Trochulus

Abstract: Costly structures need to represent an adaptive advantage in order to be maintained over evolutionary times. Contrary to many other conspicuous shell ornamentations of gastropods, the haired shells of several Stylommatophoran land snails still lack a convincing adaptive explanation. In the present study, we analysed the correlation between the presence/absence of hairs and habitat conditions in the genus Trochulus in a Bayesian framework of character evolution. Haired shells appeared to be the ancestral character state, a feature most probably lost three times independently. These losses were correlated with a shift from humid to dry habitats, indicating an adaptive function of hairs in moist environments. It had been previously hypothesised that these costly protein structures of the outer shell layer facilitate the locomotion in moist habitats. Our experiments, on the contrary, showed an increased adherence of haired shells to wet surfaces. We propose the hypothesis that the possession of hairs facilitates the adherence of the snails to their herbaceous food plants during foraging when humidity levels are high. The absence of hairs in some Trochulus species could thus be explained as a loss of the potential adaptive function linked to habitat shifts.

Abstract: Isolated oceanic islands are excellent natural laboratories to test the relative role of historical contingency and determinism in evolutionary diversification. Endemics of the marine venomous snail Conus in the Cape Verde archipelago were originated from at least two independent colonizations of ‘small’ and ‘large’ shelled species separated by 12 million years. In this study, we have reconstructed phylogenetic relationships within large-shelled Conus (C. ateralbus, C. pseudonivifer, C. trochulus, and C. venulatus) based on mitochondrial cox1 and nad4 haplotype sequences. The reconstructed molecular phylogeny revealed three well-supported and relatively divergent clades (A, B, and C) that do not correspond to current species classification based on shell colour and banding patterns. Clade A grouped specimens assigned either to C. pseudonivifer or C. trochulus, clade B is composed of specimens assigned to C. venulatus, and clade C comprises specimens assigned either to C. venulatus or C. ateralbus. Geometric morphometric analyses found significant differences between the radular teeth shape of C. pseudonivifer/C. trochulus and C. venulatus/C. ateralbus. In clades A and B, northwestern Boavista and Maio specimens cluster together to the exclusion of eastern Boavista samples. In Sal, populations form a monophyletic island assemblage (clade C). The large-shelled Conus have remarkably replicated biogeographical patterns of diversification of small-shelled Conus. Similar selective forces (i.e. nonplanktonic lecithotrophy with limited larval dispersal and allopatric diversification) together with repeated instances of low sea level stands during glacial maxima that allowed connection between islands, have overcome the effect of historical contingency, and explain the observed recurring biogeographical patterns.

Abstract: The revision of the genus Trochulus Chemnitz, 1786 is based on conchological and anatomical characters of 4,377 adult specimens (3,190 dry shells and 1,187 alcohol-preserved snails) from 303 localities. Shell descriptions with the variation ranges, based on morphometric analysis, reproductive system descriptions with figures, identification key, synonymy, and distribution maps are provided. The most significant diagnostic characters are: shell shape and colour, umbilicus shape and size, durability of hairs, penis/epiphallus length ratio, flagellum/epiphallus length ratio, number and arrangement of mucous glands, length and location of dart sacs. Three names are synonymised: T. plebeius, T. concinnus and T. hispidus. Phylogenetic analysis yielded 96 equally parsimonious trees; the strict consensus procedure resulted in an incompletely resolved cladogram, with two distinct monophyletic groups of species: the villosus group including villosus, czarnohoricus, unidentatus and bielzi, and the striolatus group, with striolatus, graminicolus, montanus, caelatus, hispidus, suberectus, edentulus, bakowskii, luridus, filicinus and leucozonus. These two groups and erjaveci, biconicus, villosulus, clandestinus, lubomirskii and piccardi, form a phylogenetic bush. The monophyletic groups appearing in the cladogram are not compatible with any of the earlier proposed divisions. Most members of Trochulus inhabit the Alps and the Carpathians. The only widely distributed species is T. hispidus. The second most widespread species is T. striolatus. The remaining species are endemics with limited ranges. The number of species within particular parts of the range points to the Alpine-Carpathian area as the diversity centre of the genus.