SUAREZ, R.K.; DARVEAU, C.-A.; O’BRIEN, D.M.; ROUBIK, D.W.; Univ. of California, Santa Barbara; Univ. of British Columbia; Swarthmore College; Smithsonian Tropical Research Institute: Heirarchical and Metabolic Regulation in the Evolution of Metabolic Scaling

The allometric scaling of metabolic rate, the evolution of flux capacities in pathways, the regulation of metabolism, and the reconciliation of mechanistic and evolutionary physiology were among the many subject areas that fascinated Peter Hochachka and were influenced by him. We examined the scaling of flux capacities (Vmax values) at several key steps in energy metabolism in about 40 species of Panamanian orchid bees, ranging in body mass from about 50 to 1,300 mg. Previous work on this group by Casey and Ellington revealed that wing-beat frequencies and mass-specific oxygen consumption rates decline with increasing body mass. We found that hexokinase activities, expressed per g thorax, decline with increasing body mass with a slope similar to that of oxygen consumption rate. In contrast, many other steps in energy metabolism scale isometrically with mass. Applying ter Kuile and Westerhoff’s method of analysis, we show that in the evolution from a common ancestor, metabolic regulation is a sufficient explanation for the inter-specific variation in metabolic flux during flight at most steps in energy production. In contrast, at hexokinase, heirarchical regulation was required and fully accounts for the mass-dependent variation in metabolic rate. A molecular phylogeny is currently in progress that will yield further insights into the evolution of allometric scaling in this group. With this system, we are well on our way towards a meaningful integration of various areas that were dear to Peter. It would have made his day to see this come to completion.