Meeting Abstract
When two functions use many of the same structures, they are considered to be “coupled,” and this coupling is known to constrain morphological evolution. This constraint can be lessened by the introduction of modularity, defined as the presence of structural units, or modules, that work together to perform a function but are not phenotypically co-evolving. In ray-finned fishes, suction feeding and gill ventilation use many of the same skeletal components. Suction feeding involves rapid expansion of the buccal chamber through the coordination of many structures that have a high degree of evolutionary integration (correlation of changes in size across phylogeny). Gill ventilation involves cyclical expansion of the buccal and gill chambers, using many structures involved with suction feeding. We quanitified evolutionary integration among structures of the buccal and gill chambers across sculpins and relatives (Cottoidei), a diverse clade of suction feeders. We reconstructed the phylogeny using molecular data from 106 cottoids and analyzed linear measurements of cranial bones from a subset of 23 taxa. Using phylogenetic generalized least squares models, we found that suction-feeding associated characters (size of lower jaw, upper jaw, and operculum) are highly correlated. However, there is weak correlation among branchiostegal size and these structures. Particularly surprising is the lack of correlation between the operculum and branchiostegals, the two actuators of the gill chamber. The branchiostegal apparatus may be a module within the gill ventilatory system that releases some constraint imposed by the close coupling of feeding and ventilation.
