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Systematic Zoology Advance Access published online on October 5, 2009
Systematic Zoology, doi:10.1093/sysbio/syp060
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© The Author(s) 2009. Published by Oxford University Press on behalf of Society of Systematic Biologists.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.5/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Radiation of Extant Cetaceans Driven by Restructuring of the Oceans

Mette E. Steeman1,2, Martin B. Hebsgaard1,2, R. Ewan Fordyce3, Simon Y. W. Ho4, Daniel L. Rabosky5,6, Rasmus Nielsen7,8, Carsten Rahbek9, Henrik Glenner1,2, Martin V. Sørensen1,2 and Eske Willerslev1,2,*

1 Centre for GeoGenetics, Natural History Museum of Denmark, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen Ø, Denmark
2 Department of Biology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen Ø, Denmark
3 Department of Geology, University of Otago, PO Box 56, Dunedin 9054, New Zealand
4 Centre for Macroevolution and Macroecology, Research School of Biology, Australian National University, Canberra ACT 0200, Australia
5 Department of Ecology and Evolutionary Biology, Cornell Lab of Ornithology, Cornell University, Ithaca, NY 14850, USA
6 Fuller Evolutionary Biology Program, Cornell Lab of Ornithology, Cornell University, Ithaca, NY 14850, USA
7 Department of Biology, University of California, Berkeley, CA 94720-314, USA
8 Department of Statistics, University of California, Berkeley, CA 94720-314, USA
9 Center for Macroecology, evolution and Climate, Department of Biology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen Ø, Denmark

* Correspondence to be sent to: Centre for GeoGenetics, Natural History Museum of Denmark and Department of Biology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen Ø, Denmark; E-mail: ewillerslev{at}bio.ku.dk.


  Abstract

The remarkable fossil record of whales and dolphins (Cetacea) has made them an exemplar of macroevolution. Although their overall adaptive transition from terrestrial to fully aquatic organisms is well known, this is not true for the radiation of modern whales. Here, we explore the diversification of extant cetaceans by constructing a robust molecular phylogeny that includes 87 of 89 extant species. The phylogeny and divergence times are derived from nuclear and mitochondrial markers, calibrated with fossils. We find that the toothed whales are monophyletic, suggesting that echolocation evolved only once early in that lineage some 36–34 Ma. The rorqual family (Balaenopteridae) is restored with the exclusion of the gray whale, suggesting that gulp feeding evolved 18–16 Ma. Delphinida, comprising all living dolphins and porpoises other than the Ganges/Indus dolphins, originated about 26 Ma; it contains the taxonomically rich delphinids, which began diversifying less than 11 Ma. We tested 2 hypothesized drivers of the extant cetacean radiation by assessing the tempo of lineage accumulation through time. We find no support for a rapid burst of speciation early in the history of extant whales, contrasting with expectations of an adaptive radiation model. However, we do find support for increased diversification rates during periods of pronounced physical restructuring of the oceans. The results imply that paleogeographic and paleoceanographic changes, such as closure of major seaways, have influenced the dynamics of radiation in extant cetaceans.

Keywords: Cetacea; evolution; molecular phylogeny; palaeo-ocean restructuring; speciation

Received March 16, 2009; Revised May 18, 2009; Accepted August 24, 2009

Mette E. Steeman and Martin B. Hebsgaard contributed equally to this work and should be considered joint first authors.

Associate Editor: Susanne S. Renner


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