Although the results of a particular analysis may be
favored a priori, it is still worth exploring the effect of
assumptions on these results.
Molecular systematists commonly use taxonomic
congruence across different methods of data analysis as
a measure of clade robustness. Our varied analyses
generally shared more than 50% of the clades, except
optimization alignment with gap costs of 4–8 (Table 2).
Static alignments that dismiss gap information (gap as
missing and Bayesian inference, Table 2) are most similar
to the equal cost optimization alignment results.
This surprising result may relate to the way optimization
alignment treats gaps. Optimization alignment minimizes
the numbers of indel events necessary to explain
the data for given gap and base transformation costs.
Our analyses corroborate this point, although at first
sight it may seem the opposite. Optimization alignment
implied more characters than did static Clustal (2825
and 2562, respectively). However, shorter alignments do
not necessarily result in most parsimonious explanations
of the data. In this particular situation, optimization
and static alignments are difficult to compare because
parameter costs vary (gap cost 1, ts/tv 1 in the former,
gap opening 8, gap extension 2 or 4, ts/tv 0.5 in Clustal).
The number of informative characters is a less tricky
comparison. Implied alignment yields fewer number of
informative characters (916) than the static alignment,
regardless of the gap treatment (975 as missing data,
1092 as 5th state). Fewer informative indels (gaps in a
static alignment) probably affect the final output less,
making the results more similar to the static alignment
analyses when gaps are not considered. Of course, the
generality of these comments must await further research
on alternative alignment methods and in additional
taxa and genes.