Physiol Biochem Zool. 2020 Jul/Aug;93(4):282-295. doi: 10.1086/709538.
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 () 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.
能量供应和输出的限制被认为对许多形态和行为特征的进化有深远的影响。有人认为，哺乳动物的繁殖性能经常受到内在生理因素的限制，例如乳腺产奶的能力（外周限制[PL]假说）或身体散热的能力（散热限制[HDL]假说）。然而，对各种小型哺乳动物的研究迄今为止还没有明确支持其中一种假说。我们在环境温度为 21°C 和 30°C 下，通过人为控制两个（从自然窝仔数中取出三到四只幼崽）、五个、八个（向自然窝仔数中添加两到三只幼崽）和 12 个（向自然窝仔数中添加五到七只幼崽）幼崽的窝仔数，测试了雌性条纹仓鼠（）中的 PL 和 HDL 假说。在整个哺乳期测量了母亲的能量摄入和产奶量、窝仔数和窝仔质量。还测量了几个表明消化酶活性和与食物摄入有关的下丘脑神经肽基因表达的标志物。随着窝仔数的增加，食物消耗和产奶量增加，但在 12 只幼崽时达到上限，导致 12 只幼崽的窝仔质量和幼崽体重明显低于窝仔数较少的窝仔。30°C 时的窝仔质量和母体代谢率、产奶量、麦芽糖酶、蔗糖酶和肠内氨基肽酶活性以及下丘脑食欲肽的基因表达均明显低于 21°C，而在 12 只幼崽时，这些差异更为显著。这些结果表明，PL 和 HDL 可以同时起作用，但在较高温度下，HDL 假说可能更为有效。我们的研究结果表明，未来气候中环境温度的升高可能会通过散热限制来限制繁殖产量。
