Data from: Allegory of a cave crustacean: systematic and biogeographic reality of Halosbaena (Peracarida: Thermosbaenacea) sought with molecular data at multiple scales

Halosbaena Stock, 1976 are small crustaceans found in a number of distant, isolated subterranean locations in the Northern (Caribbean and Canary Islands) and Southern Hemispheres (Christmas Island and north-western Australia in Cape Range, Barrow Island and Pilbara regions). This distribution is surprising for an animal that produces few eggs, has no free-living larval stage, and succours their young in a dorsal brood pouch. It is usually explained by the passive movement of ancestral populations on tectonic plates as the ancient Tethys Ocean spread. We used molecular data (one mitochondrial and three nuclear genes) to reconstruct phylogenies and time-trees to understand their biogeography at the global scale and at four diminishing scales within the Southern Hemisphere. We found: (1) a basal split between species in the Northern and Southern Hemispheres, but the inferred ages of divergences between species are not old enough to be associated with the spread of the Tethys; (2) a recently discovered species from Christmas Island which is the sister to Australian mainland taxa; (3) the one described species from mainland Australia, H. tulki, probably constitutes at least five separate species that reflect local geography (Cape Range west, Cape Range east, Barrow Island, Pilbara low elevation, Pilbara high elevation); (4) the Pilbara high elevation taxon is likely not old enough to have been stranded high inland during an Eocene marine transgression; and (5) phylogeographic breaks within Cape Range west are congruent with other breaks in sympatric cave species.

Halosbaena属（Stock, 1976）为一类小型甲壳动物，分布于南北半球多处偏远孤立的地下生境：北半球包括加勒比海地区与加那利群岛，南半球则涵盖圣诞岛，以及澳大利亚西北部的开普山脉、巴罗岛和皮尔巴拉区域。该类群产卵量稀少、无自由生活的幼虫阶段，且依托背侧育幼囊抚育幼体，其上述分布格局却颇具反常性。这一分布模式通常被解释为古特提斯洋扩张时期，祖先种群随构造板块发生的被动漂移。本研究借助分子数据（1个线粒体基因与3个核基因）构建系统发育树与时间树，以解析该类群在全球尺度以及南半球内四个逐级缩小尺度下的生物地理学格局。研究结果如下：
（1）南北半球物种间存在基部分化分支，但物种间的推测分化时间不足以对应古特提斯洋的扩张事件；
（2）近期在圣诞岛发现的新种为澳大利亚本土类群的姊妹类群；
（3）澳大利亚本土已描述的唯一物种H. tulki可能至少包含5个独立物种，其分化与当地地理格局高度匹配，涉及开普山脉西部、开普山脉东部、巴罗岛、皮尔巴拉低海拔区域以及皮尔巴拉高海拔区域；
（4）皮尔巴拉高海拔类群的分化时间较晚，不足以在始新世海侵时期被隔离于内陆高地；
（5）开普山脉西部类群内的系统地理分化断点，与同域分布的其他洞穴物种的分化断点相一致。