It's ‘claw’-some: Ontogenetic claw shape changes in mites (Acari, Oribatida) as a consequence of ecological shifts

Claw characteristics of oribatid mites are strongly correlated with environmental factors and these characters remain constant throughout development when immatures and adults share the same ecology and lifestyle. In the present study, claw traits of oribatid mite species with constant ecology were compared with those of species showing a clear ecological shift between juvenile and adult stage. The arboreal Sellnickia caudata and the saxicolous Niphocepheus nivalis dwell in the same microhabitat during their life-cycle, whereas immatures of the terrestrial Carabodes areolatus and Mycobates carli, as well as of the aquatic Hydrozetes lemnae, are, in contrast to their adults, endophagous, meaning they feed and burrow within lichen and plant tissue. We performed a geometric morphometric investigation of their claws and could reveal significant differences in the claw shapes of immatures and adults of all species, except for N. nivalis. Claws of the endophagous juveniles of C. areolatus, M. carli and H. lemnae are generally sharper and higher than those of their adult counterparts. The burrowing lifestyle of the immatures apparently necessitates such specific claw morphologies. Despite having a constant ecology, the arboreal S. caudata also shows distinct differences between immature and adult claw traits, with juveniles possessing stronger curved and sharper claws. But immature stages also possess an additional tarsal adhesive pad which lacks in the adult stage. The presence or absence of this additional adhesive pad apparently requires changes in claw morphology to allow firm attachment on diverse plant surfaces. The present results demonstrate that claw characteristic can change during the development depending on the given ecological factors faced by each developmental stage and depending on the presence of additional attachment devices.