Green means go

Natural History, March, 2004 by Stephan Reebs, Bioluminescent

If moviemakers ever need a new insect to star as, say, a living traffic light in a sequel to Antz or A Bug's Life, they could do worse than to cast the Jamaican click beetle. Unique among bioluminescent animals, Pyrophorus plagiophthalamus emits light of different colors from different organs: a pair on its back (yellow-green to green light) and a loner on its belly (yellow-green to orange).

Uwe Stolz, a biologist formerly at the University of Notre Dame in Indiana, and his colleagues have established which 9ene the click beetle's belly organ activates to make luciferase, the enzyme involved in biological light emission. They've also found that evolutionary changes in key amino acids in the luciferase have translated into a shift toward orange. What's driving the changes? Sexual selection, perhaps.

Flying overhead during mating season, the males switch on their belly lights; down in the brush, females that find the lights attractive respond with their back lights. These days, guys that flash orange may be getting the green light more often than those that flash old-fashioned yellow-green. ("Darwinian natural selection for orange bioluminescent color in a Jamaican click beetle," Proceedings of the National Academy of Sciences 100:14955-59, December 9, 2003)