Why Do Fireflies Glow? New Research Upends Current Origin Theories

Recent genomic research shows firefly bioluminescence predates their toxic traits, possibly evolving as a response to oxidative stress.

Genomic analysis has overturned the leading hypothesis for the origin of firefly lights. Previously, it was believed that the Lampyridae family of beetles, commonly known as fireflies, initially evolved their bright lights as a warning signal advertising their toxicity to predators, which was later adopted as a mating signal. This explanation would explain why eggs, larvae, and pupae also glow.

Genetic Insights into Firefly Bioluminescence

Researcher Ying Zhen and colleagues put the conventional wisdom to the test by compiling a family tree of fireflies and tracing the evolution of the chemical compounds that make fireflies toxic: lucibufagins. The team collected fresh samples for 16 species of Lampyridae from diverse locations across China, along with two related species, which they analyzed along with preexisting collections and genetic data. In total, the authors compiled genomic-level data from 41 species. For each species, the authors also looked for lucibufagins using liquid chromatography-mass spectrometry.

Bioluminescence vs. Toxin Presence in Fireflies

Their study revealed that the lucibufagins are only found in one subfamily of fireflies, whereas bioluminescence is found widely across the entire family, strongly suggesting that the toxin evolved after the development of bioluminescence.

New Hypothesis on the Origin of Firefly Light

So why did fireflies first begin to shine? The substrate of firefly bioluminescence, luciferin, has previously been shown to have antioxidant properties. Ying Zhen and colleagues found that firefly ancestors evolved and diversified during a historical period when atmospheric oxygen levels continued to rise from a historical low after the Toarcian Oceanic Anoxic Event. The authors also note that glowing millipedes are thought to initially evolved bioluminescence to cope with oxidative stress in hot, dry environments and suggest that perhaps the fireflies followed a similar path.

Reference: “Firefly toxin lucibufagins evolved after the origin of bioluminescence” by Chengqi Zhu, Xiaoli Lu, Tianlong Cai, Kangli Zhu, Lina Shi, Yinjuan Chen, Tianyu Wang, Yaoming Yang, Dandan Tu, Qi Fu, Jing Huang and Ying Zhen, 25 June 2024, PNAS Nexus.
DOI: 10.1093/pnasnexus/pgae215

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