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| Mesoplodon eueu Carroll, McGowen, McCarthy, Marx, Aguilar, Dalebout, Dreyer, Gaggiotti, Hansen, ... et Olsen, 2021 |
Abstract
The deep sea has been described as the last major ecological frontier, as much of its biodiversity is yet to be discovered and described. Beaked whales (ziphiids) are among the most visible inhabitants of the deep sea, due to their large size and worldwide distribution, and their taxonomic diversity and much about their natural history remain poorly understood. We combine genomic and morphometric analyses to reveal a new Southern Hemisphere ziphiid species, Ramari's beaked whale, Mesoplodon eueu, whose name is linked to the Indigenous peoples of the lands from which the species holotype and paratypes were recovered. Mitogenome and ddRAD-derived phylogenies demonstrate reciprocally monophyletic divergence between M. eueu and True's beaked whale (M. mirus) from the North Atlantic, with which it was previously subsumed. Morphometric analyses of skulls also distinguish the two species. A time-calibrated mitogenome phylogeny and analysis of two nuclear genomes indicate divergence began circa 2 million years ago (Ma), with geneflow ceasing 0.35–0.55 Ma. This is an example of how deep sea biodiversity can be unravelled through increasing international collaboration and genome sequencing of archival specimens. Our consultation and involvement with Indigenous peoples offers a model for broadening the cultural scope of the scientific naming process.
Keywords: True's beaked whale, Mesoplodon mirus, Ramari's beaked whale, Mesoplodon eueu, taxonomy, biodiversity
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| Figure 1. Sampling locations in the NA (black circles) and SH (yellow circle). Global map viewed as a Spilhaus projection that shows the connectedness of the ocean, with sampling locations and distribution of Mesoplodon mirus and proposed species Mesoplodon eueu shown by the key, with the artist's impression of the species in top right. Credit: Vivian Ward, University of Auckland. |
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| Figure 4. Skull and morphological distinctiveness of Mesoplodon eueu shown by holotype (NMNZ MM003000). (a) Skull in dorsal (left), ventral (centre) and left lateral (right) view (b) periotic in dorsal (left) and ventral (right) view; (c) tympanic bulla in dorsal (left) and ventral (right) view; (d) mandible in dorsal (top) and lateral (bottom) view; (e) mandibular tusks in medial (left) and lateral (right) view. (f) PCA of cranial and mandibular measurements showing clear separation between M. eueu from the SH and M. mirus from the NA. Percentages next to principal components (PCs) denote the total variance explained. Filled stars are holotypes and hollow stars paratypes. |
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| Skull of Mesoplodon eueu shown by holotype (NMNZ MM003000), in dorsal, ventral and left lateral view. |
Systematic biology
Cetacea Brisson 1762
Ziphiidae Gray 1865
Mesoplodon Gervais 1850
Mesoplodon eueu sp. nov.
Holotype: NMNZ MM003000, a pregnant, 5.06 m long adult female named Nihongore by Te Rūnanga o Makaawhio. Collected by Ramari Stewart, Nathaniel Scott and Don Neale after beachcast on 27 November 2011. The complete skeletons of the female and fetus are held by Museum of New Zealand Te Papa Tongarewa (NMNZ, Wellington, Aotearoa New Zealand; specimen MM003000), and a tissue sample is held in the New Zealand Cetacean Tissue Archive (NZCeTA, University of Auckland, Auckland, Aotearoa New Zealand; all institutional abbreviations in electronic supplementary material, S1).
Type locality: Waiatoto Spit, South Westland, Aotearoa New Zealand.
Diagnosis:
Molecular characteristics
M. eueu differs from M. mirus based on nuclear DNA markers, and from M. mirus and its closest relatives M. europaeus, M. ginkgodens and M. bidens using mtDNA markers (figure 2). M. mirus is distinct from all other mesoplodont species based on previous mitochondrial and nuclear DNA trees [7,20,24].
Mitochondrial DNA: analysis of mitochondrial data includes sequences from the holotypes of both M. mirus and M. eueu at all sequence lengths. Over the 304 bp mitochondrial control region segment, M. eueu is distinguished by seven fixed differences from M. mirus, with FST = 0.85 (p < 0.01), dA = 0.04 between the two species. At the full mitochondrial genome lengths, M. eueu is distinguished by 579 fixed differences from M. mirus with FST = 0.96 (p < 0.01) and dA = 0.04 (electronic supplementary material, table S2).
Nuclear DNA: reduced representation sequencing with ddRAD showed M. eueu had a distinct admixture pattern to M. mirus (figure 2), and an FST = 0.64 (p < 0.0001) was estimated between the two species. M. mirus and M. eueu were distinguished by 1909 fixed differences (12%, per SNP allele error rate = 0.002), across a dataset of 15 671 SNPs found between or within both species. Comparison of one whole nuclear genome each from M. mirus and M. eueu showed a level of nucleotide divergence of 0.28%.
Morphological characters:
M. eueu is a larger (5.3 m) species of Mesoplodon differing from all other members of the genus except M. mirus, M. hectori and M. perrini in having tusks positioned at the tip of the mandible. It also differs from M. hectori and M. perrini in having smaller, less triangular tusks and from M. mirus in having a relatively shorter rostrum with a wider base, a shorter mandibular symphysis, wider premaxillary sac fossae and crests, and a taller cranium.
Etymology: The scientific and common names acknowledge links with Indigenous communities in South Africa and Aotearoa New Zealand, respectively, and were chosen in consultation with these peoples. Most of the South African strandings come from territory inhabited by the Khoisan peoples. Guided by the Khoisan Council, we chose the name //eu//’eu (simplified to eueu to fit nomenclature standards; correct pronunciation available in associated audio clip a1 in the electronic supplementary material), which means ‘big fish’ in Khwedam (from the Khoe language family). In Aotearoa New Zealand, Māori cultural expert Brad Haami developed a shortlist of potential names meaningful in the Māori language, which was then sent for comment to Te Rūnanga o Ngāi Tahu. The selected common name, Ramari's beaked whale, pays homage to Māori tohunga (expert) Ramari Stewart, who has kept traditional knowledge alive, contributed extensively to scientific research on marine mammals, and helped prepare the skeleton of the holotype. The word ‘Ramari’ means a rare event in the Māori language, reflecting the elusive nature of most beaked whales.
Emma L. Carroll, Michael R. McGowen, Morgan L. McCarthy, Felix G. Marx, Natacha Aguilar, Merel L. Dalebout, Sascha Dreyer, Oscar E. Gaggiotti, Sabine S. Hansen, Anton van Helden, Aubrie B. Onoufriou, Robin W. Baird, C. Scott Baker, Simon Berrow, Danielle Cholewiak, Diane Claridge, Rochelle Constantine, Nicholas J. Davison, Catarina Eira, R. Ewan Fordyce, John Gatesy, G. J. Greg Hofmeyr, Vidal Martín, James G. Mead, Antonio A. Mignucci-Giannoni, Phillip A. Morin, Cristel Reyes, Emer Rogan, Massimiliano Rosso, Mónica A. Silva, Mark S. Springer, Debbie Steel and Morten Tange Olsen. 2021. Speciation in the Deep: Genomics and Morphology reveal A New Species of Beaked Whale Mesoplodon eueu. Proc. R. Soc. B. 288. 20211213: 20211213. DOI: 10.1098/rspb.2021.1213
