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Reef fish endemism and genetic connectivity: Phylogeography of endemic damselfishes in the Hawaiian Archipelago

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While it was once widely accepted that there is plentiful larval dispersal and high levels of connectivity in marine populations, studies detecting self-recruitment and local larval retention in reef fishes have revealed that not all marine organisms demonstrate broad-scale dispersal. Isolated oceanic islands with their abundance of endemic species serve as excellent systems for studying the factors that may be influencing dispersal in marine populations. Furthermore, understanding patterns of dispersal in endemic species is relevant to conservation and management efforts that seek to protect these unique and vulnerable species. This dissertation employed molecular techniques to analyze the phylogeography of damselfishes endemic to the Hawaiian Archipelago and to draw conclusions about patterns of connectivity in endemic reef fishes. The endemic damselfishes that have been surveyed throughout the archipelago thus far all exhibit population structure (Chapter 1). This is consistent with the assumption that the low dispersal ability of endemic species results in population structure. However, some Hawaiian endemic reef fishes lack genetic structure in the archipelago, so population structure may be characteristic of endemics only in certain taxonomic families, such as the Pomacentridae. In contrast to their endemic counterparts, widespread damselfishes that have broad distributions across the Indo-Pacific show high levels of connectivity across the Hawaiian Archipelago (Chapter 2). This side-by-side comparison of widespread and endemic damselfishes lends support to a proposed correlation between range size and dispersal ability, at least within the spatial scale of the archipelago. These widespread damselfishes, together with several species of widespread reef fishes that lacked population structure in the Hawaiian Islands, show genetic differentiation across the spatial scale of the Indo-Pacific. Thus, at a larger spatial scale (between archipelagoes), the relationship between range size and dispersal ability is more tenuous. Patterns of connectivity even vary with spatial scale in the endemic damselfish Chromis verater found on shallow and mesophotic reefs in the Hawaiian Archipelago and Johnston Atoll (Chapter 3). The dispersal abilities of Chromis verater do not appear to limit it in terms of vertical connectivity (7-113 m in this study), but there are some restrictions to horizontal connectivity across the Hawaiian Archipelago (2600 km) and between the archipelago and Johnston Atoll (separated by 860 km). Overall, the results from this dissertation lend support to the assumption that the low dispersal ability of endemic species results in less connectivity and more population structure than in widespread species. However, it remains unclear whether this applies to all reef fish families or if it holds true in locations besides the Hawaiian Archipelago. Also, these results illustrate the importance of considering spatial scale and phylogenetic constraint when drawing conclusions about dispersal in reef fishes.

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