Concentration of myoglobin in different functional muscles groups of stranded marine mammals

Supervisor: Yara Bernaldo Quirós (University of Texas & University of Las Palmas de Gran Canaria)
Marine mammals possess increased muscle myoglobin (Mb) concentration as compared to terrestrial mammals, increasing their onboard oxygen stores and thus, their aerobic diving limit (ADL). The ADL is the longest dive that an air-breathing animal can perform relying on its oxygen storage holding an aerobic metabolism. Previous estimates of muscle oxygen (O2) stores in cetaceans have often been determined by measuring the Mb concentration in the longissimus dorsi, the muscle powering the upstroke of the caudal fin, and multiplying that value by the animal’s locomotor muscle mass, assuming homogenous muscle Mb concentration. We tested the hypothesis that myoglobin concentration is similar across body muscles by calculating Mb concentration in six muscles (mastohumeralis, dorsal scalenus, sternohyoid, epaxial, hypaxial and rectus abdominis), representative of different functional groups (caudal fin movement, pectoral fin movement, feeding and respiration) in four cetacean species (Phocoena phocoena n=1; Delphinus delphis n=4; Stenella coeruleoalba n=4; Globicephala macrorhynchus n=1) and two pinniped species (Zalophus californianus n=1; Halichoerus grypus n=1). Oxygen stored in each functional group was determined by multiplying the mean Mb concentration value of each representative muscle by the muscle mass of that functional group, and considering the Mb-O2 binding affinity. Total muscle oxygen stored was the summation of the oxygen stores in the different muscle functional groups. Results showed that Mb concentration was heterogeneously distributed between and within muscles. Statistically significant differences in Mb concentration were found between locomotor and non-locomotor muscles of the species studied. Locomotor muscles were the major contributors to total muscle oxygen stores due to both, high Mb concentration and a large muscle mass. Moreover, previous methods assuming homogenous Mb concentration distribution underestimated muscle oxygen stores when only locomotor muscles were considered and overestimated it when total muscle mass was considered compared to the present method, proving the need of a new simple method for more accurate muscle oxygen stores and ADL calculations.

Finally, factors like the specie, age or body condition seemed to affect the animal´s Mb concentration thus, influencing their muscle oxygen stored, and consequently their ADL.

Further studies are needed to increase the number of animals studied, allowing to draw strong conclusions and to propose an accurate but simple method for muscle oxygen stored calculation.