Hidden diversity: Phylogeography of genus Ototyphlonemertes Diesing, 1863 (Ototyphlonemertidae: Hoplonemertea) reveals cryptic species and high diversity in Chilean populations

Ototyphlonemertes is a cosmopolitan genus of meiofaunal nemerteans. Their morphological characters are insufficient to reliably identify and delimit species. Consequently, some of the species are considered cosmopolitan despite anticipated low dispersion capability of the adults and a short planktonic larval phase. Indeed, recent studies show that some species actually comprise cryptic species, and populations are connected by stochastic events of long-distance dispersion. Based solely on morphological traits, a Lactea and a Pallida morph of Ototyphlonemertes are recognized here from collections at eight and five locations respectively along the Chilean coast. To assess the phylogeographic patterns of their populations, two mitochondrial markers (COI and COX3) of 162 specimens of Lactea and 25 of Pallida were sequenced. Final sequences are 605bp and 362bp for COI and COX3, respectively. Results from phylogenetic and haplotype network analyses suggest that the Lactea morph comprises up to three independent evolutionary units (one with only COX3 sequences). A COI gene tree including other previously published Ototyphlonemertes sequences groups the Chilean Lactea with other Lactea, while the Chilean Pallida is grouped with other Pallida. Different structuring and gene flow patterns found for the four groups support the hypothesis that these are four independent evolutionary entities with different ecological, dispersal and demographical characteristics.盲微纽虫属（Ototyphlonemertes）是一类广布的微型底栖纽形动物类群。该属物种的形态特征不足以可靠地完成物种鉴定与界限划分。因此，尽管该属成体扩散能力较弱且浮游幼虫期较短，部分物种仍被认为具有广布性。事实上，近期研究表明，部分被视为广布的物种实则为隐存物种复合群，其种群间的联系依赖于长距离扩散的随机事件。仅基于形态性状，本研究从智利沿岸8个和5个采样点的采集样本中，分别鉴定出盲微纽虫属的Lactea型与Pallida型。为评估其种群的系统地理学格局，本研究对162份Lactea型样本与25份Pallida型样本的两个线粒体标记基因——细胞色素c氧化酶亚基I（COI）与细胞色素c氧化酶亚基3（COX3）——进行了测序。COI与COX3的最终有效序列长度分别为605 bp与362 bp。系统发育与单倍型网络分析结果表明，Lactea型可划分为至多3个独立的进化单元（其中1个仅包含COX3序列）。将本研究获得的COI序列与此前已发表的其他盲微纽虫属序列整合构建基因树后发现，智利沿岸的Lactea型与其他地区的Lactea型聚为一支，而智利沿岸的Pallida型则与其他地区的Pallida型聚为一支。针对这四个类群所发现的不同种群结构与基因流模式，佐证了以下假说：这四个类群均为独立的进化实体，各自具有独特的生态、扩散与种群统计学特征。