Meeting Abstract
Cichlid fishes exhibit functional decoupling between their oral and pharyngeal jaws allowing independent control of prey capture and processing. By decoupling different structures in the feeding system, it has been proposed that each can evolve independently as separate modules. However, patterns of genetic modularity in the cichlid skull exhibit a trend whereby elements of the upper and lower jaws are under distinct genetic control, and the lower jaw (LJ) shares a common genetic basis with the pharyngeal jaw (PJ). Thus, it remains unclear how modules in the feeding system are patterned and evolve. Here we investigate the degree of evolutionary decoupling among five major components of the cichlid feeding system: premaxilla (PMX), maxilla (MX), LJ, PJ, and the interopercle (IOP) bone. We use Malawi cichlids, and focus on the Tropheops species complex given their wide trophic diversity. We hypothesized that the PMX and MX would form separate modules to the LJ, and that the LJ would form a module with the IOP and PJ, a pattern that closely matches the genetic data. We used 3D geometric morphometrics to quantify shape of the feeding system. We then constructed a phylogenetic tree of 165 individuals based on 7593 amplified fragment length polymorphism loci and used phylogenetic regression to test for correlations among feeding structures. We find that the strongest correlations were among shape variables that define depth of the different structures. We also find strong support for correlated evolution between the LJ, IOP and PJ, and not between elements of the upper and lower jaw. Taken together, our data suggests that genetic modularity has a strong influence on patterns of evolution, and that key components of the oral and pharyngeal jaws are coupled at the phylogenetic level.
