Tonic immobility in terrestrial isopods: intraspecific and interspecific variability

Abstract

Many arthropods, including terrestrial isopods, are capable of entering a state of tonic immobility upon a mechanical disturbance. Here we compare the responses to mechanical stimulation in three terrestrial isopods Balloniscus glaber, Balloniscus sellowii and Porcellio dilatatus. We applied three stimuli in a random order and recorded whether each individual was responsive (i.e. showed tonic immobility) or not and the duration of the response. In another trial we related the time needed to elicit tonic immobility and the duration of response of each individual. Balloniscus sellowii was the least responsive species and Porcellio dilatatus was the most, with 23% and 89% of the tested individuals, respectively, being responsive. Smaller Balloniscus sellowii were more responsive than larger individuals. Porcellio dilatatus responded more promptly than the Balloniscus spp. but it showed the shortest response. Neither sex, size nor the type of stimulus explained the variability found in the duration of tonic immobility. These results reveal a large variability in tonic immobility behavior, even between closely related species, which seems to reflect a species-specific response to predators with different foraging modes.

Fine mapping of complex traits in non-model species: using next generation sequencing and advanced intercross lines in Japanese quail

“…Our objective was to develop a dedicated quail SNP (Single Nucleotide Polymorphism) panel, in order to fine map a QTL for duration of tonic immobility. Tonic immobility (TI) is an innate fear-related behaviour which occurs throughout the Animal Kingdom [23,24] and has been studied extensively in poultry (see [25]). Its duration (dTI) is considered to be a measure of fearfulness, representing an antipredatory behaviour.…”

Personality affects defensive behaviour of Porcellio scaber (Isopoda, Oniscidea)

“…If smaller animals can be easily overlooked by predator, the frequency of using this strategy by small animals can be higher than by bigger animals. This pattern was confirmed in some studies ( Hals and Beal 1982 ; Quadros et al 2012 ) but not found in other ones or in other species ( Hazlett and Bach 2010 ; Quadros et al 2012 ) for several crustaceans including terrestrial isopods.…”

“…Behavioural experiments followed the design used by Quadros et al (2012) ; each isopod was exposed to several treatments. One experimental set contained three types of treatments to induce tonic immobility (TI): touch, squeeze, and drop.…”

“…Tonic immobility in non-conglobating forms of isopods is characterised by the contraction of the body and the contraction and folding of the legs towards the ventral side while holding the antennae folded or extended backwards and pressed against the dorsal part of the first pereonites (see fig. 1 in Quadros et al 2012 ). During this posture the organism lacks motional responsiveness to external stimulation.…”

“…typical for the genus Cylisticus ) is less effective as uropods and antennae are not well protected. Nevertheless, tonic immobility is a much more general behaviour than conglobation and it is used by isopods ( Quadros et al 2012 ). Tonic immobility in non-conglobating forms of isopods is characterised by the contraction of the body and the contraction and folding of the legs towards the ventral side while holding the antennae folded or extended backwards and pressed against the dorsal part of the first pereonites (see fig.…”