title: Development enhances hypometabolism in northern elephant seal pups (Mirounga angustirostris).
abstract: Investigation into the development of oxygen storage capacity in air-breathing marine predators has been performed, but little is known about the development of regulatory factors that influence oxygen utilization. Strategies for efficiently using oxygen stores should enable marine predators to optimize time spent foraging underwater.We describe the developmental patterns of oxygen use during voluntary breath-holds in northern elephant seals (Mirounga angustirostris) at 2 and 7 weeks post-weaning. We measured 1) changes in oxygen consumption (VO2), and 2) changes in venous pH, partial pressure of oxygen (pO2), haemoglobin saturation (sO2), oxygen content (O2ct), partial pressure of carbon dioxide (pCO2), haematocrit (Hct) and total haemoglobin (tHb). To examine the effect of the dive response on the development of oxygen utilization, voluntary breath-hold experiments were conducted in and out of water.Suppression of VO2during voluntary breath-holds increased significantly between 2 and 7 weeks post-weaning, reaching a maximum suppression of 53% below resting metabolic rate and 56% below Kleiber's standard metabolic rate. From 2 to 7 weeks post-weaning, breath-hold VO2was reduced by 52%. Between the two age classes, this equates to a mean breath-hold VO2reduction of 16% from resting VO2. Breath-hold VO2also declined with increasing breath-hold duration, but there was no direct effect of voluntary submergence on reducing VO2.Age did not influence rates of venouspO2depletion during breath-holds. However, voluntary submergence did result in slowerpO2depletion rates when compared to voluntary terrestrial apnoeas. The differences in whole body VO2during breath-holds (measured at recovery) and venouspO2(reflective of tissue O2-use measured during breath-holds), likely reflects metabolic suppression in hypoxic, vasoconstricted tissues.ConsistentpCO2values at the end of all voluntary breath-holds (59.0 ± 0.7 mmHg) suggests the physiological cue for stimulating respiration in northern elephant seal pups is the accumulation of CO2.Oxygen storage capacity and metabolic suppression directly limit diving capabilities and may influence foraging success in low-weaning weight seals forced to depart to sea prior to achieving full developmental diving capacity.
authors.affiliation: Department of Biology, Sonoma State University, 1801 East Cotati Ave, Rohnert Park, CA 94928, USA.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Tift
authors.forename: Elizabeth C
authors.initials: EC
authors.lastname: Ranalli
authors.forename: Dorian S
authors.initials: DS
authors.lastname: Houser
authors.forename: Rudy M
authors.initials: RM
authors.lastname: Ortiz
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Crocker
keywords: Blood gas; VO2; diving physiology; facial immersion; haemoglobin; metabolic rate pCO2; pO2; pinniped; sleep apnoea