| The Solomon Islands is one of the largest and most biologically complex archipelagos in Northern Melanesia. I collected tissues and voucher specimens from widespread bird species found on five island groups, providing the first opportunity to apply molecular methods to this avifauna. Using the mitochondrial markers ND2 and cytochrome b, I constructed a series of intraspecific phylogenies for 23 ecologically and taxonomically diverse (13 families from 5 order) species. Intraspecific comparisons across islands revealed a broad range of genetic differentiation, ranging as high as 4–8% in species such as Ceyx lepidus, and Dicaeum aeneum. For many species, endemic and otherwise, molecular phylogenetic relationships closely match those delineated by morphology. However, for some, notably Monarcha castaneiventris, Monarcha barbatus, and Myzomela lafargei, patterns of molecular differentiation suggest that monophyly is not well supported for some endemic taxa, revealing the limits of morphology in tracking complex evolutionary histories. With intraspecific phylogenies, I applied comparative phylogeographic techniques to evaluate historic processes of diversification for Solomon Island birds. Across taxa, the spatial relationship among islands consistently linked the Pleistocene land-bridge group of Choiseul, Isabel and Guadalcanal. The absence of strong temporal patterns, however, suggests that the arrival times of individual species mitigates the effects of geology and climate. Endemic species analyses and estimates of phylogenetic diversity (PD) identified Guadalcanal, Malaita and New Georgia as islands with the most distinct avifaunas. Specifically, the New Georgia island group is the most phylogeographically distinct area and is home to a disproportionate number of the archipelago's endemic species. Gene flow analysis using data from the mitochondrial control region from samples of Monarcha castaneiventris and Monarcha barbatus indicated no gene flow between the Pleistocene land bridge group (Choiseul, Isabel and Guadalcanal) and New Georgia and Malaita. Furthermore, using a new methodological approach (Mdiv), I could not reject the null hypothesis of zero migration within the land-bridge group, suggesting that even very short water gaps are powerful isolating mechanisms for these two Solomon Island monarch taxa. |
