Aging in Weddell Seals: Proximate mechanisms of age-related changes in adaptations to breath-hold hunting in an extreme environment

Evolutionary aging theories predict that elderly diving seals should exhibit senescence. This should be exacerbated by surges in the generation of oxygen free radicals via hypoxia-reoxygenation during breath-hold diving and hunting, which are implicated in age-related damage to cellular mitochondria. Surprisingly, limited observations of non-threatened pinniped populations indicate that senescence does not occur to a level where reproductive output is affected. Aging humans by contrast exhibit marked reduction in aerobic and physical exercise capacities, as well as circulatory system changes.

The ability of pinnipeds to avoid apparent senescence when reasoning suggests them as excellent candidates for aging is remarkable, giving rise to two questions:

1. What specific physiological and morphological changes occur with advancing age in pinnipeds?
   • This project proposes that the bulk of these changes will relate to diving ability; namely oxygen handling and muscular performance.
2. What subtle adjustments are made by these animals to cope with such changes?
   • This investigation will be the first to describe specific, small-scale physiological and behavioral changes relating to dive capability with advancing age in a model pinniped.

To answer these questions, collected data will be compared between Weddell seals in the peak, and near the end, of their reproductive age range. We will assess the ability to do external work (i.e. diving) as well as muscle functionality (ability to do internal work). Comparisons will be made between: 1) overall body condition; 2) calculated aerobic dive limit; 3) manifestation and regulation of the diving response; 4) blood oxygen storage and transport; 5) natural diving/foraging behavior (including stroking patterns and swim speeds); 6) plasticity of the dive response; 7) muscle fiber cross-sectional area; 8) myocyte density; 9) cellular oxidative status; 10) cellular protective mechanisms. Methodology designed to meet these objectives include the attachment of instrument packs to the backs of seals foraging in an “isolated hole” which will monitor and record seal movement, including depth and swim speed; flipper stroking patterns; and heart rate/ECG. Work load will be experimentally altered by the attachment of drag blocks to assess plasticity of diving responses. Hematology and contractile capacity of a peripheral vascular bed will be assessed under anesthesia. Muscle samples will be collected to assess functionality (including oxidative and antioxidant status). This project hypothesizes that senescence does occur in Weddell seals at the level of small-scale, proximate physiological effects and performance, but that behavioral plasticity allows for a given degree of compensation.

This project is directed by the Pinniped Ecology Applied Research Laboratory in cooperation with the Alaska SeaLife Center.

This project is supported by:

The National Science Foundation

This research is carried out under NMFS Permit number 1034-1854 and ACA number 2007-007.