Biogeography of spiders on remote oceanic islands of the Pacific: archipelagoes as stepping stones?

Aim The composition of species in any given island community may directly reflect the processes of immigration such that species on a more remote island comprise a nested subset of those on the nearest less remote land mass. Alternatively, new species can arise on islands by less frequent colonization but subsequent evolutionary differentiation. In the current study the species composition of spiders is examined in native communities on three remote oceanic archipelagoes to test hypotheses concerning the relative importance for species accumulation of (i) immigration from the nearest land mass, vs. (ii) in situ speciation. Location The study focuses on three volcanic hot‐spot archipelagoes in the Pacific: the Hawaiian, Marquesas and Society Islands. Methods Tetragnatha spiders were collected from the three remote Pacific archipelagoes as well as Australasia and America. Sequences of mitochondrial DNA (Cytochrome Oxidase I and 16S ribosomal DNA) were obtained from the spiders and a phylogenetic approach was used to examine relatedness among island endemic lineages of spiders, as well as associations between species on different archipelagoes with continental congeners. Results Within archipelagoes, species groups are largely monophyletic. When species groups are compared between archipelagoes, those on one archipelago are never the sister group to those on another archipelago. Rather, each archipelago has a mainland congener as its closest sister group. Main conclusions First, colonization of the Hawaiian, Marquesas and Society archipelagoes by Tetragnatha spiders appears to have occurred independently, most likely in each case from a continental source, but not from the nearest archipelago. Secondly, in situ speciation has occurred in the Marquesas and Society Islands in a similar manner to that in Hawaii, although apparently on a smaller scale.