Meeting Abstract

123.3  Tuesday, Jan. 7 14:00  Hedgehog signaling mediates adaptive variation in a complex functional system in the cichlid skull HU, Y.*; ALBERTSON, R.C.; UMass-Amherst; UMass-Amherst yinan@cns.umass.edu

Adaptive variation in the craniofacial skeleton is a key component of resource specialization and divergence in vertebrates, but the genetic mechanisms that underlie complex patterns of craniofacial variation are largely unknown. In this study we show that pleiotropic effects of the hedgehog pathway receptor Patched1 (ptch1) mediate variation in a complex functional system in Lake Malawi cichlids. The opercular 4-bar linkage apparatus is a well-known anatomical unit that participates in lower jaw depression in teleost fishes. In general terms, species that feed from the water column possess 4-bar systems characterized by high kinematic transmission (KT) and fast jaw movements, whereas species that forage from the benthos possess systems with relatively lower KT and slow but powerful jaw rotation. We demonstrate here that ptch1 influences the development of the retroarticular (RA) process and the interopercle (IOP) bone, which in turn alters three out of the four links in the opercular 4-bar system. Specifically, the evolutionarily derived ptch1 allele is associated with the development of a shorter RA and relatively narrower, longer IOP. In functional terms, these shifts in anatomy translate to a 4-bar system with a higher KT (fast and weak). Alternatively, the ancestral allele is associated with the development of a longer RA and relatively wider, shorter IOP that translates to a lower KT (slower and powerful). These results provide the first empirical support for genetic variation at a single locus mediating widespread variation in a complex functional system. Moreover, they offer Hedgehog signaling as a specific link between developmental and functional integration, shedding new light on the mechanisms that promote craniofacial variability in these fishes.