Williams, J.B.*; Tieleman, B.I.: Evolutionary Physiology of larks

Conventional wisdom holds that arid-zone birds occupy these climes because of the possession of physiological design features common to all members of the class Aves. Using broad scale comparisons, we tested the idea that desert birds have reduced energy expenditure and water loss compared to mesic counterparts. We showed that desert birds have a reduced basal metabolic rate (BMR), a reduced field metabolic rate, and a lower total evaporative water loss. Conventional analysis of covariance indicated that desert birds have reduced water flux in the field, but an analysis based on phylogenetically independent contrasts did not support this finding. We further searched for physiological specialization amongst members of the Alaudidae from mesic habitats in the Netherlands and from arid habitats in Saudi Arabia. Using DNA sequences from the mitochondrial b gene, we constructed a phylogeny of larks from Europe and from the Middle East, and then selected species for physiological studies based on our results. We found that BMR and TEWL is reduced in larks from deserts compared to larks from more mesic areas supporting our hypothesis of evolutionary specialization. The evolutionary significance of our finding that BMR and TEWL is reduced in desert birds remains unresolved because differences may result from physiological acclimation, from genetic sculpting by natural selection, or from a combination of both. We conducted an experiment on the phenotypic flexibility of BMR in Hoopoe Larks from Arabia. We exposed groups to either 15oC or 36oC for 3 weeks. For larks in the 15oC group, BMR averaged 142% higher than larks in the 36oC group, a result attributable, in part, to a larger kidney, liver, and small intestine. Similar experiments are in progress on larks in the Netherlands.