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First published online January 30, 2009
Journal of Experimental Biology 212, 483-493 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.025262

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Physiological variation in amethyst sunbirds (Chalcomitra amethystina) over an altitudinal gradient in winter

Claire V. Lindsay, Colleen T. Downs^* and Mark Brown

School of Biological and Conservation Sciences, University of KwaZulu-Natal, Private Bag X01, Pietermaritzburg, 3201, South Africa

^* Author for correspondence (e-mail: downs{at}ukzn.ac.za)

Accepted 20 November 2008

Flexibility of metabolic rates within a species allows for the colonization of different habitats along an altitudinal and thus temperature gradient. The distribution range of amethyst sunbirds (Chalcomitra amethystina) within southern Africa includes an altitudinal gradient from the Drakensberg to the coast of KwaZulu-Natal. We expected that over this altitudinal gradient amethyst sunbirds would exhibit variation in winter metabolic rates, particularly basal metabolic rates (BMR) and resting metabolic rate (RMR) pre- and post-acclimation. Sunbirds from three locations, Underberg (1553 m above sea level; asl), Howick (1075 m asl) and Oribi Gorge (541 m asl) were used for this study. Upon capture, metabolic rate was measured indirectly by quantifying oxygen consumption (_O2) using flow-through respirometry, at 5 and 25°C. Birds were then acclimated at 25°C for 6 weeks on a 12 h:12 h L:D cycle. _O2 was measured post-acclimation at eight different temperatures (15, 5, 10, 20, 30, 28, 25 and 33°C). We found little variation in winter _O2 between individuals from the same locality, whereas significant variation was observed in _O2 at the same temperatures between individuals from the different localities and thus between altitudes. In particular, winter BMR decreased significantly with decreasing altitude post-acclimation. This study emphasizes the need to understand plasticity/flexibility in metabolic rates and to acknowledge altitudinal differences within a species, to make accurate predictions about the thermal physiology of a species and its responses to changes in ambient temperatures.

Key words: altitudinal variation, amethyst sunbird, metabolic rates, phenotypic plasticity, phenotypic flexibility

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