Meeting Abstract
The perciform group Labroidei (cichlids, labrids, damselfish, and surfperches), have independently evolved pharyngognathy, a highly derived set of upper and lower pharyngeal jaws (U-LPJ). The muscle that retracts the UPJ, the retractor dorsalis (RD), connects the UPJ to the anterior vertebrae and functions to process prey. Cichlids are unique in having developed a ventrally projected pair of processes at the posterior connection between the RD and vertebrae, typically on the third vertebrae. It is not uncommon to find these projections shifted anteriorly, which shortens the RD muscle and has consequences for UPJ performance. Here we characterize the shape and development of the vertebral projections using morphometric and genetic methods. We sought to answer two questions: 1, how functionally integrated is the UPJ musculoskeletal system, and 2, can we take a candidate gene approach to find regions of the genome responsible for vertebral projection development? We µCT scanned 640 individuals from a hybrid cross between two Malawi cichlids and used 3D morphometrics to characterize neurocranium and vertebral shape. We then extracted shape scores from our vertebral data, which reflected projection positioning, and performed quantitative trait loci (QTL) mapping. We found a strong association between the vertebral and neurocranium shapes, suggesting an anterior shift of the projections produces a change to the mechanics of UPJ retraction. We also gain two significant QTL peaks in our map, which reveal a possible role for the SIK pathway in regulating the development of these projections. Taken together, this suggests a small developmental change in the pathway regulating projection positioning can produce large-scale changes the mechanics of UPJ performance.
