PATTERNS OF DIVERSIFICATION IN PHYTOPHAGOUS INSECTS

molecular phylogenetics including phylogeography sensu Avise (2000), which is not
treated here.
Phylogenesis of Host Range
Special attention has focused on the evolution of diet breadth, i.e. the diversity of
host plants fed on by a single herbivore species. Restriction to a small subset of the
available plants is a dominant feature of phytophagous insect ecology. In addition to
demanding an explanation in its own right (Bernays and Chapman 1994), it has made
herbivorous insects a leading exemplar for investigating the ecological and evolutionary
consequences of specialization (Schluter 2000, Funk et al. 2002). Phylogenies can
potentially serve three roles in the study of host range. First, they delimit independent
contrasts for identifying traits or circumstances whose occurrence is correlated with
evolutionary changes in host range, facilitating both comparative and experimental
studies of the adaptive significance and consequences of those changes. Second, the rate
and direction of changes in host range inferred on a phylogeny can point to
genetic/phylogenetic constraints or lack thereof on host range evolution. Third,
phylogenies can in principle detect differential effects of broad versus narrow host range
on diversification rates. Analyses of the second and third kinds could potentially support
non-adaptive, macroevolutionary explanations for the predominance of host specificity,
such as more frequent speciation in specialists than in generalists, in contrast to
hypotheses invoking a prevailing individual advantage (Futuyma and Moreno 1988).
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