Genome Size in North American Fireflies: Substantial Variation Likely Driven by Neutral Processes

Abstract

Eukaryotic genomes show tremendous size variation across taxa. Proximate explanations for genome size variation include differences in ploidy and amounts of noncoding DNA, especially repetitive DNA. Ultimate explanations include selection on physiological correlates of genome size such as cell size, which in turn influence body size, resulting in the often-observed correlation between body size and genome size. In this study, we examined body size and repetitive DNA elements in relationship to the evolution of genome size in North American representatives of a single beetle family, the Lampyridae (fireflies). The 23 species considered represent an excellent study system because of the greater than 5-fold range of genome sizes, documented here using flow cytometry, and the 3-fold range in body size, measured using pronotum width. We also identified common genomic repetitive elements using low-coverage sequencing. We found a positive relationship between genome size and repetitive DNA, particularly retrotransposons. Both genome size and these elements were evolving as expected given phylogenetic relatedness. We also tested whether genome size varied with body size and found no relationship. Together, our results suggest that genome size is evolving neutrally in fireflies.

Firefly genomes illuminate parallel origins of bioluminescence in beetles

“…By analyzing the genomic synteny and molecular evolution of the beetle luciferases and their extant and inferred-ancestral homologs, we found strong support for the independent origins of luciferase, and therefore bioluminescence, between fireflies and click beetles. Our approaches and analyses lend molecular evidence to the previous morphology-phylogeny based hypotheses of parallel gain, first proposed by Darwin and others (11,32,(45)(46)(47)(48). Additional genomic information from basal fireflies (e.g.…”

“…Firefly bioluminescence is postulated to have first evolved as an aposematic warning of larval chemical defenses (32). Lucibufagins are major unpalatable defense steroids found in certain North American firefly species, most notably in the genera Photinus (5) and Ellychnia (37), and hence are candidates for ancestral firefly defense compounds.…”

“…The karyotype of P. pyralis was previously reported to be 2n=20 with XO sex determination (male, 18A+XO; female, 18A+XX) (31). The genome sizes of four P. pyralis adult males were previously determined to be 422 ± 9 Mbp (SEM, n=4), whereas the genome sizes of five P. pyralis adult females were determined to be 448 ± 7 (SEM, n=5) by nuclear flow cytometry analysis (32). From these analyses, the size of the X-chromosome is inferred to be ~26 Mbp.…”

Colonisation of subterranean ecosystems leads to larger genome in waterlouse (Aselloidea)

“…Instead, alternative measures of selection efficacy linked to long-term population size may serve as better predictors of genome size. We hope that this study will stimulate additional work testing the link between Ne and genome size variation in other taxonomical groups [8][9]. Using genome sequences instead of the transcriptome approach applied here may concomitantly further our understanding of the molecular mechanisms underlying genome size change.…”

RepeatProfiler: a pipeline for visualization and comparative analysis of repetitive DNA profiles

“…Despite their critical roles in genome and phenotype evolution and their known rapid turnover between closely related species (e.g. (Lower et al, 2017;Sproul, Khost, et al, 2020;Strachan, Coen, Webb, & Dover, 1982;Tetreault & Ungerer, 2016;Ugarković & Plohl, 2002)), repeat dynamics are seldom considered in evolutionary studies aiming to understand species boundaries and recent genome evolution. One caveat to using repeats in evolutionary studies is that their abundance may fluctuate widely across samples, even below the species level (Bosco, Campbell, Leiva-Neto, & Markow, 2007;McLain, Rai, & Fraser, 1987;Mestrović, Plohl, Mravinac, & Ugarković, 1998;Raskina, Barber, Nevo, & Belyayev, 2008).…”