Genomic and Radiocarbon Insights into the Mystery of Mouse Mummies on the Summits of >6000 m Andean Volcanoes

Our understanding of the limits of animal life is continually revised by scientific exploration of extreme environments. Here we report the discovery of numerous mummified cadavers of leaf-eared mice, Phyllotis vaccarum, from the summits of three different Andean volcanoes at elevations 6029-6233 m (19,780-20,449 ft) above sea level in the Puna de Atacama (Chile-Argentina). Such extreme elevations were previously assumed to be completely uninhabitable by mammals. In combination with a live-captured specimen of the same species from the nearby summit of Volcan Llullaillaco (6739 m [=22,110 ft]), the 13 summit mummies represent the highest physical records of mammals in the world. We report a chromosome-level genome assembly for P. vaccarum in combination with a whole-genome re-sequencing analysis and radiocarbon dating analysis that provide insights into the provenance and antiquity of the summit mice. We test alternative hypotheses to explain the existence of mouse graveyards on the summits of Atacama volcanoes. Radiocarbon data indicate that the most ancient of the mummies were at most a few centuries old. Genomic polymorphism data revealed a high degree of continuity between the summit mice and conspecifics from lower elevations in the surrounding Altiplano. Genomic data also revealed equal numbers of males and females among the summit mice and evidence of close kinship between some individuals from the same summit groups. These findings bolster evidence for self-sustaining populations of Phyllotis at elevations >6000 m and challenge assumptions about the environmental limits of vertebrate life and the physiological tolerances of small mammals.