UC Berkeley

Species-rich coral reef systems present a paradox to evolutionary biologists. Many reef invertebrates and fish have enormous dispersal potential via a planktonic larval stage, presumably leading to widespread patterns of genetic panmixia at large spatial scales. In the context of such high connectivity, how can we begin to get diversification? In this dissertation, I examine this question in two different systems, Caribbean corals and Indo-Pacific parrotfishes, and in two dimensions - time and space. The timing and tempo of species diversification can tell us how geological and environmental change is correlated to species formation. At the same time, the spatial distribution of genetic variation can reveal how contemporary processes may have contributed to population splitting and eventually speciation.

In Chapter 1, I examine the history of reef systems in the Caribbean basin by looking at macroevolutionary patterns in faviid coral. Combining a newly compiled fossil stratigraphy with a time-calibrated molecular phylogeny of extant Caribbean Faviidae, I show that these Caribbean corals are not related to their Mediterranean confamilials, and that all living species appear to have originated during a period of rapid environmental change in Mio-Pliocene. In Chapter 2, I examine cryptic speciation and the patterns of diversity in the parrotfish, Scarus ghobban. Though this species was thought to have a pan-Indo-Pacific distribution, a new mitochondrial phylogeny shows deep divergence between Indian and Pacific Ocean clades. Furthermore, these clades form a species complex with a Panamanian endemic species, Scarus compressus, and a newly described Western Australian endemic species. Finally, in Chapter 3, I use population genetics methods to take a deeper look at the history of these fishes in the Pacific and assess the spatiotemporal structuring of diversity. My results suggest those Pleistocene sea level fluctuations, peripheral isolation, and hybridization all played significant roles in creating and maintaining diversity in this complex.

By assessing taxonomic and population dynamics in the framework of historic environmental processes, I begin to answer fundamental questions about evolution in both Caribbean and Indo-Pacific tropical marine systems. The linking of patterns of diversity over multiple time scales can provide clues about processes that are important to ecology of marine taxa both in the past and in the present. Further, understanding the distribution of basic evolutionary units (e.g. species or ESUs) identifies fundamental units for conservation. With coral reef ecosystems currently highly threatened by anthropogenic change, this knowledge will be essential in future conservation efforts.