Kruckenhauser Luise, Haring Elisabeth, Tautscher Barbara, Cadahía Luis, Zopp Laura, Duda Michael, Harl Josef, Sattmann Helmut
Natural History Museum Vienna, Central Research Laboratories, Burgring 7, 1010, Vienna, Austria.
Department of Integrative Zoology, University of Vienna, Althanstraße 14, 1090, Vienna, Austria.
BMC Evol Biol. 2017 Jun 13;17(1):138. doi: 10.1186/s12862-017-0977-0.
Cylindrus 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.
The 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.
The 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.
钝圆柱螺是东阿尔卑斯山最著名的特有蜗牛物种之一。它仅限于海拔1500米以上的高山草甸和钙质岩石栖息地。在其东部种群的生殖道中观察到了特殊的种内差异，与恋矢囊相关的两个黏液腺高度可变，而西部种群几乎没有变化。这就提出了一个问题，即各个种群的繁殖方式和成功率是否不同。为了弄清楚这些解剖学差异是否反映了基因分化，而基因分化可能是不同冰期避难所的一个指标，我们研究了线粒体细胞色素氧化酶亚基1基因（COI）的一个650bp片段（280个个体）以及来自覆盖该物种整个分布范围的样本（来自29个种群的487个个体）的9个微卫星位点。
COI序列显示东部、中部和西部种群之间存在地理分化。最西部的地区在冰川期被冰盖覆盖，其特点是变异性极低。所有个体之间的总体遗传距离很小（最大p距离为1.7%）。微卫星分析揭示了种群之间的高度分化，这意味着基因流动受到限制。中部种群的遗传变异性最高。值得注意的是，东部种群中几乎所有个体的生殖器形态更具变异性，尽管在种群内部发现了不同的等位基因，但它们在所有微卫星位点上都是纯合的。
该研究最奇特的结果是，最东部种群的微卫星数据表明钝圆柱螺存在强烈的自交证据。同一种群中黏液腺的变形支持了这一发现。由于黏液腺在有性繁殖中起重要作用，在自交生物中这些结构减少似乎是合理的。COI序列揭示的系统地理学结构表明，该物种在钙质阿尔卑斯山内度过了冰河时代。所有个体之间较小的遗传距离（最大1.7%）表明钝圆柱螺在过去经历了严重的瓶颈。
