Gp. Burness et al., Effect of brood size manipulation on offspring physiology: An experiment with passerine birds, J EXP BIOL, 203(22), 2000, pp. 3513-3520
The environment experienced during ontogeny has a significant impact on the
physiological condition of offspring, This, in turn, forecasts survival pr
obabilities and future reproductive potential, Despite the prominent role t
hat the concept of condition plays in evolutionary studies, the physiologic
al and biochemical characters that define it remain relatively unexplored,
In this study, we quantified the impact of brood size manipulations on the
physiology and biochemistry of nestling tree swallows (Tachycineta bicolor)
shortly before they hedged, Over two breeding seasons, we either increased
or decreased the number of individuals in a brood by a single nestling. Ev
ery 2-4 days, we determined the resting rate of oxygen consumption (V) over
dot (O2) of individuals in each brood, Growth was followed until 16 days o
f age, at which time, to look for potential trade-offs in energy allocation
, we measured total lipid mass, skeletal muscle and organ mass, indices of
blood oxygen-carrying capacity and the activities of key metabolic enzymes
in various tissues. Surprisingly, there was a minimal response of most char
acters to brood manipulation, suggesting that physiological and biochemical
development is relatively invariant except perhaps under extreme condition
s. Individuals reared in artificially enlarged broods, however, had a signi
ficantly lower body mass, body-size-adjusted (V) over dot (O2) , gizzard ma
ss and total lipid mass, These individuals also had decreased activity of c
ardiac 3-hydroxyacyl CoA dehydrogenase, suggesting a decreased capacity for
oxidation of fatty acids. How these characters affect survival or the futu
re adult phenotype remains unknown.