Identification of Cenocrons - Evolutionary Biogeography - page 275

1. Most species are composed of geographic populations whose members
occupy recognizable matrilineal branches of an extended intraspecific
pedigree. Populations of most species display significant phylogeographic
structure supported by mtDNA data.
2. Species with limited or shallow phylogeographic population structure have
life histories conducive to dispersal and have occupied ranges free of firm,
long-standing impediments to gene flow. Nonsubdivided, high-dispersal
species may have limited phylogeographic structure.
3. Intraspecific monophyletic groups distinguished by large genealogical
gaps usually arise from long-term extrinsic biogeographic barriers to gene
flow. Major phylogeographic units within a species reflect long-term histor-
ical barriers to gene flow. This hypothesis has four corollaries representing
four aspects of genealogical agreement ( fig. 7.5 ):
a. Agreement across sequence characters within a gene ( fig. 7.5a ) :
Everydeepphylogenetic split intheintraspecific genetreeissupported
concordantly by multiple diagnostic characters (e.g., nucleotides or re-
striction sites) within the mitochondrial genome. If this is not the case,
such matrilineal splits would not be evident in the analysis, nor would
they receive significant support.
b. Agreement in significant genealogical partitions across multiple genes
within a species ( fig. 7.5b ) : Empirical examples show general agree-
ment between deep phylogeographic topologies in multiple gene trees
(e.g., mitochondrial and nuclear) within the species analyzed. These
deep branch separations characterize the same sets of geographic
populations.
c. Agreement in the geography of gene tree partitions across multiple
codistributed species ( fig. 7.5c ) : Several sympatric species with com-
parable natural histories or habitat needs proved to be phylogeograph-
ically structured in similar fashion. In particular, divergent branches in
the intraspecific gene trees might map consistently to the same geo-
graphic regions.
d. Agreement of gene tree partitions with spatial boundaries between
traditionally recognized biogeographic units ( fig. 7.5d ) : An emerging
generality from phylogeographic analyses is that deeply separated
phylogroups at the intraspecific level are confined to biogeographic
provinces or districts as identified by systematic biogeography.