Beetle bioluminescence outshines aerial predators

Abstract

Bioluminescence is found across life and has many functions. Yet we understand very little about its timing and origins, particularly as a predator avoidance strategy. Understanding the timing between bioluminescence and predator origins has yet to be examined and can help elucidate the evolution of the ecologically important signal aposematism. Using the most prevalent bioluminescent group, fireflies, where bioluminescence primarily functions as aposematic and sexual signals, the timing for the origins of both potential predators of fireflies and bioluminescence is explored. Divergence time estimations were performed using a genomic-scale phylogenetic reconstruction Lampyridae, and multiple fossil calibration points, allowing for a robust estimate for the origin of beetle bioluminescence as both a terrestrial and aerial signal. Our results recover the origins of terrestrial beetle bioluminescence at 141 mya and aerial bioluminescence at 133 mya. These ages predate the origins of all known extant aerial predators (i.e., bats and birds) and support the much older terrestrial predators (frogs, ground beetles, lizards, snakes, and hunting spiders) as the most likely drivers of bioluminescence in beetles.

A Time-calibrated Firefly (Coleoptera: Lampyridae) Phylogeny: Using Genomic Data for Divergence Time Estimation

“…Instead, we selected three different data subsets and found that divergence time estimates agreed for all clades that were identical between analyses (Figure S18). We estimated a crown age of Lampyridae of 139.85 [108.43, 165.68] Ma which is considerably older than some previous estimates (Kusy et al 2018;Zhang et al 2018;Amaral et al 2019;McKenna et al 2019) but matches recent findings of earliest fossils belonging to Lampyridae (Kazantsev 2015) and is in agreement with some other studies (Bocak et al 2016;Toussaint et al 2017;Powell et al 2021) obtained from taxonomically broader studies. Thus, divergence time estimation using hundreds of loci is robust if a representative data subset is chosen.…”

“…Our divergences times overlap with the recent estimates by Powell et al (2021) using the same AHE dataset. The main difference in the two analysis are (i) the number of loci used (436 in Powell et al (2021) and up to 37 loci in this study), (ii) the chosen fossil calibrations, (iii) the fossil calibration approach (node dating vs the fossilized-birth-death process), and (iv) the software vs .…”

“…dataset. The main difference in the two analysis are (i) the number of loci used (436 in Powell et al (2021) and up to 37 loci in this study), (ii) the chosen fossil calibrations, (iii) the fossil calibration approach (node dating vs the fossilized-birth-death process), and (iv) the software BEAST vs RevBayes. It is very reassuring to see the large overlap in divergence time estimates despite these differences in the performed analysis.…”

“…Fireflies (Coleoptera: Lampyridae) consist of more than 2,000 globally distributed described species renowned for their charismatic lighted mating signals. A time-calibrated phylogeny of fireflies would be useful to study their diversification, biogeographical history, and the evolution of their bioluminescence (Fallon et al 2018; Powell et al 2021). Furthermore, divergence times on a genus and species level can provide new insights into recent population genetic processes.…”

“…Furthermore, divergence times on a genus and species level can provide new insights into recent population genetic processes. However, a robust time-calibrated phylogeny of widely-sampled Lampyrids does not currently exist (but see Powell et al (2021)). The lack of a time-calibrated phylogeny might be surprising given the enigmatic status of fireflies but is possibly due to debated phylogenic relationships (Branham and Wenzel 2001; Stanger-Hall et al 2007; Martin et al 2017) and general challenges in dating beetle phylogenies (Toussaint et al 2017).…”