How can we detect the signature of coevolution?
• First the phylogeny for the hostplant species should parallel the phylogeny for the herbivore. • In addition, the complexity of toxins in plants should be found in the youngest clades of herbivores. The host preferences of the herbivores and the ability of the herbivores to detoxify the toxins should mirror the acquistion of plant toxins. • Finally, the two groups should show similar ages so that true coevolution is occurring, each branch point coincides with the branch point in the other clade. I have cartooned the idealized clades for hostplant and herbivore below. Note that there is a perfect correspondence between clades in the ideal case. Nature presents us with some near perfect examples. I will discuss Farrel’s data on the coevolution between beetles and their milkweed hosts. The beetles have a tight association with their hosts which is required for true coevolution and eggs in that larvae and adults require the milkweed. We can contrast the beetle associations with butterfli
