Prehistoric anthropogenic introduction of partulid tree snails in Papua New Guinean archipelagos

Abstract

Aim  Members of the tropical tree snail family Partulidae are endemic to Pacific high oceanic islands and typically have single-island ranges. Two nominal Papua New Guinean species, Partula carteriensis and Partula similaris, deviate from familial norms by having extensive multi-island ranges that include low islands. We hypothesized that undocumented anthropogenic introductions may underlie this regional biogeographical anomaly and evaluated this hypothesis with novel field distributional and genotypic data.

Location  Papua New Guinean archipelagos between 1.4 and 11.4° S and 146.5 and 154.2° E.

Methods  Ethanol-preserved museum lots of P. carteriensis (from New Britain, Bismarck Archipelago) and P. similaris (from Woodlark, Boiaboiawaga and Goodenough islands) were genotyped for a standard mitochondrial marker, cytochrome c oxidase subunit I (COI), and the resulting haplotypes were subjected to phylogeographical analyses.

Results  All four genotyped populations showed very little genetic or conchological differentiation, irrespective of nominal taxonomic status, the archipelago sampled or whether the island was low, high, oceanic or continental. Partula carteriensis and P. similaris exhibit atypical distributions on larger high islands, being restricted to coastal villages and absent from native forest.

Main conclusions  Our results strongly indicate that P. carteriensis and P. similaris are conspecific, although a formal taxonomic revision is beyond the scope of this present study. They collectively exhibit the most heterogeneous geographical range known among partulids and their explicitly synanthropic association with high island coastal villages strongly implicates human introduction as the regional dispersal mechanism. We currently lack insights into the timeframe (apart from regional prehistory) and cultural context of these translocations. We also lack a convincing source population, and it may be necessary to survey the partulid fauna of the neighbouring Solomon Islands to identify one. Partulids are critically endangered throughout much of their range and the discovery of populations that apparently thrive in human-altered landscapes is noteworthy. Their study may provide clues of broad relevance to partulid conservation.