| Summary: | This project explores species boundaries, coevolution, biodiversity, parasite life cycles, and ecology using the cestode (tapeworm) fauna parasitizing the spiny dogfish, Squalus acanthias, and several of its close relatives. One of the aims was to verify the species identity of all the shark specimens from which cestodes were collected. Chapter 1 details use of the elasmobranch "barcoding" gene, NADH2, to verify host identifications, as well as to raise doubt about the wisdom of recognizing the Black Sea population of S. acanthias as a distinct subspecies. Chapter 2 examines diversity in the monotypic cestode genus, Trilocularia, throughout the widespread anti-tropical distribution of S. acanthias (i.e., the North and South Pacific, the North Atlantic, and the Black Sea), and in its congeners. An integrative approach, including morphological (i.e., light microscopy, histology, and scanning electron microscopy) and molecular methods (i.e., 28S, ITS1, 16S genes), was employed. Results reveal a large amount of undiscovered diversity in this genus and suggest that species of Trilocularia may be undergoing speciation more rapidly than their hosts. Chapter 3 describes one of the new species discovered, Trilocularia eberti n. sp. from S. cf. mitsukurii, and provides a prototype for future descriptions of species in this genus. Chapter 4 investigates microthrix variation in Trilocularia from the stomach and the spiral intestine of S. acanthias off Rhode Island. Results suggest that variation seen within a host individual is likely due to developmental changes rather than species differences. Chapter 5 aims to further the understanding of cestode infections in a marine environment through space and time by examining seasonal infection parameters in the cestode community of S. acanthias from Rhode Island across three years. While some general trends may be maintained across disparate localities, spatial variation is likely due to differences in accessibility to intermediate hosts and host diet across sites. The knowledge gained from understanding cestode infections in the vast ocean environment allows us to speculate about the factors driving fluctuations in parasite infections in elasmobranchs.
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