Meeting Abstract
58.1 Jan. 6 Thermogenic capacity in wintering and migratory shorebirds is driven by body mass-related changes in organ size V�ZINA, F.*; JALVINGH, K.M.; DEKINGA, A.; PIERSMA, T.; NIOZ; NIOZ; NIOZ; NIOZ, University of Groningen fvezina@nioz.nl
Cold acclimatization in birds involves an array of metabolic adjustments resulting in increased shivering endurance and improved cold tolerance. These adjustments often result in elevated summit metabolic rate (Msum), a measure of maximal thermogenic capacity and an indicator of sustainable heat production. However, several aspects of this phenomenon are poorly understood. Contradictory findings with regard to variations in basal metabolic rate (BMR) raise the question whether an increase in BMR contributes to improved cold tolerance or only reflects the physiological upregulation necessary to tolerate cold. Furthermore, few avian studies have examined individual flexibility in organ size in response to life in the cold. Here, we investigated physiological adjustments associated with thermal acclimation, in long-distance migrant Red Knots (Calidris canutus). Compared to birds acclimated to thermoneutrality, cold-acclimated (4-5�C) captive red knots were 15% heavier and exhibited a BMR and Msum 26% and 13% higher, respectively. Although the improvement in thermogenic capacity was directly related to the difference in body mass, likely through larger heat producing pectoral muscles (measured by ultrasonography), body mass-independent BMR remained 15% higher in cold acclimated birds. During the premigratory fattening period, all birds increased their body mass (up to 31%) and pectoral muscle size (up to 14%). This gain of mass was associated with improved thermogenic capacity (up to 16%), independent of thermal treatment. We suggests that in cold acclimated red knots, increase in thermogenic capacity is achieved via modulation of body mass and muscle size and that changes in size of other internal organs, such as the liver, are responsible for variations in BMR.
