Tahitian tree snail mitochondrial clades survived recent mass extirpation

Oceanic islands frequently support endemic faunal radiations that are highly vulnerable to introduced predators [1]. This vulnerability is epitomized by the rapid extinction in the wild of all but five of 61 described Society Islands partulid tree snails [2], following the deliberate introduction of an alien biological control agent: the carnivorous snail Euglandina rosea[3]. Tahiti's tree snail populations have been almost completely extirpated and three of the island's eight endemic Partula species are officially extinct, a fourth persisting only in captivity [2]. We report a molecular phylogenetic estimate of Tahitian Partula mitochondrial lineage survival calibrated with a 1970 reference museum collection that pre-dates the predator's 1974 introduction to the island [4]. Although severe winnowing of lineage diversity has occurred, none of the five primary Tahitian Partula clades present in the museum samples is extinct. Targeted conservation measures, especially of montane refuge populations, may yet preserve a representative sub-sample of Tahiti's endemic tree snail genetic diversity in the wild.     

Halimeda contribution to organic and inorganic production in a Tahitian reef system

Of the seven species of Halimeda inhabiting a lagoon on Moorea island, three representing 10% of the algal covering and averaging 111 g of dry weight m^-2, have been studied in the course of a year. The biomass, measured bimonthly, stresses a slight seasonal variability in the species life. The main decrease was reported for H. opuntia after a fruiting event, which happened in October. The primary production was assessed, in situ, periodically over a year, by measuring oxygen variations in enclosures. Either expressed on specific-weight basis or in area units, the highest primary productions were recorded for H. opuntia. Productions and biomasses vary simultaneously during the year. The three species produce all together about 6 g C m^-2y^-1. The growth rate of the sand-dwelling H. incrassata f. ovata was followed during the year by staining, in the field, individuals with alizarin Red-S. The average rates measured were 3.3 segments ind^-1d^-1 and 0.17 gdw d^-1m^-2. The contribution of the three species to the carbonate budget of the reef was estimated by total alkalinity measurements during 24-h cycles. H. opuntia had the highest CaCO₃ production. For the three species studied, CaCO₃ production of 1.4 kg m^-2y^-1, which could correspond to a 0.4mm/year accretion of the studied reefal system, was estimated.     

Neotropical roots of a Polynesian spice: the hybrid origin of Tahitian vanilla, Vanilla tahitensis (Orchidaceae)

Absent in the wild, Tahitian vanilla (V. tahitensis) is a gourmet spice restricted in distribution to cultivated and feral stands in French Polynesia and Papua New Guinea. Its origins have been elusive. Our objective was to test the purported hybrid derivation and parentage of V. tahitensis from aromatic, neotropical progenitors. Nucleotide sequences from V. tahitensis and neotropical Vanilla were assayed for phylogenetic relatedness in two independently inherited genomic regions, the nuclear ITS region, and the trnH-psbA noncoding region of chloroplast DNA. As predicted to occur for early generation hybrids, placement of V. tahitensis was nonconcordant. All V. tahitensis clustered with V. planifolia from analysis of cpDNA sequences, suggesting V. planifolia as the maternal genome contributor. Phylogenetic reconstruction of ITS sequences showed that most V. tahitensis nested incongruently with V. odorata, but others remained sister to V. planifolia. Recovery of ITS clones in V. tahitensis related to both V. planifolia and V. odorata also supports its biphyletic origin from these two taxa. We interpret the high percentage (95%) of additive polymorphic sites in V. tahitensis relative to its parents as indication of a recent, and probably human-mediated, evolutionary origin.     

Zierane sesquiterpene lactone,cembrane and fusicoccane diterpenoids,from the Tahitian liverwort Chandonanthus hirtellus

Cembrane-type diterpenoids, 13,18,20-epi-iso-chandonanthone (1) and (8E)-4α-acetoxy-12α,13α-epoxycembra-1(15),8-diene (2), two fusicoccane-type diterpenoids, fusicoauritone 6α-methyl ether (3) and 6β,10β-epoxy-5β-hydroxyfusicocc-2-ene (4) and a zierane sesquiterpene γ-lactone, chandolide (5) were isolated from the Tahitian liverwort Chandonanthus hirtellus (Web.) Mitt., together with eight known diterpenoids, chandonanthine (6), fusicogigantone A (7), fusicogigantone B (8), fusicogigantepoxide (9), anadensin (10), fusicoauritone (11), ent-verticillol (12) and ent-epi-verticillol (13). Their structures were established by a combination of extensive NMR spectroscopy and/or X-ray crystallographic analyses. Compounds 1, 5 and 10 showed weak cytotoxic activity against HL-60. Compound 3 also indicated weak cytotoxic activity against KB cell lines.     

Microbioerosion in Tahitian reefs: a record of environmental change during the last deglacial sea-level rise (IODP 310)

The main motivation for Integrated Ocean Drilling Program Expedition 310 to the Tahitian Archipelago was the assumption that the last deglacial sea‐level rise is precisely recorded in the coral reefs of this far‐field site. The Tahitian deglacial succession typically consists of coral framework subsequently encrusted by coralline algae and microbialites. The high abundance of microbialites is uncommon for shallow‐water coral reefs, and the environmental conditions favouring their development are still poorly understood. Microbioerosion patterns in the three principal framework components (corals, coralline algae, microbialites) are studied with respect to relative light availability during coral growth and subsequent encrustation, in order to constrain the palaeobathymetry and the relative timing of the encrustation. Unexpectedly for a tropical, light‐flooded setting, ichnotaxa typical for the deep‐euphotic to dysphotic zone dominate. The key ichnotaxa for the shallow euphotic zone are scarce in the analysed sample set, and are restricted to the base of the deglacial succession, thus reflecting the deglacial sea‐level rise. At the base of the deglacial reef succession, the ichnocoenoses present in the corals indicate shallower bathymetries than those in the encrusting microbialites. This is in agreement with radiocarbon data that indicate a time gap of more than 600 years between coral death and microbialite formation. At the top of the deglacial reef succession, in contrast, the microbioerosion patterns in the three framework components indicate a uniform palaeobathymetry, and radiocarbon ages imply that encrustation took place shortly after coral demise. An enigma arises from the fact that the ichnocoenoses imply photic conditions that appear very deep for zooxanthellate coral growth. During the deglacial sea‐level rise increased nutrients and fluvial influx may have led to (seasonal?) eutrophication, condensing the photic zonation. This would have exerted stress on the coral ecosystem and played a significant role in initiating microbialite development.     

Potential use of ageing cultures ofIsochrysis aff.galbana (Isochrysis Tahitian,T. Iso) as starter cultures for live algal food production in tropical aquaculture

When grown in batch culture for a prolonged period (up to 11 months), the cells ofIsochrysis aff.galbana (Isochrysis Tahitian strain T. Iso) lost their capacity to divide and became enlarged, with a reduction in the content of photosynthetic pigment and photosynthetic capacity. Upon returning to fresh medium, the cells of a 11-month-old culture regained their capacity to divide within 3 days under light conditions. The resulting cells possessed similar size, photosynthetic pigment and photosynthetic capacity as those of logarithmic growth phase. The results suggest that the aged cultures ofIsochrysis can be used as starter cultures for the production of live food for aquaculture animals.     

Monogamy in a feeding generalist, <Emphasis Type="Italic">Chaetodon trichrous</Emphasis>, the endemic Tahitian Butterflyfish

Butterflyfishes have been well studied for their feeding ecology and mating systems. In particular, studies of corallivorous butterflyfishes have supported models of monogamy based on their predictable, low quality food; a patch of coral that is economically defensible by a pair. Moreover, pairs often exhibit trade-offs in territorial defense (greater by males) and feeding (greater by females) that improve their reproductive success. However, this model has not been well tested for more generalist feeders. In addition, recent hypotheses for monogamy in fish have emphasized parental care, but butterflyfishes do not provide parental care. This study tests five hypotheses for monogamy in the endemic Tahitian butterflyfish, Chaetodon trichrous: 1) uniform distribution of limiting resources, 2) joint defense of a territory, 3) low mate availability, 4) predator detection, and 5) benefits of cooperative behavior. Chaetodon trichrous was the most abundant butterflyfish in bays. Pairs jointly patrolled feeding territories. They preferentially fed over hard substrate other than live coral, however, this substrate was available outside of territories. They also ate plankton. Pairs were sorted positively for size, and all pairs were heterosexual. Males were larger than their partners, but females fed at higher rates. These results suggest that C. trichrous is monogamous, but reject the hypotheses that pairs form for joint defense of a territory (pairs swam together), that pairs remain together because of low mate availability (frequent interactions with neighbors), or that pairs form for predator detection (no homosexual pairs). Monogamy in C. trichrous is associated with the uniform distribution of hard substrate, although this resource is not limiting. Further, the higher feeding rate of females may represent a benefit provided by their monogamous mates.