Postembryonic development in pseudoscorpions: allometry in Geogarypus italicus (Pseudoscorpiones: Geogarypidae)

Abstract

Pseudoscorpions are arachnids featuring three nymphal instars before reaching the adult age. Instars can be mostly recognized based on the number of trichobothria which lie along the chelal axis: as the individual grows, further trichobothria are added. The study of the post-embryonic growth based on trichobothria position has been the most widely used approach. However, other body parts can be subjected to particular growth patterns that need to be explored to fully understand post-embryonic development processes. Rigorous numerical approaches that allow meaningful statistical inference within growth regressions are now available. The recently described Mediterranean species Geogarypus italicus Gardini, Galli & Zinni, 2017 gave the authors the chance to review studies carried out in the past with the modern statistical approach mentioned above. Results confirm the main hypothesis about the growth process of the chelal axis but showed some differences that may be related to taxonomical aspects. Moreover, the study of body allometry during postembryonic growth showed that not all body parts undergo the same trend from protonymphs to males, on one side, and to females, on the other. Finally, the study of proportions between body parts through the analysis of ratios between their linear measurements pointed out a marked sexual dimorphism of pedipalps in spite of similar sizes and proportions of other body regions. The analysis led us to think that more interesting information could come from applying this approach to multispecies studies.