Data from: Constraint and opportunity: the genetic basis and evolution of modularity in the cichlid mandible

Modular variation, whereby the relative degree of connectivity varies within a system, is sometimes thought to evolve through natural selection. In this way, modularity may facilitate evolution. Alternatively, conserved patterns of modularity may act to constrain evolution by preventing certain functions from evolving. A comprehensive understanding of the interplay between these phenomena will require knowledge of both the inheritance and genetic basis of modularity. Here we explore these ideas in the cichlid mandible by investigating modularity at the genus, species, and through a new approach, the individual level. Specifically, we assessed patterns of covariation in Lake Malawi cichlid species that employ alternate 'biting' and 'suction-feeding' modes of feeding, and in a hybrid cross between these two ecotypes. Across the suction-feeding genus, patterns of modularity were conserved and reflected function. In contrast, the 'biting' species displayed a pattern of modularity that closely matched developmental modules. The modularity pattern present in our F2 population was similar to the pattern exhibited by our biter, suggesting a role for dominance. We also demonstrated that our individual-level metrics of modularity (IMM) were a valid quantitative traits and used them to map modularity QTL. In all, our findings suggest that modularity is both a constraining and evolvable force in cichlid evolution, with distinct patterns between species and variation among individuals.