Our understanding of how air-breathing marine predators cope with environmental variability is limited by our inadequate knowledge of their ecological and physiological parameters. Because of their wide distribution along both coasts of the sub-continent, South American sea lions (Otaria byronia) provide a valuable opportunity to study the behavioral and physiological plasticity of a marine predator in different environments. We measured the oxygen stores and diving behavior of South American sea lions throughout most of its range, allowing us to demonstrate that diving ability and behavior vary across its range. We found no significant differences in mass-specific blood volumes of sea lions among field sites and a negative relationship between mass-specific oxygen storage and size, which suggests that exposure to different habitats and geographical locations better explains oxygen storage capacities and diving capability in South American sea lions than body size alone. The largest animals in our study (individuals from Uruguay) were the shallowest and shortest duration divers, and had the lowest mass-specific total body oxygen stores, while the deepest and longest duration divers (individuals from southern Chile) had significantly larger mass-specific oxygen stores, despite being much smaller animals. Our study suggests that the physiology of air-breathing diving predators is not fixed, but that it can be adjusted, to a certain extent, depending on the ecological setting and or habitat. These adjustments can be thought of as a ‘training effect’: as the animal continues to push its physiological capacity through greater hypoxic exposure, its breath-holding capacity increases.
The authors declare no competing or financial interests.
Conceived and design the study: L.A.H. and D.P.C. Performed the experiments: L.A.H., D.P.C., F.R.-S., V.F.-T., A.M.M.B., R.A.O., J.P.Y.A., M.S., M.S.-C. and D.P.C. Analyzed the data: L.A.H. and M.S.T. Contributed reagents/materials/analysis tools: D.P.C., A.M.M.B., J.P.Y.A., M.S. and J.M.B. Wrote the paper: L.A.H., M.S.T. and D.P.C.
This study was supported by the Compañía Minera Doña Inés de Collahuasi [GMS 2010/22] (northern Chile); Celulosa Arauco (central Chile); INNOVA-CORFO [07CN13IPM-170] (southern Chile); and the Shackleton Scholarship Fund (Centenary award), Project AWARE, Rufford Small Grants, Sea World and Busch Gardens Conservation Fund, Joint Nature Conservation Council and the Falkland Islands Government (Falkland Islands). Further support was provided by the US Marine Mammal Commission (E4047335), Office of Naval Research (ONR) [grants N00014-09-1-1195, N00014-13-1-0134 and N00014-10-1-0356], NSF Office of Polar Programs [grant ANT-0838937] and E&P Sound and Marine Life Joint Industry Programme of the International Association of Oil and Gas Producers [contract no. JIP 22 07-23].
Supplementary information available online at http://jeb.biologists.org/lookup/doi/10.1242/jeb.138677.supplemental
- Received February 10, 2016.
- Accepted May 17, 2016.
- © 2016. Published by The Company of Biologists Ltd