Beetle bioluminescence outshines extant aerial predators

Abstract

We understand very little about the timing and origins of bioluminescence, particularly as a predator avoidance strategy. Understanding the timing of its origins, however, can help elucidate the evolution of this ecologically important signal. Using fireflies, a prevalent bioluminescent group where bioluminescence primarily functions as aposematic and sexual signals, we explore the origins of this signal in the context of their potential predators. Divergence time estimations were performed using genomic-scale datasets providing a robust estimate for the origin of firefly bioluminescence as both a terrestrial and as an aerial signal. Our results recover the origin of terrestrial beetle bioluminescence at 141.17 (122.63-161.17) Ma and firefly aerial bioluminescence at 133.18 (117.86-152.47) Ma using a large dataset focused on Lampyridae; and terrestrial bioluminescence at 148.03 (130.12-166.80) Ma, with the age of aerial bioluminescence at 104.97 (99.00-120.90) Ma using a complementary Elateroidea dataset. These ages pre-date the origins of all known extant aerial predators (i.e. bats and birds) and support much older terrestrial predators (assassin bugs, frogs, ground beetles, lizards, snakes, hunting spiders and harvestmen) as the drivers of terrestrial bioluminescence in beetles. These ages also support the hypothesis that sexual signalling was probably the original function of this signal in aerial fireflies.

Keywords: Lampyridae; aposematism; divergence time estimation; phylogeny; predation.

Figure 1.

Two divergence-time calibrated phylogenies of Elateroidea using LN and BD (based on data from Martin et al. [36], top, and Douglas et al. [37], bottom) with results of ancestral state reconstruction for both terrestrial and aerial bioluminescence depicted at appropriate nodes. Grey vertical bars represent 50 million years. (Online version in colour.)

Figure 2.

Comparison of divergence time estimates for nodes representing the origins of both terrestrial (green line) and aerial (blue line) bioluminescence and with published clade origin ages for potential extant (black) [,–,–71] and extinct (grey) predator groups [63]. Times are written out for Opiliones, Anura and Araneae due to age and figure constraints. Dotted vertical lines represent 50 million-year intervals. (Online version in colour.)