Polytypy, clines, and fragmentation:The bulimes of New Caledonia revisited(Pulmonata, Orthalicoidea, Placostylidae)

摘要

Placostylus land snails, locally known in New Caledonia as "bulimes", were historically abundant, and every museum collectioncontains one or several drawers of shells collected in the second half of the 19th century. Their bewildering variation caused theestablishment of as many as 141 names at the rank of species, subspecies or variety, but it was not understood what part of thisvariation was between species, within species / between populations, and within species / within populations. Populations collectedin the 1970-1990s throughout New Caledonia, the Loyalty Islands, and adjacent islands, were analyzed to understand geographicalvariation, essentially based on shells, and species limits were studied essentially based on genital anatomy. We conclude thatthere are only 6 valid species, albeit with discrete geographical subspecies. The considerable intraspecific shell variation does notexclude convergence between species, which makes the recognition of species based on shells a difficult exercise. The Ile des Pinshas two species, the Loyalty Islands have one, all 6 species are found on mainland New Caledonia, and all are endemic. The centreof species richness is in the north of mainland New Caledonia, with 4 species, and up to 3 of which co-occur in the same valleyalthough not necessarily syntopically. Populations on the west coast and the North of New Caledonia are now severely fragmenteddue to loss of habitat, especially of dry forest; several forms described in the 1860s are extinct, and a number of local populationshave even become extinct during the course of this research, rendering the test of our taxonomical hypotheses through molecularapproaches problematical. Historical collections were revisited, all extant types recorded and illustrated, and the significance ofthe names involved discussed. A neotype is designated for Placostylus fibratus, historically named based on a shell collected duringCook's voyage of discovery.