Firefly genomes illuminate parallel origins of bioluminescence in beetles

Fireflies and their fascinating luminous courtships have inspired centuries of scientific study. Today firefly luciferase is widely used in biotechnology, but the evolutionary origin of their bioluminescence remains unclear. To shed light on this long-standing question, we sequenced the genomes of two firefly species that diverged over 100 million-years-ago: the North American Photinus pyralis and Japanese Aquatica lateralis. To compare bioluminescent origins, we also sequenced the genome of a related click-beetle, the Caribbean Ignelater luminosus, with bioluminescent biochemistry near-identical to fireflies, but anatomically unique light organs, suggesting the intriguing but contentious hypothesis of parallel gains of bioluminescence. Our analyses support two independent gains of bioluminescence between fireflies and click-beetles, and provide new insights into the genes, chemical defenses, and symbionts that evolved alongside their luminous lifestyle. MethylC-seq libraries were prepared from high molecular weight (HMW) DNA extracted from four Photinus pyralis Mercer Meadows New Jersey (MMNJ) males according to a previously published protocol (Urich et al. 2015; doi:10.1038/nprot.2014.114) and sequenced on an Illumina NextSeq 500 to an expected depth of ~36x. Sequencing data was aligned to Ppyr1.3 assembly using the latest version of methylpy (Schultz et al. 2015; doi:10.1038/nature14465; https://bitbucket.org/schultzmattd/methylpy/wiki/Home). In total, 49.4M reads were mapped corresponding to an actual sequencing depth of ~16x. A sodium bisulfite non-conversion rate of 0.17% was estimated from Lambda phage genomic DNA.