Association between integration structure and functional evolution in the opercular four‐bar apparatus of the threespine stickleback, Gasterosteus aculeatus (Pisces: Gasterosteidae)
A boundary between two modules that subdivides the lever apparatus corresponds to the region of most prominent morphological evolution. The matched modular phenotypic and functional architecture of head and jaw structures of stickleback therefore may be important for facilitating their rapid adaptive transitions between highly divergent habitats.