Data from: The effect of brain size evolution on feeding propensity, digestive efficiency and juvenile growth

One key hypothesis in the study of brain size evolution is the expensive tissue hypothesis; the idea that increased investment into the brain should be compensated by decreased investment into other costly organs, for instance the gut. While the hypothesis is supported by both comparative and experimental evidence, little is known about the potential changes in energetic requirements or digestive traits following such evolutionary shifts in brain and gut size. Organisms may meet the greater metabolic requirements of larger brains despite smaller guts via increased food intake or better digestion. But increased investment in the brain may also hamper somatic growth. To test these hypotheses we here used guppy (Poecilia reticulata) brain size selection lines with a pronounced negative association between brain and gut size and investigated feeding propensity, digestive efficiency, and juvenile growth rate. We did not find any difference in feeding propensity or digestive efficiency between large- and small-brained individuals. Instead, we found that large-brained females had slower growth during the first ten weeks after birth. Our study provides experimental support that investment into larger brains at the expense of gut tissue carries costs that are not necessarily compensated by a more efficient digestive system.

脑尺寸进化研究中的一项核心假说为昂贵组织假说（expensive tissue hypothesis）：即对大脑的投入增加，应当通过减少对其他耗能器官（例如肠道）的投入来获得补偿。尽管该假说得到了比较研究与实验证据的双重支持，但目前人们对脑与肠道尺寸发生此类进化转变后，能量需求或消化特征的潜在变化仍知之甚少。尽管肠道体积更小，生物体仍可通过增加食物摄取量或提升消化能力，来满足更大大脑的更高代谢需求。但对大脑的投入增加，也可能阻碍躯体生长。为验证这些假说，本研究选用了脑尺寸与肠道尺寸呈现显著负相关的孔雀鱼（Poecilia reticulata）脑尺寸选择品系，对其摄食倾向、消化效率以及幼体生长速率进行了研究。研究未发现大脑尺寸较大与较小的个体在摄食倾向或消化效率上存在任何差异。相反，我们发现大脑尺寸较大的雌性个体在出生后的前10周生长速度更慢。本研究通过实验证实：以肠道组织为代价加大对大脑的投入，其代价未必能通过更高效的消化系统得到弥补。