_e0134207_Fig_7a.jpg)
Numbers of migration events required in genetically structured vs un-structured populations
Consider a population of 16 individuals distributed
over four populations. All populations originate from
one of the four populations [shown here in blue, but the color
makes no difference]. (a) If the data show that all the
individuals in any one population are members of the same
genetic lineage (the populations are distinct), the
distribution can be explained by a minimum of L=3
migration events (cross-bars), to establish four distinct
populations. (b) If the data show that all populations
consist of equal numbers of individuals from the different
lineages (the populations are homogeneous), this
distribution requires a minimum of L=12 migration
events. (c) If the population comprises two
sub-populations whose members are from two separate lineages,
and the two sub-populations are heterogeneous, the
distribution can be explained by a minimum of L=9
events. However, (e) if one of the sub-populations is
itself structured as two distinct sub-populations, for a total
of three sub-populations, a minimum of L=6 migration
events is required, and (d) If the structure is
basically as in (e), but the two sub-sub-populations
are not completely distinct, a minimum of L=7
migration events is required.
Structured populations required fewer migration events than do random populations, and the number increases as the structure decreases. As the number of individuals increases, the range of the number of events increases, and the number of events required by the observed tree can be compared with the lengths of trees drawn at random.
Structured populations required fewer migration events than do random populations, and the number increases as the structure decreases. As the number of individuals increases, the range of the number of events increases, and the number of events required by the observed tree can be compared with the lengths of trees drawn at random.