Within species support for the expensive tissue hypothesis: a negative association between brain size and visceral fat storage in females of the Pacific seaweed pipefish

The brain is one of the most energetically expensive organs in the vertebrate body. Consequently, the high cost of brain development and maintenance is predicted to constrain adaptive brain size evolution (the expensive tissue hypothesis, ETH). Here, we test the ETH in a teleost fish with predominant female mating competition (reversed sex roles) and male pregnancy, the pacific seaweed pipefish Syngnathus schlegeli. The relative size of the brain and other energetically expensive organs (kidney, liver, heart, gut, visceral fat, and ovary/testis) was compared among three groups: pregnant males, nonpregnant males and egg producing females. Brood size in pregnant males was unrelated to brain size or the size of any other organ, whereas positive relationships were found between ovary size, kidney size, and liver size in females. Moreover, we found that the size of energetically expensive organs (brain, heart, gut, kidney, and liver) as well as the amount of visceral fat did not differ betwe...大脑是脊椎动物体内能量消耗最高的器官之一。据此，大脑发育与维持的高能耗被认为会限制适应性脑容量演化（昂贵组织假说（expensive tissue hypothesis, ETH））。本研究以雌性主导交配竞争（性别角色反转）且雄性怀孕的硬骨鱼——太平洋海藻海龙（Syngnathus schlegeli）为研究对象，对该假说进行检验。本研究比较了三组个体的脑及其他高能耗器官（肾脏、肝脏、心脏、肠道、内脏脂肪以及卵巢/精巢）的相对大小：怀孕雄性、非怀孕雄性与产卵雌性。结果显示，怀孕雄性的育幼幼崽数量与脑容量及其他任一器官的大小均无关联，而雌性的卵巢大小、肾脏大小与肝脏大小之间存在正相关关系。此外，本研究发现，高能耗器官（大脑、心脏、肠道、肾脏与肝脏）的大小以及内脏脂肪含量在...之间并无显著差异。