Mapping of Genetic Regions for Head Size in Catfish: The Involved GTPase Pathway Is Evolutionarily Conserved for Skull Morphometric Traits

Skull morphology is fundamental to biological adaptation of species to its environments. With aquaculture fish species, head size is also important for economic reasons because of its direct impact on fillet yield. For instance, channel catfish generally have a larger head than blue catfish, and hybrid catfish provide a greater percentage of fillet yield than channel catfish. However, little is known about the underlying genetic basis. In this study, we performed a genome-wide association study using the catfish 250k SNP array with backcross hybrid catfish to identify the QTLs for head size. Several QTLs were identified, including one significantly associated region on linkage group (LG) 9 and four suggestively associated regions on LGs 7, 16, 28 for head length, five significantly associated regions on LGs 5, 7, 9, 29 and two suggestively associated regions on LGs 7, 27 for head width, and one suggestively associated region on LG 26 for head depth. Two of the QTLs on LG 7 were associated with both head length and head width. Phenotypic variance explained by the associated SNPs for head length, head width, and head depth were 0.16, 0.18, and 0.02 from the associated regions respectively. It is notable that each of these associated regions is rich of small GTPase related genes. Comparative analysis indicated that small GTPase pathway genes are also involved in skull morphology in various other species ranging from amphibian to mammalian species, suggesting evolutionary conservation of small GTPase pathway in the control of skull morphologies.