Abstract

Baleen whales (suborder Mysticeti) comprise 11 extant species that are classified into four families. Although several phylogenetic hypotheses about these taxa have been proposed, their phylogenetic relationships remain confused. We addressed this problem using short interspersed repetitive element (SINE) insertion data, which now are regarded as almost ideal shared, derived characters at the molecular level. We reconstructed the phylogenetic relationships of baleen whales by characterizing 36 informative SINE loci. One of the intriguing conclusions is that balaenopterids and eschrichtiids radiated very rapidly during a very short evolutionary period. During this period, speciation occurred in balaenopterids and eschrichtiids while newly inserted SINE loci remains polymorphic. Later on, these SINEs were sorted incompletely into each lineage. Thus, there are now inconsistencies among species regarding the presence or absence of a given SINE. This is in sharp contrast to the phylogeny of toothed whales, for which no SINE inconsistencies have been found. Furthermore, we found monophyletic groupings between humpback and fin whales as well as between (sei + Bryde's) whales and blue whales, both of which have not previously been recognized. The comprehensive SINE insertion data, together with the mitochondrial DNA phylogeny that was recently completed (Sasaki, T., M. Nikaido, H. Healy et al. 2005. Mitochondrial phylogenetics and evolution of mysticete whales. Syst. Biol. 56:77-90; Rychel, A. L., T. W. Reeder, and A. Berta. 2004. Phylogeny of mysticete whales based on mitochondrial and nuclear data. Mol. Phylogenet. Evol. 32:892-901), provide a nearly complete picture of the evolutionary history of baleen whales.