Based on the ‘free radical theory of aging,’ I hypothesized that hypoxia caused
by the mammalian dive response induces free radical production which could modulate
or accelerate cellular aging. On the other hand, to prevent free radical “stress” (pro-
/antioxidant imbalance), divers could display elevated protective mechanisms.
Additionally, the unusual connection between diving physiology and foraging ecology
implies that aging physiology is significant to our understanding of ecology for divers.
This study examines three aspects of aging in representative diving mammals.
First, gracilis muscle morphology was analyzed for old/young shrews (water
shrew, Sorex palustris (diver); short-tailed shrew, Blarina brevicauda (non-diver)).
Extracellular space was elevated in old animals (10% diver, ~70% non-diver; P=0.021),
which corresponded to a larger extracellular collagen component of old muscle (~60%;
P=0.008). Muscle was dominated by Type I collagen, and the ratio of collagen Type I:
III more than doubled with age (P=0.001).
Second, oxidative stress markers, protective antioxidant enzymes and apoptosis
were examined in muscle of the two shrew species. The activities of antioxidant enzymes catalase and glutathione peroxidase were statistically identical at each age in
both species. The Cu,Zn superoxide dismutase isoform was, however, elevated in older
animals (115% diver, 83% non-diver, P=0.054). Only one indicator of oxidative stress
(lipid peroxidation) increased with age (P=0.009), whereas the other markers declined
(4-hydroxynonenal content, P=0.008, dihydroethidium oxidation, P=0.025). Apoptosis
occurred in <1% of myocytes, and did not change with age. On balance, diving water
shrews did not have adaptations to combat oxidative stress, yet they do not display
excessive oxidative tissue damage. Apoptosis was similar between species.
The third study component was the development of a predictive simulation
model for the energetics of old/young foraging Weddell seals, Leptonychotes weddellii.
With advancing age, the model predicts declining net energy gain associated with a
decrease in muscle contractile efficiency. The effects of age are exacerbated when good
prey patches are scarce. In such cases, declines in old seal energy gain caused by
increased buoyancy and decreased aerobic dive limit become apparent. The model also
addresses the idea that behavioral plasticity may allow older animals to compensate for
age-related performance constraints.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2615 |
| Date | 15 May 2009 |
| Creators | Hindle, Allyson Gayle |
| Contributors | Davis, Randall W, Horning, Markus |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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