Bootstrap confidence with larger vs smaller data sets

    Evolutionary relationships among Gadid fishes (cods & pollocks) were analyzed first with partial (0.8 Kbp, Diagrams B & C, below) and later with complete mtDNA genomes (16.0 Kbp, above). The 20-fold increase in data allows resolution of phylogenetic relationships by the bootstrap with greater confidence. Note that all but one of the within- & among-species relationships in the upper tree are resolved at >95% confidence, whereas a minority of branches are so resolved in the smaller data set.

    Resolution of the branching order shows that (1) the two Pacific Gadid species, Pacific Cod (Gadus macrocephalus) and Alaska Pollock (Theragra chalcogramma) are separate invasions of the Pacific basin, (2) the latter should be included in Gadus as Gadus chalcogrammus, rather than placed in a separate genus, and (3) Greenland cod (G. ogac) are genetically almost identical to Pacific Cod (G. macrocephalus) despite their geographic separation, which suggests a relatively recent re-invasion of the Arctic / Atlantic basin by the former.

B & C: 0.8 Kbp analysis from Carr et al. 1999, by Neighbor-Joining and Maximum Parsimony methods;
(A) 16.0 Kbp Whole-genome analysis from Coulson et al. 2006