Glowing insects evolved surprisingly recently

Fireflies, one of the most conspicuous of nocturnal insects, are a relatively recent addition to the twilight world. A new analysis of all bioluminescent species suggests that those living on land might be mere tens of millions of years old ? a fraction of the age of bioluminescing marine groups.

Bioluminescence serves many purposes, from communication to finding mates, scaring off predators to attracting prey. Yet while many marine species bioluminesce, very few terrestrial animals have evolved the ability. Besides fireflies and a few other insects, only one snail, a few earthworms and a handful of millipedes can produce light.

To better understand this striking difference between land and sea Peter Vr?ansk?, a palaeobiologist at the Slovak Academy of Sciences in Bratislava, and his colleagues, studied the evolutionary history of all known marine and terrestrial groups of bioluminescent species.

Their results show that most marine light-producing animals can trace their origins back to the Devonian period, at least 400 million years ago. Bioluminescent landlubbers are all much younger ? no more than 65 million years old.

"There are unexpected, but very important indications for a modern origin of luminescence on land," says Vr?ansk?.

It's possible that luminescent species appeared on land only when night life began to diversify, says Vr?ansk? ? although there are indications that some of the dinosaurs and early birds living before the bioluminescent insects evolved were nocturnal.

Another possibility is that terrestrial species have only recently cracked the problem of disposing of the toxic by-products of bioluminescence ? less of an issue in the marine realm where temperatures are often cooler and more stable than in tropical forests.

Whatever the reason for the discrepancy, the future for terrestrial bioluminescent species might not be bright, says Vr?ansk?. "While bioluminescent insects have diversified into 13 known species, most of them are known from a single collected individual," he says. "That suggests they are extremely rare and vulnerable to extinction."

That includes new species that are only just being described by science. Vr?ansk?'s analysis, for example, took in a new species of bioluminescent cockroach his team has named Lucihormetica luckae. Uniquely, it produces light on its body in the same pattern and at the same frequency as the click beetle (Pyrophorus). Because Pyrophorus is toxic ? and Lucihormetica luckae is not ? it seems likely that the cockroach is the first known species to use bioluminescence to mimic another species for defence purposes.

Journal reference: Naturwissenschaften, DOI: 10.1007/s00114-012-0956-7

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