Biogeographic insights on Pacific Coprosma (Rubiaceae) indicate two colonizations to the Hawaiian Islands

摘要

Most archipelagos of the Pacific Ocean, including the Hawaiian Islands, are volcanic in origin and were never connected to continental land masses. The derivation of the Hawaiian flora is entirely the result of long-distance dispersal and in situ speciation from various source areas, including the Americas, Asia and islands of Oceania. To assess the origins of Hawaiian Coprosma (Rubiaceae), one of the largest and most widely distributed genera across the Pacific, molecular phylogenetic analyses were performed utilizing sequences from internal and external transcribed spacer regions (ITS and ETS) of nuclear ribosomal DNA and the rps16 plastid DNA intron, from which phylogeographic patterns within the genus were assessed. Our analyses suggest two independent colonization events of Coprosma to the Hawaiian Islands. Twelve of the 13 Hawaiian Coprosma spp. form a monophyletic group and are closely related to species from the Marquesas Islands and one species from the Austral Islands. Coprosma ernodeoides represents a separate colonization of the Hawaiian Islands from an uncertain origin, but is closely associated to C. atropurpurea of New Zealand and C. pumila of Tasmania. Similar to the Hawaiian Islands, the pattern of multiple independent colonization events to a single Pacific locality was also found for six South Pacific localities and for Australia. Understanding the origins of Hawaiian Coprosma adds a new pattern of plant dispersal to our understanding of Pacific biogeography, particularly in reference to multiple independent colonizations to single insular localities