Incorporating Animal Social Context in Ecotoxicology: Can a Single Individual Tell the Collective Story?

Social context mediates the expression of a personality trait in a gregarious lizard

The social environment is a key factor that influences behavioural traits across a wide array of species. Yet, when investigating individual differences in behaviour, studies tend to measure animals in isolation from other conspecifics—even in social species. Surprisingly, whether behavioural traits measured in isolation are predictive of individual-level behaviour when in social groups is still poorly understood. Here, we repeatedly measured risk-taking behaviour (i.e. boldness; 741 total trials) in both the presence and absence of conspecifics in a social lizard, the delicate skink (Lampropholis delicata). Further, we manipulated food availability during group trials to test whether the effect of the social environment on risk-taking behaviour was mediated by competition over resources. Using 105 lizards collected from three independent populations, we found that individual risk-taking behaviour was repeatable when measured in either social isolation or within groups both with and without food resources available. However, lizards that were bolder during individual trials were not also bolder when in groups, regardless of resource availability. This was largely driven by individual differences in social behavioural plasticity, whereby individual skinks responded differently to the presence of conspecifics. Together, this resulted in a rank order change of individual behavioural types across the social conditions. Our results highlight the importance of the social environment in mediating animal personality traits across varying levels of resource availability. Further, these findings suggest that behavioural traits when measured in isolation, may not reflect individual variation in behaviour when measured in more ecologically realistic social groups.

Frontiers in quantifying wildlife behavioural responses to chemical pollution

Animal behaviour is remarkably sensitive to disruption by chemical pollution, with widespread implications for ecological and evolutionary processes in contaminated wildlife populations. However, conventional approaches applied to study the impacts of chemical pollutants on wildlife behaviour seldom address the complexity of natural environments in which contamination occurs. The aim of this review is to guide the rapidly developing field of behavioural ecotoxicology towards increased environmental realism, ecological complexity, and mechanistic understanding. We identify research areas in ecology that to date have been largely overlooked within behavioural ecotoxicology but which promise to yield valuable insights, including within- and among-individual variation, social networks and collective behaviour, and multi-stressor interactions. Further, we feature methodological and technological innovations that enable the collection of data on pollutant-induced behavioural changes at an unprecedented resolution and scale in the laboratory and the field. In an era of rapid environmental change, there is an urgent need to advance our understanding of the real-world impacts of chemical pollution on wildlife behaviour. This review therefore provides a roadmap of the major outstanding questions in behavioural ecotoxicology and highlights the need for increased cross-talk with other disciplines in order to find the answers.

Predicting the impacts of chemical pollutants on animal groups

Chemical pollution is among the fastest-growing agents of global change. Synthetic chemicals with diverse modes-of-action are being detected in the tissues of wildlife and pervade entire food webs. Although such pollutants can elicit a range of sublethal effects on individual organisms, research on how chemical pollutants affect animal groups is severely lacking. Here we synthesise research from two related, but largely segregated fields - ecotoxicology and behavioural ecology - to examine pathways by which chemical contaminants could disrupt processes that govern the emergence, self-organisation, and collective function of animal groups. Our review provides a roadmap for prioritising the study of chemical pollutants within the context of sociality and highlights important methodological advancements for future research.

Exposure to an androgenic agricultural pollutant does not alter metabolic rate, behaviour, or morphology of tadpoles

Globally, amphibian species are experiencing dramatic population declines, and many face the risk of imminent extinction. Endocrine-disrupting chemicals (EDCs) have been recognised as an underappreciated factor contributing to global amphibian declines. In this regard, the use of hormonal growth promotants in the livestock industry provides a direct pathway for EDCs to enter the environment-including the potent anabolic steroid 17β-trenbolone. Emerging evidence suggests that 17β-trenbolone can impact traits related to metabolism, somatic growth, and behaviour in non-target species. However, far less is known about possible effects of 17β-trenbolone on anuran species, particularly during early life stages. Accordingly, in the present study we investigated the effects of 28-day exposure to 17β-trenbolone (mean measured concentrations: 10 and 66 ng/L) on body size, body condition, metabolic rate, and anxiety-related behaviour of tadpoles (Limnodynastes tasmaniensis). Specifically, we measured rates of O₂ consumption of individual tadpoles as a proxy for metabolic rate and quantified their swimming activity and their time spent in the upper half of the water column as indicators of anxiety-related behaviour. Counter to our predictions based on effects observed in other taxa, we detected no effect of 17β-trenbolone on body size, metabolic rate, or behaviour of tadpoles; although, we did detect a subtle, but statistically significant decrease in body condition at the highest 17β-trenbolone concentration. We hypothesise that 17β-trenbolone may induce taxa-specific effects on metabolic function, growth, and anxiety-related behaviour, with anurans being less sensitive to disruption than fish, and encourage further cross-taxa investigation to test this hypothesis.

Context is Key: Social Environment Mediates the Impacts of a Psychoactive Pollutant on Shoaling Behavior in Fish

Behavior-modifying drugs, such as antidepressants, are increasingly being detected in waterways and aquatic wildlife around the globe. Typically, behavioral effects of these contaminants are assessed using animals tested in social isolation. However, for group-living species, effects seen in isolation may not reflect those occurring in realistic social settings. Furthermore, interactions between chemical pollution and other stressors, such as predation risk, are seldom considered. This is true even though animals in the wild are rarely, if ever, confronted by chemical pollution as a single stressor. Here, in a 2 year multigenerational experiment, we tested for effects of the antidepressant fluoxetine (measured concentrations [±SD]: 42.27 ± 36.14 and 359.06 ± 262.65 ng/L) on shoaling behavior in guppies (Poecilia reticulata) across different social contexts and under varying levels of perceived predation risk. Shoaling propensity and shoal choice (choice of groups with different densities) were assessed in a Y-maze under the presence of a predatory or nonpredatory heterospecific, with guppies tested individually and in male-female pairs. When tested individually, no effect of fluoxetine was seen on shoaling behavior. However, in paired trials, high-fluoxetine-exposed fish exhibited a significantly greater shoaling propensity. Hence, effects of fluoxetine were mediated by social context, highlighting the importance of this fundamental but rarely considered factor when evaluating impacts of environmental pollution.