Molecular dating and biogeography of the neritic krill Nyctiphanes
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The genus Nyctiphanes (Malacostraca, Euphausiacea) comprises four neritic species that display antitropical geographic distribution in the Pacific (N. simplex and N. australis) and Atlantic (N. couchii and N. capensis) Oceans. We studied the origin of this distribution applying methods for phylogenetic reconstruction and molecular dating of nodes using a Bayesian MCMC analysis and the DNA sequence information contained in mtDNA 16S rDNA and cytochrome oxidase (COI). We tested hypotheses of vicariance by contrasting the time estimates of cladogenesis with the onset of the major barriers to ocean circulation. It was estimated that Nyctiphanes originated in the Pacific Ocean during the Miocene, with a lower limit of 18 miilion years ago (Mya). An Atlantic–Pacific cladogenic event (95% HPD 3.2–9.6) took place after the closure of the Tethyan Sea, suggesting that dispersal occurred from the Indo-Pacific, most likely via southern Africa. Similarly, the antitropical distribution pattern observed in the eastern Atlantic Ocean likely resulted from recent Pliocene–Pleistocene (95% HPD 1.0–4.97) northward dispersal from the southern hemisphere. Our results imply that dispersal appears to have had a significant role to play in the evolution of this group.
KeywordsMarkov Chain Monte Carlo Method Divergence Time Estimate Vicariant Event Molecular Clock Model High Posterior Density Interval
We would like to thank G. Tarling, S.N. Jarman and J. Gomez for supplying us with specimens of Nyctiphanes couchii, N. australis and N. simplex. Financial support for MED was provided by the National Research Foundation—Royal Society SET Program. Gordon W. Harkins is funded by the Atlantic Philanthropies and NRF Grant 62302. The Bioinformatics Capacity Development Research Unit from the South African Medical Research Council funds Tulio de Oliveira. Peter Teske was supported by a postdoctoral research fellowship from the NRF and an overseas study grant from the Ernest Oppenheimer Memorial Trust. Sampling and laboratory procedures comply with the current laws of the country.
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