|
|
|
|
|
|
|
||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | ||||
|
Fig. 9. Evolution of O/P specification mechanisms in clitellate annelids deduced
from phylogenetic analysis. The relationship of the three Helobdella
laboratory populations used here is based on cytochrome oxidase I sequence
analysis by A. Bely (personal communication); the oligochaete Tubifex
hattai is an outgroup. Branch lengths do not reflect the genetic distance
between taxa. Evolutionary changes of developmental characters are marked by
short bars striking across the tree branches, and are assigned on the basis of
parsimony. The role of the Q lineage as a P fate inducer evolved either as an
apomorphy (1a) on the branch leading to the Helobdella leech species
shown here, or is a plesiomorphic trait lost (1b) on the branch leading to
Tubifex. The role of mesoderm as a redundant P fate inducer appears
to have evolved as an apomorphy (2) on the branch leading to H.
robusta (Austin) following its separation from H. robusta
(Sacramento).
|
