Morphological variation of snails from the genus Trochulus is so huge that their taxonomy is unclear. The greatest variability concerns forms hispidus and sericeus/plebeius, which are often considered as separate spec...Morphological variation of snails from the genus Trochulus is so huge that their taxonomy is unclear. The greatest variability concerns forms hispidus and sericeus/plebeius, which are often considered as separate species. To evidence the species barriers, we carried out crossbreeding ex- periments between these two sympatric morphs. Moreover, we compared the shell morphology of laboratory-bred offspring with their wild parents to test if the variation can be explained by the phenotypic plasticity model. We found that the two Trochulus morphs show no reproductive bar- riers. The fecundity rates, the mean clutch size, and F~ viability observed for all crosses were not significantly different. In hybrid crosses （in F2 generation）, we also recorded reproduction compati- bility, similar fecundity, and hatching success as in their parents. Accordingly, phylogenetic ana- lyses revealed the significant grouping of sequences from these different morphs and supported no constrains in reproduction between them. Comparison of shell morphology between wild and laboratory samples showed that various characters appeared highly plastic. The average shell shape of the hispidus morph changed significantly from flat with wide umbilicus to elevated with narrower umbilicus such as in the sericeus/plebeius morph. All these findings indicate that the examined morphs do not represent separate biological species and the evolutionary process is not advanced enough to separate their genetic pool. Therefore, phenotypic plasticity has played a sig- nificant role in the evolution of Trochulus shell polymorphism. The two morphs can evolve inde- pendently in separate phylogenetic lineages under the influence of local environmental conditions.展开更多
文摘Morphological variation of snails from the genus Trochulus is so huge that their taxonomy is unclear. The greatest variability concerns forms hispidus and sericeus/plebeius, which are often considered as separate species. To evidence the species barriers, we carried out crossbreeding ex- periments between these two sympatric morphs. Moreover, we compared the shell morphology of laboratory-bred offspring with their wild parents to test if the variation can be explained by the phenotypic plasticity model. We found that the two Trochulus morphs show no reproductive bar- riers. The fecundity rates, the mean clutch size, and F~ viability observed for all crosses were not significantly different. In hybrid crosses （in F2 generation）, we also recorded reproduction compati- bility, similar fecundity, and hatching success as in their parents. Accordingly, phylogenetic ana- lyses revealed the significant grouping of sequences from these different morphs and supported no constrains in reproduction between them. Comparison of shell morphology between wild and laboratory samples showed that various characters appeared highly plastic. The average shell shape of the hispidus morph changed significantly from flat with wide umbilicus to elevated with narrower umbilicus such as in the sericeus/plebeius morph. All these findings indicate that the examined morphs do not represent separate biological species and the evolutionary process is not advanced enough to separate their genetic pool. Therefore, phenotypic plasticity has played a sig- nificant role in the evolution of Trochulus shell polymorphism. The two morphs can evolve inde- pendently in separate phylogenetic lineages under the influence of local environmental conditions.
