Patterns, causes, and consequences of connectivity within a coral reef fish metapopulation

Abstract

Population connectivity influences virtually all ecological and evolutionary processes within metapopulations including population dynamics, persistence, and divergence. A comprehensive analysis of connectivity must consider the exchange of both individuals and alleles among populations, representing demographic and genetic connectivity, respectively. For many marine species, connectivity is driven by larval dispersal. However, despite the widespread recognition that dispersal is key to predicting metapopulation dynamics and effectively managing networks of marine reserves, empirical data are scarce due to the methodological challenges of tracking larvae. This dissertation is an integrative study of the patterns, causes, and consequences of marine connectivity using the sponge-dwelling reef fish Elacatinus lori as a study system. I begin by describing the distribution and abundance patterns of E. lori and its host sponge on the Belize barrier reef. Next, I study demographic connectivity by using genetic parentage analysis to quantify dispersal. I conduct an intra-population study to identify self-recruiting dispersal trajectories and develop a method to approximate a dispersal kernel based on the distribution of habitat patches. I then complete a large-scale parentage analysis to produce the first statistically-robust marine dispersal kernel. I find that dispersal declines exponentially with respect to distance in E. lori, with no dispersal events exceeding 16.2 km. Notably, dispersal probabilities are unrelated to the number of days an individual spends in the larval phase and other biological variables. Finally, to elucidate the long-term microevolutionary consequences of genetic connectivity, I investigate spatial genetic structure in the Belizean metapopulation. In a preliminary study based on mitochondrial and microsatellite data, I find high levels of pairwise genetic differentiation between sites separated by only 20 km. In a follow-up study, I use a high-throughput multiplex approach to resolve fine-scale patterns of genetic structure throughout the species' range. Seascape genetic analyses reveal that genetic connectivity is consistent with the shape of the dispersal kernel. Collectively, this dissertation generates novel insights regarding the spatial scale at which marine fish populations are connected. Given the alarming rate of population declines on coral reefs globally, these results have important and time-sensitive conservation implications.