Data from: Sky island diversification meets the multispecies coalescent – divergence in the spruce-fir moss spider (Microhexura montivaga, Araneae, Mygalomorphae) on the highest peaks of southern Appalachia

Microhexura montivaga is a miniature tarantula-like spider endemic to the
highest peaks of the southern Appalachian mountains and is known only from
six allopatric, highly disjunct montane populations. Because of severe
declines in spruce-fir forest in the late 20th century, M. montivaga was
formally listed as a US federally endangered species in 1995. Using DNA
sequence data from one mitochondrial and seven nuclear genes, patterns of
multigenic genetic divergence were assessed for six montane populations.
Independent mitochondrial and nuclear discovery analyses reveal obvious
genetic fragmentation both within and among montane populations, with five
to seven primary genetic lineages recovered. Multispecies coalescent
validation analyses [guide tree and unguided Bayesian Phylogenetics and
Phylogeography (BPP), Bayes factor delimitation (BFD)] using nuclear-only
data congruently recover six or seven distinct lineages; BFD analyses
using combined nuclear plus mitochondrial data favour seven or eight
lineages. In stark contrast to this clear genetic fragmentation, a survey
of secondary sexual features for available males indicates morphological
conservatism across montane populations. While it is certainly possible
that morphologically cryptic speciation has occurred in this taxon, this
system may alternatively represent a case where extreme population genetic
structuring (but not speciation) leads to an oversplitting of lineage
diversity by multispecies coalescent methods. Our results have clear
conservation implications for this federally endangered taxon and
illustrate a methodological issue expected to become more common as
genomic-scale data sets are gathered for taxa found in naturally
fragmented habitats.

山地微蛛（Microhexura montivaga）是一种体型微小的类狼蛛蜘蛛，仅特有分布于阿巴拉契亚山脉南部的最高山峰区域，目前仅记录到6个异域间断分布的山地种群。20世纪后期，云杉冷杉林遭遇严重衰退，该物种于1995年被正式列入美国联邦濒危物种名录。研究人员借助1个线粒体基因与7个核基因的序列数据，对这6个山地种群的多基因遗传分化模式进行了评估。独立的线粒体与核基因探索性分析显示，山地种群内部及种群间均存在显著的遗传破碎化，共检出5至7个主要遗传支系。基于仅核基因数据的多物种溯祖验证分析[包括向导树贝叶斯系统发育与种群地理学（Bayesian Phylogenetics and Phylogeography, BPP）法、无向导贝叶斯因子界定法（Bayes factor delimitation, BFD）]，一致检出6至7个独立支系；而结合核基因与线粒体基因的联合数据分析显示，BFD法支持7至8个支系。与上述清晰的遗传破碎化格局形成鲜明对比的是，对现有雄性个体第二性征的调查显示，不同山地种群间的形态特征高度保守。尽管该类群存在隐形态物种形成的可能性，但本研究体系也可能代表一种极端情形：即极强的种群遗传结构（而非物种形成）导致多物种溯祖分析法对支系多样性做出了过度划分。本研究结果对这一联邦濒危类群具有明确的保护学启示，同时也揭示了一个随着基因组规模数据集被应用于自然生境破碎化类群的研究时，愈发常见的方法学问题。