Abstract
BackgroundCylindrus obtusus is one of the most prominent endemic snail species of the Eastern Alps. It is restricted to alpine meadows and calcareous rocky habitats above 1500 m. Peculiar intraspecific differences have been observed in its genital tract in the eastern populations the two mucus glands associated with the love dart sac are highly variable, while almost no variation was observed in the western populations. This raises the question whether the mode and success of reproduction of the respective populations are different. To find out whether these anatomical differences reflect genetic differentiation, which might be an indication for distinct glacial refugia, we investigated a 650 bp fragment of the mitochondrial cytochrome oxidase subunit 1 gene (COI) (280 individuals) and 9 microsatellite loci from samples (487 individuals from 29 populations) covering the whole distribution range of the species.ResultsThe COI sequences show a geographic differentiation between eastern, central and western populations. The westernmost localities, which were covered under ice sheets during glacial periods, are characterized by extreme low variability. Overall genetic distances among all individuals are small (max. 1.7% p-distance). The microsatellite analysis reveals a high differentiation between populations, implying restriction of gene flow. The highest genetic variability was found in the central populations. Remarkably, nearly all individuals from the eastern populations, which are more variable in their genital morphology, are homozygous in all microsatellite loci, although different alleles were found within populations.ConclusionsThe most peculiar outcome of the study is the strong evidence for selfing in C. obtusus as indicated by the microsatellite data in the easternmost populations. This finding is supported by the deformation of the mucus glands in the same populations. Since mucus glands play an important role in sexual reproduction, it seems plausible that in selfing organisms these structures are reduced. The phylogeographic structure revealed by COI sequences implies that the species has survived the ice ages within the Calcareous Alps. The small genetic distances among all individuals (max. 1.7%) suggest that C. obtusus has experienced severe bottlenecks in the past.
Highlights
Cylindrus obtusus is one of the most prominent endemic snail species of the Eastern Alps
We present results from a DNA sequence analysis of sections of the mitochondrial cytochrome oxidase subunit I (COI) gene as well as a population genetic analysis based on nine microsatellite loci
There are three main haplogroups, one of them mainly consisting of western populations, one comprising almost exclusively samples of the easternmost populations and a central one consisting mainly of populations from a central area (Veitsch to Gesäuse; 19 localities)
Summary
Cylindrus obtusus is one of the most prominent endemic snail species of the Eastern Alps. Peculiar intraspecific differences have been observed in its genital tract in the eastern populations the two mucus glands associated with the love dart sac are highly variable, while almost no variation was observed in the western populations. This raises the question whether the mode and success of reproduction of the respective populations are different. Due to its outstanding position within the Ariantinae in terms of shell morphological differentiation and geographical restriction to high mountain regions, C. obtusus is one of the most prominent endemics of the Eastern Alps
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