Theoretical study of evolution of egg size and early life history of aquatic organisms

一些海洋中上层鱼类的幼虫，如金枪鱼和马林鱼，已经知道有大的颚，但这种独特的形态特征的生态意义在进化生态学中几乎没有分析过。远洋产卵鱼的卵体积小，营养不良，远洋洄游鱼类的产卵和苗圃营养不足。我们推测同类相食可能是幼虫期的一种生活方式，而大嘴巴可能是在少营养的远洋环境中同类相食的一种适应性形态特征。结果表明，公海中上层产卵者的嘴张尺寸明显大于近海/沿海中上层产卵者。一个数学模型表明，同类相食倾向于在公海环境中进化。我们的研究结果表明，在远洋鱼类的幼体阶段存在一种同类相食的进化模式。

Larvae of several ocean pelagic fish species, such as tunas and marlins, have been known to have large jaws, but the ecological significance of this unique morphological character has been hardly analyzed in evolutionary ecology. Pelagic spawners produce small and nutrition-poor ova, and spawning and nursery grounds of the open ocean migratory fishes are oligotrophic. We hypothesize that cannibalism would be a possible life style in the larval period and the large mouth gape would be an adaptive morphological characteristic for a cannibal in the oligotrophic pelagic environment. We showed that mouth gape size of the open ocean pelagic spawners is significantly larger than that of offshore/coastal pelagic spawners. A mathematical model demonstrated that cannibalism would tend to evolve in high sea environment. Our findings suggest an evolutionary pattern of cannibalism trait in the larval stage of pelagic fishes.