Empirical Evidence Supporting Frequent Cryptic Speciation in Epiphyllous Liverworts: A Case Study of the Cololejeunea lanciloba Complex

Cryptic species are frequently recovered in plant lineages, and considered an important cause for divergent of morphological disparity and species diversity. The identification of cryptic species has important implications for the assessment of conservation needs of species aggregates. The mechanisms and processes of the origin of cryptic species diversity are still poorly understand based on the lack of studies especially in context of environment factors. Here we explored evidence for cryptic species within the epiphyllous liverworts Cololejeunea lanciloba complex based on two loci, the plastid trnL-F region and the nuclear ribosomal ITS region. Several analytic approaches were employed to delimit species based on DNA sequence variation including phylogenetic reconstruction, statistical parsimony networks analysis and two recently introduced species delimitation criteria: Rosenberg’s reciprocal monophyly and Rodrigo’s randomly distinct. We found evidence for thirteen genetically distinct putative species, each consisting of more than one haplotype, rather than four morphologically-circumscribed species. The results implied that the highly conserved phenotypes are not congruent with the genetic differentiation, contributing to incorrect assessments of the biodiversity of epiphyllous liverworts. We hypothesize that evolution of cryptic species recovered may be caused by selection of traits critical to the survival in epiphyllous habitats combined with limited developmental options designed in the small body.隐存种（cryptic species）在植物支系中频繁被检出，被认为是引发形态差异度与物种多样性分化的重要诱因。隐存种的鉴定对于评估物种聚集体的保护需求具有关键意义。然而，由于相关研究尤其是结合环境因子的研究较为匮乏，学界对隐存种多样性起源的机制与过程仍知之甚少。本研究依托两个分子标记——质体trnL-F区域与核核糖体ITS区域，对叶附生苔类披针叶薄鳞苔复合群（Cololejeunea lanciloba complex）内的隐存种证据展开探究。研究采用多种基于DNA序列变异的物种界定分析方法，包括系统发育重建、统计简约网络分析，以及两种新近提出的物种界定准则：罗森伯格互单系性标准（Rosenberg’s reciprocal monophyly）与罗德里戈随机区分标准（Rodrigo’s randomly distinct）。结果显示，该复合群存在13个遗传上独立的推定物种，每个推定物种均包含至少一个单倍型，而非此前基于形态界定的4个物种。研究结果表明，高度保守的表型与遗传分化并不一致，这会导致对叶附生苔类生物多样性的评估出现偏差。我们推测，本次检出的隐存种的演化，可能是叶附生生境中生存必需性状的选择作用，与小型植物体本身固有的有限发育潜能共同作用的结果。