Date Awarded

2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Virginia Institute of Marine Science

Advisor

Eric Hilton

Abstract

Although the form and function of the structure of the feeding apparatus and diet are linked in adult fishes, it is often not clear when during ontogeny the ecomorphological patterns enable early life history stage fishes (ELHS) to partition their foraging niches and reduce competition. Sciaenid (family Sciaenidae) species exhibit variability in the structure of the feeding apparatus, which allows them to exploit more foraging habitats as adults than any other family in the Chesapeake Bay. In this study, ELHS and juvenile sciaenids representing three foraging guilds (pelagic: n=92, 2.9-48.2 mm SL; generalist: n=71, 4.3-53.8 mm SL; and benthic: n=75, 1.9-43.2 mm SL) were captured during weekly, shore-based ichthyoplankton and trawl surveys throughout the lower Chesapeake Bay, York River, and tidal inlets on Eastern Shore of Virginia. Stomachs were removed, specimens were cleared and double stained, and elements of the feeding apparatus were measured. A smaller subset of specimens (n=17) were stained using a 1% phosphotungstic acid solution and then scanned using micro-computed tomography to determine sensory modality in ELHS sciaenids representing the same foraging guilds. A dietary shift occurred first in pelagic sciaenids (16 mm SL), which corresponded to an expansion of sensory modalities, particularly gustation and audition that augment vision. The dietary shift was observed next in benthic sciaenids at 20 mm SL, which corresponded to the acquisition of oral and pharyngeal specializations suited to exploiting benthic prey even though they lacked sensory specializations. Finally, generalist sciaenids experienced a dietary shift at 35 mm SL, which occurred after the expansion of sensory modality (particularly vision, olfaction, gustation, and mechanoreception) but before specializations to the feeding apparatus were observed. Phylogenetic signal, measured as Pagel's lambda, was also calculated for oral jaw elements using a molecular and a morphological topology to determine if evolutionary history may constrain the configuration of these elements and to understand how topology may influence the detected phylogenetic signal. Pagel's lambda was low for pelagic sciaenids in premaxilla, lower jaw, and ascending process length, regardless of the topology used in the analysis. The signal was variable for benthic sciaenids depending on the topology used in the analysis; the signal was low when a morphological topology was used but was high for lower jaw and ascending process length when a molecular topology was used. In benthic sciaenids, Pagel's lambda, was intermediate for premaxilla length when the molecular topology was used, suggesting that the length of the premaxilla is influenced by natural selection despite some phylogenetic constraints. Therefore, the morphological patterns detected in ELHS sciaenids are not constrained exclusively by evolutionary history and represent ecomorphological, which suggest that sciaenids are able to partition foraging in nursery habitats during these early stages.

DOI

https://dx.doi.org/doi:10.25773/v5-pry1-hx22

Rights

© The Author

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