The limitations on energy availability and outputs have been implied to have a profound effect on the evolution of many morphological and behavioral traits. It has been suggested that the reproductive performance of mammals is frequently constrained by intrinsic physiological factors, such as the capacity of the mammary glands to produce milk (the peripheral limitation [PL] hypothesis) or that of the body to dissipate heat (the heat dissipation limitation [HDL] hypothesis). Research on a variety of small mammals, however, has so far failed to provide unequivocal support for one hypothesis over the other. We tested the PL and HDL hypotheses in female striped hamsters (Cricetulus barabensis) with artificially manipulated litter sizes of two (three or four pups removed from natural litter size), five, eight (two or three pups added to natural litter size), and 12 (five to seven pups added to natural litter size) pups at ambient temperatures of 21° and 30°C. Energy intake and milk output of mothers, litter size, and litter mass were measured throughout lactation. Several markers indicating digestive enzyme activity and the gene expression of hypothalamic neuropeptides related to food intake were also measured. Food consumption and milk output increased with increasing litter size but reached a ceiling at 12 pups, causing 12-pup litters to have significantly lower litter mass and pup body mass than litters composed of fewer pups. Litter mass and maternal metabolic rate, milk output, maltase, sucrase, and aminopeptidase activity in the small intestine, and gene expression of hypothalamic orexigenic peptides were significantly lower at 30°C than at 21°C, and these differences were considerably more pronounced in 12-pup litters. These results suggest that PL and HDL can operate simultaneously but that the HDL hypothesis is probably more valid at warmer temperatures. Our results suggest that increased environmental temperatures in future climates may limit reproductive output through heat dissipation limits.

中文翻译：

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在温暖条件下，具有更大繁殖力的条纹仓鼠的散热能力很可能是其哺乳期更重要的限制。

已经暗示了对能量可用性和输出的限制对许多形态和行为特征的演变具有深远的影响。有人提出，哺乳动物的生殖能力经常受到内在的生理因素的制约，例如乳腺产生乳汁的能力（外围限制[PL]假设）或身体的散热能力（散热）。局限性[HDL]假设）。然而，迄今为止，对各种小型哺乳动物的研究未能为一个假设提供明确的支持。我们用人工操纵的窝仔大小为2（从天然窝仔大小中删除了3或4个幼崽），雌性带仓鼠（Cricetulus barabensis）检验了PL和HDL假设。在21°C和30°C的环境温度下，有8只幼崽（增加了自然垃圾大小的两只或三只幼崽）和12只（增加了天然垃圾的大小增加了5至7只幼崽）的幼崽。在整个泌乳期间，测量母亲的能量摄入和产奶量，产仔数和产仔量。还测量了指示消化酶活性和与食物摄入有关的下丘脑神经肽的基因表达的几种标记。食物的消耗和牛奶产量随着窝数的增加而增加，但达到了12只幼仔的上限，导致12只幼仔的幼仔质量和幼仔体重明显低于由更少的幼仔组成的幼仔。小肠的产仔量和产妇代谢率，产奶量，麦芽糖酶，蔗糖酶和氨肽酶活性，下丘脑成虫肽的基因表达水平在30°C时显着低于21°C，而这些差异在12窝幼仔中更为明显。这些结果表明PL和HDL可以同时运行，但HDL假设在较热的温度下可能更有效。我们的结果表明，未来气候中环境温度的升高可能会通过散热限制来限制生殖输出。