Title:
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Evaluating Nested Clade Phylogeographic Analysis Under Models of Random Mating and Restricted Gene Flow
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Phylogeography is a field that has been constantly developing. Many methods
exist that can be used to tease apart the demographic processes and
events that affect a species evolution. One method in particular, Nested
Clade Phylogeographic Analysis (NCPA), has become a popular method for
doing this. It claims that the distance statistics it uses can discriminate between
multiple demographic scenarios. However, a major limitation of NCPA
is that it does not provide estimates of error. Lack of automation of two stages
in NCPA has meant few datasets can be simulated. A fully automated package,
ANeCA, is developed, tested and applied to published datasets to recover
published inferences. Many inferences are recovered showing that ANeCA is
representative of a typical application of NCPA. ANeCA is also applied to
data simulated under a model of panmixia. Results show on average 76%
of datasets gave rise to at least one inference of an event or process when
there was no geographic association. This is due to the generation of multiple
statistics per clade, and multiple clades per dataset. It is also shown that the
statistics are not independent of each other, making it difficult to correct the
multiple tests performed. ANeCA is also applied to simulated data under
three models of gene flow; an island model; a stepping stone model; and a lat-
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tice model with some long distance dispersal. The results show that NCPA
has a tendency to infer Restricted Gene Flow with Isolation By Distance,
and Contiguous Range Expansion, under panmixia and the three gene flow
models. Unlike the panmictic model where other inferences were rare, many
inferences are found in higher frequencies irrespective of the underlying gene
flow model. Comparison between the island and stepping stone models show
that NCPA is unable to discriminate between long and short distance movements.
Three classical summary statistics; AMOVAj Fu's FSj and the Mantel
test, were also calculated on each dataset. Results show false positives rates
to be around 5% for the AMOVA method and Mantel test, and 3% for Fu's
Fs at the deme level. In general the AMOVA method is more sensitive to
population structure than NCPA, and the Mantel test is more sensitive to
isolation by distance than NCPA. The results that have been obtained in this
study suggest that previous publications that have used NCPA have most
likely made false inferences and it is recommended that classical, and most
probably model-based, methods of inference should be used in preference to
NCPA.
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