Meeting Abstract
P2.177 Saturday, Jan. 5 Flight muscle size but not cellular aerobic capacity is correlated with thermogenic capacity in American goldfinches Spinus tristis . ZHANG, Y.*; KING, M.O.; SWANSON, D.L.; University of South Dakota yufeng.zhang@usd.edu
Concurrent seasonal variation in thermogenic capacity (= summit metabolic rate, Msum) and flight muscle size in small birds suggests that seasonal changes in flight muscle size are a major contributor to seasonal changes in Msum. In addition, seasonal variation in cellular aerobic capacity may also contribute to seasonal variation in Msum. However, few studies have directly addressed the relationship between flight muscle size, cellular aerobic capacity and Msum in individual birds, so whether they are consistently correlated among individuals remains uncertain. In this study, we measured flight muscle size by ultrasonography, pectoralis and supracoracoideus masses, and activities of key catabolic enzymes, and correlated these measurements with Msum for individual American goldfinches (Spinus tristis). Ultrasonographic measures of flight muscle width were significantly positively correlated with flight muscle mass, demonstrating that ultrasonographic measures of muscle size accurately track flight muscle mass. Flight muscle mass was significantly positively correlated with Msum and ultrasonographic muscle width was also correlated with Msum, although not quite significantly so (P = 0.054). Allometric residuals of flight muscle mass were also significantly positively correlated with allometric residuals of Msum. In contrast, mass-specific activities for citrate synthase, beta-hydroxyacyl CoA dehydrogenase and carnitine palmitoyl tranferase in pectoralis muscle were not significantly correlated with Msum. These data suggest that flight muscle size, but not cellular aerobic capacity, is a primary driver of variation in thermogenic capacity in goldfinches. This is consistent with phenotypic flexibility of flight muscle size serving as a general mechanism by which birds can alter metabolic capacities to meet changing energy demands throughout the annual cycle.
