Date of Award

2022

Degree Type

Thesis

Degree Name

Master of Science in Biological and Environmental Sciences (MSBES)

Department

Biological Sciences

First Advisor

Jacqueline Webb

Abstract

Vertebral number and lateral line (LL) scale number are common meristiccharacters used to describe and compare species of bony fishes. These two characters have a spatial relationship originating in embryogenesis, with neuromasts located in register with myomeres, and each LL scale developing in association with a neuromast, resulting in typically one LL scale per vertebra (a 1:1 ratio). However, some fishes are known to have large numbers of lateral line scales, despite having a relatively small number of vertebrae, producing a 2:1 or even a 3:1 ratio. In Chapter 1, variation in this ratio (RLLS:V) is explored for the first time by examining teleosts native to the freshwaters of the eastern United States east of the Mississippi and to the Atlantic coast of the US. Data were gathered on lateral line scale and vertebral number from the literature in order to calculate RLLS:V for 464 species. These patterns raise questions about the developmental origins of variation in RLLS:V, phylogenetic constraints, and the functional and sensory implications of this variation. In Chapter 2, two teleosts, Salvelinus fontinalis (Salmoniformes: Salmonidae) and Menidia menidia (Atheriniformes: Atherinopsidae) were used to compare the ontogeny of the development of the relationship between the number of neuromasts (LL scales) and myomeres (vertebrae). An ontogenetic series of each species was analyzed using fluorescent imaging (4-Di-2-ASP), scanning electron microscopy (SEM), and cleared and stained specimens. The ontogeny of the neuromasts (number, morphology and spatial arrangement) and the ontogeny of the lateral line scales (progression of scale ossification and formation of the trunk canal) were described in both species. Results show that although M. menidia hatches with one neuromast every two to four myomeres along the trunk, by ~10 mm SL or ~10 dph, one neuromast is present per myomere (RLLS:V = 1:1). This series of trunk neuromasts becomes enclosed in the trunk canal as a series of discrete, non-overlapping canal segments. In contrast, S. fontinalis hatches with one neuromast per myomere along the entire length of the trunk and by ~87 dph (175 dpf), two neuromasts are present in association with each myomere, as a result of the addition of small neuromasts alternating with the larger neuromasts already present. All of these neuromasts become enclosed in tubed LL scales so that there are two LL scales per vertebra (RLLS:V = 2:1) forming a continuous trunk canal. These results emphasize the importance of examining the development of the LL system with multiple methodologies to understand the evolution of variation in LL meristics among species.

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