The Evolution of Air‐breathing Revised

Abstract

The evolution of air‐breathing represents one the most pronounced changes in the cardio‐respiratory physiology of vertebrates. While a lot is known about the physiological transitions required for air‐breathing evolution, there is limited information available on the evolutionary dynamics in breathing mode. Previous analyses suggest 34–67 independently origins of air‐breathing within extant vertebrates, but nothing is known about when in geological time air‐breathing originated or if air‐breathing has been secondarily lost. This study aimed to 1) provide more robust estimates on the number of air‐breathing origins, 2) identify if air‐breathing has been secondarily lost within clades of air‐breathing fishes, and 3) identify the timing of these events. To do this, we used an updated list of air‐breathing fishes, a fully resolved, time‐calibrated fish phylogeny and Bayesian phylogenetic comparative methods. We show that air‐breathing evolved 74–80 times within extant vertebrates, which is significantly higher the previously proposed 34–67 independent origins. Further, we show strong support for 7 secondary losses of air‐breathing, where pure water‐breathing was adapted from an air‐breathing ancestor. Finally, we show that the majority of air‐breathing clades radiated within the last 65 million years. This study adds novel dimensions to the evolution of air‐breathing and identifies an unprecedented evolutionary plasticity in breathing mode, where air‐breathing has been gained and lost repeatedly during the evolutionary history of vertebrates.Support or Funding InformationChristian Damsgaard is supported by the Carlsberg Foundation.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.