title: Radiation and speciation of pelagic organisms during periods of global warming: the case of the common minke whale, Balaenoptera acutorostrata.
abstract: How do populations of highly mobile species inhabiting open environments become reproductively isolated and evolve into new species? We test the hypothesis that elevated ocean-surface temperatures can facilitate allopatry among pelagic populations and thus promote speciation. Oceanographic modelling has shown that increasing surface temperatures cause localization and reduction of upwelling, leading to fragmentation of feeding areas critical to pelagic species. We test our hypothesis by genetic analyses of populations of two closely related baleen whales, the Antarctic minke whale (Balaenoptera bonaerensis) and common minke whale (Balaenoptera acutorostrata) whose current distributions and migration patterns extent are largely determined by areas of consistent upwelling with high primary production. Phylogeographic and population genetic analyses of mitochondrial DNA control-region nucleotide sequences collected from 467 whales sampled in four different ocean basins were employed to infer the evolutionary relationship among populations of B. acutorostrata by rooting an intraspecific phylogeny with a population of B. bonaerensis. Our findings suggest that the two species diverged in the Southern Hemisphere less than 5 million years ago (Ma). This estimate places the speciation event during a period of extended global warming in the Pliocene. We propose that elevated ocean temperatures in the period facilitated allopatric speciation by disrupting the continuous belt of upwelling maintained by the Antarctic Circumpolar Current. Our analyses revealed that the current populations of B. acutorostrata likely diverged after the Pliocene some 1.5 Ma when global temperatures had decreased and presumably coinciding with the re-establishment of the polar-equatorial temperature gradient that ultimately drives upwelling. In most population samples, we detected genetic signatures of exponential population expansions, consistent with the notion of increasing carrying capacity after the Pliocene. Our hypothesis that prolonged periods of global warming facilitate speciation in pelagic marine species that depend on upwelling should be tested by comparative analyses in other pelagic species.
authors: Institute of Cetacean Research, 4-5 Toyomi-cho, Chuo-ku, Tokyo 104-0055, Japan. pastene@cetacean.jp
authors: Luis A
authors: LA
authors: Pastene
authors: Mutsuo
authors: M
authors: Goto
authors: Naohisa
authors: N
authors: Kanda
authors: Alexandre N
authors: AN
authors: Zerbini
authors: Dan
authors: D
authors: Kerem
authors: Kazuo
authors: K
authors: Watanabe
authors: Yoshitaka
authors: Y
authors: Bessho
authors: Masami
authors: M
authors: Hasegawa
authors: Rasmus
authors: R
authors: Nielsen
authors: Finn
authors: F
authors: Larsen
authors: Per J
authors: PJ
authors: Palsbøll
mesh_terms: D000818:Animals; D001483:Base Sequence; D017931:DNA Primers; D004272:DNA, Mitochondrial / Q000235:genetics; D019143:Evolution, Molecular; D049810:Genetic Speciation; D005828:Genetics, Population; D005843:Geography; D017752:Greenhouse Effect; D050636:Minke Whale / Q000235:genetics*; D008969:Molecular Sequence Data; D009792:Oceans and Seas; D010802:Phylogeny; D011157:Population Dynamics; D017422:Sequence Analysis, DNA; D013045:Species Specificity; D013696:Temperature
chemical_list: D017931:DNA Primers; D004272:DNA, Mitochondrial