Myoglobin primary structure reveals multiple convergent transitions to semi-aquatic life in the world's smallest mammalian divers

Identifying the phylogenomic underpinnings of specialized phenotypes that fueled evolutionary transitions into new adaptive zones is central to evolutionary biology. The order Eulipotyphla (e.g., moles, shrews, and hedgehogs) is ideally suited to address this question as semi-fossorial, fossorial, and semi-aquatic forms have repeatedly arisen from terrestrial forbearers. However, our understanding of the ecomorphological pathways leading to these diverse lifestyles has been confounded by a fragmentary fossil record and potential morphological convergence. The net surface charge of myoglobin (ZMb) is readily determined from its primary structure and provides an objective target to map ancient evolutionary transitions due to mechanistic linkages of ZMb with myoglobin concentration. Myoglobin facilitates O2 storage and transport in muscle and its concentration is sharply elevated in breath-hold divers relative to terrestrial mammals, with fossorial and high-elevation species only showing m...