Morphology-based identification and classification of sponge species is complicated, because their morphological features are highly variable. Therefore, molecular markers are ideal tools for delimiting sponge species. In this study, we compared the variability of two sections of COI (the standard 5′-end fragment and the I3-M11 fragment) for closely related Baikal sponge species. Although the mean interspecific variability for both fragments was higher than the mean intraspecies divergence, these values overlapped in some cases. Based on the results of the study, we concluded that the I3-M11 fragment and the standard 5′-end fragment were not suitable when used in the canonical fashion for identifying Baikal species. However, the consistency in differences between lineages in number of non-synonymous substitutions of the two investigated COI fragments indicated that nucleotide substitutions in the I3-M11 fragment of COI are evolutionarily more informative for delimiting species. We also detected new divergent haplotypes of Baikal sponges using these markers. Seven new haplotypes in the standard 5′-end fragment of COI and 10 in the I3-M11 fragment were observed. These findings potentially indicate cryptic speciation in Baikal sponges, and further study is required to elucidate how this cryptic speciation evolved.

中文翻译：

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用于新条形码标记开发的密切相关的贝加尔湖海绵物种的mtDNA变异性分析

基于形态学的海绵种类识别和分类很复杂，因为它们的形态特征高度可变。因此，分子标记是划定海绵种类的理想工具。在这项研究中，我们比较了COI的两个部分的变异性（标准5'-末端片段和I3-M11片段）用于密切相关的贝加尔湖海绵物种。尽管两个片段的平均种间变异性高于平均种内差异，但在某些情况下，这些值重叠。根据研究结果，我们得出结论，当以规范方式用于识别贝加尔湖物种时，I3-M11片段和标准5'-末端片段不适合。然而，在这两个研究非同义置换的数目谱系之间的差的一致性COI片段指示的的I3-M11片段核苷酸取代COI在进化上对划定物种更具参考价值。我们还使用这些标记物检测了贝加尔湖海绵的新发散单倍型。在标准的COI 5'末端片段中发现了七个新的单倍型，在I3-M11片段中观察到了十个新的单倍型。这些发现可能表明贝加尔湖海绵体中存在隐性物种，需要进一步研究以阐明该隐性物种如何演变。