The diversification of plant-feeding insects is seen as a spectacular
example of evolutionary radiation. Hence, developing hypotheses to
explain this diversification, and methods to test them, is an important
undertaking. Some years ago, we presented the oscillation hypothesis as a
general process that could drive diversification of this and similar
interactions, through repeated expansions and contractions of host
ranges. Hamm and Fordyce recently presented a study with the outspoken
intention of testing this hypothesis where they concluded that the
oscillation hypothesis was not supported. We point out several problems
with their study, owing both to a misrepresentation of our hypothesis
and to the methods. We provide a clarifying description of the
oscillation hypothesis, and detail some predictions that follow from it.
A reanalysis of the data demonstrated a troubling sensitivity of the
“SSE” class of models to small changes in model specification, and we
caution against using them for tests of trait-based diversification.
Future tests of the hypothesis also need to better acknowledge the
processes behind the host range oscillations. We suspect that doing so
will resolve some of the apparent conflicts between our hypothesis and
the view presented by Hamm and Fordyce.