Day Julia J, Steell Elizabeth M, Vigliotta Thomas R, Withey Lewis A, Bills Roger, Friel John P, Genner Martin J, Stiassny Melanie L J
Department of Genetics, Evolution and Environment, University College London, Gower Street, London WC1E 6BT, UK.
Department of Genetics, Evolution and Environment, University College London, Gower Street, London WC1E 6BT, UK.
Mol Phylogenet Evol. 2023 May;182:107754. doi: 10.1016/j.ympev.2023.107754. Epub 2023 Mar 9.
Endeavours in species discovery, particularly the characterisation of cryptic species, have been greatly aided by the application of DNA molecular sequence data to phylogenetic reconstruction and inference of evolutionary and biogeographic processes. However, the extent of cryptic and undescribed diversity remains unclear in tropical freshwaters, where biodiversity is declining at alarming rates. To investigate how data on previously undiscovered biodiversity impacts inferences of biogeography and diversification dynamics, we generated a densely sampled species-level family tree of Afrotropical Mochokidae catfishes (220 valid species) that was ca. 70 % complete. This was achieved through extensive continental sampling specifically targeting the genus Chiloglanis a specialist of the relatively unexplored fast-flowing lotic habitat. Applying multiple species-delimitation methods, we report exceptional levels of species discovery for a vertebrate genus, conservatively delimiting a staggering ca. 50 putative new Chiloglanis species, resulting in a near 80 % increase in species richness for the genus. Biogeographic reconstructions of the family identified the Congo Basin as a critical region in the generation of mochokid diversity, and further revealed complex scenarios for the build-up of continental assemblages of the two most species rich mochokid genera, Synodontis and Chiloglanis. While Syndontis showed most divergence events within freshwater ecoregions consistent with largely in situ diversification, Chiloglanis showed much less aggregation of freshwater ecoregions, suggesting dispersal as a key diversification process in this older group. Despite the significant increase in mochokid diversity identified here, diversification rates were best supported by a constant rate model consistent with patterns in many other tropical continental radiations. While our findings highlight fast-flowing lotic freshwaters as potential hotspots for undescribed and cryptic species diversity, a third of all freshwater fishes are currently threatened with extinction, signifying an urgent need to increase exploration of tropical freshwaters to better characterise and conserve its biodiversity.
在物种发现方面所做的努力，尤其是对隐存物种的特征描述，因将DNA分子序列数据应用于系统发育重建以及进化和生物地理过程的推断而得到了极大的帮助。然而，在生物多样性正以惊人速度下降的热带淡水区域，隐存和未描述的生物多样性程度仍不明确。为了研究此前未被发现的生物多样性数据如何影响生物地理学推断和多样化动态，我们构建了一个采样密集的非洲热带蝌蚪鲶科（Mochokidae）鲶鱼的物种水平系统发育树（共220个有效物种），其完整性约为70%。这是通过广泛的大陆范围采样实现的，特别针对奇洛拉鲶属（Chiloglanis）进行采样，该属是相对未被充分探索的急流栖境的专家。应用多种物种界定方法，我们报告了一个脊椎动物属的物种发现达到了异常水平，保守地界定出约50个假定的新奇洛拉鲶物种，使该属的物种丰富度近乎增加了80%。对该科的生物地理重建确定刚果盆地是蝌蚪鲶多样性产生的关键区域，并进一步揭示了两个物种最丰富的蝌蚪鲶属——歧须鲶属（Synodontis）和奇洛拉鲶属——大陆组合形成的复杂情况。虽然歧须鲶在淡水生态区域内的大多数分化事件与主要的原地多样化一致，但奇洛拉鲶的淡水生态区域聚集程度要低得多，这表明扩散是这个较古老类群多样化的关键过程。尽管在此确定的蝌蚪鲶多样性有显著增加，但多样化速率最能得到与许多其他热带大陆辐射模式一致的恒定速率模型的支持。虽然我们的研究结果突出了急流淡水作为未描述和隐存物种多样性潜在热点的地位，但目前所有淡水鱼中有三分之一面临灭绝威胁，这意味着迫切需要加强对热带淡水的探索，以更好地描述和保护其生物多样性。
