The genomes of Hercules beetles reveal putative adaptive loci and distinct demographic histories in pristine North American forests

<p><span>Beetles, despite their remarkable biodiversity and a long history of research, remain lacking in reference genomes annotated with structural variations of loci of adaptive significance. We sequenced and assembled high-quality chromosome-level genomes of four Hercules beetles which exhibit divergence in male horn size and shape, and body coloration. The four Hercules beetle genomes were assembled to 11 pseudo-chromosomes, where the three genomes assembled using Nanopore data (<em>Dynastes grantii,</em> <em>D. hyllus</em>, and <em>D. tityus</em>) were mapped to the genome assembled using PacBio + Hi-C data (<em>D. maya</em>). </span><span>We demonstrated a striking similarity in genome structure among the four species. This conservative genome structure may be attributed to our use of the <em>D. maya</em> assembly as the reference; however, it is worth noting that such a conservative genome structure is a recurring phenomenon among scarab beetles</span><span>. We further identified homologs of nine and three candidate-gene families that may be associated with the evolution of horn structure and body coloration, respectively. Structural variations in <em>Scr</em> and <em>Ebony2</em> were detected and discussed for their putative impacts on generating morphological diversity in beetles. We also reconstructed the demographic histories of the four Hercules beetles using heterozygosity information from the diploid genomes. We found that the demographic histories of the beetles closely recapitulated historical changes in suitable forest habitats driven by climate shifts. </span></p>