Date of Award

2017

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

First Advisor

Jacqueline F. Webb

Abstract

The lateral line (LL) system is a key non-visual sensory modality founded in all fishes and larval and adult aquatic amphibians. In bony fishes, the LL system consists of series of superficial neuromasts (on the skin surface) and canal neuromasts (housed in bony canals). Differences in LL canal phenotype have consequences for LL sensory capabilities, and, as such, could contribute to speciation. The LL system develops with a process of neuromast patterning followed by the genesis of canals from dermal bone around a subset of neuromasts. This study used histochemical methods to describe canal morphogenesis by assessing osteoblast (OB, bone building cells) and osteoclast (OC, bone resorbing cells) activity through ontogeny. OB and OC activity was studied along the length and around the circumference of the mandibular LL canal in two species of Lake Malawi cichlids. Aulonocara stuartgranti (widened canals) and Tramitichromis sp. (narrow canals) are known to develop their different canal phenotypes as a result of dissociated heterochrony. In both species, OB activity is concentrated in the canal roof and floor (behind the neuromast), while OC activity is focused primarily in the canal walls. Further, both species demonstrate one pulse of bone deposition early in ontogeny and another pulse of bone resorption later in ontogeny, but in Aulonocara not Tramitichromis, the pulse of bone resorption is accompanied by high levels of OB activity. Thus, the second pulse of bone cell activity in Aulonocara is defined by bone resorption and bone deposition: active bone remodeling by the simultaneous action of OBs and OCs. These results corroborate the observation of dissociated heterochrony (Bird and Webb, 2014) at the cell level, suggesting that the nature of neuromast-centered canal morphogenesis may differ depending on LL canal phenotypes.

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