Data from: Head shape modulates diversification of a classic cichlid pharyngeal jaw innovation

Functional innovations are often invoked to explain the uneven
distribution of ecological diversity. Innovations may provide access to
new adaptive zones by expanding available ecological opportunities and may
serve as catalysts of adaptive radiation. However, diversity is often
unevenly distributed within clades that share a key innovation,
highlighting the possibility that the impact of the innovation is mediated
by other traits. Pharyngognathy is a widely recognized innovation of the
pharyngeal jaws that enhances the ability to process hard and tough prey
in several major radiations of fishes, including marine wrasses and
freshwater cichlids. We explored diversification of lower pharyngeal jaw
shape, a key feature of pharyngognathy, and the extent to which it is
influenced by head shape in Neotropical cichlids. While pharyngeal jaw
shape was unaffected by either head length or head depth, its disparity
declined dramatically with increasing head width. Head width also
predicted the rate of pharyngeal jaw evolution such that higher rates were
associated with narrow heads. Wide heads are associated with exploiting
prey that require intense processing by pharyngeal jaws that have expanded
surfaces for the attachment of enlarged muscles. However, we show that a
wide head constrains access to adaptive peaks associated with several
trophic roles. A constraint on the independent evolution of pharyngeal jaw
and head shape may explain the uneven distribution of ecological diversity
within a clade that shares a major functional innovation.

功能创新（functional innovations）常被用于阐释生态多样性的非均匀分布格局。创新可通过拓展可利用的生态机遇，为生物开辟新的适应区（adaptive zones），亦可作为适应辐射（adaptive radiation）的催化剂。然而，携带同一关键创新（key innovation）的进化支（clades）内，多样性往往仍呈现非均匀分布，这提示创新的影响可能受其他性状介导。咽颌型（pharyngognathy）是广受认可的咽颌结构创新，其可提升包括隆头鱼科鱼类（marine wrasses）与淡水慈鲷（freshwater cichlids）在内的多个鱼类大辐射类群处理坚硬、韧性猎物的能力。本研究以新热带区慈鲷（Neotropical cichlids）为对象，探究了作为咽颌型核心特征的下咽颌形态（lower pharyngeal jaw shape）的演化分异，以及头部形态对其的影响程度。研究结果显示，尽管下咽颌形态不受头长或头深的影响，但随着头部宽度增加，其形态差异度（disparity）显著降低。头部宽度同样可预测下咽颌的演化速率：头部越窄，下咽颌的演化速率越高。宽头部类群通常会利用需要咽颌通过扩大的肌肉附着面进行高强度处理的猎物。但本研究表明，宽头部会限制类群进入与多种营养生态位角色（trophic roles）相关的适应峰（adaptive peaks）。咽颌与头部形态难以独立演化这一演化约束，或可解释共享这一重要功能创新的进化支内生态多样性的非均匀分布格局。