How far would leaf-eating insects go to dine on their favorite food? Perhaps the other side of the world, according to researchers at Penn State who found insect damage on fossil leaves from South America that is nearly identical to what is seen today on those trees' living relatives in Australia.
The findings, recently published in the journal New Phytologist, suggest multiple insect herbivore lineages have fed off gum trees, which are plants in the well-known Australian genus Eucalyptus, for at least 52 million years and in locations across the Southern Hemisphere.
"The big stunning result is that every type of insect damage on the fossils survives today on Eucalyptus," said L. Alejandro Giraldo, a doctoral student in the Department of Geosciences at Penn State and lead author of the study. "It suggests that the insects that were eating the Eucalyptus plants in the past tracked their plant food through time."
Fossil plant and insect relationships can provide important information about how terrestrial ecosystems evolve through geologic time, but fossil evidence that directly links associations from deep time to the modern-day has been scarce, the researchers said.
"There is an evolutionary arms race between plants and insects," Giraldo said. "Plants evolve new defenses, insects find a way to go around them to continue to feed, and this cycle repeats through time. This work shows nicely that the evolutionary association between herbivorous insects and their plant food can be stable through time. We are showing that all the damage you see in the fossils you can see in the present, so those relationships may be fairly consistent."
