Masters Thesis

How the devil ray got its horns

A central goal of evolutionary-developmental biology is to elucidate the genetic underpinnings of body plan evolution. Batoids (skates and rays) are basal gnathostomes, known for their distinctive disc-like pectoral fins that develop via novel gene expression patterns at the anterior. Devil rays and their charismatic relatives of the family Myliobatidae are batoids with a particularly derived body plan, exhibiting kite-shaped pectoral fins and a unique set of fleshy appendages at the anterior of the body called, "cephalic lobes". Cephalic lobes are used for feeding and are morphologically similar to the anterior pectoral fins of other batoid species. However, the process by which cephalic lobes develop is unknown and their presumed homology with the anterior pectoral fins of other batoids has not been demonstrated at a developmental or molecular level. We therefore examined the morphological and molecular development of the cownose ray, a myliobatid genus that is sister to the devil rays. We found that cephalic lobes unequivocally develop as anterior extensions of the pectoral fins. Using comparative transcriptomics, we found developmental gene expression profiles in cephalic lobes that are indicative of homology with the anterior pectoral fins of skates. Combined, our data provide strong evidence that cephalic lobes are specialized anterior pectoral fin domains rather than independent appendages.

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