Collaborative research: ENSO-enhanced gene flow across the Eastern Pacific Barrier

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Coral reefs constitute the world's most-species-rich marine ecosystems, but anthropogenic changes threaten their health and jeopardize economies that depend on them. Populations of corals living in the eastern Pacific Ocean are especially precarious, as they inhabit a region where environmental conditions already dictate a marginal existence and they are isolated from other Pacific reef corals by 5000-8000 km of uninhabitable deep water (the Eastern Pacific Barrier, EPB). Managing these corals requires knowledge of which populations share common evolutionary histories and how dispersal presently links populations. This information has gone lacking because 1) the mitochondrial DNA markers often used to infer population relationships have proven invariant within coral species and thus uninformative, and 2) genetic analyses based on allele frequency data estimate migration averaged over thousands of generations, which may not reflect present patterns of population connectivity. Recent increases in the intensity of El-Nino Southern Oscillation (ENSO) events may have altered patterns of inter-population dispersal over the last few generations. Such ENSO events halve the eastward transport time of propagules traveling from luxuriant central Pacific coral reefs to the eastern Pacific. This project will employ a combination of genetic techniques to determine 1) when populations of corals in the eastern Pacific diverged from those in the central Pacific, 2) how present-day coral populations in these regions are linked by dispersal, and 3) whether recent changes in currents caused by ENSO events have altered these patterns of exchange. Critical to the success of the work will be the application of new genetic analyses designed to recognize groups of populations that have been isolated only very recently (20 generations) and can reveal past changes in population sizes. The work will focus on a major Pacific reef builder, Porites lobata. Samples of about 40 individuals will be made from each of 12 localities spanning the EPB. Alternative hypotheses for divergence times will be evaluated by comparing the distribution of monophyletic and paraphyletic gene genealogies to modeled expectations and by using coalescent analyses. Nuclear gene sequences from 15 single copy loci (obtained from random sampling of cDNA libraries) will be used for this purpose. Microsatellite loci (12-15 per species) will provide multi-locus genotypes for input into model-based clustering and assignment programs. These genetic analyses will provide a picture of how migration presently connects central and eastern Pacific corals and whether and how changes in ENSO events have altered these patterns. The genetic data to be gathered here will provide critical information for managing a natural resource upon which many people depend. The proposed research will provide training opportunities to undergraduate and graduate students at an institution that serves a region with a large minority population.