Pillbug: A Toolbox for Feminisation

Wolbachia-induced feminisation is an extended phenotype that has been observed in only three models: isopods, butterflies and leafhoppers. Even among these, the process of feminisation differs markedly, especially since sexual differentiation is coordinated body-wide by a hormone in isopods, whereas in insects it is a chromosomally determined process and enforced cell by cell. For isopods, Armadillidium vulgare has contributed substantially to an understanding of Wolbachia-mediated feminisation, because a wide array of know-how and methods has been tailored to this model. Here, we describe establishment and maintenance of Wolbachia-infected laboratory lineages from animals collected in the field, the grafting of an androgenic gland to demonstrate the mode of action of Wolbachia (i.e. the disruption of the Androgenic Hormone pathway), and transinfection of naïve adults with Wolbachia. Finally, we describe selection of a ZZ genetic background in lineages created from transinfected WZ females, which is necessary to benefit from a property intrinsic to the naturally infected lineages: In a ZZ background, the vertical transmission rate of Wolbachia directly equates to the female ratio in the progeny. These protocols provide the essential framework for investigating molecular aspects of Wolbachia-induced feminisation.

Is the morphology of Culicoides intersexes parasitized by mermithid nematodes a parasite adaptation? A morphometric approach to Culicoides circumscriptus (Diptera: Ceratopogonidae)

Mermithidae is a family of endoparasitic nematodes known to cause intersexuality in arthropods. Intersexes of the genus Culicoides parasitized by mermithids have been the object of several studies aiming to describe their particular morphology. Culicoides intersexes are specimens with male genitalia and feminized sexually dimorphic structures, i.e. antennae, mouthparts and wings. To date, these specimens have only been described qualitatively and a quantitative approach supported by statistical analysis is lacking. Here we conduct morphometric analyses of sexually dimorphic structures in a sample of Culicoides circumscriptus that includes 34 intersexes with the aim of describing precisely the intersexual morphology. The morphology of antennae and the mouthparts was studied by multivariate statistical analysis of linear measures, and wing form by implementing geometric morphometrics techniques. While intersex wings proved to have a similar size to male wings, their shape was intermediate between males and females. However, when allometric shape variation was removed, the wing shape of intersexes was almost identical to that of females. The intersex antennae were morphometrically of the female type, especially when size variation was considered. In contrast, the measured mouthparts (the labrum and the third palpal segment) were halfway between males and females, even when body size was considered. Overall, the antennae and the wings showed a higher degree of feminization than the mouthparts. These findings indicate that the degree of feminization depends both on the morphological structure and on body size. Moreover, we propose that the feminization of the wings and antennae has an adaptive meaning for the parasite, which would favor female-like traits in order to access more easily its breeding sites, where the parasite has plenty of new hosts to infect. Female-like antennae would be beneficial to detect these sites, while having female-like wings would favor the host's capacity of dispersal to these sites.