Figure 1.
The SPR move makes coordinated changes to the species tree and the gene trees to avoid
conflicts between the proposed species tree and the gene trees. The species tree is
represented by the light blue boundary pipes while the gene tree is represented by lines
running inside the species-tree branches. The SPR move prunes off branch
-
on the species tree
(including clade 
) and reattaches it to a randomly-chosen
target branch 
, while changing the gene trees through
similar SPR moves to avoid conflict. Moved nodes on the gene tree reside in species
(
) or in a species on the
path from 
to 
(the common ancestor of
and 
), and have exactly one
daughter node with descendents in 
only. They are marked by
, and are pruned off and regrafted
to a randomly chosen branch on the gene tree that resides in a species on the path from
to 
. Other affected nodes,
marked by 
, 
or
, have their population IDs changed by
the move.