Developmental determination of fish jaw protrusion mechanics

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This project is targeted at understanding the developmental underpinnings of evolutionary success. Experiments will be carried out to determine how changes in skull development alter one of the most useful biomechanical abilities to ever evolve: Jaw protrusion. One third of living vertebrates belong to two fish lineages that independently evolved the ability to project their upper jaws forward from the face during feeding. These two lineages have remarkably similar protrusion mechanisms and in both cases small changes in upper jaw shape dramatically alter protrusion distance. Fishes with extensive protrusion occupy different ecological niches than those that have limited protrusion due to specialization on different food types. Jaw protrusion does not appear until late development, usually after a pronounced metamorphosis. Thyroid hormone signaling is a major regulator of both metamorphosis and bone formation. Preliminary data demonstrate that changes in thyroid hormone levels can have pronounced effects on the development of protrusion ability. Very little is known about the controls of cranial formation during late development, yet it is during this period that most organisms begin to remodel their bodies in ways that allow them to occupy their adult ecological niches. This project has the potential to illuminate a developmental period of extreme evolutionary significance that has not yet received much investigative attention. This research is being performed in collaboration with a high-school biology teacher-scientist. Aspects of the work are being incorporated in to all units of their biology course and students are performing a study of fish skull development in the classroomFish jaw protrusion during feeding is linked to extraordinary evolutionary success. This study will further integrate the fields of evolutionary functional morphology and developmental biology by investigating the late-developmental controls of skull morphogenesis. A great deal is known about the evolution of skull mechanics, but most studies have examined adult specimens. There is also a large literature on skull development, but most studies have examined early life stages. Adult cranial mechanics arise during juvenile to adult transitions in late development, so understanding the developmental factors that have shaped skull evolution requires study of this time period. Preliminary data indicate that juvenile diet and thyroid hormone signaling are important determinants of protrusion ability via their affects on the formation of the premaxillary bone. Premaxilla shape determines maximum protrusion ability. This project will investigate the developmental determinants of premaxilla shape variation in order to better understand the evolvability of jaw protrusion. Research will examine the developmental controls of jaw protrusion in the zebrafish and two closely related species with different protrusion abilities. This project has the following aims: 1) to determine if thyroid hormone production affects the development of zebrafish jaw protrusion; 2) to determine if feeding on biomechanically different diets affects protrusion development in the zebrafish and two closely related species; 3) to determine if altered thyroid hormone production affects mRNA expression levels in developing zebrafish jaws; and 4) to identify genetic loci associated with jaw protrusion ability.