Scientist Paul Marek attempted to explain the origin of bioluminescence in a species of millipede living in California. According to his study, the property evolved as a way to cope with dry environments and grew into a warning signal for predators only later.
Bioluminescence in millipedes. Photo credits: National Geographic Society Expeditions Council.
Millipedes residing in California have a bright way of discouraging predators from feeding on them: they glow in the dark as a sign of warning of their toxicity to enemies. Scientists have provided more insight into this ability of theirs: bioluminescence might not have evolved as a way to repel predators, but just as a survival tactic in a hot and dry habitat. The paper has been published in the Proceedings of the National Academy of Sciences on the 4th of May.
According to the scientists, the discovery implies that small evolutionary steps have ultimately led to complex features displayed in organisms.
“Living things glow in many different colors and for many different reasons, but now we know that the early evolutionary role of bioluminescence may be completely different than its modern day function,” said Paul Marek, an assistant professor of entomology in the College of Agriculture and Life Sciences.
“This discovery clarifies the evolutionary origins of many complex traits, not just bioluminescence.”
The bioluminescent trait of millipedes was a foggy subject because of its unknown origins; it was difficult to understand how the characteristic came to be.
“Because we’re looking at a trait that has been shaped by millions of years of evolution, these traits often bear little resemblance to their ancestral form,” Marek said.
However, Marek alleged having solved the enigma after he revisited a millipede from California. The bug was collected decades ago, back in 1967. It has only been rediscovered by Marek during a fieldwork in San Luis Obispo, California.
The millipede, small in size, lives at a lower elevation with few predators. Initially, it was not thought to belong to the genus of millipedes that bioluminesce, the Motyxia. After its DNA was sequenced though, it was renamed by the scientists and its name was changed to Motyxia bistipita.
The bioluminescent property of the M. bistipita that confers onto it a green-blue glow is due to the reaction of a photoprotein that requires magnesium. This process might have evolved because of its properties as an antioxidant. The organism might have used it to cope with a low-lying, dry habitat. Thereafter, the ability to glow might have extended as a nocturnal warning to predators in millipedes living on higher elevations with more enemies.
“After we sequenced them we were able to place the millipede on an evolutionary tree with other bioluminescent species in Motyxia,” Marek said.
“We demonstrated the faint bioluminescence of the low-lying millipedes represented an older trait and the brighter luminescence of their mountain cousins represented a newer trait.”
“Evolution of a complex feature such as bioluminescence is difficult to understand at first glance but totally makes sense when considered in an evolutionary context,” Marek said.
“We showed that bioluminescence, a trait typically used as a warning pattern evolved gradually and for a different purpose.”