Telomere Dynamics in Magellanic penguins (Spheniscus magellanicus)
Cerchiara, Jack Andrew
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Lifespans among taxa vary widely, however, most all species undergo a reduction in physiological function with increasing age, often termed aging. One theory suggest that aging occurs as a result of the accumulation of damage during life, and though maintenance and repair mechanisms have evolved, they are not sufficient to completely mitigate the accrual of damage, resulting in aging pathologies. This theory also suggests that the variation of lifespan among species could be a result of the variable ability of maintenance systems to mitigate damage. Particularly long-lived species should evolve processes that maintain physiological systems linked to survival. Magellanic penguins (Spheniscus magellanicus) are an outlier among bird species and live 26% longer than their mass-predicted maximum lifespan. Telomeres, tandem repeating, non-coding sequences that protect the coding regions of DNA during cell replication, are linked to survival. Telomeres shorten with age in most species. We show that Magellanic penguins maintain their telomeres over their lifespan, resisting the stressors of growth, reproduction and environment. This may be a key factor in their enhanced longevity. We found telomere lengths for adults from 4 years to more than 27 years of age were similar. We found telomeres of adult Magellanic penguins remained similar in length over a 3-year period. Telomere length did not predict re-sighting, nor did telomeres shorten with more reproductive effort or reproductive success. Our results suggest that Magellanic penguins maintain their telomeres. If telomere length is important to survival, adults should have strong mechanisms maintaining telomere length. Chick growth is energetically costly, and is characterized by high levels of cell proliferation, which is linked to shorter telomeres in other species. Mitochondria are the source of both energy production, and damaging reactive oxygen species that can shorten telomeres. We characterized the dynamics of telomere length and mitochondria number during the fastest growth and throughout the lifespan of Magallenic penguins. We tested how growth impacted telomeres by taking blood from wild known-age Magellanic penguin chicks as they grew and measured telomere length and mitochondria number. Telomeres shortened during early rapid growth but by fledging telomeres were similar to their length at hatching and stay at this length throughout life. Mitochondrial copy number increased significantly after hatch as the chick grew, probably to meet energetic demands, than returned to their number at hatching by 45 days of age. When the penguins reach 7 to 8 years of age the number of mitochondria decreased to the level at hatching, remaining at this abundance throughout adulthood. Our results indicate that while telomeres shorten during growth, characterized by increased mitochondria number, Magellanic penguins elongate telomeres and enter breeding age with telomeres similar to their hatch day. Magellanic penguins also live in captivity, where the stressors they experience undoubtedly differ from those of wild penguins, but could have equally potent effects on maintenance systems. In captivity, confinement and living in non-native habitats may be stressors, shortening telomeres. If so, telomeres in Magellanic penguins should shorten more in captivity than in the wild. We found that telomeres do not shorten with age in males or females, in captivity. Telomeres were similar in length in captive and wild Magellanic penguins. Magellanic penguins appear to maintain their telomeres in captivity, the same as in the wild, which is consistent with their longer than predicted lifespan. Magellanic penguins’ enhanced longevity may be explained, at least in part, by the maintenance of telomeres. By understanding the aging physiology of seabird species like Magellanic penguins we are likely to find insights into the evolutionary processes that drive the aging phenotypes we observe in nature.
- Biology