Université Paris-Est, Ecole Nationale Vétérinaire d'Alfort, UMR 7179, CNRS, MNHN, Maisons-Alfort, France.
PLoS One. 2012;7(3):e33553. doi: 10.1371/journal.pone.0033553. Epub 2012 Mar 16.
Within their litter, young altricial mammals compete for energy (constraining growth and survival) but cooperate for warmth. The aim of this study was to examine the mechanisms by which huddling in altricial infants influences individual heat production and loss, while providing public warmth. Although considered as a textbook example, it is surprising to note that physiological mechanisms underlying huddling are still not fully characterised.
METHODOLOGY/PRINCIPAL FINDINGS: The brown adipose tissue (BAT) contribution to energy output was assessed as a function of the ability of rabbit (Oryctolagus cuniculus) pups to huddle (placed in groups of 6 and 2, or isolated) and of their thermoregulatory capacities (non-insulated before 5 days old and insulated at ca. 10 days old). BAT contribution of pups exposed to cold was examined by combining techniques of infrared thermography (surface temperature), indirect calorimetry (total energy expenditure, TEE) and telemetry (body temperature). Through local heating, the huddle provided each pup whatever their age with an ambient "public warmth" in the cold, which particularly benefited non-insulated pups. Huddling allowed pups facing a progressive cold challenge to buffer the decreasing ambient temperature by delaying the activation of their thermogenic response, especially when fur-insulated. In this way, huddling permitted pups to effectively shift from a non-insulated to a pseudo-insulated thermal state while continuously allocating energy to growth. The high correlation between TEE and the difference in surface temperatures between BAT and back areas of the body reveals that energy loss for non-shivering thermogenesis is the major factor constraining the amount of energy allocated to growth in non-insulated altricial pups.
CONCLUSIONS/SIGNIFICANCE: By providing public warmth with minimal individual costs at a stage of life when pups are the most vulnerable, huddling buffers cold challenges and ensures a constant allocation of energy to growth by reducing BAT activation.
在幼小动物的巢穴中，幼崽之间会为了争夺能量（限制生长和生存）而竞争，但也会为了取暖而合作。本研究的目的是探讨幼崽挤在一起的行为如何影响个体的产热和散热，同时提供公共热量。尽管挤在一起被认为是一个典型的例子，但令人惊讶的是，支撑挤在一起的生理机制尚未完全被描述。
方法/主要发现：通过评估兔子（Oryctolagus cuniculus）幼崽挤在一起的能力（放在 6 只或 2 只一组或单独放置）和它们的体温调节能力（5 天前不隔热，约 10 天前隔热），来评估棕色脂肪组织（BAT）对能量输出的贡献。通过红外热成像（表面温度）、间接测热法（总能量消耗，TEE）和遥测（体温）相结合的技术，研究了暴露在寒冷环境下的幼崽的 BAT 贡献。通过局部加热，无论幼崽的年龄如何，挤在一起的行为都会为它们提供一个寒冷环境中的“公共温暖”，这尤其有利于没有隔热的幼崽。挤在一起可以让幼崽在面对逐渐变冷的挑战时，通过延迟其产热反应的激活来缓冲环境温度的下降，尤其是当它们有毛隔热时。这样，挤在一起可以让幼崽有效地从非隔热状态转变为伪隔热状态，同时持续将能量分配给生长。TEE 与 BAT 和身体背部之间的表面温度差之间的高度相关性表明，非颤抖产热的能量损失是限制非隔热幼崽生长分配能量的主要因素。
结论/意义：在幼崽最脆弱的生命阶段，通过提供最小个体成本的公共温暖，挤在一起可以缓冲寒冷的挑战，并通过减少 BAT 的激活来确保持续将能量分配给生长。
