When snails inform about geology: Pliocene emergence of islands of Vanuatu indicated by a radiation of truncatelloidean freshwater gastropods (Caenogastropoda: Tateidae)

Abstract

The South Pacific archipelago Vanuatu has a very complex geological history including three major phases of volcanism creating island belts and phases of repeated submergence and re‐emergence. An important issue for the evolution of the biota of Vanuatu ambiguously discussed in the geological literature is the question whether the entire archipelago has been submerged until the early Pleistocene or if at least parts of the island of Espiritu Santo have remained subaerial throughout the Pliocene. We used a time‐calibrated phylogenetic analysis of freshwater gastropods of the family Tateidae based on COI, 16S rRNA and ITS2 to infer the colonization history of Vanuatu. Our analyses suggested that Espiritu Santo was colonized c. 3 Mya. Espiritu Santo was probably the place of origin for the subsequent colonization of the island of Erromango (2 Mya) and the Pleistocene radiation across the remaining archipelago. We describe 10 new species largely based on morphological and anatomical data. The genetic data in particular of the species from the young islands are taxonomically incongruent probably due to incomplete lineage sorting typical for young radiations. In contrast, the paraphyly of Fluviopupa espiritusantoana appearing in three distant clades indicates either the existence of cryptic species or the long survival of the stem species of almost the entire radiation.

New insights into tateid gastropods and their radiation on Fiji based on anatomical and molecular methods (Caenogastropoda: Truncatelloidea)

“…Respective investigations for Australia have not yet been performed. These land masses were probably the source areas for the spread North to New Guinea (Bernasconi, ) and Sulawesi (Zielske, Glaubrecht & Haase, ), on the one hand, and across the South Pacific, on the other hand, where tateids have colonized Norfolk and Lord Howe Island (Ponder, , ), New Caledonia (Haase & Bouchet, ), Vanuatu (Haase, Fontaine & Gargominy, ; Zielske & Haase, in press), Fiji (Haase, Ponder & Bouchet, ), and the Austral Islands, the southernmost archipelago of French Polynesia (Haase, Gargominy & Fontaine, ).…”

The enigmatic pattern of long‐distance dispersal of minute freshwater gastropods (Caenogastropoda, Truncatelloidea, Tateidae) across the South Pacific

“…The islands of Vanuatu were initially colonized c . 3.56 (3.0–4.1) Ma a figure generally in accordance with our previous results, although this dating now applies to a higher node, then estimated almost 1.5 Myr younger (Zielske & Haase, ; node II in Fig. ).…”

“…For example, Fluviopupa would have evolved on one of the older, western AI, spread to the east, than gone extinct in the west to give room for the colonization of the ancestors of the species we see today from the east. Also Vanuatu with its complex history of repeated sea level changes would have been colonized more than a million years earlier than assumed by Zielske & Haase (2014a), which is hard to match with the geological evidence (Taylor, 1992;Robin et al, 1993). Similarly, the onset of the radiation in NZ would predate the re-emergence of all or at least much of NZ by several millions of years (Trewick et al, 2007; but see Mildenhall et al, 2014;Carr et al, 2015).…”

“…The next dispersal step was the archipelago of Vanuatu, which was apparently reached twice independently. Hence, the colonization of Vanuatu by Fluviopupa was more complex than assumed by Zielske & Haase (2014a), who considered oceanic dispersal events sufficiently rare to assume monophyly of the Vanuatu species. In addition, a third lineage may have originated on Fiji (see below).…”

“…Here, we focus on small (few mm in length) freshwater gastropods of the family Tateidae, which probably originated in Australia (Wilke et al ., ) and have a peculiar SP distribution, being known from five islands/archipelagos: (1) Lord Howe Island (LHI) harbours 15 species‐group taxa in three genera (Ponder, ), its volcanic rocks are maximally 6.9 Myr old (McDougall et al ., ); (2) NC harbours seven genera with more than 50 species (Haase & Bouchet, ; Zielske & Haase, ) and was presumably colonized after a phase of submergence 37 Ma (e.g. Swenson et al ., ); (3) Vanuatu with 20 species all attributed to Fluviopupa (Haase et al ., ; Zielske & Haase, ) and continuously emergent probably only since the latest Pliocene (Robin et al ., ; Greene et al ., ); (4) Fiji with 28 known Fluviopupa species (Haase et al ., ; Zielske & Haase, ) and a complex geological history (Rodda, ); and (5) the Austral Islands (AI) in French Polynesia harbouring six Fluviopupa species (Haase et al ., ) extend over 1200 km from the McDonald Seamount volcano in the east to the island of Rimatara in the west and are formed by three volcanic hotspot chains with the oldest island emergent since maximally 12.1 Myr (Bonneville, ; Maury et al ., ). Apart from the Australian mainland and Tasmania, where the estuarine genus Tatea T. Woods, 1879 (Ponder et al ., ) occurs, tateids are known from brackish water habitats only in NZ, where they invaded freshwater three times independently (Haase, ).…”