Contributions to Zoology, 86 (2) – 2017Roberto Guidetti; Sandra J. McInnes; Michele Cesari; Lorena Rebecchi; Omar Rota-Stabelli: Evolutionary scenarios for the origin of an Antarctic tardigrade species based on molecular clock analyses and biogeographic data
Origin and distribution of Mopsechiniscus

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Mopsechiniscus in the sub-Antarctic islands

The presence of Mopsechiniscus on two sub-Antarctic islands is intriguing. South Georgia, where M. imberbis is found, is recognised as a micro-continent that has geological links with the Patagonian Andean Mountains, situated to the east of the Beagle Channel and attached to the southern margin of the Burdwood Bank (Dalziel et al., 1975). There is some debate over the positioning and subsequent movement of this micro-continental plate during the late Cretaceous-early Paleogene period (Dalziel et al., 1975; Barker, 2001; Thomson, 2004). Lawver and Gahagan (2003) provide a computerised continental break-up history of whole Antarctica, placing South Georgia to the south of Burdwood Bank and in close proximity to Tierra del Fuego. With the addition of our results for the estimated molecular clock division between two phylogenetic lineages (the Antarctic M. franciscae and the South American M. granulosus), the latter scenario is congruent with the hypothesis that Mopsechiniscus was present on South Georgia before it broke away from Tierra del Fuego.

Mopsechiniscus frenoti of the Crozet Islands is morphologically very similar to M. franciscae from Antarctica (Guidetti et al., 2014) and, based on the available data, we can infer that the two species represent sister taxa within the genus. The volcanic rocks of the sub-Antarctic Crozet archipelago have a relatively recent origin (ca. 8.8 Mya; Giret et al., 2003). However, the origins of the islands on the Crozet Plateau are debated (see Craig, 2003). Suggested interpretations of palaeogeographic data put these islands near India, close to Madagascar or off Antarctica over a period between late Cretaceous (ca. 70 Mya) to the Palaeocene (60–63 Mya) (Craig, 2003). The Crozet Islands host a number of indigenous species including plants, carabid beetles, and black flies (Chown et al., 1998; Vernon et al., 1999; Craig et al., 2003). How these indigenous flora and fauna, and indeed Mopsechiniscus, reached the islands is unknown. Winds and birds are potential vectors, especially as the Crozet Islands would have been formed 1,000 km closer to Africa during the Palaeocene (Schlich et al., 1974), but there is no evidence that passive long distance dispersal is common for Mopsechiniscus.

It is entirely possible that Mopsechiniscus species indigenous of South Georgia and the Crozet Islands could also be present in localities we have not yet discovered. Alternatively, they may have become isolated on the islands by traversing land/island bridges that have by now vanished.