Trace and Environmental DNA (TrEnD) Laboratory, School of Molecular and Life Sciences, Curtin University, Bentley, WA, 6102, Australia.
The Australian National Herbarium, CSIRO, Bldg 502 Clunies Ross Street, Acton, ACT, 2601, Australia.
Nat Commun. 2023 Feb 28;14(1):914. doi: 10.1038/s41467-023-36405-3.
The systematics of Madagascar's extinct elephant birds remains controversial due to large gaps in the fossil record and poor biomolecular preservation of skeletal specimens. Here, a molecular analysis of 1000-year-old fossil eggshells provides the first description of elephant bird phylogeography and offers insight into the ecology and evolution of these flightless giants. Mitochondrial genomes from across Madagascar reveal genetic variation that is correlated with eggshell morphology, stable isotope composition, and geographic distribution. The elephant bird crown is dated to ca. 30 Mya, when Madagascar is estimated to have become less arid as it moved northward. High levels of between-clade genetic variation support reclassifying Mullerornis into a separate family. Low levels of within-clade genetic variation suggest there were only two elephant bird genera existing in southern Madagascar during the Holocene. However, we find an eggshell collection from Madagascar's far north that represents a unique lineage of Aepyornis. Furthermore, divergence within Aepyornis coincides with the aridification of Madagascar during the early Pleistocene ca. 1.5 Ma, and is consistent with the fragmentation of populations in the highlands driving diversification and the evolution of extreme gigantism over shorts timescales. We advocate for a revision of their taxonomy that integrates palaeogenomic and palaeoecological perspectives.
马达加斯加已灭绝的象鸟的系统发育仍然存在争议，这是因为化石记录存在很大的空白，而且骨骼标本的生物分子保存情况较差。在这里，对 1000 年前的化石蛋壳进行的分子分析首次描述了象鸟的系统地理学，并深入了解了这些不会飞的巨鸟的生态和进化。来自马达加斯加各地的线粒体基因组揭示了与蛋壳形态、稳定同位素组成和地理分布相关的遗传变异。象鸟的冠部可追溯到约 3000 万年前，当时马达加斯加向北移动，估计变得不那么干旱。种间遗传变异水平较高支持将 Mullerornis 重新分类为一个单独的科。种内遗传变异水平较低表明，在全新世期间，仅在马达加斯加南部存在两种象鸟属。然而，我们发现了来自马达加斯加最北部的一个蛋壳收藏，它代表了 Aepyornis 的一个独特谱系。此外，Aepyornis 内部的分化与马达加斯加在早更新世（约 150 万年前）的干旱化相一致，这与高地上种群的碎片化导致多样化以及在短时间内进化出极端巨型化相一致。我们主张对其分类进行修订，将古基因组学和古生态学的观点纳入其中。
