Plasma Lipid Metabolites Provide Information on Mass Change over Several Days in Captive Western Sandpipers

Individual quality is often assessed using a static measure of body condition, such as size-corrected body mass. Plasma metabolites have the potential to provide information on the dynamics of physiological state and thus may be better measures of individual performance capacity (and fitness). We studied relationships between rate of mass change and circulating levels of triglycerides, glycerol, and 3-hydroxybutyrate in captive Western Sandpipers (Calidris mauri). The rate of mass change over one and two days prior to blood sampling was positively related to residual triglyceride (controlling for body mass at sampling) and negatively related to residual glycerol and residual fi-hydroxybutyrate. The relationship between metabolite level and mass change was still apparent over a seven-day interval for glycerol, but not for the other two metabolites. In a stepwise multiple regression of mass change over two days (controlling for body mass), only p-hydroxybutyrate and glycerol were entered in the model at P < 0.15. Analysis of group means for seven sampling events showed that body-mass change in a group of individuals was related to mean circulating levels of each metabolite, i.e. to a characteristic metabolite profile. Thus, it may be feasible to employ these metabolites to assess habitat quality based on animal performance (e.g. at migratory stopover sites), or to understand the effects of climatic or anthropogenic factors on the health and survival of animals.