Community assembly on remote islands: a comparison of Hawaiian and Mascarene spiders

Abstract

AbstractAimSpider communities on oceanic islands are assembled through multiple immigration and/or diversification events. In this study, we use a phylogenetic approach to investigate the role of such processes in shaping current patterns of diversity in Tetragnatha spiders from the Mascarene archipelago and to compare these patterns with those found in the Hawaiian archipelago.LocationMascarene archipelago, south‐western Indian Ocean; Hawaiian archipelago, Pacific Ocean.MethodsPrimary techniques included phylogeny reconstruction (mitochondrial cytochrome c oxidase subunit I; histone H3) with and without time calibration, delimitation of species using the general mixed Yule coalescent (GMYC) model, and testing for the presence of gene flow between geographically separated populations using the model of isolation with migration (IMa).ResultsThe current diversity of Tetragnatha on the Mascarenes has arisen through three independent colonization events with no evidence for in situ diversification. This finding is in stark contrast to the pattern observed in Hawaiʻi where two to four independent colonization events have been followed by two massive in situ diversification episodes leading to at least 38 species in total.Main conclusionsWhile net rates of immigration by Tetragnatha lineages appear relatively similar in the two archipelagos, in situ diversification in Tetragnatha only occurred in Hawaiʻi, possibly associated with the extreme geographical isolation of this archipelago relative to the Mascarene archipelago. Owing to the greater geographical proximity of the Mascarene archipelago to source pools such as Madagascar, it seems likely that the persistence of gene flow between the source and the islands and/or niche pre‐emption by other spider lineages may have reduced opportunities for diversification despite an apparently favourable ecological context.