The legacy of a snail conquest: from pattern to process in a presumably ancient radiation of freshwater gastropods across the South Pacific
Final Report Abstract
This project aimed at the reconstruction of the peculiar distribution of the family Tateidae across the South Pacific, where representatives occur on New Caledonia, Vanuatu, Fiji, the Austral Islands, New Zealand and Lord Howe Island. In “peripheral” studies, we established that Sulawesidrobia from Sulawesi belongs to the Asian branch of Tateidae and were involved in a family level analysis defining the family as well as its closest relatives. Both papers were important for the selection of outgroup taxa in the final, comprehensive analysis, which included also Australasian species. The project was “modularized”, i.e. first focused on the local radiations of Vanuatu, Fiji, and New Caledonia. Based on these analyses and foregoing papers on tateids from New Zealand and Australia, we selected representatives of each phylogenetic lineage for the reconstruction of the global picture. We discovered a total of c. 40 new species on the archipelagos of Vanuatu and Fiji as well as on New Caledonia. Our analyses of tateid gastropods from six islands of Vanuatu revealed three deep clades and suggested that parts of the island of Espiritu Santo must have been continuously emergent for c. 3 My, which is roughly 1 My longer than previously thought. Like the species from Vanuatu, those from Fiji, where we collected on Viti and Vanua Levu, were closer related to taxa from New Zealand than to Australian ones. The colonization history of Fiji appeared to mirror the geological evolution with the oldest land masses emerging in the Late Miocene in the South and South West of Viti Levu. Other regions and Vanua Levu emerged only in the Pliocene. However, branch lengths of our molecular phylogeny suggested that the entire radiation of tateid gastropods across Fiji with three major clades is considerably younger. On New Caledonia, we failed to collect two of the five described genera. Both have very narrow distributions in areas accessible only with local guides which were not available during our field campaign. Nevertheless, our analyses confirmed the remaining three genera and revealed two new ones. The New Caledonian radiation is probably much older and of Oligocene origin. The preliminary comprehensive analysis including representatives from all major lineages as well as Australian and Asian taxa provided provided a number of surprises as in several aspects the colonization pattern across the Pacific definitely did not follow expectations based on parsimony, i.e. a stepping stone pattern from the continental land masses out into the Pacific. In line with expectations, though, was the assumption of separate major lineages from Australia toward NW including Sulawesi, and toward the Pacific Islands, respectively. However, the colonization of the Pacific was obviously very complex. New Caledonia was colonized from Australia, and the remaining archipelagos via New Zealand. The genus Fluviopupa, egg-laying and occurring on Vanuatu, Fiji, and the Austral Islands, was sister group to the New Zealand clade consisting primarily of egg-laying species, while the other two clades are ovoviviparous. Surprisingly, this genus originated on the geographically most distant Austral Islands (> 3,500 km!), and these were colonized against the “progression rule”, i.e. against the island ages with Rurutu being the oldest. The Austral Islands appeared to be hub for three dispersal events, 1) to Lord Howe Island (5,000 km!), 2) to Vanuatu (c. 4,500 km), and 3) to Fiji (c. 3,200 km!). From there, Vanuatu was colonized again, possibly even twice (c. 900-1,100 km). These results indicate that we will have to re-interpret or complement our conclusions for Vanuatu. And these results are of course preliminary and await confirmation or modification through Bayesian phylogenetic analyses including time-trees, topology tests comparing the unconstrained tree with geographically constrained trees, as well as ancestral area reconstructions. These analyses will most likely reveal some ambiguities considering some weakly supported nodes and short branches. Ultimately, we will compare the most likely scenario with patterns in other taxa. In any case, at this point we are not aware of any other group of organisms with a similar colonization history across the South Pacific.
Publications
- 2011. Origin and radiation of rissooidean gastropods (Caenogastropoda) in ancient lakes of Sulawesi. Zoologica Scripta 40: 221-237
Zielske, S., Glaubrecht, M. & Haase, M.
(See online at https://doi.org/10.1111/j.1463-6409.2010.00469.x) - 2013. Pushing short DNA fragments to the limit: Phylogenetic relationships of ‘hydrobioid’ gastropods (Caenogastropoda: Rissooidea). Molecular Phylogenetics and Evolution 66: 715-736
Wilke, T., Haase, M., Hershler, R., Liu, H.-P., Misof, B. & Ponder, W.
(See online at https://doi.org/10.1016/j.ympev.2012.10.025) - When snails inform about geology: Pliocene emergence of islands of Vanuatu indicated by a radiation of truncatelloidean freshwater gastropods (Caenogastropoda: Tateidae). Journal of Zoological Systematics and Evolutionary Research
Zielske, S. & Haase, M.
(See online at https://doi.org/10.1111/jzs.12053)
