图片来源：National Veterinary School of Alfort
一群睡着的兔宝宝并不仅仅是看起来可爱——它们对于种群的延续也很重要。
新降生的小兔子会为了妈妈的奶水而展开竞争，而成功的幼崽则会长得更加结实，并更有可能将它们的基因传递给下一代。
然而根据本月发表在《科学公共图书馆—综合》上的一项研究成果，作为竞争对手，这些兄弟姐妹们会搁置分歧，彼此保护以抵御寒冷。
利用红外摄像机，以及一些温度从23摄氏度缓慢降至11摄氏度的房间，英国格拉斯哥大学的动物学家Dominic J. McCafferty和同事发现，当温度降低后，生下来不足5天的没毛兔宝宝会挤在一起取暖。
就像投资者联合创业一样，这种合作会花费较少的个体成本。
这是因为利用身体的脂肪产生热量会耗费氧气，而使用太多的氧气则会阻碍小兔子的生长。但是通过分享热量，兔宝宝能够互相确保它们的兄弟姐妹不会使用太多的能量来抵御寒冷，从而有助于全部存活下来，为今后种群的发展作出贡献。（生物谷 bioon.com）
doi:10.1371/journal.pone.0033553
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Private Heat for Public Warmth: How Huddling Shapes Individual Thermogenic Responses of Rabbit Pups
Caroline Gilbert1, Dominic J. McCafferty, Sylvain Giroud, André Ancel, Stéphane Blanc
Background 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.
