In addition, deciphering the genetic basis of craniofacial variation represents an important clinical objective, as many human craniofacial disorders are caused by genetic mutations that disrupt morphogenesis and result in phenotypes that fall outside of the spectrum of normal variation ( Trainor 2010 Twigg and Wilkie 2015). Identifying the genetic programs that underlie variation in the form and function of the craniofacial complex is a longstanding goal with implications in diverse biological fields, including evolutionary biology, ecology, embryology, molecular biology, and genetics. Throughout vertebrate evolution, dramatic diversification of craniofacial morphology has accompanied successful occupation of diverse ecological and dietary niches. The vertebrate skull serves essential roles in numerous biological processes, including respiration, feeding, communication, and protecting the brain and sense organs. We find that in domestic pigeons, a complex blend of both independent and coupled genetic effects underlie three-dimensional craniofacial morphology. Some of these loci control coordinated changes between different structures, while others explain variation in the size and shape of specific skull and jaw regions.
Using a combination of genome-wide quantitative trait locus scans and multi-locus modeling, we identified a set of genetic loci associated with complex shape variation in the craniofacial skeleton, including beak curvature, braincase shape, and mandible shape. We used traditional and geometric morphometrics to quantify craniofacial variation in an F 2 laboratory cross derived from the straight-beaked Pomeranian Pouter and curved-beak Scandaroon pigeon breeds. The domestic pigeon ( Columba livia) provides an exceptional opportunity to study the genetic underpinnings of craniofacial variation because of its unique balance of experimental accessibility and extraordinary phenotypic diversity within a single species. One of the most stunning examples of craniofacial diversification is the adaptive radiation of birds, in which the beak serves essential roles in virtually every aspect of their life histories. Deciphering the genetic basis of vertebrate craniofacial variation is a longstanding biological problem with broad implications in evolution, development, and human pathology.
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