Bootstrap confidence with larger
and 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- and 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.
The significance
of resolution of the branching order includes the results 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) is genetically almost identical
to Pacific Cod (G. macrocephalus), 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; (A) 16.0 KbpWhole-genome analysis from Coulson et al. 2006]