Shell shape of the land snail Cornu aspersum in North Africa: unexpected evidence of a phylogeographical splitting

Abstract

Anatomical and molecular characters used to differentiate populations of the land snail Cornu aspersum (Helix aspersa) exhibit, in the western Mediterranean, definite and concordant patterns of correlation with geography. Scenarios involving Pliocene geological changes and postglacial expansion during the Pleistocene were proposed in previous studies to account for the establishment of this geographical structure. In the present work, we have performed a spatial analysis of variation in shell morphometrics, after the partitioning of the overall variation into size and shape components by means of a principal component-based approach (Cadima and Jolliffe, 1996). In order to know if the same historical events have also structured shell variation, the analysis includes all the populations from North Africa which were investigated for anatomical and molecular surveys. Contrary to shell size, which shows a significant spatial heterogeneity essentially related to environmental pressures, variation in shell shape components splits the populations according to a geographical pattern reflective of hypotheses suggested for molecular markers and genital anatomy. This implies that the selective forces often invoked to explain spatial changes in shell shape are not the deciding factors in the present case. Moreover, within each of the two geographical clusters defined, Mantel correlograms show that the similarity between populations declines according to an isolation by distance model. Because of the different allometric relationships between shell size and genitalia measurements in Western and Eastern entities of North Africa, mechanical constraints, possibly leading to a precopulatory isolation in the contact zone, are involved.

Bioaccumulative and conchological assessment of heavy metal transfer in a soil-plant-snail food chain

“…Flatter shells facilitate movement on substrates with foliated structures (e.g., leaf litter), whereas higher shells are more advantageous on substrate with a fine particle structure (e.g., soil) [48]. Several studies demonstrated that this feature is primarily genetically determined, but, within a given form, it may also be influenced by phenotype [49]. Therefore, the sampled snails have originated from habitats with different substrates or they belong to different subspecies.…”

Variation in Thermal Sensitivity and Thermal Tolerances in an Invasive Species across a Climatic Gradient: Lessons from the Land Snail Cornu aspersum

“…This land snail exhibits a great shell variation across geographical regions [43] and is characterized by physiological and morphological adaptations (e.g., metabolic depression, reduction of water-loss rate, thicker shell, reduced shell aperture, thicker epiphragm and supercooling ability) that enable it to inhabit dryer, colder and/or hotter environments by increasing the amount of time the snail can remain inactive [44]–[46]. Additionally, empirical evidence suggests that C. aspersum snails are energetically constrained by the mode of locomotion [47] and the cost of shell production during ontogeny [48].…”

Spatial mosaic evolution of snail defensive traits

“…To characterize shell size, we conducted a principal components analysis of log10-transformed linear shell measurements. To characterize shell shape, we performed a covariance PCA [35], which finds shape components that are separate from size. Covariance PCA analysis was conducted in ADE-4 [36], and PCA shape scores were obtained by an R program subroutine provided by A. Bellido.…”