Unrecognised (species) diversity in New Guinean passerine birds

Species represent an important unit for the study of diversity, but may not always be delimited consistently across regions and clades. Many of these taxonomic inconsistencies are due to the variable views of taxonomists. In recent years, however, new methodologies have attempted to circumvent this problem by assigning more objective criteria for the delimitation of species, drawing on a wide range of data such as DNA, morphology, vocalisation and ecology. Here, we apply a genetic screening approach in which we sequence the mitochondrial gene ND2 for all recognised subspecies of 16 species in eight genera (a mix of lowland and montane species) from the geologically complex tropical island of New Guinea. We show that populations within some species are genetically highly divergent despite little morphological differentiation, but we also find an example in which populations from five morphologically distinct species are genetically very similar. Overall, our data show higher levels of genetic differentiation than expected, but also highlight the difficulty of predicting which groups contain unrecognised diversity. These results are interesting in their own right, but also have implications for further analyses that focus on increasing our understanding of how diversity builds up over time.

物种是生物多样性研究的核心单元之一，但在不同地理区域与演化支中，其界定标准往往难以保持统一。这类分类学上的不一致，多源于分类学家的观点差异。近年来，研究者们开始借助DNA、形态学、鸣声与生态学等多维度数据，建立更为客观的物种界定准则，以规避上述难题。本研究采用基因筛查策略，对地质构造复杂的热带岛屿新几内亚的8个属、共16个物种（涵盖低地与山地类群）的所有已认定亚种，进行线粒体基因ND2的测序分析。结果显示，部分物种种群间虽形态分化微弱，却存在极高的遗传差异；同时也发现一例特殊现象：5个形态特征迥异的物种种群，其遗传相似度却极高。总体而言，本研究的数据表明遗传分化水平高于预期，同时也凸显了难以预判哪些类群中存在未被认知的生物多样性。本研究结果不仅本身具有重要学术价值，也为后续聚焦解析生物多样性随时间演化形成机制的相关研究提供了重要参考。