Yoko Matsumura

Female genital diversity and co-evolution of female and male genitalia have been increasingly unveiled, particularly through recent studies. These findings highlight the importance of genital coupling in genital studies. In this pilot study, I examined membranous elements of female and male genitalia that come into physical contact during copulation in five representative species of shining leaf beetles by employing stereomicroscopy and scanning electron microscopy. The female genital surfaces are largely smooth, but a thickened sensilla-bearing patch is present. In contrast, the male surfaces are at least partially covered with microprotrusions. I present distribution maps of these microstructures for all study species. By comparing the results with those of previous studies, I discuss their possible functions and future research directions in this field.

Research on Chrysomelidae 10 Editorial

Diverse female and male genitalia have evolved. Although the evolutionary mechanisms behind this phenomenon have been studied extensively, the mechanical interactions between female and male genitalia are much less understood. Here, we provide an in-depth biomechanical study on the intromission of elongated tube-like female and male genitalia, termed the spermathecal duct and flagellum, in tortoise leaf beetles. Our findings reveal that this seemingly straightforward penetration mechanism is underpinned by structural and material specializations of the genitalia. We employed synchrotron-based micro-computed tomography and confocal laser scanning microscopy (CLSM) to visualize the precise mechanical interactions between female and male genitalia. Mechanical tests revealed a stiffness gradient within the flagellum and correlated stiffness variations between the sexes. Combining CLSM and cryo-microtome techniques, we characterized a heterogeneous material distribution at the flagellum tip; this specialization was more remarkable in the species with a more sclerotized spermathecal duct. Finite element analyses incorporating the observed material properties demonstrated that the observed material distribution reduced the penetration force required tremendously and dispersed the stress at the flagellum tip. This study unveils that structural and material adaptations in female and male genitalia have probably coevolved and highlights the importance of biomechanics in genital studies.

Female genital diversity and co-evolution of female and male genitalia have been increasingly unveiled, particularly through recent studies. These findings highlight the importance of genital coupling in genital studies. In this pilot study, I examined membranous elements of female and male genitalia that come into physical contact during copulation in five representative species of shining leaf beetles by employing stereomicroscopy and scanning electron microscopy. The female genital surfaces are largely smooth, but a thickened patch bearing sensilla is present. In contrast, the male surfaces are at least partially covered with microprotrusions. I present distribution maps of these microstructures for all study species. By comparing the results with those of previous studies, I discuss their possible functions and future research directions in this field.

Cimicidae are well-known for traumatic insemination, and males pierce females with their parameres and transfer sperm through them. The shape of parameres is relatively stable in the family, but in some genera, the paramere is elongated, appearing less resistant against lateral deflection. To understand the mechanical limitations of the paramere, we studied its penetration mechanics of the common bed bug, Cimex lectularius . We examined the post-abdominal morphology, paramere geometry and material properties and conducted breaking stress experiments on the paramere under wet and dry conditions. Mechanical property gradients are present with the paramere tip as the stiffest region and the base as the most flexible one. These mechanical properties relate to the presence of Ca, Zn and Si. The basal wing-shaped structure is flexible, enabling it to interlock with the anal region during mating. The paramere is slightly twisted; the tip region is circular in cross-section, and the geometry of the rest is rather complex. In the mechanical tests, wet parameres mainly buckled, while dried parameres broke off. The level of structural failures depended on directions from which the compression forces were applied. Structural, material and mechanical strengthening mechanisms preventing the paramere from mechanical failure are discussed.

A new species of the order Zoraptera, Zorotypus komatsui Matsumura, Maruyama, Ntonifor & Beutel, sp. nov., is described from Cameroon. The female and male morphology of another species, Z. vinsoni, is re-described, and its new distribution in Madagascar is recorded. A particular focus is on the male postabdominal morphology. This is apparently a crucial body region in the very small order with an extreme variation of the genital apparatus but otherwise a very uniform morphology. The male of the newly described species shares rudimentary male genitalia and well-developed postabdominal projections with the distantly related Spermozoros impolitus, apparently a result of parallel evolution. Whether males of Z. komatsui also perform external sperm transfer like S. impolitus remains to be shown. The collecting of the material used for this study suggests that the present knowledge of zorapteran species diversity of the Afrotropical region is very fragmentary.

Green dock beetles Gastrophysa viridula exhibit sexual dimorphism in tarsal attachment setae: females have only pointed, lanceolate and spatula-like setae, while males additionally possess discoidal ones. The sexual dimorphism is probably attributed to the necessity of male discoidal setae to adhere to the smooth back of the female during copulation. We aimed to understand its possible mechanism of attachment with G. viridula . Pull-off forces of both females and males were measured on (i) alive females, (ii) dead and dried females, and (iii) resin replicas of fresh females. The attachment ability tended to increase on dead and replicated female surfaces in both sexes, which indicates that the epicuticular grease layer on the integument of alive intact beetles decreases the attachment. This tendency was prominent in females. The present study clearly showed that in G. viridula discoidal setae enable the males to adhere stronger to female surfaces. The divergent performance found between the sexes differing in their setal composition is probably caused by the stiffness difference between the setae types and by the specific shape of the setal tips. A peculiar reproductive biology in G. viridula is probably attributed to this remarkable divergence of labour in their attachment pads between the sexes.

Coevolution of male and female genitalia is widespread in animals. Nevertheless, few studies have examined the mechanics of genital interactions during mating. We characterized the mechanical properties of the elongated female genitalia, the spermathecal duct, of the small cassidine beetle,Cassida rubiginosa. The data were compared with the mechanical properties of the elongated male genitalia, the flagellum. We analysed the material distributions of the spermathecal duct using a microscopy technique, established a tensile test setup under a light microscope and conducted tensile tests. Diameter and tensile stiffness gradients were present along the spermathecal duct, but its Young's modulus and material distribution were more or less homogeneous. The results confirmed the hypothesis based on numerical simulations that the spermathecal duct is more rigid than the flagellum. In the study species, the penile penetration force is simply applied to the base of the hyper-elongated flagellum and conveyed along the flagellum to its tip. Considering this simple penetration mechanism, the relatively low flexibility of the spermathecal duct, compared to the flagellum, is likely to be essential for effective penetration of the flagellum.