Institute for Applied Ecology, University of Canberra, Canberra, Australian Capital Territory, Australia.
Natural History Museum of Los Angeles County, Los Angeles, California.
Mol Ecol. 2018 Dec;27(24):5195-5213. doi: 10.1111/mec.14925. Epub 2018 Dec 10.
Understanding the evolutionary history of diversifying lineages and the delineation of evolutionarily significant units and species remains major challenges for evolutionary biology. Low-cost representational sampling of the genome for single nucleotide polymorphisms shows great potential at the temporal scales that are typically the focus of species delimitation and phylogeography. We apply these markers to a case study of a freshwater turtle, Emydura macquarii, whose systematics has so far defied resolution, to bring to light a dynamic system of substantive allopatric lineages diverging on independent evolutionary trajectories, but held back in the process of speciation by low level and episodic exchange of alleles across drainage divides on various timescales. In the context of low-level episodic gene flow, speciation is often reticulate, rather than a bifurcating process. We argue that species delimitation needs to take into account the pattern of ancestry and descent of diverging lineages in allopatry together with the recent and contemporary processes of dispersal and gene flow that retard and obscure that divergence. Underpinned by a strong focus on lineage diagnosability, this combined approach provides a means for addressing the challenges of incompletely isolated populations with uncommon, but recurrent gene flow in studies of species delimitation, a situation likely to be frequently encountered. Taxonomic decisions in cases of allopatry often require subjective judgements. Our strategy, which adds an additional level of objectivity before that subjectivity is applied, reduces the risk of taxonomic inflation that can accompany lineage approaches to species delimitation.
了解多样化谱系的进化历史以及进化意义上的单位和物种的划定仍然是进化生物学的主要挑战。 对单核苷酸多态性进行低成本的基因组代表性采样，在物种划定和系统地理学通常关注的时间尺度上具有巨大的潜力。 我们将这些标记应用于淡水龟 Emydura macquarii 的案例研究，该系统的分类学迄今仍未得到解决，揭示了一个动态的系统，其中实质性的异域谱系沿着独立的进化轨迹分化，但由于在各种时间尺度上通过等位基因的低频和偶发性交换跨越水系分隔而在物种形成过程中受阻。 在低频偶发性基因流动的背景下，物种形成通常是网状的，而不是分叉的过程。 我们认为，物种划定需要考虑异域分化谱系的祖先和后代的模式，以及最近和当代的扩散和基因流动过程，这些过程会阻碍和掩盖这种分化。 这种综合方法以谱系可诊断性为重点，为解决具有不常见但反复出现基因流动的不完全隔离种群的物种划定问题提供了一种手段，这种情况可能经常遇到。 在异域情况下的分类决策通常需要主观判断。 我们的策略在应用主观性之前增加了一个额外的客观性水平，降低了伴随谱系方法进行物种划定的分类膨胀的风险。
