Living in the fast lane: rapid development of the locomotor muscle in immature harbor porpoises (Phocoena phocoena)

A study in the Journal of Comparative Physiology shows that muscle development necessary for diving can take several years to mature in harbor porpoises. Scientists argue that this may make immature harbor porpoises more vulnerable than adults to impacts from boat traffic or other disturbances. 

Harbor porpoise. Photo courtesy of the National Park Service.
Harbor porpoise. Photo courtesy of the National Park Service.

Abstract

Cetaceans (dolphins and whales) are born into the aquatic environment and are immediately challenged by the demands of hypoxia and exercise. This should promote rapid development of the muscle biochemistry that supports diving, but previous research on two odontocete (toothed whales and dolphins) species showed protracted postnatal development for myoglobin content and buffering capacity. A minimum of 1 and 1.5 years were required for Fraser's (Lagenodelphis hosei) and bottlenose (Tursiops truncatus) dolphins to obtain mature myoglobin contents, respectively; this corresponded to their lengthy 2 and 2.5-year calving intervals (a proxy for the dependency period of cetacean calves). To further examine the correlation between the durations for muscle maturation and maternal dependency, we measured myoglobin content and buffering capacity in the main locomotor muscle (longissimus dorsi) of harbor porpoises (Phocoena phocoena), a species with a comparatively short calving interval (1.5 years). We found that at birth, porpoises had 51 and 69 % of adult levels for myoglobin and buffering capacity, respectively, demonstrating greater muscle maturity at birth than that found previously for neonatal bottlenose dolphins (10 and 65 %, respectively). Porpoises achieved adult levels for myoglobin and buffering capacity by 9-10 months and 2-3 years postpartum, respectively. This muscle maturation occurred at an earlier age than that found previously for the dolphin species. These results support the observation that variability in the duration for muscular development is associated with disparate life history patterns across odontocetes, suggesting that the pace of muscle maturation is not solely influenced by exposure to hypoxia and exercise. Though the mechanism that drives this variability remains unknown, nonetheless, these results highlight the importance of documenting the species-specific physiological development that limits diving capabilities and ultimately defines habitat utilization patterns across age classes.

Citation

Noren, S. R., D. P. Noren, and J. K. Gaydos. 2014. Living in the fast lane: rapid development of the locomotor muscle in immature harbor porpoises (Phocoena phocoena). Journal of Comparative Physiology. Volume 184, Issue 8, pp 1065-1076.