POPULATION GENETICS OF THE CALIFORNIA HORN SHARK (HETERODONTUS FRANCISCI)

Abstract

Sharks (superorder Selachimorpha) display a wide range of dispersal capabilities, with some species undertaking migrations that span ocean basins, and others undertaking comparatively short migrations limited to coastal margins. The spatial scale of population genetic structure among shark taxa is similarly variable, with some oceanic species showing little to no structure on a global scale, and other, more coastal species displaying structure over distances on the order of 150 km. The identification of discrete populations is critical to the development and implementation of conservation measures, allowing managers to determine appropriate spatial scales for management initiatives, identify populations in need of special protection, and maximize the genetic diversity and adaptive potential of a species. Additionally, understanding the mechanisms underlying population structure can shed light on evolutionary processes that generate and maintain biodiversity in the marine environment. To date, population genetic studies in sharks have focused on large-bodied, highly mobile species, while smaller, coastal species with limited dispersal have received little attention. Here, I utilized multiple genetic techniques to assess population genetic structure of the California horn shark (Heterodontus francisci), a small, benthic species inhabiting shallow coastal habitat from California, U.S.A. to the Gulf of California, Mexico. First, I present a Restriction Fragment Length Polymorphism (RFLP) method to quickly and cheaply distinguish between the three species of Heterodontus occupying eastern Pacific shorelines (Chapter 2). Then, I present analyses of population genetic structure across the range of H. francisci using the mitochondrial control region (mtCR; Chapter 3) and 9,063 neutral SNP loci (Chapter 4). Analyses of the mtCR and neutral SNP datasets both support the role of deep-water channels as barriers to dispersal among island and mainland populations over unprecedented small spatial scales. Analysis of SNP loci revealed a population break between northern and southern Channel Islands that was not detected with the mtCR, supporting the assumption of greater resolution with SNP technology. The published suggestion that a cryptic evolutionary lineage exists within the East Pacific was not supported by any of the three genetic approaches. These analyses indicate that barriers limiting the dispersal of demersal elasmobranchs can exist at spatial scales much smaller than previously detected, highlighting a need for further research on this understudied component of shark biodiversity.