Personality affects defensive behaviour of Porcellioscaber (Isopoda, Oniscidea)

Sex-specific effects of a parasite on stress-induced freezing behavior in a natural beetle-nematode system

Some animals react to predation threats or other stressors by adopting a freezing posture in an attempt to avoid detection, and the duration of this behavior usually corresponds with individual personality, such that timid individuals freeze longer. Despite decades of research on this or related behaviors (thanatosis), never has the impact of parasitism been considered. Parasites could prolong the duration, if hosts are less motivated to move (i.e. lethargic), or they could reduce it, if hosts are motivated to forage more to compensate for energy drain. We examined this behavior within a natural beetle-nematode system, where hosts (horned passalus beetles, Odontotaenius disjunctus) are parasitized by a nematode, Chondronema passali. We exposed beetles (n = 238) to four stressors in our lab, including noise, vibration, light and inversion, and recorded how long they adopt a frozen stance. Afterward, we determined nematode burdens, which can range from dozens to hundreds of worms. Beetles tended to freeze for 20 seconds on average, with some variation between stressors. We detected no effect of beetle mass on the duration of freezing, and this behavior did not differ in beetles collected during the breeding or non-breeding season. There was a surprising sex-based difference in the impact of nematodes; unparasitized females remained frozen twice as long as unparasitized males, but for beetles with heavy nematode burdens, the opposite was true. From this we infer that heavily parasitized females are more bold, while males with heavy burdens would be more timid. The explanation for this finding remains elusive, though we can rule out many possibilities based on prior work on this host-parasite system.

Personality-mediated speed-accuracy tradeoffs in mating in a 17-year periodical cicada

There exists growing evidence that animal personality (consistent between individual differences in behavior) can influence an individual’s fitness. Furthermore, limitations in behavioral plasticity may cause personality-mediated tradeoffs to occur, for example, between speed and accuracy in decision making. We explored whether various measures of personality could predict speed-accuracy tradeoffs in mate selection using Pharaoh cicadas (Magicicada septendecim) and examined the phenotypic traits predicting male mating performance and advertisement rates. We assessed whether male exploration behavior, boldness, and weight could predict a male’s overall copulation attempt rate (the number of attempted copulations with conspecifics of either sex), the number of errors a male made when selecting a mate (the number of same-sex copulation attempts), and male reproductive performance (whether a male successfully copulated with a female). We also assessed whether personality-dependent variation in male advertisement rate (the number of calling song bouts) might underpin the correlation between exploration behavior and mating performance. Although male exploration behavior did not predict male advertisement rate, we found that faster-exploring males exhibited higher overall rates of attempted copulations while also attempting more same-sex copulations, compared to slower-exploring males, suggesting a personality-mediated speed-accuracy tradeoff. Despite making more mate choice errors, however, faster explorers were more likely to successfully copulate with females, compared to slower explorers, indicating that speed may be favored over accuracy in systems where heavily male-biased sex ratios lead to scramble competition. Overall, this work highlights the role of personality in sexual selection and demonstrates that personality can influence speed-accuracy trade-offs in mating.

Antipredatory strategies of terrestrial isopods

Terrestrial isopods (Oniscidea) represent a widespread group of land Crustacea that have been able to successfully adapt to the terrestrial environment and occupy newly formed ecological niches. During the colonisation of land, they faced numerous challenges, including finding an effective way to avoid their new terrestrial predators. In response to predation pressure, they have developed various behavioural and morphological adaptations. These include tonic immobility, conglobation, clinging to the ground, releasing strongly acidic secretions, jumping, and efficient running away. Furthermore, terrestrial isopods can aggregate with other individuals, use stridulation, or change their typical activity time. Some of them also developed spiny tergites and aposematic colouration or posture. The majority of these strategies have not yet been studied.

Biotremology in arthropods

Effective communication is essential in animal life to allow fundamental behavioral processes and survival. Communicating by surface-borne vibrations is likely the most ancient mode of getting and exchanging information in both invertebrates and vertebrates. In this review, we concentrate on the use of vibrational communication in arthropods as a form of intraspecific and interspecific signaling, with a focus on the newest discoveries from our research group in terrestrial isopods (Crustacea: Isopoda: Oniscidea), a taxon never investigated before in this context. After getting little attention in the past, biotremology is now an emerging field of study in animal communication, and it is receiving increased interest from the scientific community dealing with these behavioral processes. In what follows, we illustrate the general principles and mechanisms on which biotremology is based, using definitions, examples, and insights from the literature in arthropods. Vibrational communication in arthropods has mainly been studied in insects and arachnids. For these taxa, much evidence of its use as a source of information from the surrounding environment exists, as well as its involvement in many behavioral roles, such as courtship and mating, conspecific recognition, competition, foraging, parental care, and danger perception. Recently, and for the first time, communication through surface-borne waves has been studied in terrestrial isopods, using a common Mediterranean species of the Armadillidae family as a pilot species, Armadillo officinalis Duméril, 1816. Mainly, for this species, we describe typical behavioral processes, such as turn alternation, aggregation, and stridulation, where vibrational communication appears to be involved.

Post-contact immobility and half-lives that save lives

A wide variety of animals become completely immobile after initial contact with a potential predator. This behaviour is considered to be a last-ditch escape strategy. Here, we test the hypothesis that such immobility should have an extremely unpredictable duration. We find that it spans more than three orders of magnitude in antlion larvae. We also analyse the second period of immobility that follows the first bout of immobility, and consider the distributions of both first and second immobility periods within the context of the intermittence that characterizes the movement of most organisms. Both immobility durations were fitted best by exponential distributions. Therefore, both were characterized by high variability and hence, unpredictability. The immobility half-life, its mean duration and standard deviation were greater for the first than the second immobility. Furthermore, individual consistency was weak or absent in repeated measures of the first immobility and between the first and second immobilities. Our quantitative approach can be replicated across taxa and would help link an understanding of immobility after an initial predator contact in both vertebrates and invertebrates. To facilitate this, we contend that the terminology should be simplified, and we advocate the use of the term post-contact immobility (PCI).

Are terrestrial isopods able to use stridulation and vibrational communication as forms of intra and interspecific signaling and defense strategies as insects do? A preliminary study in Armadillo officinalis

The capability of producing sounds and vibrations is well known in insects and is thought to be a form of intra- and interspecific communication. Sounds and vibrations are used and modulated for several aims such as interacting with conspecifics, getting information from the environment, and defending against predators. This phenomenon is less known but also present in other arthropods, including a few roller-type terrestrial isopods. In this study, we used a Y-shape test apparatus to investigate the behavior of adult individuals of Armadillo officinalis Duméril, 1816 (Crustacea: Isopoda: Oniscidea) when exposed to two particular vibrational stimuli, namely species-specific stridulations and non-specific substrate-borne vibrations. Our results showed that adults of A. officinalis significantly react to the presence of both types of vibrational stimuli, by moving away from the vibrational source as if they experienced these vibrations as a sign of danger or disturbance. A. officinalis can produce stridulations only when it rolls into a ball during the so-called conglobation, a possible defense mechanism against predators. Stridulation might thus be a secondary form of defense used during conglobation to deter a predator following contact with it and might be experienced as an alert by conspecifics nearby. The high sensitivity to non-specific substrate-borne vibrations might provide A. officinalis with the possibility to anticipate dangers and adverse conditions, giving it a better chance of survival.

Roll with the fear: environment and state dependence of pill bug (Armadillidium vulgare) personalities

Most studies on animal personality evaluate individual mean behaviour to describe individual behavioural strategy, while often neglecting behavioural variability on the within-individual level. However, within-individual behavioural plasticity (variation induced by environment) and within-individual residual variation (regulatory behavioural precision) are recognized as biologically valid components of individual behaviour, but the evolutionary ecology of these components is still less understood. Here, we tested whether behaviour of common pill bugs (Armadillidium vulgare) differs on the among- and within-individual level and whether it is affected by various individual specific state-related traits (sex, size and Wolbachia infection). To this aim, we assayed risk-taking in familiar vs. unfamiliar environments 30 times along 38 days and applied double modelling statistical technique to handle the complex hierarchical structure for both individual-specific trait means and variances. We found that there are significant among-individual differences not only in mean risk-taking behaviour but also in environment- and time-induced behavioural plasticity and residual variation. Wolbachia-infected individuals took less risk than healthy conspecifics; in addition, individuals became more risk-averse with time. Residual variation decreased with time, and individuals expressed higher residual variation in the unfamiliar environment. Further, sensitization was stronger in females and in larger individuals in general. Our results suggest that among-individual variation, behavioural plasticity and residual variation are all (i) biologically relevant components of an individual's behavioural strategy and (ii) responsive to changes in environment or labile state variables. We propose pill bugs as promising models for personality research due to the relative ease of getting repeated behavioural measurements.

Rotational stress influences sensitized, but not habituated, exploratory behaviors in the woodlouse, Porcellio scaber

Terrestrial isopods (or woodlice), like the members of the other arthropod taxa, have a sophisticated nervous system that makes them sensitive to specific environmental factors. They can search for survival-related opportunities (e.g., approaching food sources or avoiding sunny areas). Two experiments examined how rotational stress could influence the propensity of common woodlice, Porcellio scaber to exhibit survival-related behaviors such as traveling and rearing up in a hostile environment. Experiment 1 assessed the behaviors of stressed and nonstressed woodlice exposed to a familiar or a novel environment without rewards. Experiment 2 assessed the effects of stress in woodlice given a free choice between a familiar and a novel environment without rewards. In the nonstressed individuals, the results showed a decrease in locomotor activity (habituation) and an increase in the time spent rearing up (sensitization) on the arena's walls over time. In the stressed individuals, repeated rotation had a detrimental effect on the time spent rearing up, but locomotion was decreased only in the stressed individuals that were not preexposed to the test environment beforehand. In addition, immobilization periods-as a plausible indicator of stress-were longer in the absence of preexposure. It is suggested that preexposure had some antistress protective effects on habituated but not on sensitized, exploratory behaviors in woodlice.