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Abstract
The historical biogeography of many lineages-of both terrestrial and marine ocean habitats-remains poorly investigated even though remote ocean habitat covers approximately 66% of the Earth's surface. One such lineage with poorly understood biogeographic affinities across vast ocean habitat is the genus Coprosma (Rubiaceae) with numerous species, and a widespread and disjunct distribution among the far-flung insular localities of multiple Pacific Islands. Here, the first taxonomically robust phylogeny for Coprosma s.s. was dated using molecular clock techniques and indicated Coprosma s.s. diverged from its sister genus Nertera likely during or shortly after the Oligocene Marine Transgression of New Zealand. Diversification of the five major clades identified occurred in New Zealand during the Miocene, which was then followed by multiple independent dispersals from New Zealand to various localities in many directions. The pattern of Coprosma's distribution in the Pacific appears stochastic both temporally and spatially, but evolution of an orange to red fruit colour prior to nearly all inferred dispersals hints at endozoochory by birds. The number of inferred long-distance dispersals of Coprosma s.s. (>30), and number of repeated dispersals to the same insular locality from unrelated Coprosma s.s. sublineages (>8) is perhaps the most currently known for a remote Pacific-centred genus investigated to date. A New Zealand origin for a Pacific-wide dispersal of taxa is not novel, but the manner in which the temporal and spatial distribution for Coprosma s.s. was achieved contributes to a novel understanding of the historical biogeography of widespread Pacific genera that have origins in the Southern Hemisphere.
Highlights
Biogeographic patterns of plant lineages distributed across extremely remote insular localities remain poorly understudied compared to their mainland counterparts, but are being slowly elucidated from recent studies (Winkworth et al 2002; Gillespie et al 2008; Muellner et al 2008)
The Bayesian Inference (BI) and Maximum Likelihood (ML) phylogenetic analyses agreed in topology and inferred that Coprosma s.l. is not monophyletic as C. talbrockiei and C. moorei are more closely related to Durringtonia paludosa than to other Coprosma taxa sensu stricto (Fig. 2)
An incomplete submergence of New Zealand is suggested by phylogenetic reconstructions of Onychophora (Allwood et al 2010) Astelia (Birch et al 2012), Agathis (Knapp et al 2007) and giant weta taxa (Anostostomatidae: Trewick and Morgan-Richards 2005), but at this point it is not possible to say which is the most accurate scenario regarding the evolution of Coprosma s.s. and Nertera
Summary
Biogeographic patterns of plant lineages distributed across extremely remote insular localities remain poorly understudied compared to their mainland counterparts, but are being slowly elucidated from recent studies (Winkworth et al 2002; Gillespie et al 2008; Muellner et al 2008) Perhaps this is a consequence of the difficulties of working among the most isolated localities on Earth, resulting in a poor understanding of species relationships to each other and their area of origin (Price and Wagner 2004; Keeley and Funk 2011). Cowie and Holland (2006) argue that it is long overdue to accept long-distance dispersal as a well-supported biological process for which new research could and will help predict biogeographic distributions of plants, in isolated landmasses for which dispersal is a fundamental process for arriving organisms to new insular localities (and where vicariance has little to do with the establishment of novel lineages) Scientists supporting the dispersal school of thought refuted this arguing dispersal had significant evolutionary implications, for insular localities that were never connected to tectonically active continents. Cowie and Holland (2006) argue that it is long overdue to accept long-distance dispersal as a well-supported biological process for which new research could and will help predict biogeographic distributions of plants, in isolated landmasses for which dispersal is a fundamental process for arriving organisms to new insular localities (and where vicariance has little to do with the establishment of novel lineages)
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