Polymorphism in Nemoria arizonaria juveniles

Nature fascinates me both biologically artistically. Following a some brutal cramming  diligent, well-managed studying for my Ecology exam, my brain has been in a bit of Biology hyperdrive throughout the week, and one study concerning phenotypic plasticity has stuck with me.

The Nemoria arizonaria (emerald moth) lay two sets of eggs, once during early spring and again in the summer. Those larvae that hatch in the spring feed on Oak Catkins and thus, take on the appearance of these plants while those that hatch in the summer feed on Oak Leaves and take on a completely different appearance. There is no discernible genetic difference between offspring hatched during different times of the season. In fact the offspring are genetically identical (clones), thus the change in phenotype is derived from a developmental alteration where different genes are activated based  on environmental cues. Through experimentation these cues have been determined to be completely diet based. Oak catkins and oak leaves are very chemically different, containing different amounts of tannin (polyphenols). Depending on the plant that the caterpillars consumed, they took on the same appearance.

Catkin Juvenile

Oak leaf-twig Juvenile 

Experimentation, of course involved controlled environments with extraction of the plant chemicals to determine that these were in fact the cause of the polymorphism, and juveniles that were supplemented with larger amounts of polyphenol (more abundant in Oak leaves) and then fed catkins, still developed to look like the twigs from which oak leaves sprout. This plasticity is a display of unique adaptation since camouflage greatly increases changes of evading predation by birds. Plus, they just look pretty awesome as well. The adult moths also resemble oak leaves, further increases chances of survival.

Adult Nemoria arizonaria 

Greene, E. 1989. A diet-induced developmental polymorphism in a caterpillar.  Science 243:643-646.