Multiple colonizations of a remote oceanic archipelago by one species: how common is long-distance dispersal?

Aim It is well established that many groups of plants and animals have undergone long-distance dispersal, but the extent to which this continues beyond initial colonization is largely unknown. To provide further insight into the frequency of gene flow mediated by long-distance dispersal, we investigated the origins of the fern Asplenium hookerianum on the Chatham Islands, and present a review of the contribution of molecular data to elucidating the origins of this archipelago's biota. Location Chatham Islands and New Zealand. A. hookerianum is scarce on the Chatham Islands but common in New Zealand, some 800 km to the west. Methods We compared chloroplast trnL-trnF DNA sequence data from Chatham Islands'A. hookerianum with extensive phylogeographic data for this genetically variable species in mainland New Zealand. Results Our sequencing revealed the presence of two haplotypes in Chatham Islands'A. hookerianum. These haplotypes differed by four mutational events and were each more closely related to haplotypes found in New Zealand than to each other. Main conclusions Despite the rarity of A. hookerianum on the Chatham Islands, its populations there appear to derive from at least two long-distance dispersal events from New Zealand, these possibly originating from different areas. We suggest that long-distance transoceanic dispersal, and the gene flow it can mediate, may be more common than is generally appreciated.