The emergence and development of behavioral individuality in clonal fish

Intelligence, brain structure, dendrites, and genes: Genetic, epigenetic and the underlying of the quadruple helix complexity

Intelligence can be referred to as the mental ability to learn, comprehend abstract concepts, and solve complex problems. Twin and adoption studies have provided insights into the influence of the familial environment and highlighted the importance of heritability in the development of cognition. Detecting the relative contribution of brain areas, neuronal structures, and connectomes has brought some understanding on how various brain areas, white/gray matter structures and neuronal connectivity process information and contribute to intelligence. Using histological, anatomical, electrophysiological, neuropsychological, neuro-imaging and molecular biology methods, several key concepts have emerged: 1) the parietofrontal-hippocampal integrations probably constitute a substrate for smart behavior, 2) neuronal activity results in structural plasticity of dendritic branches responsible for information transfer, critical for learning and memory, 3) intelligent people process information efficiently, 4) the environment triggers mnemonic epigenomic programs (via dynamic regulation of chromatin accessibility, DNA methylation, loop interruption/formation and histone modification) conferring cognitive phenotypes throughout life, and 5) single/double DNA breaks are prominent in human brain disorders associated with cognitive impairment including Alzheimer's disease and schizophrenia. Along with these observations, molecular/cellular/biological studies have identified sets of specific genes associated with higher scores on intelligence tests. Interestingly, many of these genes are associated with dendritogenesis. Because dendrite structure/function is involved in cognition, the control of dendrite genesis/maintenance may be critical for understanding the landscape of general/specific cognitive ability and new pathways for therapeutic approaches.

Division of labour in colony defence in a clonal ant

Division of labour (DOL) plays a key role across all scales of biological organization, but how its expression varies across contexts is still poorly understood. Here, we measure DOL in a crucial task, colony defence, in a social insect that affords precise experimental control over individual and colony traits, the clonal raider ant (Ooceraea biroi). We find that DOL in defence behaviour emerges within colonies of near-identical workers, likely reflecting variation in individual response thresholds, and that it increases with colony size. Additionally, colonies with pupae show higher defence levels than those without brood. However, we do not find evidence for a behavioural syndrome linking defence with exploration and activity, as previously reported in other systems. By showing how colony composition and size affect group response to potential threats, our findings highlight the role of the social context in shaping DOL.This article is part of the theme issue 'Division of labour as key driver of social evolution'.

A neural correlate of individual odor preference in Drosophila

Behavior varies even among genetically identical animals raised in the same environment. However, little is known about the circuit or anatomical origins of this individuality. Here, we demonstrate a neural correlate of Drosophila odor preference behavior in the olfactory sensory periphery. Namely, idiosyncratic calcium responses in projection neuron (PN) dendrites and densities of the presynaptic protein Bruchpilot in olfactory receptor neuron (ORN) axon terminals correlate with individual preferences in a choice between two aversive odorants. The ORN-PN synapse appears to be a locus of individuality where microscale variation gives rise to idiosyncratic behavior. Simulating microscale stochasticity in ORN-PN synapses of a 3062 neuron model of the antennal lobe recapitulates patterns of variation in PN calcium responses matching experiments. Conversely, stochasticity in other compartments of this circuit does not recapitulate those patterns. Our results demonstrate how physiological and microscale structural circuit variations can give rise to individual behavior, even when genetics and environment are held constant.

State-behaviour feedbacks between boldness and food intake shape escape responses in fish (Gasterosteus aculeatus)

Consistent differences in intrinsic state, amplified through state-dependent behaviour, could explain the ubiquity of animal personality variation. Boldness is often positively associated with a high metabolism and food intake. Even though a high food consumption is known to compromise oxygen-demanding activities, the influence of food intake on anti-predator escape responses has rarely been considered. By conducting experiments with three-spined sticklebacks (Gasterosteus aculeatus) in a setup with real-time tracking and a decoy heron predator, we show that bolder fish benefited from a higher food intake than shy fish, and reacted faster to a predator attack when food intake was the same before being attacked. However, a higher food intake slowed down the escape responses. These results shine light on how the fitness of shy and bold tactics could be balanced in the wild: the faster reaction of bold fish is impaired by their higher food consumption.

Fast, bioluminescent blinks attract group members of the nocturnal flashlight fish Anomalops katoptron (Bleeker, 1856)

BACKGROUND

During their nighttime shoaling, the flashlight fish Anomalops katoptron produce fascinating, bioluminescent blink patterns, which have been related to the localization of food, determination of nearest neighbor distance, and initiation of the shoal's movement direction. Information transfer e.g., via alarm signals is an important aspect in group living species especially when being under threat. In dark environments, bioluminescence has the potential to accurately transfer such information. Under threat A. katoptron show increased swimming speeds and a higher group cohesion accompanied by fast blink frequencies.

RESULTS

In this study we used a two-choice paradigm to test the preferences for typical blink characteristics e.g., frequency and duration. Our data show that individuals decided within short periods (< 4 s) for faster blink frequencies of artificial light organs and the preference for the higher blink frequencies became more pronounced as the difference between the presented frequencies increased. The preference correlated with the frequency rather than the duration.

CONCLUSION

Our study suggests that fast, bioluminescent blinks of light organs lead to aggregations of A. katoptron.

Competitive social feedback amplifies the role of early life contingency in male mice

Contingency (or "luck") in early life plays an important role in shaping individuals' development. By comparing the developmental trajectories of functionally genetically identical free-living mice who either experienced high levels of resource competition (males) or did not (females), we show that competition magnifies early contingency. Male resource competition results in a feedback loop that magnifies the importance of early contingency and pushes individuals onto divergent, self-reinforcing life trajectories, while the same process appears absent in females. Our results indicate that the strength of sexual selection may be self-limiting, and they highlight the potential for contingency to lead to differences in life outcomes, even in the absence of any underlying differences in ability ("merit").

Predator exposure early in life shapes behavioral development and individual variation in a clonal fish

Predation risk is one of the most important factors generating behavioral differences among populations. In addition, recent attention focusses on predation as a potential driver of patterns of individual behavioral variation within prey populations. Previous studies provide mixed results, reporting either increased or decreased among-individual variation in response to risk. Here, we take an explicit developmental approach to documenting how among-individual variation develops over time in response to predator exposure, controlling for both genetic and experiential differences among individuals. We reared juveniles of naturally clonal Amazon mollies, Poecilia formosa, either with or without a predator visible during feedings over 4 weeks and analyzed activity during feedings, time spent feeding and number of visits to the feeding spot. (I) Predator-exposed fish did not differ from control fish in average feeding behavior, but they were less active during feeding trials. (II) In the absence of the predator, substantial changes in among-individual variation over time were detected: among-individual differences in feeding duration increased whereas differences in activity decreased, but there were no changes in feeder visits. In contrast, in the presence of a predator, among-individual variation in all three behaviors was stable over time and often lower compared to control conditions. Our work suggests that predation risk may have an overall stabilizing effect on the development of individual variation and that differences in predation risk may well lead to population-wide differences in among-individual behavioral variation.

Drift in Individual Behavioral Phenotype as a Strategy for Unpredictable Worlds

Individuals, even with matched genetics and environment, show substantial phenotypic variability. This variability may be part of a bet-hedging strategy, where populations express a range of phenotypes to ensure survival in unpredictable environments. In addition phenotypic variability between individuals ("bet-hedging"), individuals also show variability in their phenotype across time, even absent external cues. There are few evolutionary theories that explain random shifts in phenotype across an animals life, which we term drift in individual phenotype. We use individuality in locomotor handedness in Drosophila melanogaster to characterize both bet-hedging and drift. We use a continuous circling assay to show that handedness spontaneously changes over timescales ranging from seconds to the lifespan of a fly. We compare the amount of drift and bet-hedging across a number of different fly strains and show independent strain specific differences in bet-hedging and drift. We show manipulation of serotonin changes the rate of drift, indicating a potential circuit substrate controlling drift. We then develop a theoretical framework for assessing the adaptive value of drift, demonstrating that drift may be adaptive for populations subject to selection pressures that fluctuate on timescales similar to the lifespan of an animal. We apply our model to real world environmental signals and find patterns of fluctuations that favor random drift in behavioral phenotype, suggesting that drift may be adaptive under some real world conditions. These results demonstrate that drift plays a role in driving variability in a population and may serve an adaptive role distinct from population level bet-hedging.

Significance Statement

Why do individuals animals spontaneously change their preferences over time? While stable idiosyncratic behavioral preferences have been proposed to help species survive unpredictable environments as part of a bet-hedging strategy, the role of intraindividual shifts in preferences is unclear. Using Drosophila melanogaster , we show the stability of individual preferences is influenced by genetic background and neuromodulation, and is therefore a regulated phenomenon. We use theoretical modeling to show that shifts in preferences may be adaptive to environments that change within an individual's lifespan, including many real world patterns of environmental fluctuations. Together, this work suggests that the stability of individual preferences may affect the survival of species in unpredictable worlds - understanding that may be increasingly important in the face of anthropogenic change.

Nonshared environment: Real but random

Background

In the excitement about genomics, it is easy to lose sight of one of the most important findings from behavioural genetics: At least half of the variance of psychopathology is caused by environmental effects that are not shared by children growing up in the same family, which includes error of measurement. However, a 30-year search for the systematic causes of nonshared environment in a line-up of the usual suspects, especially parenting, has not identified the culprits.

Method

I briefly review this research, but primarily consider the conceptual framework of the search for 'missing' nonshared environmental effects.

Results

The search has focused on exogenous events like parenting, but nonshared environment might not be caused by anything we would call an event. Instead, it might reflect endogenous processes such as noisy biological systems (such as somatic mutations and epigenetics) or, at a psychological level, idiosyncratic subjective perceptions of past and present experiences, which could be called nonshared environmental experience to distinguish it from exogenous events. Although real, nonshared environment might be random in the philosophy of science sense of being unpredictable, even though it can have stable effects that predict subsequent behaviour.

Conclusion

I wade into the weeds of randomness and suggest that this so-called 'gloomy prospect' might not be so gloomy.

Sex-specific competitive social feedback amplifies the role of early life contingency in male mice

Contingency (or 'luck') in early life plays an important role in shaping individuals' development. When individuals live within larger societies, social experiences may cause the importance of early contingencies to be magnified or dampened. Here we test the hypothesis that competition magnifies the importance of early contingency in a sex-specific manner by comparing the developmental trajectories of genetically identical, free-living mice who either experienced high levels of territorial competition (males) or did not (females). We show that male territoriality results in a competitive feedback loop that magnifies the importance of early contingency and pushes individuals onto divergent, self-reinforcing life trajectories, while the same process appears absent in females. Our results indicate that the strength of sexual selection may be self-limiting, as within-sex competition increases the importance of early life contingency, thereby reducing the ability of selection to lead to evolution. They also demonstrate the potential for contingency to lead to dramatic differences in life outcomes, even in the absence of any underlying differences in ability ('merit').

Behavioural ecology meets oncology: quantifying the recovery of animal behaviour to a transient exposure to a cancer risk factor

Wildlife is increasingly exposed to sublethal transient cancer risk factors, including mutagenic substances, which activates their anti-cancer defences, promotes tumourigenesis, and may negatively impact populations. Little is known about how exposure to cancer risk factors impacts the behaviour of wildlife. Here, we investigated the effects of a sublethal, short-term exposure to a carcinogen at environmentally relevant concentrations on the activity patterns of wild Girardia tigrina planaria during a two-phase experiment, consisting of a 7-day exposure to cadmium period followed by a 7-day recovery period. To comprehensively explore the effects of the exposure on activity patterns, we employed the double hierarchical generalized linear model framework which explicitly models residual intraindividual variability in addition to the mean and variance of the population. We found that exposed planaria were less active compared to unexposed individuals and were able to recover to pre-exposure activity levels albeit with a reduced variance in activity at the start of the recovery phase. Planaria showing high activity levels were less predictable with larger daily activity variations and higher residual variance. Thus, the shift in behavioural variability induced by an exposure to a cancer risk factor can be quantified using advanced tools from the field of behavioural ecology. This is required to understand how tumourous processes affect the ecology of species.

The genomic case against genetic determinism

Animal studies reveal that the molecular wiring of the brain can be altered by heredity, the environment, and their interaction. A deeper molecular understanding of these interactions could be a potent antidote to societal concerns of genetic determinism for human behavior, but this requires a paradigm that extends beyond traditional genome-wide association study (GWAS).

Reproductive individuality of clonal fish raised in near-identical environments and its link to early-life behavioral individuality

Recent studies have documented among-individual phenotypic variation that emerges in the absence of apparent genetic and environmental differences, but it remains an open question whether such seemingly stochastic variation has fitness consequences. We perform a life-history experiment with naturally clonal fish, separated directly after birth into near-identical (i.e., highly standardized) environments, quantifying 2522 offspring from 152 broods over 280 days. We find that (i) individuals differ consistently in the size of offspring and broods produced over consecutive broods, (ii) these differences are observed even when controlling for trade-offs between brood size, offspring size and reproductive onset, indicating individual differences in life-history productivity and (iii) early-life behavioral individuality in activity and feeding patterns, with among-individual differences in feeding being predictive of growth, and consequently offspring size. Thus, our study provides experimental evidence that even when minimizing genetic and environmental differences, systematic individual differences in life-history measures and ultimately fitness can emerge.

Time-specific convergence and divergence in individual differences in behavior: Theory, protocols and analyzes

Over the years, theoreticians and empiricists working in a wide range of disciplines, including physiology, ethology, psychology, and behavioral ecology, have suggested a variety of reasons why individual differences in behavior might change over time, such that different individuals become more similar (convergence) or less similar (divergence) to one another. Virtually none of these investigators have suggested that convergence or divergence will continue forever, instead proposing that these patterns will be restricted to particular periods over the course of a longer study. However, to date, few empiricists have documented time-specific convergence or divergence, in part because the experimental designs and statistical methods suitable for describing these patterns are not widely known. Here, we begin by reviewing an array of influential hypotheses that predict convergence or divergence in individual differences over timescales ranging from minutes to years, and that suggest how and why such patterns are likely to change over time (e.g., divergence followed by maintenance). Then, we describe experimental designs and statistical methods that can be used to determine if (and when) individual differences converged, diverged, or were maintained at the same level at specific periods during a longitudinal study. Finally, we describe why the concepts described herein help explain the discrepancy between what theoreticians and empiricists mean when they describe the "emergence" of individual differences or personality, how they might be used to study situations in which convergence and divergence patterns alternate over time, and how they might be used to study time-specific changes in other attributes of behavior, including individual differences in intraindividual variability (predictability), or genotypic differences in behavior.

Automated behavioral scoring: Do we even need humans?

The development of automated behavior scoring technology has been a tremendous boon to the study of social behavior. However, completely outsourcing behavioral analysis to a computer runs the risk of overlooking important nuances, and researchers risk distancing themselves from their very object of study. Here, I make the case that while automating analysis has been valuable, and overautomating analysis is risky, more effort should be spent automating the collection of behavioral data. Continuous automated behavioral observations conducted in situ have the promise to reduce confounding elements of social behavior research, such as handling stress, novel environments, one-time "snapshot" measures, and experimenter presence. Now that we have the capability to automatically process behavioral observations thanks to machine vision and machine learning, we would do well to leverage the same open-source ethos to increase the throughput of behavioral observation and collection. Fortunately, several such platforms have recently been developed. Repeated testing in the home environment will produce higher qualities and quantities of data, bringing us closer to realizing the ethological goals of studying animal behavior in a naturalistic context.

Behavioral ecology: New technology enables a more holistic view of complex animal behavior

As any animal observer will tell you, behavior is complex. A more holistic view of this complexity is emerging as technological advances enable the study of spatiotemporal variability and expand the focus from single components to behavioral systems.

Challenges of mismatching timescales in longitudinal studies of collective behaviour

How individuals' prior experience and population evolutionary history shape emergent patterns in animal collectives remains a major gap in the study of collective behaviour. One reason for this is that the processes that can shape individual contributions to collective actions can happen over very different timescales from each other and from the collective actions themselves, resulting in mismatched timescales. For example, a preference to move towards a specific patch might arise from phenotype, memory or physiological state. Although providing critical context to collective actions, bridging different timescales remains conceptually and methodologically challenging. Here, we briefly outline some of these challenges, and discuss existing approaches that have already generated insights into the factors shaping individual contributions in animal collectives. We then explore a case study of mismatching timescales-defining relevant group membership-by combining fine-scaled GPS tracking data and daily field census data from a wild population of vulturine guineafowl (Acryllium vulturinum). We show that applying different temporal definitions can produce different assignments of individuals into groups. These assignments can then have consequences when determining individuals' social history, and thus the conclusions we might draw on the impacts of the social environment on collective actions. This article is part of a discussion meeting issue 'Collective behaviour through time'.

Leveraging big data to uncover the eco-evolutionary factors shaping behavioural development

Mapping the eco-evolutionary factors shaping the development of animals' behavioural phenotypes remains a great challenge. Recent advances in 'big behavioural data' research-the high-resolution tracking of individuals and the harnessing of that data with powerful analytical tools-have vastly improved our ability to measure and model developing behavioural phenotypes. Applied to the study of behavioural ontogeny, the unfolding of whole behavioural repertoires can be mapped in unprecedented detail with relative ease. This overcomes long-standing experimental bottlenecks and heralds a surge of studies that more finely define and explore behavioural-experiential trajectories across development. In this review, we first provide a brief guide to state-of-the-art approaches that allow the collection and analysis of high-resolution behavioural data across development. We then outline how such approaches can be used to address key issues regarding the ecological and evolutionary factors shaping behavioural development: developmental feedbacks between behaviour and underlying states, early life effects and behavioural transitions, and information integration across development.