Numerous groups of insects and other organisms colonizing islands of the Pacific have undergone radical and unexpected shifts in habitat use, often associated with adaptive radiation. An example of this pattern is found within a genus of sap-feeding planthoppers in the genus Nesosydne (Hemiptera: Delphacidae), one of the largest genera in a widespread planthopper family. What is striking about the Pacific Nesosydne is that their current host plant associations are not representative of those for continental species in the family. In continental regions species within the Delphacidae feed primarily on monocots, especially grasses and sedges. Like these other delphacids, individual species in the Pacific are largely host-specialists feeding on, and associated with, a single plant species. However in the Pacific, different planthopper species feed on different plant species, representing a broad diversity of plant families. In the Hawaiian Archipelago for example, hosts of Nesosydne species total 28 plant families, mostly dicots. Remarkably, this pattern is repeated (although to a lesser extent) within several other isolated archipelagoes, including the Marquesas, Societies, and Australs. Based on morphological work, Fennah (1958), and more recently Asche (1997), have hypothesized a handful of independent colonization events on each archipelago, followed by in situ speciation. The genus is likely polyphyletic. Here, these hypotheses are re-evaluated using DNA sequence data from mitochondrial and nuclear loci. Results to date indicate that at least some lineages within the genus have diversified in association with particular plant groups. Colonization of different islands, however, is often associated with marked changes in plant hosts. These results support the earlier suggestion by Gagne (republished in 1997) that diverse, yet specialized, species on Pacific islands can arise from specialized colonists.
Species 1: Hemiptera Delphacidae Nesosydne
Keywords: colonization, phylogeography
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