Biogeographic History of the Antarctic freshwater copepod Boeckella poppei Mrázek 1901 (Crustacea, Calanoide, Centropagidae)
It is widely assumed that the current impoverished biodiversity in the Antarctic terrestrial and freshwater ecosystems has been strongly influenced by climate and tectonic changes during the Cenozoic era. In particular, ice sheet expansion and contraction during the Last Glacial Maximum (LGM) and pr...
| Autor: | |
|---|---|
| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2020 |
| País: | Chile |
| OAI Identifier: | oai:repositorio.anid.cl:10533/246553 |
| Acceso en línea: | https://hdl.handle.net/10533/246553 |
| Access Level: | acceso abierto |
| Palabra clave: | Ciencias Naturales Otras Ciencias Naturales |
| Sumario: | It is widely assumed that the current impoverished biodiversity in the Antarctic terrestrial and freshwater ecosystems has been strongly influenced by climate and tectonic changes during the Cenozoic era. In particular, ice sheet expansion and contraction during the Last Glacial Maximum (LGM) and previous maxima across the Antarctic would have repeatedly driven much of the continent’s terrestrial biota extinct. Two main hypotheses have been proposed to explain how these climatic events have shaped the contemporary distribution of terrestrial biota in Antarctica. The dispersal hypothesis suggests that the contemporary biodiversity is the result of postglacial colonization from lower latitude regions that had remained ice-free. In contrast, the in situ refugia hypothesis suggests that some Antarctica biota survived within the region throughout the multiple glaciations of the Pleistocene and earlier eras. The genus Boeckella is the most widespread freshwater calanoid copepod genus in the Southern Hemisphere. Its current distribution includes Australia, New Zealand, Tasmania, New Caledonia, South America, the Antarctic continent and Peninsula, and various sub-Antarctic islands (i.e. South Georgia, Marion, Prince Edward, Crozet, Kerguelen, Heard and Macquarie). Among Boeckella species, B. poppei exhibits the broadest distribution and is the only representative of the genus, and more widely the only terrestrial or freshwater invertebrate, currently reported from southern South America, sub-, maritime and continental Antarctica. This thesis elucidated the origin and diversification of the genus and determinate the phylogeographic pattern of B. poppei, in order to understand the microevolutionary processes that have molded its biogeographic history. First, we provided an upgrade of the occurrence of the genus at high latitudes, based on our sampling and published records, along with an updated revision of the nomenclatural history, to have a comprehensive description of the distribution and a synthesis of systematic of the genus. Second, we proposed a hypothesis of the origin and diversification of the genus on the basis of multiple loci phylogenetic and ancestral geographic range along its complete distribution. Third, we assessed whether the current distribution of maritime Antarctic populations of B. poppei is the result of post-LGM colonization or of survival in glacial refugia in Antarctica throughout the LGM and previous glaciations. Finally, we determined the level of genetic structure of B. poppei at smaller scale at a single maritime Antarctic island location, to evaluate the dispersal and establishment potential, considering possible scenarios of persistence in refugia and long-distance colonization. This detailed molecular-based study reveals that the genus Boeckella has a Gondwanan origin, with initial vicariant diversification coincident with Gondwanan break-up timescales. Further diversification within the genus occurred after the physical separation of the continental landmasses through long-distance dispersal and establishment. We identified a continuous decline in the species accumulation rate within the genus since the early Eocene, suggesting that the diversification rate decreased in concert with progressive cooling throughout the Cenozoic era, probably also linked with a general decline in available freshwater habitats. The current Antarctic and sub-Antarctic distribution of the species B. poppei likely derived from two contrasting and independent biogeographic events. We find evidence supporting long-term refugial persistence in situ in parts of the maritime Antarctic (the South Orkney Islands) throughout the Quaternary glaciations, as well as for post-LGM colonization of parts of the maritime Antarctic and of sub-Antarctic South Georgia from southern South America. Finally, we found evidence of strong small-scale genetic structure at a location (Signy Island) in the putative maritime Antarctic refugial region. The identification of rare long-distance dispersal and establishment event(s) rather than the occurrence of regular gene flow raises further questions about the mechanisms of dispersal and possible post-dispersal barriers impacting new potential colonizers. |
|---|