Abstract
Despite similarities in winter distribution, habitat selection, and food choice, Dark-eyed Juncos (Junco hyemalis) and Tree Sparrows (Spizella arborea) differ in the extent to which they store fat during winter, with juncos accumulating greater stores. Anticipating that Tree Sparrows might have some means of conserving energy during fasting and thus suffer no disadvantage when weather prevents feeding, we compared the species for weight loss, body temperature, and locomotor activity during fasting and noted relative fasting endurance. Because both species exhibit geographic variation in sex ratio during winter, we also made sexual comparisons, anticipating that males would be able to fast longer than females. The species responded similarly to fasting by (a) lowering body temperature, especially at night, and (b) becoming hyperactive, progressively more so as fasting time increased. Tree Sparrows did not exhibit these responses to a greater degree (although they became hyperactive sooner) and were not able to fast as long as juncos. No sexual differences in fasting ability were observed. Because the species-specific difference in tendency toward fat accumulation cannot be attributed to differences in energy expenditure while fasting, at least in the laboratory, other explanations are considered.
Modeling human brain tumours in flies, worms, and zebrafish: From proof of principle to novel therapeutic targets
