Molecular cloning and functional characterization of the sex-determination gene doublesex in the sexually dimorphic broad-horned beetle Gnatocerus cornutus (Coleoptera, Tenebrionidae).

Hiroki Gotoh,Mai Ishiguro,Kensuke Okada,Hideto Nishikawa,Teruyuki Niimi,Takahisa Miyatake,Toshinobu Yaginuma,Shinichi Morita

doi:10.1038/srep29337

Abstract

Various types of weapon traits found in insect order Coleoptera are known as outstanding examples of sexually selected exaggerated characters. It is known that the sex determination gene doublesex (dsx) plays a significant role in sex-specific expression of weapon traits in various beetles belonging to the superfamily Scarabaeoidea. Although sex-specific weapon traits have evolved independently in various Coleopteran groups, developmental mechanisms of sex-specific expression have not been studied outside of the Scarabaeoidea. In order to test the hypothesis that dsx-dependent sex-specific expression of weapon traits is a general mechanism among the Coleoptera, we have characterized the dsx in the sexually dimorphic broad-horned beetle Gnatocerus cornutus (Tenebrionidea, Tenebirionidae). By using molecular cloning, we identified five splicing variants of Gnatocerus cornutus dsx (Gcdsx), which are predicted to code four different isoforms. We found one male-specific variant (GcDsx-M), two female-specific variants (GcDsx-FL and GcDsx-FS) and two non-sex-specific variants (correspond to a single isoform, GcDsx-C). Knockdown of all Dsx isoforms resulted in intersex phenotype both in male and female. Also, knockdown of all female-specific isoforms transformed females to intersex phenotype, while did not affect male phenotype. Our results clearly illustrate the important function of Gcdsx in determining sex-specific trait expression in both sexes.

Highlights

Various types of weapon traits found in insect order Coleoptera are known as outstanding examples of sexually selected exaggerated characters
The developmental mechanisms of the sex-specific expression of weapon traits have long remained elusive, recent progress using molecular tools in several beetle species revealed that the sex-determination gene doublesex plays an important role in sex-specific expression of weapon traits[3,5,6,7]
Our results clearly demonstrate the significant function of dsx in G. cornutus weapon development

Summary

Sexually dimorphic weapons in beetles

Selected weapon traits are among the most prominent morphological characteristics in animals[1]. It is unlikely that the weapons of these beetles share a common evolutionary origin[11], all have their sex-specific expression organized by Dsx (reviewed in[3,12]) All of these beetles are closely related, belonging to the superfamily Scarabaeoidea, and functional studies of dsx in weapon trait expression outside of the Scarabaeoidea have been limited. The broad-horned beetle Gnatocerus cornutus is a sexually dimorphic, weaponed beetle belonging to the superfamily Tenebrionidea and family Tenebrionidae In this species, males have well-developed mandibles which are used for combat[13]. Estimated divergence time between Tenebrionidea and Scarabaeoidea is approximately 240 million years ago[17] Considering these characteristics and phylogenetic position (distant from other weaponed scarab beetles and close to T. castaneum), G. cornutus can be an important new model system for investigating molecular mechanisms of the sex-specific expression of weapon traits. Our results clearly demonstrate the significant function of dsx in G. cornutus weapon development

Materials and Methods

Results and Discussion

Lethal stage larva pupa

Additional Information