Development in the cold renders bird mitochondria more susceptible to heat stress

Research on birds suggests that extreme weather events during development may have long-lasting consequences on form and function. The underlying cellular mechanisms mediating such phenotypic effects are poorly studied. We raised Japanese quail in warm (30°C) or cold (10°C) temperatures from hatching until adulthood, and then measured mitochondrial metabolism in intact blood cells at representative normothermic body temperature (41°C) and a hyperthermic temperature (45°C) that quail commonly attain when heat stressed. To investigate whether any developmental effects were reversible, half of the cold- and warm-acclimated birds were assigned to a common garden (20°C) 3 weeks before the measurements. Across groups, hyperthermia was associated with increased proton leak, but decreases in both phosphorylating respiration (where ATP is produced) and working capacity of the mitochondria. Cold-acclimated birds were more strongly affected by heat stress: the increase in proton leak was 1.6-fold higher, and the decrease in phosphorylating capacity during endogenous respiration was 1.7-fold greater, compared to warm-acclimated birds. These differences did not remain in the common-garden birds. Our study suggests that developmental cold acclimation is traded off against heat tolerance at the level of cellular metabolism, with implications for our understanding of avian responses to climate change.