RESUMEN

Clarifying the mechanisms underlying shape alterations during insect metamorphosis is important for understanding exoskeletal morphogenesis. The large horn of the Japanese rhinoceros beetle Trypoxylus dichotomus is the result of drastic metamorphosis, wherein it appears as a rounded shape during pupation and then undergoes remodeling into an angular adult shape. However, the mechanical mechanisms underlying this remodeling process remain unknown. In this study, we investigated the remodeling mechanisms of the Japanese rhinoceros beetle horn by developing a physical simulation. We identified three factors contributing to remodeling by biological experiments - ventral adhesion, uneven shrinkage, and volume reduction - which were demonstrated to be crucial for transformation using a physical simulation. Furthermore, we corroborated our findings by applying the simulation to the mandibular remodeling of stag beetles. These results indicated that physical simulation applies to pupal remodeling in other beetles, and the morphogenic mechanism could explain various exoskeletal shapes.

Asunto(s)

Escarabajos , Animales , Japón , Simulación por Computador , Mandíbula , Pupa

RESUMEN

What limits the size of nature's most extreme structures? For weapons like beetle horns, one possibility is a tradeoff associated with mechanical levers: as the output arm of the lever system-the beetle horn-gets longer, it also gets weaker. This "paradox of the weakening combatant" could offset reproductive advantages of additional increases in weapon size. However, in contemporary populations of most heavily weaponed species, males with the longest weapons also tend to be the strongest, presumably because selection drove the evolution of compensatory changes to these lever systems that ameliorated the force reductions of increased weapon size. Therefore, we test for biomechanical limits by reconstructing the stages of weapon evolution, exploring whether initial increases in weapon length first led to reductions in weapon force generation that were later ameliorated through the evolution of mechanisms of mechanical compensation. We describe phylogeographic relationships among populations of a rhinoceros beetle and show that the "pitchfork" shaped head horn likely increased in length independently in the northern and southern radiations of beetles. Both increases in horn length were associated with dramatic reductions to horn lifting strength-compelling evidence for the paradox of the weakening combatant-and these initial reductions to horn strength were later ameliorated in some populations through reductions to horn length or through increases in head height (the input arm for the horn lever system). Our results reveal an exciting geographic mosaic of weapon size, weapon force, and mechanical compensation, shedding light on larger questions pertaining to the evolution of extreme structures.

Asunto(s)

Evolución Biológica , Escarabajos , Cuernos , Animales , Masculino , Fenómenos Biomecánicos/fisiología , Escarabajos/anatomía & histología , Escarabajos/crecimiento & desarrollo , Escarabajos/fisiología , Cuernos/anatomía & histología , Cuernos/crecimiento & desarrollo , Cuernos/fisiología , Elevación , Caracteres Sexuales , Japón

RESUMEN

Nudivirus-infected Korean rhinoceros beetles (Trypoxylus dichotomus) were first identified in 2015, and while a complete genome sequence of the virus has long been uploaded to the NCBI database, it has not been examined in detail. Here, we describe the genomic characteristics of Trypoxylus dichotomus nudivirus (TdNV), which represents a new Oryctes rhinoceros nudivirus (OrNV) strain, isolated from infected T. dichotomus in the Republic of Korea. We examined factors derived by the cross-species infection of OrNV from nucleotide levels to the whole genome level. Our genomic analysis study suggests that TdNV-Korea is highly conserved with other OrNVs in terms of genomic structures and genome size. Our investigation of the genomic structure revealed that TdNV-Korea has the least number of open reading frames (ORFs) of all available OrNV genomes; three hypothetical genes were notably absent only in TdNV-Korea. In addition, the genomic alteration of the nudivirus core genes discloses that various amino acid mutations caused by single-nucleotide polymorphism and short indels (insertion/deletion) were found in most of the nudivirus core genes of TdNV-Korea. Our findings provide a valuable resource for those seeking a greater understanding of cross-species nudivirus transmission and will certainly provide valuable insight for reconstruction and reinterpretation of future and previously identified OrNV strains.

Asunto(s)

Escarabajos , Nudiviridae , Animales , República de Corea , Perisodáctilos

RESUMEN

In the Japanese rhinoceros beetle Trypoxylus dichotomus, various candidate genes required for a specific phenotype of interest are listed by next-generation sequencing analysis. Their functions were investigated using RNA interference (RNAi) method, the only gene function analysis tool for T. dichotomusdeveloped so far. The summarized procedure for the RNAi method used for T. dichotomusis to synthesize double-stranded RNA (dsRNA), and inject it in larvae or pupae of T. dichotomus. Although some dedicated materials or equipment are generally required to inject dsRNA in insects, the advantage of the protocol described here is that it is possible to inject dsRNA in T. dichotomuswith one syringe.