Dissertation Abstract

In polar marine ecosystems, diving marine vertebrates such as penguins, seals, and cetaceans act as top-level predators with significant ecological impact. Understanding the physiological limits to the diving ability of these animals is critical to understand their foraging ecology. In order to remain metabolically active and purse prey while submerged, these predators have increased globin-bound oxygen stores including hemoglobin (Hb) in the blood and myoglobin (Mb) in the muscle. Due to the unique oxygen demands of diving birds and mammals, these vertebrates can have Mb concentrations ten-fold those found in their terrestrial counterparts. While Mb concentration is adaptive in diving vertebrates, less is known about molecular adaptation of Mb functional properties. We developed novel methods to extract Mb from frozen muscle and determine Mb oxygen affinity (P50) by generating a high resolution oxygen dissociation curve at 37°C. For comparison, Mb P50 was determined for 25 species of diving and terrestrial birds and mammals. Myoglobin P50 was conserved among terrestrial vertebrates and most cetaceans at approximately 3.7 mmHg with the exception of the melon-headed whale that had a significantly higher P50 (lower oxygen affinity) of 4.85 mmHg. Among pinnipeds (seals and sea lions) the P50 ranged from 3.23-3.81 mmHg and showed a trend for higher oxygen affinity in species with longer dive durations. Among diving birds the P50 ranged from 2.40-3.36 mmHg and also showed a trend of higher affinities in species with longer dive durations. Both myoglobin concentration and oxygen affinity appear adaptive in diving vertebrates to maintain aerobic metabolism and minimize hypoxic cellular damage in ischemic muscle. This research provides a greater understanding of molecular adaptation that influences the physiological ecology of diving marine predators in polar marine ecosystems.