Morphogenesis of the Mechanosensory Lateral Line System in an Elasmobranch: Developmental Origins of Structural Diversity in a Vertebrate Sensory System (Funded by the URI College of the Environment and Life Sciences and a Laura and Arthur Colwin Endowed Summer Research Fellowship at the Marine Biological Laboratory, Woods Hole)

The morphology and development of the mechanosensory lateral line (LL) system differs dramatically in the cartilaginous fishes (incl. elasmobranchs) and bony fishes (incl. teleosts), the two clades of jawed vertebrates. The proposed study of the development of the elasmobranch LL system will provide new insights into the evolutionary origins of diversity in the LL system.  We are using embryos of the little skate (Leucoraja erinacea, a model elasmobranch) and both traditional (histological analysis) and state-of-the-art methods in experimental embryology (fate mapping, fluorescent vital staining, immunofluorescence) to answer fundamental questions about elasmobranch LL development: 1) How and when do differentiation of hair cell-based neuromast receptor organs and LL canal morphogenesis occur in elasmobranchs? Are they discrete and sequential processes as in bony fishes?  2) How do cranial LL canals move into their characteristic locations on the expanded pectoral fins in batoid elasmobranchs? This work is being carried out at the MBL (Woods Hole).

This is the first study to address the post-placodal development of the mechanosensory LL in cartilaginous fishes using modern experimental methods; it is also the first study of its development in batoid fishes. In its broadest sense, it will contribute to our understanding of the evolutionary developmental biology of vertebrate sensory systems and how differences in ontogenetic processes may provide sources of both morphological and functional novelty between and within major lineages. The comparative development of the mechanosensory LL system in cartilaginous vs. bony fishes provides a novel framework for understanding how a system originates in the same embryonic tissue, but follows different developmental trajectories resulting in distinct adult morphologies that nevertheless, share common behavioral roles (in this case, the origin in placodes, divergent morphogenetic patterns and ultimately a common role in the detection of low frequency water flows [<200Hz] critical for survival). The dramatic evolution in body form (dorso-ventral flattening, and fusion of enlarged pectoral fins to the head) and the spread of the cranial LL canals onto the wing-like pectoral fins in the little skate, and in all batoid fishes, are of functional and ecological interest because such ontogenetic changes are presumably adaptive for post-embryonic (juvenile and adult) sensory function. From a developmental perspective, the process by which the LL canals move from the head onto the pectoral fins appears to be a rare example of large-scale migration of differentiated tissues/organs during vertebrate embryogenesis.

Publications

Webb. JF & Gillis, JA. (2013). Lateral line morphogenesis in chondrichthyan vs. osteichthyan fishes: new perspectives on an old problem. Integ. Comp. Biol., (Abstract) in press.

Students Trained

S. Insley Haciski (MS student 2007-2010; BS, Dickinson College) “Developmental morphology of the lateral line system in embryonic little skate, Leucoraja erinacea”

Conference Presentations

Webb. JF & Gillis, JA. (2013). Lateral line morphogenesis in chondrichthyan vs. osteichthyan fishes: new perspectives on an old problem. SICB Jan. 2013, San Francisco.