Dépraz Aline, Hausser Jacques, Pfenninger Markus
Lab Centre, Biodiversity & Climate Research Centre, Biocampus Siesmayerstrasse, D-60054 Frankfurt am Main, Germany.
BMC Evol Biol. 2009 Jul 21;9:171. doi: 10.1186/1471-2148-9-171.
Mitochondrial DNA sequencing increasingly results in the recognition of genetically divergent, but morphologically cryptic lineages. Species delimitation approaches that rely on multiple lines of evidence in areas of co-occurrence are particularly powerful to infer their specific status. We investigated the species boundaries of two cryptic lineages of the land snail genus Trochulus in a contact zone, using mitochondrial and nuclear DNA marker as well as shell morphometrics.
Both mitochondrial lineages have a distinct geographical distribution with a small zone of co-occurrence. In the same area, we detected two nuclear genotype clusters, each being highly significantly associated to one mitochondrial lineage. This association however had exceptions: a small number of individuals in the contact zone showed intermediate genotypes (4%) or cytonuclear disequilibrium (12%). Both mitochondrial lineage and nuclear cluster were statistically significant predictors for the shell shape indicating morphological divergence. Nevertheless, the lineage morphospaces largely overlapped (low posterior classification success rate of 69% and 78%, respectively): the two lineages are truly cryptic.
The integrative approach using multiple lines of evidence supported the hypothesis that the investigated Trochulus lineages are reproductively isolated species. In the small contact area, however, the lineages hybridise to a limited extent. This detection of a hybrid zone adds an instance to the rare reported cases of hybridisation in land snails.
线粒体DNA测序越来越多地导致人们识别出基因上有差异但形态上难以区分的谱系。在共发生区域依赖多条证据的物种界定方法对于推断它们的物种地位特别有效。我们利用线粒体和核DNA标记以及壳形态测量学，研究了接触区域内陆地蜗牛属Trochulus两个难以区分的谱系的物种界限。
两个线粒体谱系都有独特的地理分布，且共发生区域较小。在同一区域，我们检测到两个核基因型簇，每个簇都与一个线粒体谱系高度显著相关。然而，这种关联也有例外情况：接触区域内少数个体表现出中间基因型（4%）或细胞核-细胞质不平衡（12%）。线粒体谱系和核簇都是壳形状的统计学显著预测因子，表明存在形态差异。尽管如此，谱系形态空间在很大程度上重叠（后验分类成功率分别较低，为69%和78%）：这两个谱系确实难以区分。
使用多条证据的综合方法支持了这样的假设，即所研究的Trochulus谱系是生殖隔离的物种。然而，在小接触区域内，这些谱系有一定程度的杂交。这种杂交区域的发现为陆地蜗牛中罕见的杂交报道案例增添了一个实例。
