Hagfish: Champions of CO2 tolerance question the origins of vertebrate gill function
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Issue Date
2015-06-09
Authors
Baker, Daniel W.
Sardella, Brian
Rummer, Jodie L.
Sackville, Michael
Brauner, Colin J.
License
This article is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
Subject
Abstract
The gill is widely accepted to have played a key role in the adaptive radiation of early vertebrates
by supplanting the skin as the dominant site of gas exchange. However, in the most basal extant
craniates, the hagfishes, gills play only a minor role in gas exchange. In contrast, we found
hagfish gills to be associated with a tremendous capacity for acid-base regulation. Indeed, Pacific
hagfish exposed acutely to severe sustained hypercarbia tolerated among the most severe blood
acidoses ever reported (1.2 pH unit reduction) and subsequently exhibited the greatest degree of
acid-base compensation ever observed in an aquatic chordate. This was accomplished through an unprecedented increase in plasma [HCO3−] (>75 mM) in exchange for [Cl−]. We thus propose that the first physiological function of the ancestral gill was acid-base regulation, and that the gill was later co-opted for its central role in gas exchange in more derived aquatic vertebrates.