Evolutionary Biogeography of Catfishes (Siluriformes, Actinopterygii): The Influence of Habitat and Landscape on Gene Flow and Genetic Diversification

Abstract

A fundamental goal of evolutionary biology is to understand what processes have led to the great diversity of organisms we see today. An important factor of diversification is an organism’s environment. Abiotic factors can shape the evolutionary trajectory of species by affecting fundamental mechanisms of evolution, including mutation, gene flow, genetic drift, and natural selection. In my thesis, I investigated how abiotic factors, such as habitat and landscape, have influenced the genetic diversification of catfishes (Siluriformes). More specifically, I compared genetic data within and between species to understand how natural barriers have shaped the origins and evolutionary trajectory of species. In Chapter 1, I investigated whether habitat preferences and segregation of breeding populations in lacustrine-like and fluvial habitats affected the genetic structure of a sympatric population of channel catfish (Ictalurus punctatus). In Chapter 2, I elucidated the origins of cave species within North American catfishes (Ictaluridae), determining whether they shared a common ancestor or evolved in parallel from surface-dwelling ancestors. In Chapter 3, I tested whether impermeable and semi-permeable boundaries between South American river basins have restricted gene flow and resulted in potentially new species within the widespread ornate pim catfish (Pimelodus ornatus). In Chapter 4, I determined whether orogenesis and river capture corresponded with speciation events and cladogenesis within Neotropical long-whiskered catfishes (Pimelodidae). Throughout my thesis, I observed evolutionary patterns related to gene flow, vicariance, and dispersal. Physical barriers imposed on populations often coincided with genetic diversification and allopatric speciation. These barriers reduced gene flow, allowing populations to genetically diverge in response to unique selective pressures. As these barriers changed over time, dispersal opportunities may have further promoted diversification as species radiated into new areas. I also observed that ecological gradients, such as water chemistry, may have facilitated parapatric speciation; however, differences between habitats do not always restrict gene flow. Given that patterns of genetic diversification and speciation are not uniform across the tree of life, it is important for evolutionary biologists to document trends among different taxa to elucidate macroevolutionary patterns.