Changes in turn alternation pattern in terrestrial isopods as a response to substrate-borne vibrations

Armadillo officinalis, is a xeric woodlouse (Isopoda, Oniscidea) that can produce vibrations, audible even by the human ear, by means of a ledge of scales situated on the propodus of the fourth and fifth pereopod. This work investigates the behavior of this species in terms of turn alternation in response to substrate-borne vibrations, in a multiple T-maze. We collected data about the turn alternation, meant as number of times that the animal turns on the opposite side in a predefined path, in four groups of animals: i) adults of A. officinalis exposed and ii) not exposed to micro- vibrations, iii) juveniles of A. officinalis exposed to micro-vibrations, and iv) adults of Armadillidium vulgare exposed to micro-vibrations. Hence, we were able to assess the pattern of the turn alternation at a level of i) exposure to micro-vibrations (not exposed vs. exposed), ii) animal’s state (adults vs. juveniles), and iii) species (A. vulgare vs. A. officinalis). A Poisson regression with robust standard errors was used. The models highlighted a statistically significant association between turn alternation and the micro-vibration, animal’s state, and species, with a higher number of turn alternations in the adults of A. officinalis exposed to micro-vibrations compared to i) the adults of A. officinalis not exposed, ii) the juveniles exposed, and iii) A. vulgare exposed. The adults of A. officinalis seem to be very sensible to vibrations, unlike A. vulgare. The sensitiveness also seems increasing passing from the juvenile state to the adult condition. This might be related to the peculiarity of this species to emit vibrations. The reactivity of A. officinalis to an external substrate-borne vibration as well as its capability to produce vibrations might be linked to an interspecific signaling and/or an intraspecific communication.