Effect of growth rate and body mass on resting metabolic rate in galliform chicks.

In this study, we asked whether within-species variation in chick resting metabolic rate was related to variation in growth and whether this relationship changed during development in three galliform species (turkey, Meleagris gallopavo, guinea fowl, Numida meleagris, and Japanese quail, Coturnix coturnix japonica). Resting metabolic rate increased by a bi- or triphasic pattern with body mass. For each phase, the relationship between metabolic rate and growth was studied by residual analysis, with two measures of growth: growth rate and body mass. Chick mass reflects the net result of accumulated growth, while hatchling mass reflects embryonic growth. In hatchlings, high metabolic rates coincided with low growth rates in turkeys and guinea fowl. These species delay initial food intake, and under these circumstances high metabolic expenditure may preclude conversion of yolk energy into body mass. No relationship was present between residual hatching metabolic rate and residual body mass. In older chicks, residual metabolic rate was positively linearly related with residual growth rate (turkeys and young quail) or residual body mass (guinea fowl and older quail). The similarity of the slopes suggests that growth rate and accumulated growth affected maintenance metabolism to the same extent throughout development. These findings suggest that growth models must take ontogenetic adjustments of metabolic rate into account in addition to costs of maintenance.