Meeting Abstract

61.8  Friday, Jan. 6  Ontogeny Influences the Capacity for Bradycardia in Dolphins NOREN, S.R.*; WILLIAMS, T.M.; UC Santa Cruz; UC Santa Cruz norenkramer@yahoo.com

Bradycardia is a key component of the dive response that facilitates prolonged breath-holds of marine mammals. Previous research demonstrated that mean steady-state heart rate (HR) during 2-3 min dives was greater for immature dolphins than adults and that these differences were attributable to age rather than body mass or dive duration. Here we expand the range of dive durations to include the preferred shorter duration dives (30 - 225 seconds) of bottlenose dolphin calves to examine ontogenetic control of diving bradycardia. HR was collected from dolphins (age: 1.7 years to adulthood) that were trained to submerge to 4 -5 m depth in a natural saltwater lagoon. We found that within individuals, average HR over the entire dive cycle (breath-submergence-breath) was correlated with dive duration (P < 0.05). In contrast, steady-state HR during submergence did not vary with dive duration. Although immature dolphins demonstrated a distinct bradycardia while diving, steady-state HR during submergence and absolute minimum HR during submergence (measured in beats per minute) decreased significantly with age for 1.7 - 5.44 year-olds (n = 14), where Steady-state HR = -3.19age + 60.71 (F1,12 = 7.449, P = 0.018) and Absolute minimum HR = -4.46 age + 60.01 (F1,12 = 18.259, P = 0.001). Maximum HR measured during surface intervals between dive bouts did not vary with age (r = 0.323, P = 0.260). In view of this, the primary ontogenetic change in cardiac control for diving dolphins appears to a progressive development in the intensity of bradycardia over a 4-5 year period until the level of bradycardia approaches adult capacities. Because the movement of blood gases is correlated to HR in marine mammals, these results have important implications for age-related capacities for foraging duration as well as for responding to anthropogenic disturbances.