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Figure 9.18
Phylogenetic relationships among nine different ciliates based on
sequences of the rDNA gene (Hewitt et al., unpublished).
rDNA sequences match. Thus, in comparisons between pairs of organisms, the
sequence of the rDNA gene in
Euplotes aediculatus
has the least similarity
with the rDNA sequence of any of the other eight organisms. Consequently,
Euplotes
must have been the first to split away from the ancestral line leading
to the other eight organisms in Figure 9.18.
Urostyla grandis
split away next,
followed by
Engelmanniella mobilis
, and then by
Stylonychia lemnae
. Finally,
the evolutionary line split into two lines, one leading to the three
Sterkiella
species and the other to
Stylonychia pustulata
and
Oxytricha
sp. (Misty).
In Figure 9.19 the structures of the micronuclear actin I genes in the nine
organisms are arranged in the evolutionary pathway defined by the rDNA tree
in Figure 9.18. The pathway begins with a common progenitor of the nine
organisms, whose micronuclear actin I gene contained no IESs. The common
progenitor gave rise to two lines of descent (Figure 9.19). One line led to
contemporary
Euplotes aediculatus
, in which no IESs have been inserted into
