Digestive plasticity in birds: Mechanisms and ecological consequences

CAVIEDES VIDAL, E.; KARASOV, W. H.

Salvador

Congreso; 7th Internactional Congress of Comparative Physiology; 2007

Digestion is important ecologically because it may determine diet niche and constrain intake and thus production.  Birds? reserve digestive capacity is relatively low, making plasticity crucial for adjusting to changing ecological conditions.  We review recent, growing understanding of digestive plasticity in birds during their life cycle and highlight ecological implications and constraints.  Altricial nestlings attempt to regulate food intake by inverse matching of begging intensity to intake.  Over a range of feeding levels they hold digesta retention time and thus digestive efficiency constant, but may have limited reserve digestive capacity to accommodate high intakes.  There is no evidence that altricial species can increase digestive capacity, which may limit their catch-up growth.  Adults, in contrast, increase digestive capacity to meet the demands of high food intake during cold acclimatization and probably reproduction by increasing intestine size and thus biochemical capacity. Reversible changes in gut size and biochemical capacity are also important in migrants, which fly with small guts but then increase gut size during stopovers to refuel, though this strategy may extend migration time.  Up- or down- modulation of digestive enzymes or nutrient transporters to match changes in diet composition does not seem to occur in many birds, in contrast to mammals, but birds have a compensatory feature.  They exhibit a high level of intestinal passive permeability permitting a direct matching of absorption of water soluble nutrients to luminal concentration, although it also exposes them to water soluble toxins.