Not completely lost: two partulid tree snail species persist on the highest peak of Raiatea, French Polynesia

Abstract

The spectacular partulid tree snail fauna of the Society Islands has been almost completely extirpated in recent decades following the deliberate introduction of the alien carnivorous snail Euglandina rosea. The greatest loss has occurred on the island of Raiatea, French Polynesia, home to an estimated 34 species (including 33 single-island endemics), all of which have been deemed extirpated in the wild. However, we report here the February 2006 discovery of two surviving Raiatean partulid lineages on the upper slopes of Mount Tefatua, the highest peak on the island. They have been identified using morphological and molecular phylogenetic analyses, the latter approach employing available museum and captive reference samples. One population, at 750 m elevation, consisted of Samoana attenuata. It has a multi-island distribution within the archipelago and surviving populations persist also on Tahiti and Moorea. A second population, present just below the summit at 950 m, consisted of a previously unstudied morphospecies and it has been formally described as Partula meyeri. It is unclear if a stable altitudinal refuge from E. rosea predation exists on Mount Tefatua but the unexpected discovery of these two surviving montane populations raises the possibility of preserving some fraction of Raiatea's endemic tree snail diversity in the wild.

Evolutionary history of a vanishing radiation: isolation-dependent persistence and diversification in Pacific Island partulid tree snails

“…Previous partulid molecular phylogenies [35,39,43-45] have either ignored or under-sampled Western Pacific taxa, the most comprehensive representation being 4 western species of Partula [44]. We were able to incorporate 14 Western Pacific species (Table 2) in our analyses, including for the first time Samoana fragilis, the sole western member of that genus, and 2 of the 3 endemic Partula species in Palau, the westernmost archipelago of the family’s range (Figure 1).…”

“…All available data suggest that Partulidae have had a long evolutionary history in Oceania, dispersing to new islands as older ones sink below sea level. Pilsbry and Cooke [42] partitioned Partulidae into 3 genera ( Partula , Samoana and Eua ), based primarily on male genital characters, and these have been substantially corroborated by independent molecular character sets [35,39,43-45], with the exception of one Tahitian species complex with highly variable genitalia [46]. …”

“…Land snail gene trees that have included all three genera [39] have placed Eua basally, a topology that positions the last common ancestor of extant Partulidae in the central part of the present-day partulid range. Partulid phylogenies rooted with Eua species [35,44,45] have consistently recovered reciprocally monophyletic Samoana and Partula genera. Goodacre and Wade’s [44] nuclear ribosomal phylogeny supported an eastward expansion of Samoana species from Samoa to the Society and Marquesan archipelagoes, but the Partula clade had a pronounced basal polytomy and yielded little historical insight into this genus’s disjunct distribution.…”

Deconstructing an infamous extinction crisis: Survival of Partula species on Moorea and Tahiti

“…We sequenced 93 specimens Table S1). These specimens characterized a majority of the taxonomic species (14/18;Gerlach, 2016) and all known mt cytochrome c oxidase subunit I (COI) clades Lee et al, 2009Lee et al, , 2014Lee et al, , 2008Lee, Burch, Jung et al, 2007). Our goal here was to include as many species and sampling locations, but our sampling of the valleys and montane regions was not exhaustive.…”

“…The DNA of the 120 partulid individuals genotyped in this study was previously extracted using a Qiagen DNEasy Kit (Qiagen, Valencia, CA, USA) or an E.Z.N.A. Mollusk DNA kit (Omega Bio-Tek, Norcross, GA; Lee, Burch, Coote et al, 2007;Lee et al, 2009Lee et al, , 2014Lee et al, , 2008Lee, Burch, Jung et al, 2007) and then stored at −80°C. sites, barcodes, and Illumina adapters (based on Fastqc results; parameter 16 setting 2) then were trimmed from raw sequence reads, and bases with low quality scores (Phred-score <20, parameter 10 setting 33) replaced with N. Sequences with >5 Ns (parameter 19) were discarded.…”