Moorean tree snail survival revisited: a multi-island genealogical perspective

Abstract

BackgroundThe mass extirpation of the island of Moorea's endemic partulid tree snail fauna, following the deliberate introduction of the alien predator Euglandina rosea, represents one of the highest profile conservation crises of the past thirty years. All of the island's partulids were thought to be extirpated by 1987, with five species persisting in zoos, but intensive field surveys have recently detected a number of surviving wild populations. We report here a mitochondrial (mt) phylogenetic estimate of Moorean partulid wild and captive lineage survival calibrated with a reference museum collection that pre-dates the predator's introduction and that also includes a parallel dataset from the neighboring island of Tahiti.ResultsAlthough severe winnowing of Moorea's mt lineage diversity has occurred, seven of eight (six Partula; two Samoana) partulid tip clades remain extant. The extinct mt clade occurred predominantly in the P. suturalis species complex and it represented a major component of Moorea's endemic partulid treespace. Extant Moorean mt clades exhibited a complex spectrum of persistence on Moorea, in captivity, and (in the form of five phylogenetically distinct sister lineages) on Tahiti. Most notably, three Partula taxa, bearing two multi-island mt lineages, have survived decades of E. rosea predation on Moorea (P. taeniata) and in the valleys of Tahiti (P. hyalina and P. clara). Their differential persistence was correlated with intrinsic attributes, such as taxonomy and mt lineages, rather than with their respective within-island distribution patterns.ConclusionConservation efforts directed toward Moorean and Tahitian partulids have typically operated within a single island frame of reference, but our discovery of robust genealogical ties among survivors on both islands implies that a multi-island perspective is required. Understanding what genetic and/or ecological factors have enabled Partula taeniata, P. hyalina and P. clara to differentially survive long-term direct exposure to the predator may provide important clues toward developing a viable long term conservation plan for Society Island partulid tree snails.

Foot mucus stored on FTA® cards is a reliable and non-invasive source of DNA for genetics studies in molluscs

“…All of the Moorean partulids were thought to be extirpated by 1987 following the deliberate introduction of the alien predator Euglandina rosea about 10 years before. Intensive field surveys have recently detected a number of surviving wild populations (Lee et al 2009). The partulids sampled used in this study belong to these relictual populations.…”

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

“…Approximately 120 partulid species are currently recognized and half of this nominal diversity is endemic to a single hot spot archipelago, the Society Islands, at the eastern edge of the family’s range (Figure 1). In recent decades, Partulidae have experienced catastrophic extinction, centered on the Society Islands, where most of the archipelago’s 61 endemic species have been extirpated by Euglandina rosea [22,23,26,35].

Figure 1 Partulidae distribution map modified from [ 23 ] to show inferred anthropogenic introductions (dashed lines) of Partula species in Papua New Guinea [ 28 ] and the Cook/Austral Islands [ 34 ].

…”

“…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.…”

“…In this model, neighboring older islands (Leeward group) seeded the younger islands (Windward group), first Moorea, then Tahiti, via single colonization events and subsequent speciation occurred in situ within each island [43,46,49-53]. This model does not apply to the four endemic Society Island Samoana species, two of which have multi-island distributions [35,54,55]. …”