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Can Extensive Reticulation and Concerted Evolution Result in a Cladistically Structured Molecular Data Set?
Hierarchy is the main criterion for informativeness in a data set, even if no explicit
reference to evolution as a causal process is provided. Sequence data (nuclear
ribosomal DNA ITS) from Armeria (Plumbaginaceae) contains a certain amount
of hierarchical structure as suggested by data decisiveness (DD) and distribution
of tree lengths (DTL). However, ancillary evidence suggests that extensive gene
flow and biased concerted evolution in these multi-copy regions have significantly
shaped the ITS data set. This argument is discussed using parsimony analysis of
four data sets, constructed by combining wild sequences with those from
different generations of artificial hybrids (wild + F1, F2, and backcrosses; wild +
backcrosses; wild + F1; wild + F2). As compared to the F1 hybrids, F2 show a
certain degree of homogenization in polymorphic sites. This effect reduces
topological disruption caused by F1 and is considered to be illustrative of how
extensive gene flow and biased concerted evolution may have modeled the wild
ITS data. The possibility that hierarchy has arisen as a result of ⎯or despite a
significant contribution from⎯ those two such potentially perturbing forces raises
the question of what kind of signal are we recovering from this molecular data
set.This work has been supported by Grants DGICYT PB94-0110 and DGES PB97-1146 of the Spanish Dirección General de Enseñanza Superior e Investigación CientÃficaPeer reviewe