Wilkinson support calculated with exact probabilities: An example using Floricaula/LEAFY amino acid sequences that compares three hypotheses involving gene gain/loss in seed plants
Mw. Frohlich et Gf. Estabrook, Wilkinson support calculated with exact probabilities: An example using Floricaula/LEAFY amino acid sequences that compares three hypotheses involving gene gain/loss in seed plants, MOL BIOL EV, 17(12), 2000, pp. 1914-1925
This paper describes a method for quantifying the extent to which a charact
er supports a hypothesized monophyletic group. The basic idea was first pro
posed by Wilkinson in 1998; hence, we call it Wilkinson support. A characte
r provides Wilkinson support if it could have changed state on the branch l
eading to the hypothesized monophyletic group without requiring any extra s
teps in an evolutionary tree. We describe a method to determine the exact p
robability that a character would provide Wilkinson support for a random gr
oup of the same size as the hypothesized monophyletic group. A character's
weight is defined as the negative natural log of this probability. The sum
over all characters of these weights in a data set is a measure of total we
ighted support. We exemplify this method using 30 Floricaula/LEAFY amino ac
id sequences. One copy of this gene occurs in angiosperms, but two copies o
ccur in the other four seed plant groups. Angiosperms could have been primi
tively single-copy or could have lost either of the two paralogs. These pos
sibilities correspond to three hypotheses of monophyly. We use total weight
ed Wilkinson support to evaluate these three hypotheses, and all three are
shown to be significantly different from random as individual hypothesized
monophyletic groups. Comparing these three hypotheses for total weighted su
pport reveals that one has much more support than do the other two. This hy
pothesis favors the "mostly-male" theory of flowering-plant origins.