Universal metabolic constraints shape the evolutionary ecology of diving in animals

Diving as a lifestyle has evolved on multiple occasions when air-breathing
terrestrial animals invaded the aquatic realm, and diving performance
shapes the ecology and behaviour of all air-breathing aquatic taxa, from
small insects to great whales. Using the largest dataset yet assembled, we
show that maximum dive duration increases predictably with body mass in
both ectotherms and endotherms. Compared to endotherms, ectotherms can
remain submerged for longer, but the mass scaling relationship for dive
duration is much steeper in endotherms than in ectotherms. These
differences in diving allometry can be fully explained by inherent
differences between the two groups in their metabolic rate and how
metabolism scales with body mass and temperature. Therefore, we suggest
that similar constraints on oxygen storage and usage have shaped the
evolutionary ecology of diving in all air-breathing animals, irrespective
of their evolutionary history and metabolic mode. The steeper scaling
relationship between body mass and dive duration in endotherms not only
helps explain why the largest extant vertebrate divers are endothermic
rather than ectothermic, but also fits well with the emerging consensus
that large extinct tetrapod divers (e.g. plesiosaurs, ichthyosaurs and
mosasaurs) were endothermic.