Using Population Genomics to Disentangle the Evolutionary History and Aid Conservation of the Leach’s Storm-Petrel Species Complex (Hydrobates spp.)

Abstract

Despite their ability to overcome most geographic barriers to dispersal and to fly long distances, many seabird species exhibit strong population genetic structure. For this project, I quantify population differentiation within a pelagic seabird, the Leach’s storm-petrel species complex (Hydrobates spp.). This species complex covers a wide geographic range in the northern Atlantic and Pacific, comprising three species (H. leucorhous, H. socorroensis, and H. cheimomnestes) and two subspecies (H. l. leucorhous and H. l. chapmani). Hydrobates socorroensis and H. cheimomnestes both breed on Guadalupe Island in the Pacific, and may have undergone a form of sympatric speciation known as allochronic speciation, or speciation via differences in breeding time. As species classifications for the Leach’s storm-petrel are only based on phenotypic distinctions, further genomic work is needed to elucidate processes driving their diversification. Using double-digest restriction site-associated DNA sequencing of 141 individual Leach’s storm-petrels from 13 breeding populations throughout the species’ ranges, I identify five genetically differentiated groups, although some gene flow may still occur between subspecies and between populations separated by ocean basins. Allochronic sister taxa, H. cheimomnestes and H. socorroensis, are highly differentiated from all other populations, as is a common pattern for populations of other organisms residing on Guadalupe Island. I discovered that the Guadalupe populations first diverged from all other H. leucorhous, and then diverged from one another, supporting allochronic divergence as a viable mode of speciation. I also discovered that H. l. chapmani in the south Pacific genetically diverged from H. l. leucorhous in the north Pacific before Pacific and Atlantic H. l. leucorhous diverged, suggesting either parapatric speciation along a genetic cline, or non-geographic barriers to gene flow between north and south populations. Finally, I found 12 putatively adaptive loci possibly implicated in either local adaptation or conserved selection pressures across populations. Overall, the Leach’s storm-petrel species complex has a complicated evolutionary history, influenced by both geographical and non-geographical barriers to gene flow. My thesis also provides a framework for classifying species versus subspecies, and how these classifications can be used for conservation management.