PATTERNS OF DIVERSIFICATION IN PHYTOPHAGOUS INSECTS

phylogeny by the total number of species with known hosts, including ones not included
in the phylogenetic study. We will refer to these two estimates, in the order here
described, as maximum versus minimum. In further contrast to the earlier tabulation, this
one excluded the relatively few polyphagous species (defined here as those using more
than two plant families); several phylogenies including a high proportion of polyphagous
species were excluded, as well. A detailed tabulation of the phylogenies is given in
Supplementary Table S2 (www.chemlife.umd.edu/entm/mitterlab), while the results are
summarized in Fig. 2.1.
The histogram of Fig. 2.1 shows a result very similar to that of the earlier
tabulation, underscoring the prevalence of host conservatism. The distributions of host
family shift frequencies, strongly right-skewed, have medians of 0.08 (maximum
frequency) and 0.03 (minimum frequency). Statistical tests of the hypothesis of non-
random phylogenetic conservatism in host genus or family use have now become routine
within studies of the kind tabulated here. These most often use the so-called PTP test
(Permutation Tail Probability; Faith and Cranston 1991), in which the null distribution is
generated by random re-distribution of the observed host family associations across the
insect phylogeny. Significant “phylogenetic signal” has been detected in nearly every
instance (see e.g., Table 2.2). In addition, several authors have used randomization tests
on frequencies of shift among different host families or groups thereof to show that these
preferentially involve related high-rank host taxa (Janz and Nylin 1998, Ronquist and
Liljeblad 2001); conservatism at the level of major angiosperm clades (APGII 2003) is
probably common as well.
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