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Differences in risk-taking residual variation over time in common pill bug (Armadillidium vulgare). Estimates were obtained from the statistical model (see Table 1)
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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 precis...
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Citations
... Decreased behavioural predictability (i.e. larger rIIV) is also possible if individual variation is a product of individual state or environmental differences [7][8][9][10]. ...
... Although there is a paucity of studies examining sex differences in movement behaviour (see [29]), a handful of studies have examined sex differences in the predictability of other fitness-related behaviours [9,[30][31][32]. These studies suggest, however, that one sex is not more consistently predictable than the other. ...
Behavioural predictability describes the behavioural variability of an individual. Unpredictability can arise from many sources including non-adaptive passive plasticity in which an environmental factor acts directly on the individual to create non-adaptive phenotypic variation. In this study, I use radiotelemetry to field test the hypothesis that Cook Strait giant weta Deinacrida rugosa (Orthoptera: Anostostomatidae) exhibit a sex difference in the predictability of their nightly travel distance due to passive behavioural plasticity. As predicted, I found that male mobility (i.e. nightly travel distance) was less predictable than female mobility. Females travel short and predictable distances each night for food and refuges that are close by and readily available. In contrast, male travel is less predictable because they search for female mates that are stochastically dispersed across the landscape. Therefore, their travel distance can vary considerably across nights.
... Other research has indicated that behaving unpredictably is an adaptive response to predation threat (Briffa, 2013), and that some animals vary their behaviour in risky situations/environments (Brand et al., 2023;Horv ath et al., 2019). It could be the case here that some baboons show greater unpredictability in movement expression as a response to changing environmental risks and rewards that they encounter. ...
... Armadillidium vulgare individuals, have a behavioural ability that the P. scaber species does not, in that they can roll themselves up into a ball that internalises the ventral surfaces that transpire more water vapour than dorsal surfaces (Horváth, et al., 2019). This action (termed conglobation or volvation), as well as possessing cuticle and pleopodal lungs more adapted to terrestrial life compared to P. scaber, helps A. vulgare resist desiccation (Hornung, 2011, Warburg, 1987. ...
... While locomotor activity was not measured during the evening in the current study, this trade-off between activity and metabolism may partly explain why increased metabolic rates at higher temperatures in females resulted in lower within-individual behavioural variance. While the ecological implications of these sexdifferences in within-individual behavioural variability are unclear, we note that previous studies have identified putative associations between within-individual variance and predation in invertebrates [24,57,58]. This suggests that sexspecific effects of temperature on within-individual variation in activity rates found in the current study could lead to temperature-dependent differences between males and females in their vulnerability to predation. ...
Temperature is a key factor mediating organismal fitness and has important consequences for species' ecology. While the mean effects of temperature on behaviour have been well-documented in ectotherms, how temperature alters behavioural variation among and within individuals, and whether this differs between the sexes, remains unclear. Such effects likely have ecological and evolutionary consequences, given that selection acts at the individual level. We investigated the effect of temperature on individual-level behavioural variation and metabolism in adult male and female Drosophila melanogaster (n = 129), by taking repeated measures of locomotor activity and metabolic rate at both a standard temperature (25°C) and a high temperature (28°C). Males were moderately more responsive in their mean activity levels to temperature change when compared to females. However, this was not true for either standard or active metabolic rate, where no sex differences in thermal metabolic plasticity were found. Furthermore , higher temperatures increased both among-and within-individual variation in male, but not female, locomotor activity. Given that behavioural variation can be critical to population persistence, we suggest that future studies test whether sex differences in the amount of behavioural variation expressed in response to temperature change may result in sex-specific vulnerabilities to a warming climate.
... However, current evidence does not suggest systematic differences in (un)predictability between field and lab studies (Mitchell et al. 2021). This suggests that (un)predictability could vary according to state variables of individuals (MacDonald et al. 2006;Horvath et al. 2019a; but see Cornwell et al. 2023). Furthermore, individuals can differ in how sensitive they are in perceiving environmental cues (Briffa 2013), and in the accuracy with which they assess the environment ("organismal error," Westneat et al. 2015). ...
... If unpredictability represents a neurobiological challenge, then a predator-prey interaction might partly become a competition in the ability to change behavior and unpredictability can be under open-ended selection. Indeed, crustaceans, for example, behave more unpredictably in risk-taking behavior when exposed to predator cues (Briffa 2013) or when in an unfamiliar (potentially riskier) environment (Horvath et al. 2019a). Among insects, erratic (unpredictable) escape paths are common and have been predicted to confuse predators (Humphries and Driver 1970). ...
... It has been hardly explored if being predictable or unpredictable in risky or competitive situations is actually challenging. To our knowledge, only one study looked at the condition dependence of unpredictability (Horvath et al. 2019a). We here use a predator escape context to study if (un)predictability is affected by experimental manipulation of individual condition. ...
(Un)predictability has only recently been recognized as an important dimension of animal behavior. Currently, we neither know if (un)predictability encompasses one or multiple traits nor how (un)predictability is dependent on individual conditions. Knowledge about condition dependence, in particular, could inform us about whether predictability or unpredictability is costly in a specific context. Here, we study the condition dependence of (un)predictability in the escape behavior of the steppe grasshopper Chorthippus dorsatus. Predator–prey interactions represent a behavioral context in which we expect unpredictability to be particularly beneficial. By exposing grasshoppers to an immune challenge, we explore if individuals in poor condition become more or less predictable. We quantified three aspects of escape behavior (flight initiation distance, jump distance, and jump angle) in a standardized setup and analyzed the data using a multivariate double-hierarchical generalized linear model. The immune challenge did not affect (un)predictability in flight initiation distance and jump angle, but decreased unpredictability in jump distances, suggesting that unpredictability can be costly. Variance decomposition shows that 3–7% of the total phenotypic variance was explained by individual differences in (un)predictability. Covariation between traits was found both among averages and among unpredictabilities for one of the three trait pairs. The latter might suggest an (un)predictability syndrome, but the lack of (un)predictability correlation in the third trait suggests modularity. Our results indicated condition dependence of (un)predictability in grasshopper escape behavior in one of the traits, and illustrate the value of mean and residual variance decomposition for analyzing animal behavior.
... Similar research using computer simulations reported that human participants were less likely to capture more unpredictable "prey" in a computer game, again suggesting that decreased predictability may aid in predator avoidance (Jones et al. 2011). Furthermore, recent work found that both common hermit crabs (Pagurus bernhardus) and common pill bugs (Armadillidium vulgare) were more unpredictable in their risk-taking behavior when in more risky, unfamiliar environments (Briffa 2013;Horváth et al. 2019). Taken together, this research suggests that decreased behavioral predictability may be an adaptive strategy for dealing with predation risk in precarious environments. ...
... However, research on sex differences in predictability is limited and the studies that do exist report mixed results. For example, while a previous study reported that female guppies (Poecilia reticulata) were less predictable than males in their lateralization (McLean and Morrell 2020), other research has found no sex differences in the predictability of risk-taking behaviors (White and Briffa 2017;Horváth et al. 2019;Prentice et al. 2020). It remains unknown, however, whether these patterns are found more broadly across species and multiple behavioral traits. ...
... Together, these findings suggest that male and female mosquitofish are likely exposed to differing levels of predation risk, resulting in sex differences in risk-taking behaviors. Given the previously reported associations between behavioral predictability and risk-management (Briffa 2013;Horváth et al. 2019), these sex differences in boldness and predation risk make mosquitofish an ideal model species to investigate potential sex differences in the predictability of risk-taking behavior. ...
Recent research has found that individuals often vary in how consistently they express their behavior over time (i.e., behavioral predictability) and suggested that these individual differences may be heritable. However, little is known about the intrinsic factors that drive variation in the predictability of behavior. Indeed, whether variation in behavioral predictability is sex-specific is not clear. This is important, as behavioral predictability has been associated with vulnerability to predation, suggesting that the predictability of behavioral traits may have key fitness implications. We investigated whether male and female eastern mosquitofish (Gambusia holbrooki) differed in the predictability of their risk-taking behavior. Specifically, over a total of 954 behavioral trials, we repeatedly measured risk-taking behavior with three commonly used assays—refuge-use, thigmotaxis, and foraging latency. We predicted that there would be consistent sex differences in both mean-level risk-taking behavior and behavioral predictability across the assays. We found that risk-taking behavior was repeatable within each assay, and that some individuals were consistently bolder than others across all three assays. There were also consistent sex differences in mean-level risk-taking behavior, with males being bolder across all three assays compared to females. In contrast, both the magnitude and direction of sex differences in behavioral predictability were assay-specific. Taken together, these results highlight that behavioral predictability may be independent from underlying mean-level behavioral traits and suggest that males and females may differentially adjust the consistency of their risk-taking behavior in response to subtle changes in environmental conditions.
... Common approaches to measuring boldness vary widely across studies and include measuring the latency to emerge from a refuge (Vainikka et al. 2011;Hedrick and Kortet 2012), the tendency to approach a rival (Mazué et al. 2015;Wright et al. 2018), the distance of a threat before fleeing (Niemelä et al. 2015;Bubac et al. 2018), or the duration of death-feigning (otherwise known as tonic immobility or thanatosis; Edelaar et al. 2012). Boldness is particularly easy and relevant to measure in animals that assume a defensive position when threatened, such as pill bugs, turtles, and hermit crabs; in these cases, the latency to assume a defensive pose and subsequently resume activity after disturbance is often used as an ecologically relevant measure of risk-taking (Matsuno and Moriyama 2012;Horváth et al. 2019;Carlson and Tetzlaff 2020;Garcia et al. 2020). ...
The trait compensation and cospecialization hypotheses make contrasting predictions on how boldness is co-adapted with antipredator defences. If trait compensation occurs, then bold individuals should be equipped with better antipredator defences to compensate for their increased risk exposure. By contrast, if trait co-specialization occurs, shy individuals should be equipped with better antipredator defences to enhance overall protection from predation. Here, we test the two alternative hypotheses by evaluating the among- and within-individual relationships between boldness and chemical defences in the American giant millipede (Narceus americanus; order Spirobolida). After controlling for test sequence, body length, air temperature, and time of day, latency to conglobate (i.e. “curl up”) upon disturbance and duration of conglobation were both found to be repeatable (R = 0.28 and 0.35). Moreover, the latency and duration of conglobation were negatively correlated at both the among- and within-individual levels (r = − 0.46 and − 0.32). Hence, individuals displayed consistent differences in risk-taking along a “shy-bold” axis. Millipedes also displayed—albeit weaker—individual differences in their probability to secrete chemical defences (R = 0.12), but no significant relationship was found with conglobation latency or duration. Overall, these results suggest that chemical defences evolved separately from the shy-bold axis (as measured with conglobation behaviour) as two independent antipredator strategies in millipedes.
Significance statement
Many species assume a defensive pose when threatened to protect themselves from predators, which makes them conducive to boldness measurements in a way that is directly relevant to antipredator strategies. The question arises as to whether boldness is co-adapted with other antipredator defences. Here, we demonstrate the existence of a shy-bold axis in American giant millipedes, which both conglobate into a defensive position and secrete a defensive fluid when threatened. We also found consistent individual differences in the propensity to secrete chemical defences, but with no relationship to boldness. While many studies have looked at the relationship between boldness and morphological defences (e.g. size of a protective shell), this is the first study to have partitioned the among- and within-individual correlations between boldness and chemical defences. Despite their importance as predator deterrents, chemical defences seem to have evolved independently from boldness in this species.
... Conglobation is usually triggered by external stimuli, such as strong vibrations or pressure (Horváth et al. 2019). Cividini and Montesanto (2018a) documented that Armadillo officinalis Duméril, 1816 responded to substrate vibrations by conglobation. ...
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.
... Although behaviours often vary consistently between individuals, they also vary plastically within individuals over time or in response to environmental contexts (Dingemanse et al., 2010;Dingemanse & R eale, 2005;Dingemanse & Wolf, 2013;Dougherty, 2021). Within-individual variation in behaviour may be related to individuals' intrinsic properties such as sex (Krenhardt et al., 2021), age (Delaney et al., 2020;Dingemanse et al., 2020), breeding stage (Araya-Ajoy & Dingemanse, 2017) and immune status Horv ath et al., 2019) or to environmental conditions (reviewed in Dougherty, 2021) shaped by abiotic factors (Briffa et al., 2013), predation risk (Brown et al., 2005) or social context (Bierbach et al., 2015;Briffa et al., 2013;Brown et al., 2005;Jablonszky et al., 2021;Magellan & Magurran, 2007). Social contexts may be particularly important during courtship as courtship displays are used as signals to conspecifics. ...
Behavioural variation in courtship has become a central theme in the study of sexual selection. Courtship behaviour can vary consistently between males (between-individual variation) due to inherent characteristics of individuals, but males may also plastically adjust their courtship (within-individual variation) in response to the characteristics of the potential breeding mate or the environmental contexts. However, the relative importance of these components in courtship behaviour remains poorly understood. Here, we exposed male collared flycatchers, Ficedula albicollis, to different stimulus females simulating a female's visit to the male's territory during mate choice. We measured the male's latency to explicitly invite the female to visit the nestbox (hereafter, invitation latency), as a proxy of the male's motivation to mate. Repeated measurements of focal males (exposed to different stimulus females) and stimulus females (presented to different males) allowed us to assess the relative importance of male and female identity in male courtship, while also assessing the importance of their phenotype and other environmental sources of within-individual variation in invitation latency. We found that invitation latency was determined by male and, to a lesser extent, female identity, with the latter suggesting the existence of male mate choice in the species. We failed to identify specific traits of males and females that influenced courtship behaviour, although male responsiveness to stimulus females increased as the season advanced, possibly due to the costs of delaying breeding in temperate breeding areas. Overall, these results suggest that invitation latency is a consistent courtship attribute in males that can be adjusted plastically according to perceived female quality and environmental conditions. We emphasize that understanding within- and between-individual sources of courtship variation is essential for assessing its evolutionary potential, as plasticity in the expression of sexual signals may affect their reliability and the strength of sexual selection on them.
... We did not pick up clear signs of publication bias in the studies considered, with no effect observed of whether the original publication considered variation in rIIV (see Mitchell, 2021, for full output Contrary to the prediction that field studies would show greater variance in rIIV due to reduced control over conditions (Stamps et al., 2012;Westneat et al., 2015), field studies typically 2020; Highcock & Carter, 2014) rather than latency to emerge (e.g., Horváth et al., 2019;Stamps et al., 2012), and measures of activity were based on tracking over large spatial scales (e.g., Hertel, Niemelä, et al., 2020;Hertel, Royauté, et al., 2020) rather than tracking within an arena (e.g., Mitchell & Biro, 2017;Prentice et al., 2020). ...
Behavioral and physiological ecologists have long been interested in explaining the causes and consequences of trait variation, with a focus on individual differences in mean values. However, the majority of phenotypic variation typically occurs within individuals, rather than among individuals (as indicated by average repeatability being less than 0.5). Recent studies have further shown that individuals can also differ in the magnitude of variation that is unexplained by individual variation or environmental factors (i.e., residual variation). The significance of residual variation, or why individuals differ, is largely unexplained, but is important from evolutionary, methodological, and statistical perspectives. Here, we broadly reviewed literature on individual variation in behavior and physiology, and located 39 datasets with sufficient repeated measures to evaluate individual differences in residual variance. We then analyzed these datasets using methods that permit direct comparisons of parameters across studies. This revealed substantial and widespread individual differences in residual variance. The magnitude of individual variation appeared larger in behavioral traits than in physiological traits, and heterogeneity was greater in more controlled situations. We discuss potential ecological and evolutionary implications of individual differences in residual variance and suggest productive future research directions. Animals are typically quite unpredictable in behavior with the majority of variance unexplained. We returned to raw data of previously published work, and found almost ubiquitously that individuals vary in their predictability. We discuss potential ecological and evolutionary implications of individual differences in residual variance and suggest productive future research directions.
