Mallet proposed an alternative parapatric-based hypothesis, where color patterns evolved through a process similar to Wright's shifting balance (5).Under his hypothesis, novel color patterns became common enough locally to be fixed by frequency dependent selection.This notion is supported by recent association data showing that only loci tightly linked to the adaptive color patterns have restricted gene flow at racial hybrid zones within both butterflies is one of only a handful of cases (e.g., refs.18–20), where it is now possible to examine the history of a radiation at the loci responsible for the adaptive changes.As a test of these hypotheses, molecular markers unlinked to color pattern, including mt DNA (9–11), nuclear sequences (12), and amplified fragment length polymorphism (AFLPs) (11), have been used to more carefully dissect the timing of the two parallel radiations and the relationships among color pattern races within the two comimics.
This figure was redrawn using the range maps in refs. arose simultaneously when populations of the two species became isolated together in forest refugia during Pleistocene cooling (2–4).
This theory refuted a simple refugium hypothesis, as both species did not evolve simultaneously.
Furthermore, rather than clustering by color pattern, phylogenies from these studies cluster individuals within both species by geographic proximity, with the major lineages dividing the Amazon from the Central American/West Andean region (9–12).
By deciphering the history of such diverse phenotypes we gain a clearer understanding of the evolutionary process, including the tempo and mode of phenotypic change.
butterflies present one of the most striking examples of a recent phenotypic radiation.