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Tursiops truncatus nuuanu, a new subspecies of the common bottlenose dolphin from the eastern tropical Pacific

Abstract

In the eastern Pacific Ocean, three distinct forms of common bottlenose dolphin (Tursiops truncatus) have been identified, with suggestions they may be different species: a southern California/Mexico coastal, a northern temperate offshore, and an eastern tropical Pacific (ETP) offshore form. Currently, only one species (T. truncatus) is recognized in the region, with the first two forms described as distinct ecotypes. The goal of this study was to improve our understanding of the taxonomic status of these previously described forms through a re-examination of their morphological differentiation. We analyzed 135 skulls from the eastern and western Pacific, including the two nominal species, T. gillii and T. nuuanu, previously described for the eastern North Pacific and ETP, respectively. Additionally, we examined the holotypes of two currently recognized species in the genus, T. truncatus and T. aduncus. Our results showed significant morphological differentiation among bottlenose dolphins in the Pacific Ocean. The ETP offshore bottlenose dolphins were smaller in skull and body size and diagnostically distinct from dolphins in the western North Pacific and other regions in the eastern Pacific. Our results also indicated that, while other bottlenose dolphins in the Pacific were more similar to the globally distributed T. truncatus, the ETP offshore dolphins shared similarities with a previously described species in that region. The distinct environmental conditions in the ETP may be driving the evolutionary differentiation of these bottlenose dolphins. Given these results, we here recommend the recognition of ETP offshore bottlenose dolphins as a distinct subspecies, Tursiops truncatus nuuanu.

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Data Availability

The dataset generated and analyzed during the current study is available in the Figshare repository, https://doi.org/10.6084/m9.figshare.20769460.

Notes

  1. A majority of the CA samples (n = 61) were strandings, 11 were captured in offshore waters (around Santa Catalina and St. Miguel Islands) and three captured in coastal waters (around San Diego).

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Acknowledgements

We dedicate this work to Dr. William F. Perrin, who passed on July 11, 2022. Starting in the late 1960s, his research in the eastern tropical Pacific was instrumental in highlighting the killing of dolphins in the tuna purse-seine fishery and played a crucial role in creation of the Marine Mammal Protection Act of 1972. Additionally, he is considered the father of modern marine mammal taxonomy due to his pioneering work on both small cetaceans and large whales. Dr. Perrin approved the submission of this manuscript prior to his passing, but sadly passed before its acceptance and publication. We thank James Mead, John Ososky, and Michael McGowen (Smithsonian National Museum of Natural History) for the sample access provided to APBC and FIA. Our acknowledgements are also extended to Neil Duncan and Eleanor Hoeger (American Museum of Natural History, New York) for access to specimens, including the holotype of T. nuuanu (AMNH 35045), and to Richard Sabin (Natural History Museum, London) for his help with access to the holotype of T. truncatus (NHMUK 353a). We are grateful to Anke Klüter, who assisted FIA during the collection of measurements of some of the specimens used. We also thank all curators and collection managers that provided access to specimens to WFP in previous years (California Academy of Sciences, Los Angeles County Museum, Santa Barbara Museum of Natural History, San Diego Natural History Museum, Museum of Comparative Anatomy, American Museum of Natural History, and Smithsonian National Museum of Natural History), and to Toshio Kasuya, who collected the 19 Taiji skulls (offshore Japan – WNP) used in this study and deposited in the Smithsonian National Museum of Natural History. Special acknowledgments to Robert Brownell Jr., Thomas Jefferson, and Phillip Morin for insightful comments and suggestions on the first versions of this manuscript, and to two anonymous reviewers for their comments on the final version. The scientific results and conclusions, in addition to any views or opinions expressed herein, are those of the authors and do not necessarily reflect those of NOAA or the Department of Commerce.

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Correspondence to A. P. B. Costa.

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Deceased July 11, 2022. This work is dedicated to William F. Perrin.

A. P. B. Costa and F. I. Archer shared co-first authorship.

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Costa, A.P.B., Archer, F.I., Rosel, P.E. et al. Tursiops truncatus nuuanu, a new subspecies of the common bottlenose dolphin from the eastern tropical Pacific. J Mammal Evol 30, 213–229 (2023). https://doi.org/10.1007/s10914-022-09641-5

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Keywords

  • Cetaceans
  • Divergence
  • Environment
  • Speciation
  • Tropical