Geography Reference
In-Depth Information
geographic patterns of mtDNA. A long-term extrinsic barrier to genetic ex-
change is the most commonly invoked explanation.
Category II (deep gene tree, major lineages broadly sympatric) (
fig.
7.6b
): It is characterized by pronounced phylogenetic gaps between some
branches in a gene tree, with main lineages codistributed over a wide area.
It could arise in a species of which some anciently separated lineages might
have been retained by chance, whereas many intermediate lineages were
lost over time by gradual lineage sorting.
Category III (shallow gene tree, lineages allopatric) (
fig. 7.6c
): Most or
all haplotypes are related closely yet are localized geographically. Contem-
porary gene flow has been low enough in relation to population size to have
permitted lineage sorting and random drift to promote genetic divergence of
populations that were in historical contact recently.
Category IV (shallow gene tree, lineages sympatric) (
fig. 7.6d
): It is ex-
pected for high-gene-flow species of small effective size whose populations
have not been separated by long-term barriers.
Category V (shallow gene tree, major distributions varied) (
fig. 7.6e
):
This category is intermediate between Categories III and IV and involves
common lineages that are widespread plus closely related lineages that are
confined to one or a few nearby localities. It implies low contemporary gene
flowbetweenpopulationsthatareconnectedtightlyinhistory.Commonhap-
lotypes are often plesiomorphic, and rare haplotypes are the presumed apo-
morphic conditions.
