental factors also play a role. Adult shell shapes in A. inversus are known to show subtle differences between both coiling morphs, and it is known that in snails in general, shell shape is under environmental selection, thus creating the possibility that micro-niche use of both coiling morphs differs. In this paper, we first confirm that hatchlings also differ in shell shape. We then proceed with field studies to compare dextral and sinistral juveniles and adults for (i) direction and rate of dispersal within the vegetation and (ii) micro-niche occupation. However, we failed to detect any difference in both ecological traits. In addition to earlier data that show that there is no clustering of morphs in the field and that both morphs suffer identical predation pressure, these new data do not provide any evidence for a role for environmental factors in maintaining the coil dimorphism in this species.
Regulation of spiral growth in planorbid gastropods
Lethaia, 2007
Extensive experimentation has been performed on the planorhid Plririorbarius nietidjensis in order to determine which mechanism allows the snail to coil its shell regularly. Individuals of this species, like all Planorbidae, are permanently active and secrete their shells while crawling on the substrate. Experiments consisted of attaching weights to either side of the shell (which is carried almost vertically) in an umbilical position; these weights cause the shell to fall towards the substrate on the loaded side. It can be demonstrated, qualitatively and quantitatively, that during further growth the shell tube deviated initially (i.e. within the first halfwhorl after loading) towards the loaded side. In a later stage, when the animal is able to re-balance the shellload complex by muscular activity, the shell tube gradually deviates away from the loaded side. This behaviour is to be expected if, after loading, secretion ofthe shell continued with the aperture parallel to the substrate and forming a constant angle with the direction of growth. The main implication is that in normal conditions the living posture largely controls the correct coiling of the shell. Minor experiments made with another planorbid species, Gyraulirs laevis, confirm these conclusions. The growth pattern of planorbids requires that the snail has constant information on the orientation ofthe shell with respect to the substrate. This is permitted by the particular physiological ecology of this group, members of which, unlike terrestrial gastropods, are permanently active. OMorphology, spiral growth, coiled shells, gastropods, Planorbidae.
Journal of Experimental …, 2010
In recent years, developmental plasticity has received increasing attention. Specifically, some studies highlighted a possible association between shell shape and growth rates in intertidal gastropods. We use a growth vector model to study how hypothetical growth processes could underlie developmental plasticity in molluscs. It illustrates that variation in instantaneous shell growth rate can induce variability in allometric curves. Consequently, morphological variation is time-dependent. Basing our model parameters on a study documenting the results of transplants experiments of three gastropods ecomorphs, we reproduce the main aspects of the variation in size, shape, and growth rates among populations when bred in their own habitat or transplanted to another ecotype habitat. In agreement with empirical results, our simulation shows that a flatter growth profile corresponds to conditions of rapid growth. The model also allows the comparison of allometric slopes using different subdata sets that correspond to static and ontogenetic allometry. Our model highlights that depending on subdata sets, the ''main effects'' could be attributed to source population or environment. In addition, convergence or divergence of allometric slopes is observed depending on the subdata sets. Although there is evidence that shell shape in gastropods is to some extent growth rate dependent, gaining a general overview of the issue is challenging, in particular because of the scarcity of studies referring to allometry. We argue that the dynamics of development at the ''phenotypic level'' constitute a non-reducible level of investigation if one seeks to relate the observed amount of phenotypic variation to variability in the underlying factors.
BMC Developmental Biology, 2013
Background: Toxic substances like heavy metals can inhibit and disrupt the normal embryonic development of organisms. Exposure to platinum during embryogenesis has been shown to lead to a "one fell swoop" internalization of the shell in the ramshorn snail Marisa cornuarietis, an event which has been discussed to be possibly indicative of processes in evolution which may result in dramatic changes in body plans. Results: Whereas at usual cultivation temperature, 26°C, platinum inhibits the growth of both shell gland and mantle edge during embryogenesis leading to an internalization of the mantle and, thus, also of the shell, higher temperatures induce a restart of the differential growth of the mantle edge and the shell gland after a period of inactivity. Here, developing embryos exhibit a broad spectrum of shell forms: in some individuals only the ventral part of the visceral sac is covered while others develop almost "normal" shells. Histological studies and scanning electron microscopy images revealed platinum to inhibit the differential growth of the shell gland and the mantle edge, and elevated temperature (28-30°C) to mitigate this platinum effect with varying efficiency. Conclusion: We could show that the formation of internal, external, and intermediate shells is realized within the continuum of a developmental gradient defined by the degree of differential growth of the embryonic mantle edge and shell gland. The artificially induced internal and intermediate shells are first external and then partly internalized, similar to internal shells found in other molluscan groups.