Virtual sections and 3D reconstructions of female reproductive system in a carabid beetle using synchrotron X-ray phase-contrast microtomography

Abstract

Morphological analyses of the internal anatomy are a milestone in different fields of animal biology, such as physiology, development and reproduction, and systematic studies. Synchrotron radiation X-ray phase-contrast microtomography (SR-PhC micro-CT) has become a valuable imaging tool used for non-invasive analyses of the insect internal anatomy. The ground beetle Pterostichus melas italicus Dejean, 1828 (Coleoptera, Carabidae, Harpalinae) is an important predator of the trophic web in cropland involved in pest biological control. The anatomy of the reproductive system was first described in mature females scanning the samples at the SYRMEP beamline of the Elettra synchrotron facility in Trieste (Italy). The female reproductive tract consists of paired ovaries each containing six polytrophic ovarioles, a common oviduct and a spermatheca. Oocytes at different stages of differentiation were identified to be associated with nurse cells in the follicle. Virtual dissections and 3D rendering allowed to describe in situ the morphology of each structure. This investigation adds to the scarce information on internal genitalia of carabid females and provides a basis for further research on the reproductive strategies of P. melas. High quality images and the supplementary video from SR-PhC micro-CT analyses represent a significant advance in data collection to study insect morphology and function.