FIGURE 1: African cichlids from Lake Malawi display differences in foraging anatomy. (A) Tropheops sp . “red cheek” (TRC) has a more downturned oral jaw apparatus, and a steeply sloping craniofacial profile, adapted for benthic foraging via scraping/biting/nipping. (B) A schematic of the opercle 4-bar linkage chain, which is critical for lower jaw depression, is shown for TRC. (C) Maylandia zebra (MZ) is characterized by a more upturned oral jaw, better suited for pelagic feeding via fast jaw rotation. (D) A schematic of the opercle 4-bar linkage chain is shown for MZ. Relative to TRC, MZ possesses a longer coupler link (CL) and shorter output link (OL). (A, C) Images courtesy of Ad Koning at Cichlid Press. (B, D) Red bars indicate movable linkages - input link (IL), CL, and OL - while the black bar represents the fixed link. Blue depicts the interopercle (IOP) bone, and green shows the retroarticular process (RA) of the lower jaw, while orange is the interopercle-mandibular (ioml) ligament that connects the two bones. Throughout the text we refer to this as the IOP-RA functional complex. (E) Experimental schematic in which we fed cichlids either flake or rock food for 17 days (RNA-seq) or 28 days (ATAC-seq), with a 1 week training period. Inset shows an external view of the IOP-RA complex dissected for all experiments.