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The evolutionary history of baleen whales in an Antarctic context

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Baleen whales (Cetacea: Mysticeti) are the largest animals that have ever lived and have an Antarctic history stretching back into the late Eocene. To develop an improved estimation of substitution rate and species divergence times for the mysticetes, we implemented a relaxed-clock phylogenetic approach using three fossil calibration dates: the divergence between odontocetes and mysticetes ;34 million years ago (Ma), between the balaenids and balaenopterids ;28 Ma, and the time to most recent common ancestor within the Balaenopteridae ;12 Ma. Data examined included seven mitochondrial genomes, a large number of mitochondrial control region sequences and nine nuclear introns representing five species of whales, within which multiple species-specific alleles were sequenced to account for within-species diversity (1-15 for each locus). The total data set represents 1.65 Mbp of mitogenome and nuclear genomic sequence. We also reviewed the available evidence for phylogenetic relationships among species from all published studies. The estimated substitution rate for the humpback whale control region (3.9%/million years, My) was slow relative to other mammal species with similar generation times (e.g., human-chimp mean rate 20%/My). The nuclear and mitogenome substitution rate estimates for baleen whales were roughly consistent with an 8- to 10-fold slowing due to a combination of large body size and long generation times. Surprisingly, despite the large data set of nuclear intron sequences, there was weak and conflicting support for multiple alternate hypotheses concerning the phylogenetic relationships of balaenopterid (rorqual) whales. This result is reflected in all other publications reviewed, spanning over 40 genetic loci, and suggesting that interspecies introgressions (hybridization) or a rapid radiation during the Miocene has obscured species relationships in the nuclear genome. The fossil record of baleen species diversifications has been strongly correlated with changes in fossil diatom diversity and isotopic oxygen levels over time; since nearly all baleen whale species are still strongly associated with the polar regions, the balaenopterid radiation is discussed in the context of Antarctic environmental changes in the Miocene

This talk is part of the British Antarctic Survey series.

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