The ontogeny of oil gland chemistry in the oribatid mite Archegozetes longisetosus Aoki (Oribatida, Trhypochthoniidae)

Abstract

ABSTRACTThe so-called “glandulate Oribatida” (including Astigmata) possess large opisthonotal oil glands, which produce semiochemicals as potent agents for chemical defence against predators (allomones) as well as for intraspecific communication (pheromones). The oil gland reservoirs and their contents remain with shed exuviae, so secretions need to be synthesized de novo after each moult. The qualitative composition of chemical profiles may change dramatically between the last juvenile instar (tritonymph) and adult (e.g. Hermannia convexa Koch, Scheloribates azumaensis Enami, Nakamura & Katsumata, Oribotritia berlesei Michael), but reports about quantitative ontogenetic shifts are ambiguous. Here, we analysed the complete ontogenetic sequence (larva, protonymph, deutonymph, tritonymph, and adult) of oil gland secretions in the parthenogenetic oribatid model species Archegozetes longisetosus Aoki using gas chromatography–mass spectrometry. We show that absolute and body mass-corrected amounts of oil gland secretions increase during ontogeny and that secretion quantity scales allometrically with body mass (i.e. ontogenetic instar). Furthermore, we found highly significant ontogenetic shifts in the relative quantity of chemical components among instars, but the qualitative composition (=2,6-HMBD, neral, neryl formate, γ-acaridial, tridecane, 7-pentadecene, pentadecane, 6,9-heptadecadiene, 8-heptadecene, and heptadecane) remained stable.