Pediculus humanus capitis: a study of the male genitalia using a combined stereoscopic, confocal laser scanning, and scanning electron microscopy approach

Blanca E Álvarez-Fernández,M Adela Valero,Benjamín Nogueda-Torres,María Morales-Suárez-Varela

doi:10.1186/s13071-021-05082-w

Abstract

BackgroundThe male genital structures of arthropods are key features in the taxonomic and phylogenetic study of these organisms. The male genitalia of the head louse Pediculus humanus capitis are complex organs which are partly composed of structures that dynamically extrude during copulation.MethodsHere, we describe the morphology of the genitalia of P. humanus capitis at the copulation stage, and at rest, by using stereoscopic microscopy, confocal laser scanning microscopy (CLSM), and scanning electron microscopy (SEM).ResultsCLSM and SEM images revealed that the vesica is composed of two distinct anatomical parts, the proximal lobe and the distal lobe. Both lobes have short and narrow spines, as well as long and wide scales with either sharp or rounded tips. The rounded scales vary in size and have a wavy base and rounded tips, and thus resemble a tongue in appearance. We identified a gland-like area on the penis with 11 shallow circular depressions, and a flat area with 14–16 exit orifices. The apical end of the penis has a foliaceous trifurcation and serves to expel the contents of the ejaculatory duct. These characteristics were recorded for all the specimens analyzed, indicating that these structures are highly conserved; to our knowledge, they have not been previously reported for any suborder of lice.ConclusionsTo the best of our knowledge, our results reveal for the first time the morphological details, and complexity, of the male genitalia of the head louse P. humanus capitis at different stages of copulation. The new approach described here provided information that should be taken into consideration in future research on the genitalia of lice. Application of this approach will also impact the taxonomic and phylogenetic study of other insect taxa.Graphical

Highlights

The male genital structures of arthropods are key features in the taxonomic and phylogenetic study of these organisms
Characteristics of the specimens at the copulation stage At copulation, the male genitalia emerge through a horizontal opening, for which we propose the term “genital opening,” which is located dorsally to segment IX (Fig. 2a, b)
In this article, we describe the structures of the male genitalia of P. humanus capitis and establish the morphological differences between the genitalia at rest and when they are extruded to prepare for copulation

Summary

Introduction

The male genital structures of arthropods are key features in the taxonomic and phylogenetic study of these organisms. The male genitalia of the head louse Pediculus humanus capitis are complex organs which are partly composed of structures that dynamically extrude during copulation. In the Pediculidae, the male genitalia have been the target structures of multiple studies, with the genitalia of the Anoplura being used as one of the most common research models [9]. The male phallic organ of lice is a highly complex structure; it is stored in the genital chamber and, is not exposed to the external environment [1]. This hinders detailed study of the microstructure of the male genitalia

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