Phylogeography and morphological variability in land snails: the Sicilian Marmorana (Pulmonata, Helicidae)

Abstract

Land snails have long been recognized as suitable organisms for studying phenotypic differentiation and phylogeny in relation to geographical distribution. Morphological data (shell and anatomy biometry on different geographical scales) and partial sequences from mitochondrial genes (cytochrome oxidase subunit I, 16S rDNA) were used to test whether morphological patterns match phylogeny in a diversified group of Sicilian rock-dwelling land snails belonging to the genus Marmorana. The taxonomic implications of the three character sets (shell and anatomical biometry and molecular data) were also considered. The inferred phylogenetic relationships do not match morphological (shell and genitalia) patterns. This result may significantly modify the current taxonomy. Mitochondrial based reconstructions define several supported clades well correlated with geographic distribution and populations were found to be distributed parapatrically. The progressive decline in mitochondrial DNA sequence similarity over a distance of 250 km is consistent with a model of isolation by distance, a pattern previously recognized for other groups of land snails. For one clade of Marmorana, colonization along Mediterranean trade routes appears to be a possibility.

Historical biogeography of Tyrrhenian land snails: The Marmorana–Tyrrheniberus radiation (Pulmonata, Helicidae)

“…Black dots: Marmorana populations; white dots: Tyrrheniberus populations. Fiorentino et al (2008b) (Fig. 1).…”

“…Further analysis with a more detailed sampling design is therefore needed for Sardinian Marmorana and all the differentiated lineages which could represent distinct taxa (such as the Calabrian ones). Fiorentino et al (2008b) already noted that Marmorana sp. from Marettimo (Mt, an island off the west coast of Sicily) did not belong to the Sicilian group on the basis of morphology and genetics.…”

“…Isolation by distance probably played a key role in diversification of populations at local scale (Fiorentino et al, 2008b). This seems to have happened in the case of the Sicilian Marmorana (Fiorentino et al, 2008b) and Sardinian T. sardonius and T. villicus.…”

“…Isolation by distance probably played a key role in diversification of populations at local scale (Fiorentino et al, 2008b). This seems to have happened in the case of the Sicilian Marmorana (Fiorentino et al, 2008b) and Sardinian T. sardonius and T. villicus. The latter are close geographically as well as genetically; they are morphologically indistinguishable because they share the same set of genital characters and a gradient of shell shapes.…”

“…Marmorana has one of the highest conchological diversifications among Mediterranean land snail genera, exhibiting globular to flatshelled populations (Fiorentino et al, 2008b). Its shell variability led to the description of more than a 100 nominal taxa which were later reduced to a few species assigned to three subgenera.…”