Phylogeny and biogeography of the Japanese rhinoceros beetle, Trypoxylus dichotomus (Coleoptera: Scarabaeidae) based on SNP markers

The horns of giant rhinoceros beetles are a classic example of the elaborate morphologies that can result from sexual selection. Theory predicts that sexual traits will evolve to be increasingly exaggerated until survival costs balance the reproductive benefits of further trait elaboration. In Trypoxylus dichotomus , long horns confer a competitive advantage to males, yet previous studies have found that they do not incur survival costs. It is therefore unlikely that horn size is limited by the theoretical cost–benefit equilibrium. However, males sometimes fight vigorously enough to break their horns, so mechanical limits may set an upper bound on horn size. Here, I tested this mechanical limit hypothesis by measuring safety factors across the full range of horn sizes. Safety factors were calculated as the ratio between the force required to break a horn and the maximum force exerted on a horn during a typical fight. I found that safety factors decrease with increasing horn length, indicating that the risk of breakage is indeed highest for the longest horns. Structural failure of oversized horns may therefore oppose the continued exaggeration of horn length driven by male–male competition and set a mechanical limit on the maximum size of rhinoceros beetle horns.

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Whole-genome sequence of Clostridium lituseburense L74, isolated from the larval gut of the rhinoceros beetle, Trypoxylus dichotomus

Genomics Data ◽

10.1016/j.gdata.2016.02.008 ◽

2016 ◽

Vol 7 ◽

pp. 301-302

Author(s):

Yookyung Lee ◽

Sooyeon Lim ◽

Moon-Soo Rhee ◽

Dong-Ho Chang ◽

Byoung-Chan Kim

Keyword(s):

Genome Sequence ◽

Whole Genome Sequence ◽

Whole Genome ◽

Rhinoceros Beetle ◽

Trypoxylus Dichotomus

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The draft genome sequence of Japanese rhinoceros beetle Trypoxylus dichotomus

10.1101/2022.01.10.475740 ◽

2022 ◽

Author(s):

Shinichi Morita ◽

Tomoko F. Shibata ◽

Tomoaki Nishiyama ◽

Yuuki Kobayashi ◽

Katsushi Yamaguchi ◽

...

Keyword(s):

De Novo Assembly ◽

Molecular Mechanisms ◽

Developmental Stages ◽

De Novo ◽

Genetic Regulation ◽

Draft Genome ◽

Evolutionary Developmental Biology ◽

Rhinoceros Beetle ◽

Insect Order ◽

Trypoxylus Dichotomus

Beetles are the largest insect order and one of the most successful animal groups in terms of number of species. The Japanese rhinoceros beetle Trypoxylus dichotomus (Coleoptera, Scarabaeidae, Dynastini) is a giant beetle with distinctive exaggerated horns present on the head and prothoracic regions of the male. T. dichotomus has been used as research model in various fields such as evolutionary developmental biology, ecology, ethology, biomimetics, and drug discovery. In this study, de novo assembly of 615 Mb, representing 80% of the genome estimated by flow cytometry, was obtained using the 10x Chromium platform. The scaffold N50 length of the genome assembly was 8.02 Mb, with repetitive elements predicted to comprise 49.5% of the assembly. In total, 23,987 protein-coding genes were predicted in the genome. In addition, de novo assembly of the mitochondrial genome yielded a contig of 20,217 bp. We also analyzed the transcriptome by generating 16 RNA-seq libraries from a variety of tissues of both sexes and developmental stages, which allowed us to identify 13 co-expressed gene modules. The detailed genomic and transcriptomic information of T. dichotomus is the most comprehensive among those reported for any species of Dynastinae. This genomic information will be an excellent resource for further functional and evolutionary analyses, including the evolutionary origin and genetic regulation of beetle horns and the molecular mechanisms underlying sexual dimorphism.

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