Abstract
Closely related species can provide valuable insights into evolutionary processes through comparison of their ecology, geographic distribution and the history recorded in their genomes. In the Indo-Pacific, many reef fishes are divided into sister species that come into secondary contact at biogeographic borders, most prominently where Indian Ocean and Pacific Ocean faunas meet. It is unclear whether hybridization in this contact zone represents incomplete speciation, secondary contact, an evolutionary dead-end (for hybrids) or some combination of the above. To address these issues, we conducted comprehensive surveys of two widely-distributed surgeonfish species, Acanthurus leucosternon (N = 141) and A. nigricans (N = 412), with mtDNA cytochrome b sequences and ten microsatellite loci. These surgeonfishes are found primarily in the Indian and Pacific Oceans, respectively, but overlap at the Christmas and Cocos-Keeling Islands hybrid zone in the eastern Indian Ocean. We also sampled the two other Pacific members of this species complex, A. achilles (N = 54) and A. japonicus (N = 49), which are known to hybridize with A. nigricans where their ranges overlap. Our results indicate separation between the four species that range from the recent Pleistocene to late Pliocene (235,000 to 2.25 million years ago). The Pacific A. achilles is the most divergent (and possibly ancestral) species with mtDNA dcorr ≈ 0.04, whereas the other two Pacific species (A. japonicus and A. nigricans) are distinguishable only at a population or subspecies level (ΦST = 0.6533, P < 0.001). Little population structure was observed within species, with evidence of recent population expansion across all four geographic ranges. We detected sharing of mtDNA haplotypes between species and extensive hybridization based on microsatellites, consistent with later generation hybrids but also the effects of allele homoplasy. Despite extensive introgression, 98% of specimens had concordance between mtDNA lineage and species identification based on external morphology, indicating that species integrity may not be eroding. The A. nigricans complex demonstrates a range of outcomes from incomplete speciation to secondary contact to decreasing hybridization with increasing evolutionary depth.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 203-215 |
| Number of pages | 13 |
| Journal | Molecular Phylogenetics and Evolution |
| Volume | 101 |
| DOIs | |
| State | Published - May 1 2016 |
Bibliographical note
KAUST Repository Item: Exported on 2020-10-01Acknowledged KAUST grant number(s): CRG-1-2012-BER-002
Acknowledgements: This research was supported by the National Science Foundation grants OCE-0929031 to BWB, NOAA National Marine Sanctuaries Program MOA No. 2005-008/66882 to R.J. Toonen, Seaver Institute, KAUST Office of Competitive Research Funds under Award No. CRG-1-2012-BER-002 to MLB, baseline research funds to MLB, National Geographic Society Grant 9024-11 to JDD and by a Natural Sciences and Engineering Research Council of Canada postgraduate fellowship to JDD. For specimen collections we thank Kim Andersen, Paul Barber, J. Howard Choat, Richard Coleman, Joshua Copus, Toby Daly-Engel, Joshua Drew, Jeff Eble, Iria Fernandez-Silva, Kevin Flanagan, Michelle Gaither, Brian Greene, Song He, Matthew Iacchei, Stephen Karl, Randall Kosaki, Carl Meyer, Yannis Papastamatiou, David Pence, Mark Priest, Richard Pyle, Joshua Reece, D. Ross Robertson, Jennifer Schultz, Tane Sinclair-Taylor, Derek Smith, Zoltan Szabo, Kim Tenggardjaja, Bill Walsh, Ivor Willliams, Zeng Xiaoqi, Jill Zamzow and the crew of the R.V. Hi’ialakai. For logistic support we thank Robert Toonen, Randall Kosaki, Serge Planes, Jo-Ann Leong, Charles Sheppard, Salah Saeed Ahmed, Fouad Naseeb, Thabet Abdullah Khamis, Ahmed Issa Ali Affrar (Socotra Specialist Tours), Hawaii Department of Land and Natural Resources, Coral Reef Research Foundation, Papahānaumokuākea Marine National Monument, the Ocean University of China - College of Fisheries, Ministry of Water and Environment of Yemen, the Environment Protection Authority (EPA) Socotra, Administration of the British Indian Ocean Territory, Western Australia Department of Fisheries, Parks Australia and U.S. Fish and Wildlife Service. We thank Tane Sinclair-Taylor, Keoki Stender, Kenji Sorita and Hiroshi Senou (Kanagawa Prefectural Museum of Natural History) for providing images. Thanks to J. Howard Choat and Ben Victor for providing life-history information, Catherine Cullingham for providing a copy of HYBRIDLAB, Stefano Montanari for the map figure, members of the ToBo lab for logistic support and the Center for Genomics, Proteomics and Bioinformatics at the University of Hawai’i at Mānoa for their assistance with genotyping. We also thank Giacomo Bernardi and two anonymous reviewers for their helpful comments on an earlier version of this manuscript. This is contribution no. XX from the Hawai’i Institute of Marine Biology and no. XX from the School of Ocean and Earth Science and Technology.
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics
- Genetics
- Molecular Biology