Food insecurity increases energetic efficiency, not food consumption: an exploratory study in European starlings.
Food insecurity increases energetic efficiency, not food consumption: an exploratory study in European starlings.
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作者：
Bateson M;Andrews C;Dunn J;Egger CBCM;Gray F;Mchugh M;Nettle D
粮食不安全——定义为获得营养充足食物的机会有限或不可预测——与人类和鸟类的高体重有关。人们普遍认为，粮食不安全导致的肥胖是由粮食消费增加引起的，但几乎没有证据支持任何物种的这种说法。我们开发了一种新的技术来测量饲养在鸟笼中的欧洲椋鸟（Sturnus vulgaris）的觅食、食物摄入量和体重。在四个探索性实验中，我们证明了鸟类对1-2周的食物不安全的反应是，尽管吃得少，但体重却增加了。因此，食物不安全的鸟类提高了它们的能量效率，以每单位食物消耗所保持的体重来计算。在基线体重较轻的鸟类和在获得食物方面面临更大竞争的鸟类中，体重增加的幅度更大。在粮食不安全条件下，各试验间的增重和食用量存在差异，但能量效率总是增加的。在食物不安全的情况下，鸟粪的能量密度降低，表明从食物中吸收的能量增加。对栖息行为的观察显示，粮食不安全情况下身体活动减少的证据不一致。在恢复粮食安全后，能量效率的提高持续了1-2周，这表明对粮食不安全的反应速度和从粮食不安全中恢复的速度不对称。未来了解粮食不安全导致的体重增加机制的工作应侧重于调节能量效率增加的生物学变化，而不是增加能量消耗。
Food insecurity—defined as limited or unpredictable access to nutritionally adequate food—is associated with higher body mass in humans and birds. It is widely assumed that food insecurity-induced fattening is caused by increased food consumption, but there is little evidence supporting this in any species. We developed a novel technology for measuring foraging, food intake and body mass in small groups of aviary-housed European starlings (Sturnus vulgaris). Across four exploratory experiments, we demonstrate that birds responded to 1–2 weeks of food insecurity by increasing their body mass despite eating less. Food-insecure birds therefore increased their energetic efficiency, calculated as the body mass maintained per unit of food consumed. Mass gain was greater in birds that were lighter at baseline and in birds that faced greater competition for access to food. Whilst there was variation between experiments in mass gain and food consumption under food insecurity, energetic efficiency always increased. Bomb calorimetry of guano showed reduced energy density under food insecurity, suggesting that the energy assimilated from food increased. Behavioural observations of roosting showed inconsistent evidence for reduced physical activity under food insecurity. Increased energetic efficiency continued for 1–2 weeks after food security was reinstated, indicating an asymmetry in the speed of the response to food insecurity and the recovery from it. Future work to understand the mechanisms underlying food insecurity-induced mass gain should focus on the biological changes mediating increased energetic efficiency rather than increased energy consumption.
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