Conditioned Variation in Heart Rate During Static Breath-Holds in the Bottlenose Dolphin (Tursiops truncatus).

Previous reports suggested the existence of direct somatic motor control over heart rate (f_H) responses during diving in some marine mammals, as the result of a cognitive and/or learning process rather than being a reflexive response. This would be beneficial for O₂ storage management, but would also allow ventilation-perfusion matching for selective gas exchange, where O₂ and CO₂ can be exchanged with minimal exchange of N₂. Such a mechanism explains how air breathing marine vertebrates avoid diving related gas bubble formation during repeated dives, and how stress could interrupt this mechanism and cause excessive N₂ exchange. To investigate the conditioned response, we measured the f_H-response before and during static breath-holds in three bottlenose dolphins (Tursiops truncatus) when shown a visual symbol to perform either a long (LONG) or short (SHORT) breath-hold, or during a spontaneous breath-hold without a symbol (NS). The average f_H (if_Hstart), and the rate of change in f_H (dif_H/dt) during the first 20 s of the breath-hold differed between breath-hold types. In addition, the minimum instantaneous f_H (if_Hmin), and the average instantaneous f_H during the last 10 s (if_Hend) also differed between breath-hold types. The dif_H/dt was greater, and the if_Hstart, if_Hmin, and if_Hend were lower during a LONG as compared with either a SHORT, or an NS breath-hold (P < 0.05). Even though the NS breath-hold dives were longer in duration as compared with SHORT breath-hold dives, the dif_H/dt was greater and the if_Hstart, if_Hmin, and if_Hend were lower during the latter (P < 0.05). In addition, when the dolphin determined the breath-hold duration (NS), the f_H was more variable within and between individuals and trials, suggesting a conditioned capacity to adjust the f_H-response. These results suggest that dolphins have the capacity to selectively alter the f_H-response during diving and provide evidence for significant cardiovascular plasticity in dolphins.

Duke Scholars

Author Andreas Fahlman Marine Science and Conservation