We estimated the genome size of a relict longhorn beetle, Callipogon relictus Semenov (Cerambycidae: Prioninae)—the Korean natural monument no. 218 and a Class I endangered species—using a combination of flow cytometry and k-mer analysis. The two independent methods enabled accurate estimation of the genome size in Cerambycidae for the first time. The genome size of C. relictus was 1.8 ± 0.2 Gb, representing one of the largest cerambycid genomes studied to date. An accurate estimation of genome size of a critically endangered longhorned beetle is a major milestone in our understanding and characterization of the C. relictus genome. Ultimately, the findings provide useful insight into insect genomics and genome size evolution, particularly among beetles.
Mitochondrial genomes of the three lucanid species in the Dorcus velutinus complex – Dorcus velutinus Thomson, D. ursulus Arrow and D. tenuihirsutus Kim and Kim – were assembled and analyzed through next generation sequencing. The mitogenome sequences were used to infer phylogenetic relationships among Dorcus species. Our analyses revealed that the newly sequenced mitogenomes are comparable in their size, content, and gene arrangement to other lucanid mitogenomes reported to date. However, we confirmed the presence of a large intergenic spacer (IGS) between trnS(UCN) and ND1 genes, whose length varied from 170 bp (in D. tenuihirsutus) to 193 bp (in D. ursulus and D. velutinus). Within this IGS region, a short sequence fragment (TACTAAATT) was found uniquely across the three species of Dorcus velutinus complex. Our phylogenetic analyses show that the D. velutinus complex constitutes a distinct clade with a significant divergence from other species of the genus Dorcus sensu stricto. Furthermore, we reaffirm the validity of D. tenuihirsutus – a species originally described from Korea – as a distinct species, though the taxonomic status of D. ursulus remains to be studied further. Finally, we find the presence and location of large IGSs to be useful for studying evolutionary history and species delimitation in stag beetles.
The longhorn beetle genus Callipogon Audinet-Serville represents a small group of large wood-boring beetles whose distribution pattern exhibits a unique trans-Pacific disjunction between the East Asian temperate rainforest and the tropical rainforest of the Neotropics. To understand the biogeographic history underlying this circum-Pacific disjunct distribution, we reconstructed a molecular phylogeny of the subfamily Prioninae with extensive sampling of Callipogon using multilocus sequence data of 99 prionine and four parandrine samples (ingroups), together with two distant outgroup species. Our sampling of Callipogon includes 18 of the 24 currently accepted species, with complete representation of all species in our focal subgenera. Our phylogenetic analyses confirmed the purported affinity between the Palearctic Callipogon relictus and its Neotropical congeners. Furthermore, based on molecular dating under the fossilized birth–death (FBD) model with comprehensive fossil records and probabilistic ancestral range reconstructions, we estimated the crown group Callipogon to have originated in the Paleocene circa 60 million years ago (Ma) across the Neotropics and Eastern Palearctics. The divergence between the Palearctic C. relictus and its Neotropical congeners is explained as the result of a vicariance event following the demise of boreotropical forest across Beringia at the Eocene-Oligocene boundary. As C. relictus represents the unique relictual species that evidentiates the lineage’s expansive ancient distribution, we evaluated its conservation importance through species distribution modelling. Though we estimated a range expansion for C. relictusby 2050, we emphasize a careful implementation of conservation programs towards the protection of primary forest across its current habitats, as the species remains highly vulnerable to habitat disturbance.
Stag beetles (family Lucanidae Latreille, 1804) are one of the earliest branching lineages of scarab beetles that are characterized by the striking development of the male mandibles. Despite stag beetles' popularity among traditional taxonomists and amateur collectors, there has been almost no study of lucanid relationships and evolution. Entomologists, including Jeannel (1942), have long recognized resemblance between the austral stag beetles of the tribes Chiasognathini, Colophonini, Lamprimini, Pholidotini, Rhyssonotini, and Streptocerini, but this hypothesis of their close relationship across the continents has never been tested. To gain further insight into lucanid phylogeny and biogeography, we reconstructed the first molecular phylogeny of world stag beetles using DNA sequences from mitochondrial 16S rDNA, nuclear 18S and 28S rDNA, and the nuclear protein-coding (NPC) gene wingless for 93 lucanid species representing all extant subfamilies and 24 out of the 27 tribes, together with 14 representative samples of other early branching scarabaeoid families and two staphyliniform beetle families as outgroups. Both Bayesian inference (BI) and maximum likelihood inference (MLI) strongly supported the monophyly of Lucanidae sensu lato that includes Diphyllostomatidae. Within Lucanidae sensu stricto, the subfamilies Lucaninae and Lampriminae appeared monophyletic under both methods of phylogenetic inferences; however, Aesalinae and Syndesinae were found to be polyphyletic. A time-calibrated phylogeny based on five fossil data estimated the origin of crown group Lucanidae as circa 160 million years ago (MYA). Divergence between the Neotropical and Australasian groups of the Chiasognathini was estimated to be circa 47MYA, with the South African Colophonini branching off from the ancient Chiasognathini lineage around 87MYA. Another Gondwanan relationship was recovered between the Australasian Eucarteria and the Neotropical Casignetus, which diverged circa 58MYA. Lastly, as Jeannel's hypothesis predicted, divergence within Lampriminae between the Australasian Lamprima and the Neotropical Streptocerus was estimated to be circa 37MYA. The split of these lineages were generally concordant with the pattern of continental break-up of the super-continent Gondwana, and our biogeographic reconstructions based on the dispersal-extinction-cladogenesis model (DEC) corroborate our view that the divergences in these austral lineages were caused by vicariance events following the Gondwanan break-up. In addition, the phylogenetic position and geographic origin of the Hawaiian genus Apterocyclus was revealed for the first time. Overall, our results provide the framework toward studying lucanid relationships and divergence time estimates, which allowed for more accurate biogeographic explanations and discussions on ancestral lucanids and the evolutionary origin of the enlarged male mandibles.
This paper provides a review of the family Lucanidae in Korea, which consists of 17 species belonging to 9 genera. One new species, Dorcus tenuihirsutus sp. nov., is described and the following taxonomical changes are proposed: Aegus laevicollis Saunders, 1854 is newly identified as Aegus laevicollis subnitidus Waterhouse, 1873; Macrodorcas striatipennis Motschulsky, 1861 is removed from the Korean fauna because this record is thought to have been based on the misinterpretation of locality and misidentification; Neolucanus saundersii Parry, 1864 is removed from the Korean fauna because this record is thought to have been based on misidentification.