Serum immunoglobulin G levels in very old common terns Sterna hirundo

The evolutionary theory of aging predicts that self-maintenance functions, such as immunity, will be selectively maintained in old age when extrinsic sources of mortality are low relative to intrinsic sources. Long-lived seabirds may provide an animal model for testing this prediction. We measured serum immunoglobulin G (IgG) levels across the lifespan, especially the oldest individuals, of a wild breeding population of the common tern (Sterna hirundo) in 1999 and 2002. Our analysis indicated that IgG levels do not show the typical increase late in life observed in mammals, but showed an age-independent response to environmental conditions. Power analysis indicated that Sample sizes were sufficient to detect a minimum difference of 23% in IgG level in the very oldest cohort. These data, and other studies of this species, support the hypothesis that long-lived species sustain self-maintenance functions, even at the end of their lifespan.