My laboratory uses DNA sequences to estimate population parameters, evolutionary relationships, and diversification rates in Hawaiian Insects. Hawaiian ecosystems are especially good models for biodiversity research because they are closed systems that have evolved in isolation over millions of years, creating a natural laboratory for evolutionary studies. Recent human disturbance and global climate change are threatening fragile Hawaiian habitats and driving many species to the brink of extinction. Understanding the conditions required to create biodiversity may yield insights into how species and habitats may be conserved in the future.

My lab asks the question: how did present-day biodiversity evolve? Studying population genetics (estimating migration rates, ancestral population sizes, and other historical factors) in a recently evolved group of Hawaiian Drosophila allows us to directly test hypotheses concerning mechanisms of species formation. Another approach is to infer evolutionary histories of independent insect lineages in the Hawaiian Islands to detect similarities and differences in the tempo and mode of diversification.

Drosophilidae is one of the largest and most intensively studied families of acalyptrate Diptera, and Drosophila, with nearly 2000 described species, is the largest genus in this family. Recent work suggests that this group is not monophyletic (Remsen & O'Grady, 2002). The difficult in inferring relationships within this family is probably because this genus underwent a high rate of diversification 50-60 million years ago, roughly coincident with a great deal of ecological adaptation (fig. 1, after Markow and O'Grady, 2005). The placement and monophyly of another large rapidly evolving group, the Hawaiian Drosophilidae, is also in question. Although all molecular analyses, as well as the combined molecular and morphological analysis, support the monophyly of the Hawaiian Drosophilidae and its placement as sister to the subgenus Drosophila, some morphological studies suggest that these taxa are not closely related.

We are currently using a high throughput approach to generate sequences from about 50 nuclear gene regions, as well as a large portion of the mitochondrial genome, to infer unresolved evolutionary relationships in the family Drosophilidae. These data will be used to test the monophyly of the subgenus Drosophila and examine the placement and monophyly of the Hawaiian Drosophilidae.

With an estimated 1000 species, the endemic Hawaiian Drosophilidae account for approximately one quarter of the world's projected drosophilid diversity (Kaneshiro 1997) and serve as my primary research system. This clade is divided into two major lineages, the Hawaiian Drosophila, all of which are found only in the Hawaiian Archipelago, and the genus Scaptomyza, a group containing both Hawaiian and continental members (Throckmorton 1966). The Hawaiian Drosophila lineage is characterized by spectacular sexually dimorphic modifications of the mouthparts, wings, and/or forelegs (figs. 2, 3). The Hawaiian species have evolved within the past 25 million years on only 0.01% of the earth's land area (DeSalle 1987; Carson 1992). Extreme isolation, as a result of divergent mating behaviors, sexual selection, high host plant specificity, and numerous habitats and microhabitats generated by diverse geographic and climatic patterns present within a small region, is no doubt partially responsible for this diversity (Kaneshiro & Boake 1987). In an effort to better understand the diversity present in Hawai'i, I have begun to systematically revise each of the major species groups in the Hawaiian Drosophila lineage (Hardy et al. 2001; O'Grady et al. 2001, 2003; in press), resulting in over 40 new species descriptions. A synthetic treatment of all Hawaiian Drosophilidae, as well as a revision of the genus Scaptomyza, is currently underway.

The lab is also interested in the sister clade of the Hawaiian Drosophila, the genus Scaptomyza. This genus is a fascinating group that has, at several independent times, dispersed to some of the most remote island systems in the world. Over 70% of Scaptomyza species are single island endemics (Wheeler 1981; 1986). The greatest diversity of Scaptomyza occurs in Hawai'i, where nine subgenera, accounting for over 50% of the species-level diversity in this genus, are endemic. One subgenus, Elmomyza, has undergone a large radiation of nearly ninety described species in Hawai'i (Table 1). Some members of the remaining subgenera, accounting for about 120 known species, have also undergone "mini radiations" on various island systems, including the Tristan da Cunha complex, the Galapagos, and the Bonins.

My lab is taking a population genetic approach to understanding the factors involved in rapid species formation in the Hawaiian Drosophila. Specifically, we are investigating the spoon tarsus subgroup, a clade that has undergone recent diversification on the Big Island. There are eight closely related sympatrically distributed species that are endemic to this island and are believed to have formed in the past 500,000 years. The main goals of this project is to determine whether hybridization and founder effects, two factors that have been implicated in theoretical studies, might play a role in rapid diversification within this lineage. We are using a combination of nuclear and mitochondrial DNA sequences and rapidly evolving microsatellite markers investigate this group.

The Hawaiian Drosophila are a textbook example of adaptive radiation. For example, the progression rule predicts that more basally branching species will be found on older islands (Fig.4, after Bonacum et al., 2005). My lab is currently comparing the pattern, time and rates of colonization and diversification in other groups of Hawaiian Diptera to those known from Hawaiian Drosophila. This work will not only give up a better understanding of the patterns and processes leading to adaptive radiation in Hawaii (e.g., Fig. 5), but will also teach us about rapid species formation on other island systems. We have recently initiated phylogenetic projects on the Calliphoridae (Dyscritomyia), Dolichopodidae (Campsicnemus, with Neal Evenhuis), Limoniidae (Dicranomyia), and Muscidae (Lispocephala). In addition to the work in Hawaiian Diptera, Gordon Bennett's Ph.D. research focuses on Nesosophryne leaf hoppers.

Transposable elements (TEs) are major components of eukaryotic genomes, sometimes accounting for nearly 20% of the genome, and can give insight into how the genomic architecture might be evolving. The 13 fully sequenced Drosophila genomes offer a unique opportunity to characterize TE diversity, distribution, and abundance. Our lab has recently begun to investigate the transposons found in Drosophila grimshawi and it's relatives. Please check the AAA wiki for updates on Drosophila TE annotation.