Biogeography of the fauna of French Polynesia: diversification within and between a series of hot spot archipelagos

Abstract

The islands of French Polynesia cover an area the size of Europe, though total land area is smaller than Rhode Island. Each hot spot archipelago (Societies, Marquesas, Australs) is chronologically arranged. With the advent of molecular techniques, relatively precise estimations of timing and source of colonization have become feasible. We compile data for the region, first examining colonization (some lineages dispersed from the west, others from the east). Within archipelagos, blackflies (Simulium) provide the best example of adaptive radiation in the Societies, though a similar radiation occurs in weevils (Rhyncogonus). Both lineages indicate that Tahiti hosts the highest diversity. The more remote Marquesas show clear examples of adaptive radiation in birds, arthropods and snails. The Austral Islands, though generally depauperate, host astonishing diversity on the single island of Rapa, while lineages on other islands are generally widespread but with large genetic distances between islands. More recent human colonization has changed the face of Polynesian biogeography. Molecular markers highlight the rapidity of Polynesian human (plus commensal) migrations and the importance of admixture from other populations during the period of prehistoric human voyages. However, recent increase in traffic has brought many new, invasive species to the region, with the future of the indigenous biota uncertain.

Figure 1

The main high archipelagos in French Polynesia, with geological ages indicated (Clouard & Bonneville 2005).

Figure 2

Phylogenetic hypotheses for different lineages on the (a,b) Society and (c–e) Marquesas Islands. (a) Phylogenetic hypothesis for blackflies, Simulium (Simuliidae), from the Society Islands showing distribution and shifts in larval habitat (redrawn from Craig et al. 2001). Islands within the Society chain where each species occurs are shown (Simuliun adamsoni is the only species in the Society Island clade that does not occur in the Societies, as indicated by the black bars). Habitats range from streams, of various types, to rivers, cascades and madicolous flow (thin films of water). Line width is proportional to the number of different habitats used. The phylogeny suggests a single shift to the specialized cascade habitat with three losses (white bars on branches) and one independent gain earlier in the phylogeny (black bar to Simulium fossatiae). (b) Phylogenetic hypothesis of spiders, genus Tetragnatha (Araneae, Tetragnathidae), in the Society Islands. The data are based on sequences (approx. 750 bp) of mitochondrial COI DNA (GenBank accession numbers EU796899–EU796932). Details of methods are provided by Gillespie (2002). Analysis was by parsimony, maximum likelihood and Bayesian estimates of likelihood, and values beside nodes indicate bootstrap support (above node) and posterior probabilities (below node). (c) Phylogenetic tree for the Pomarea monarch flycatchers mapped on the Marquesas Islands (branch lengths not proportional to sequence evolution; redrawn from Cibois et al. 2004). Taxa endemic to other Polynesian archipelagos are connected to the Marquesan topology with a dashed line. Three taxa, Pomarea iphis fluxa, Pomarea mendozae nukuhivae and Pomarea iphis iphis, are basal in the tree (relative positions uncertain). All other taxa form a tight clade consistent with the age and proximity of the islands. For estimating the age of lineages, the three best-supported nodes were used, labelled as 1 (separation of the basal Marquesan monarchs), 2 (divergence between the basal Marquesan taxa and the remaining taxa) and 3 (divergence between species on Hiva Oa versus Tahuata and Fatu Hiva). Node 1 was estimated at 3.0–3.3 Ma, node 2 at 1.6–1.8 Ma and node 3 at 0.41–0.45 Ma. (d) Fitch tree based on genetic distances (allozymes) among samples and species of Samoana snails from the Marquesas and Society Islands. Numbers at each node indicate the number of times that clade appeared in 100 iterations in the bootstrap analysis (redrawn from Johnson et al. 2000). (e) Phylogenetic hypothesis of Tetragnatha spiders in the Marquesas. Data and analysis as in (b).

Figure 3

Phylogenetic hypotheses for crab spiders, M. rapaensis (Thomisidae), in the Austral Islands inferred from molecular genetic analysis (Garb & Gillespie 2006). Numbers above branches refer to parsimony bootstrap values from 1000 replicates (asterisks indicate less than 50% bootstrap support) followed by decay indices. Numbers below the branch indicate posterior probability values.

Figure 4

Evidence of the ‘express-train’ model of Polynesian island colonization by lizards (redrawn from Austin 1999). Maximum-parsimony phylogram for Lipinia noctua; localities denoted by grey circles are all genetically distinct and represent natural prehuman dispersal. Localities denoted by black circles are genetically similar (mean sequence divergence 0.008%) and represent human-mediated dispersal within the past 4000 years. Dates represent approximate time of first human settlement.