Abstract

Innovations may provide access to new resources but often result in significant trade-offs. Pharyngognathy is a classic pharyngeal jaw innovation in which the left and right lower pharyngeal jaw (LPJ) bones are united into a single structure, producing a strong bite but reduced gape. Throughout cichlids, pharyngeal suturing occurs along the entire medial border between LPJ bones, except in peacock bass (Cichla), where these bones are connected by ligaments only in their anterior region. We show that this limited attachment permits the jaw bones to spread apart and we link this feature to an increase in pharyngeal gape that is comparable to non-pharyngognathous species. The capacity of the LPJ bones to spread apart is strongest in juveniles and is mostly lost during development. Juvenile Cichla exhibit size-specific pharyngeal gape similar to non-pharyngognathous percomorphs; however, adults exhibit pharyngeal gape on par with other predatory cichlids. Relaxation of pharyngeal suturing offsets a major deleterious consequence of pharyngognathy by reducing gape limitation and we propose this may accelerate the ontogenetic transition to piscivory. Partial reversal of the classic cichlid pharyngeal jaw innovation highlights the functional trade-offs that often accompany innovations and may be a major cause of variation in their macroevolutionary consequences.

中文翻译：

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孔雀鲈（Cichla）的功能新颖性减轻了经典的丽鱼科鱼咽下颌创新所施加的约束

摘要

创新可能提供获取新资源的途径，但往往会导致重大的取舍。咽颌是一项经典的咽颌创新技术，其中，左右下咽颌（LPJ）骨头结合成一个单一的结构，咬合力强，但间隙减小。在整个丽鱼科鱼中，咽部缝合沿LPJ骨头之间的整个内侧边界进行，除了孔雀鲈（Cichla）中，这些骨头仅通过韧带在其前部区域相连。我们显示出这种有限的附着力使颚骨散开，并且我们将此功能链接到与非咽类相当的咽间隙增加。LPJ骨骼散开的能力在少年中最强，并且在发育过程中大部分丧失。少年慈鲷表现出特定大小的咽间隙，类似于非咽类蠕变体；然而，成年人表现出的咽间隙与其他掠食性丽鱼科鱼类相当。咽部缝合的松弛通过减少间隙限制而抵消了咽咽部的主要有害后果，我们建议这可能会加快从个体发育到食肉动物的过渡。经典的丽鱼科鱼咽颌创新的部分逆转凸显了通常伴随创新的功能折衷，并且可能是其宏观进化结果变化的主要原因。