Taxacom: Molecular dispersal update

[John Grehan]

Not much of an update, but I have found it endlessly fascinating how no one
will defend molecular dispersalism with respect to the Achilles Heel of the
methodology that has been raised for over a decade now (and two decades for
clade age estimation. For my own taxonomic focus with Lepidoptera I have
several times addressed the issues to authors of various papers. No one
responds. Science that does not address competing research programs is not
science, in my view.

The principle defects (I think I have these correctly stated, but OK to
correct) that have been identified are:

1. Molecular divergence based on fossil or island age calibrations can
empirically represent minimum ages only.
2. Priors that are used to set upper age limits are specified, not
calculated from the data.
3. Ancestral areas programs will generate sequential dispersal rather than
sequential vicariance for phylogenetic grades (such as where basal lineages
are in one area and more derived clades are in other areas - a sort of
derived Hennig's progression 'rule').
4. Ancestral areas programs analyze a few (almost always less than 15)
geographically bound area units that have no direct relationship to the
distributions of taxa.
5. Ancestral areas programs accept the existence of centers of origin for
allopatric taxa.
6. Most molecular studies do not study the actual distributions of taxa.

In addition, most molecular studies avoid mapping the individual
distributions of their taxa (and species or clades within) as if they are
afraid of geography.

The literature on molecular biogeography is as vast as the taxa in this
world. So if anyone has come across a detailed defense of the
abovementioned problems (which is a bit like saying that a plane without
wings is a 'problem') I would be interested to hear about that.

Cheers, John
-- 
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