Point of no return in diving emperor penguins: Is the timing of the decision to return limited by the number of strokes?

International Coastal Research Center, Atmosphere and Ocean Research Institute, The University of Tokyo, 2-106-1 Akahama, Otsuchi, Iwate 028-1102, Japan.
Journal of Experimental Biology (Impact Factor: 2.9). 01/2012; 215(Pt 1):135-40. DOI: 10.1242/jeb.064568
Source: PubMed


At some point in a dive, breath-hold divers must decide to return to the surface to breathe. The issue of when to end a dive has been discussed intensively in terms of foraging ecology and behavioral physiology, using dive duration as a temporal parameter. Inevitably, however, a time lag exists between the decision of animals to start returning to the surface and the end of the dive, especially in deep dives. In the present study, we examined the decision time in emperor penguins under two different conditions: during foraging trips at sea and during dives at an artificial isolated dive hole. It was found that there was an upper limit for the decision-to-return time irrespective of dive depth in birds diving at sea. However, in a large proportion of dives at the isolated dive hole, the decision-to-return time exceeded the upper limit at sea. This difference between the decision times in dives at sea versus the isolated dive hole was accounted for by a difference in stroke rate. The stroke rates were much lower in dives at the isolated hole and were inversely correlated with the upper limit of decision times in individual birds. Unlike the decision time to start returning, the cumulative number of strokes at the decision time fell within a similar range in the two experiments. This finding suggests that the number of strokes, but not elapsed time, constrained the decision of emperor penguins to return to the surface. While the decision to return and to end a dive may be determined by a variety of ecological, behavioral and physiological factors, the upper limit to that decision time may be related to cumulative muscle workload.

Download full-text


Available from: Katsufumi Sato, Oct 15, 2014
14 Reads
  • Source
    • "The patterns and underlying physiological controls of foraging dives have been investigated in a number of air-breathing vertebrates, including seabirds (Elliott et al., 2013; Heath et al., 2007; Shoji et al., 2015), penguins (Hanuise et al., 2013; Shiomi et al., 2012), sea snakes (Cook and Brischoux, 2014), sea turtles (Bradshaw et al., 2007; Wallace and Jones, 2008), and a host of marine mammals. Current models of the cost of foraging in these diving animals and the resultant theories of optimal foraging strategies treat the acquisition and digestion of prey as physiological processes that are independent of one another (e.g., Burns et al., 2006; Mori, 1998; Sparling et al., 2007b; Thompson and Fedak, 2001). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Past foraging success of diving air-breathing vertebrates can adversely affect future foraging capabilities and costs through changes in circulation or increased metabolic costs associated with digestion that are incompatible with efficient diving. This study tested the physiological interaction between digestion and diving by comparing the cost of diving in fasted and pre-fed trained Steller sea lions foraging under controlled conditions in the open ocean. Pre-dive and post-dive surface metabolism and diving metabolic rate were all higher in the pre-fed animals than the fasted animals, indicating an effect of digestion on metabolism. However, the sea lions displayed a significant reduction in the apparent additive effect of digestion during diving. The increase in rate of oxygen consumption associated with digestion was reduced by 54% during diving compared to the increase observed in pre-dive metabolism. This truncation of the additional cost of digestion rapidly disappeared following cessation of diving. The results suggest that Steller sea lions diving to depth demonstrate a partial deferment of digestion while actively foraging and that the classically held view that digestion and diving are incompatible processes may be much more variable and adaptable to specific diving conditions and behaviors than previously thought.
    Journal of Experimental Marine Biology and Ecology 05/2015; 469:93-97. DOI:10.1016/j.jembe.2015.04.017 · 1.87 Impact Factor
  • Source
    • "The important role for the rate of oxygen consumption and diving was recently elucidated in emperor penguins (Aptenodytes forsteri; Shiomi et al., 2012). The results of this study indicated that once "
    [Show abstract] [Hide abstract]
    ABSTRACT: Diving mammals, are under extreme pressure to conserve oxygen as well as produce adequate energy through aerobic pathways during breath-hold diving. Typically a major source of energy, lipids participate in structural and regulatory roles and have an important influence on the physiological functions of an organism. At the stoichiometric level, the metabolism of polyunsaturated fatty acids (PUFAs) utilizes less oxygen than metabolizing either monounsaturated fatty acids or saturated fatty acids (SFAs) and yields fewer ATP per same length fatty acid. However, there is evidence that indicates the cellular metabolic rate is directly correlated to the lipid composition of the membranes such that the greater the PUFA concentration in the membranes the greater the metabolic rate. These findings appear to be incompatible with diving mammals that ingest and metabolize high levels of unsaturated fatty acids while relying on stored oxygen. Growing evidence from birds to mammals including recent evidence in Weddell seals also indicates that at the whole animal level the utilization of PUFAs to fuel their metabolism actually conserves oxygen. In this paper, we make an initial attempt to ascertain the beneficial adaptations or limitations of lipids constituents and potential trade-offs in diving mammals. We discuss how changes in Antarctic climate are predicted to have numerous different environmental effects; such potential shifts in the availability of certain prey species or even changes in the lipid composition (increased SFA) of numerous fish species with increasing water temperatures and how this may impact the diving ability of Weddell seals.
    Frontiers in Physiology 06/2012; 3:184. DOI:10.3389/fphys.2012.00184 · 3.53 Impact Factor
  • Source
    01/2013; 1(1):20. DOI:10.1186/2050-3385-1-20
Show more