Although variation in effect sizes and predicted values among studies of similar phenomena is inevitable, such variation far exceeds what might be produced by sampling error alone. One possible explanation for variation among results is differences among researchers in the decisions they make regarding statistical analyses. A growing array of studies has explored this analytical variability in different fields and has found substantial variability among results despite analysts having the same data and research question. Many of these studies have been in the social sciences, but one small “many analyst” study found similar variability in ecology. We expanded the scope of this prior work by implementing a large-scale empirical exploration of the variation in effect sizes and model predictions generated by the analytical decisions of different researchers in ecology and evolutionary biology. We used two unpublished datasets, one from evolutionary ecology (blue tit, Cyanistes caeruleus, to compare sibling number and nestling growth) and one from conservation ecology (Eucalyptus, to compare grass cover and tree seedling recruitment). The project leaders recruited 174 analyst teams, comprising 246 analysts, to investigate the answers to prespecified research questions. Analyses conducted by these teams yielded 141 usable effects (compatible with our meta-analyses and with all necessary information provided) for the blue tit dataset, and 85 usable effects for the Eucalyptus dataset. We found substantial heterogeneity among results for both datasets, although the patterns of variation differed between them. For the blue tit analyses, the average effect was convincingly negative, with less growth for nestlings living with more siblings, but there was near continuous variation in effect size from large negative effects to effects near zero, and even effects crossing the traditional threshold of statistical significance in the opposite direction. In contrast, the average relationship between grass cover and Eucalyptus seedling number was only slightly negative and not convincingly different from zero, and most effects ranged from weakly negative to weakly positive, with about a third of effects crossing the traditional threshold of significance in one direction or the other. However, there were also several striking outliers in the Eucalyptus dataset, with effects far from zero. For both datasets, we found substantial variation in the variable selection and random effects structures among analyses, as well as in the ratings of the analytical methods by peer reviewers, but we found no strong relationship between any of these and deviation from the meta-analytic mean. In other words, analyses with results that were far from the mean were no more or less likely to have dissimilar variable sets, use random effects in their models, or receive poor peer reviews than those analyses that found results that were close to the mean. The existence of substantial variability among analysis outcomes raises important questions about how ecologists and evolutionary biologists should interpret published results, and how they should conduct analyses in the future.

Landraces are described as genetically diverse, dynamic populations of unimproved crops. However, studying the development of a landrace population over longer periods of time has rarely been done due to a lack of suitable archaeological materials. The indigenous grain silos of Gran Canaria provide a unique opportunity for genetically analysing multiple specimens from the same time period as well as sampling the same population at multiple time points. Here we report a genetic study of a landrace barley (Hordeum vulgare L.) sampled repeatedly over a period of 1400 years. We successfully enriched extracted aDNA for the barley exome using capture techniques and present sequencing data from ten archaeological and six extant samples. The results show that the landrace barley population of Gran Canaria has not undergone any dramatic genetic turnover or influx of new genetic material since the 7th century CE, but that the scale of cultivation seems to have varied. We detect smaller temporal changes of the genetic composition during the studied period and suggest that these changes reflect natural selection for adaptation to a changing climate and a dynamic agricultural society.

Hordeum vulgare var. nudum (naked barley) is one of the oldest and most common cereals found from Neolithic Fennoscandia. After the Bronze Age, naked barley largely disappeared and was replaced by Hordeum vulgare var. vulgare (hulled barley) and other cereals. During the early 19th century, naked barley of Asian origins was reintroduced to Fennoscandia. In this study, we have genetically characterized samples of Fennoscandian landraces of naked barley which were preserved in gene banks and museum collections. The analyses show that the Fennoscandian naked barley can be split into three groups: First, naked two-row barley, with a likely origin in Asia; second, naked six-row barley, with a likely origin in the eastern Himalayas and introduced during the 19th century; third, naked six-row barley genetically related to the original Fennoscandian hulled barley. The results suggest that this last group represents the ancient form of naked barley, which was possibly introduced in the Neolithic. At that time both naked and hulled barleys were grown and enough gene flow probably occurred between these two subspecies to create a Fennoscandian barley that is genetically distinct, irrespective of whether it is hulled or naked. This hypothesis was further supported by genotyping of the Nud gene, which is responsible for the naked phenotype. All naked barleys which we studied contained the same mutation allele, nud1.a , thus showing that naked Fennoscandian barley arose by crossings between naked and hulled barley and not by new mutations of hulled barley.

https://doi.org/10.1016/j.anbehav.2021.06.007 0003-3472/© 2021 The Authors. Published by Elsevie license (http://creativecommons.org/licenses/by/4.0/) Despite reported findings, explanations for within-species variation in behavioural performance on cognitive tests are still understudied. Cognitive processes are influenced by environmental and genetic differences, where cognitive stimulation and monoaminergic systems are predicted to be important. To explore explanations for individual variation in impulsivity (a behaviour that is negatively correlated with inhibitory control), we experimentally altered the environment of red junglefowl, Gallus gallus, by exposing chicks from newly hatched to 9 weeks old to either (1) both environmental and cognitive enrichment, (2) environmental enrichment without additional cognitive enrichment or (3) neither environmental nor cognitive enrichment. Subsequently, we measured variation in impulsivity and brain gene expression of genes from the dopaminergic system (DRD1 and DRD2) and serotonergic system (5HT2A, 5HT1B, 5HT2B, 5HT2C and TPH). We focused on two aspects of impulsivity, impulsive action and persistence, and their reduction over time. Cognitively enriched chicks tended to have higher initial impulsive action and had higher initial persistence, and our environmentally enriched chicks had slower reduction of impulsive action over time. DRD2 (a dopamine receptor gene) had lower expression in environmentally enriched chicks. Variation in impulsive action tended to correlate with expression of TPH (a gene involved in serotonin synthesis), whereas persistence correlated with both TPH and the dopamine receptor gene DRD1, and tended to correlate with the dopaminergic gene DRD2, regardless of rearing treatment. These results indicate that both environment and links to neurobiology could explain initial individual variation in, and reduction of, impulsivity. Further, distinct neurobiological pathways appear to govern impulsive action versus persistence, supporting the suggestion that impulsivity is a heterogenic behaviour. © 2021 The Authors. Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour. This is an open access article under the CC BY license (http://creativecommons.org/licenses/ by/4.0/).

Despite the prevalence and research interest of animal personality, its underlying mechanisms are not yet fully understood. Due to the essential role of monoamines in modulating behaviour, we manipulated the monoaminergic systems of Mediterranean field crickets (Gryllus bimaculatus) to explore whether this altered behavioural responses commonly used to describe animal personality. Previous work has shown that both serotonin and dopamine manipulations can alter cricket behaviour, although results differ depending on the drug in focus. Here, we investigate the effect of Fluphenazine, a dopamine antagonist which also interacts with serotonin receptors, on activity, exploration, boldness, and aggression. These results are compared with those of our earlier work that investigated the effect of drugs that more specifically target serotonin or dopamine systems (Fluoxetine and Ropinirole, respectively). Due to limited research on dose-effects of Fluphenazine, we created dose-response curves with concentrations ranging from those measured in surface waters up to human therapeutic doses. We show that compared to control animals, Fluphenazine manipulation resulted in lower levels of both exploration and boldness, but did not affect activity nor aggression. The effect on explorative behaviour contradicts our previous results of serotonin and dopamine manipulations. These results together confirm the causal role of monoamines in explaining variation in behaviour often used to describe animal personality, effects that can be both dose- and behaviour-dependent. Further, our results suggest that previous results assigned specifically to the dopaminergic system, may at least partly be explained by effects of the serotonergic system. Thus, future studies should continue to investigate the explicit underlying roles of specific monoamines in explaining behavioural variation.

Why individuals differ in behavioral responses has received intense research attention (particularly in the context of animal personality), and has typically focused on describing variation in boldness, activity, and exploration. Nevertheless, the mechanisms underlying this behavioral variation remain largely unknown. Variation in these behaviors is likely influenced by genetic differences between individuals, with genes in the monoaminergic systems commonly implicated. When examining the link between variation in boldness, activity and exploration and genes, studies have focused on different monoaminergic systems (mainly serotonergic and dopaminergic), and predominantly on mammals and passerine birds. Therefore, to replicate this general approach and examine if genes from these systems are linked to boldness, activity, and exploration, we exposed red junglefowl chicks (Gallus gallus) to behavioral assays (measuring boldness, activity, exploration) before analyzing prefrontal cortex gene expression of several dopaminergic (DRD1, DRD2) and serotonergic genes (TPH, 5HT2A, 5HT2B, 5HT2C, 5HT1B). We observed no relationships between our measured behaviors and gene expression. Together with previous studies, our results suggest that a clear link between boldness, activity and exploration and monoaminergic gene variation is lacking. We, therefore, suggest that this is due to differences among studies (e.g., methodological differences), or that the nature of the relationship between these behaviors and monoaminergic systems is more species-specific, and/or more complex than so far assumed.

When individuals are measured more than once in the same context they do not behave in exactly the same way each time. The degree of predictability differs between individuals, with some individuals showing low levels of variation around their behavioural mean while others show high levels of variation. This intra-individual variability in behaviour has received much less attention than between-individual variability in behaviour, and very little is known about the underlying mechanisms that affect this potentially large but understudied component of behavioural variation. In this study, we combine standardized behavioural tests in a chicken intercross to estimate intra-individual behavioural variability with a large-scale genomics analysis to identify genes affecting intra-individual behavioural variability in an avian population. We used a variety of different anxiety-related behavioural phenotypes for this purpose. Our study shows that intra-individual variability in behaviour has a direct genetic basis that is largely unique compared to the genetic architecture for the standard behavioural measures they are based on (at least in the detected quantitative trait locus). We identify six suggestive candidate genes that may underpin differences in intra-individual behavioural variability, with several of these candidates having previously been linked to behaviour and mental health. These findings demonstrate that intra-individual variability in behaviour appears to be a heritable trait in and of itself on which evolution can act.

Intra-species cognitive variation is commonly observed, but explanations for why individuals within a species differ in cognition are still understudied and not yet clear. Cognitive processes are likely influenced by genetic differences, with genes in the monoaminergic systems predicted to be important. To explore the potential role of these genes in association with individual variation in cognition, we exposed red junglefowl ( Gallus gallus ) chicks to behavioural assays measuring variation in learning (discriminative learning, reversal learning, and cognitive flexibility) and optimism (measured in a cognitive judgement bias test). Following this, we analysed prefrontal cortex gene expression of several dopaminergic and serotonergic genes in these chicks. Of our explored genes, serotonin receptor genes 5HT2A and 5HT2B, and dopaminergic receptor gene DRD1 were associated with measured behaviour. Chicks that had higher 5HT2A were less flexible in the reversal learning task, and chicks with higher 5HT2B also tended to be less cognitively flexible. Additionally, chicks with higher DRD1 were more optimistic, whilst chicks with higher 5HT2A tended to be less optimistic. These results suggest that the serotonergic and dopaminergic systems are linked to observed cognitive variation, and, thus, individual differences in cognition can be partially explained by variation in brain gene expression.

Adaptive integration of life history and behaviour is expected to result in variation in the pace-of-life. Previous work focused on whether 'risky' phenotypes live fast but die young, but reported conflicting support. We posit that individuals exhibiting risky phenotypes may alternatively invest heavily in early-life reproduction but consequently suffer greater reproductive senescence. We used a 7-year longitudinal dataset with >1,200 breeding records of >800 female great tits assayed annually for exploratory behaviour to test whether within-individual age dependency of reproduction varied with exploratory behaviour. We controlled for biasing effects of selective (dis)appearance and within-individual behavioural plasticity. Slower and faster explorers produced moderate-sized clutches when young; faster explorers subsequently showed an increase in clutch size that diminished with age (with moderate support for declines when old), whereas slower explorers produced moderate-sized clutches throughout their lives. There was some evidence that the same pattern characterized annual fledgling success, if so, unpredictable environmental effects diluted personality-related differences in this downstream reproductive trait. Support for age-related selective appearance was apparent, but only when failing to appreciate within-individual plasticity in reproduction and behaviour. Our study identifies within-individual age-dependent reproduction, and reproductive senescence, as key components of life-history strategies that vary between individuals differing in risky behaviour. Future research should thus incorporate age-dependent reproduction in pace-of-life studies.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

ABSTRACT Among-individual behavioral differences (i.e. animal personality) are commonly observed across taxa, although the underlying, causal mechanisms of such differences are poorly understood. Animal personality has been correlated with physiological functions as well as fitness-related traits. Variation in many aspects of monoamine systems, such as metabolite levels and gene polymorphisms, has been linked to behavioral variation. Therefore, here we experimentally investigated the potential role of monoamines in explaining individual variation in personality, using two common pharmaceuticals that respectively alter the levels of serotonin and dopamine in the brain: fluoxetine and ropinirole. We exposed three-spined sticklebacks, a species that shows animal personality, to either chemical alone or to a combination of the two chemicals, for 18 days. During the experiment, fish were assayed at four time points for the following personality traits: exploration, boldness, aggression and sociability. To quantify brain gene expression on short- and longer-term scales, fish were sampled at two time points. Our results show that monoamine manipulations influence fish behavior. Specifically, fish exposed to either fluoxetine or ropinirole were significantly bolder, and fish exposed to the two chemicals together tended to be bolder than control fish. Our monoamine manipulations did not alter the gene expression of monoamine or stress-associated neurotransmitter genes, but control, untreated fish showed covariation between gene expression and behavior. Specifically, exploration and boldness were predicted by genes in the dopaminergic, serotonergic and stress pathways, and sociability was predicted by genes in the dopaminergic and stress pathways. These results add further support to the links between monoaminergic systems and personality, and show that exposure to monoamines can causally alter animal personality.

Identifying the molecular mechanisms of animal behaviour is an enduring goal for researchers. Gaining insight into these mechanisms enables us to gain a greater understanding of behaviour and their genetic control. In this paper, we perform Quantitative Trait Loci (QTL) mapping of tonic immobility behaviour in an advanced intercross line between wild and domestic chickens. Genes located within the QTL interval were further investigated using global expression QTL (eQTL) mapping from hypothalamus tissue, as well as causality analysis. This identified five candidate genes, with the genes PRDX4 and ACOT9 emerging as the best supported candidates. In addition, we also investigated the connection between tonic immobility, meat pH and struggling behaviour, as the two candidate genes PRDX4 and ACOT9 have previously been implicated in controlling muscle pH at slaughter. We did not find any phenotypic correlations between tonic immobility, struggling behaviour and muscle pH in a smaller additional cohort, despite these behaviours being repeatable within-test.

Non-consumptive predator effects have been shown to influence a wide range of behavioural, life history and morphological traits. Extra-pair reproduction is widespread among socially monogamous birds and may incur predation costs. Consequently, altered rates of extra-pair reproduction are expected in circumstances characterized by increased adult perceived predation risk. In addition, extra-pair reproduction is expected to be most affected for birds with phenotypes that generally increase predation risk (such as more active individuals). In two consecutive years, perceived predation risk was manipulated for great tits Parus major breeding in 12 nest-box plots by broadcasting sounds of their main predator (European sparrowhawk Accipiter nisus; six plots). As a control treatment, sounds of a sympatric, avian non-predator species were broadcast (Eurasian blackbird Turdus merula; six plots). Levels of extra-pair paternity did not differ between plots with different predation risk treatments. Males that moved more in a novel environment (more active or faster exploring) tended to have offspring with fewer partners, but this effect did not vary with predation risk treatment. From an adaptive viewpoint, predation costs associated with extra-pair reproduction may be small and may not outweigh the benefits of extra-pair behaviour. Research on a broader range of taxa with different mating strategies is now needed to confirm the generality of our findings.

Animal personality has been described in a range of species with ecological and evolutionary consequences. Factors shaping and maintaining variation in personality are not fully understood, but monoaminergic systems are consistently linked to personality variation. We experimentally explored how personality was influenced by alterations in two key monoamine systems: dopamine and serotonin. This was done using ropinirole and fluoxetine, two common human pharmaceuticals. Using the Mediterranean field cricket (Gryllus bimaculatus), we focused on the personality traits activity, exploration, and aggression, with confirmed repeatability in our study. Dopamine manipulations explained little variation in the personality traits investigated, while serotonin manipulation reduced both activity and aggression. Due to limited previous research, we created a dose-response curve for ropinirole, ranging from concentrations measured in surface waters to human therapeutic doses. No ropinirole dose level strongly influenced cricket personality, suggesting our results did not come from a dose mismatch. Our results indicate that the serotonergic system explains more variation in personality than manipulations of the dopaminergic system. Additionally, they suggest that monoamine systems differ across taxa, and confirm the importance of the mode of action of pharmaceuticals in determining their effects on behaviour.

The causes of individual variation in behavior are often not well understood, and potential underlying mechanisms include both intrinsic and extrinsic factors, such as early environmental, physiological, and genetic differences. In an exploratory laboratory study, we raised three-spined sticklebacks (Gasterosteus aculeatus) under 4 different environmental conditions (simulated predator environment, complex environment, variable social environment, and control). We investigated how these manipulations related to behavior, brain physiology, and gene expression later in life, with focus on brain dopamine and serotonin levels, turnover rates, and gene expression. The different rearing environments influenced behavior and gene expression, but did not alter monoamine levels or metabolites. Specifically, compared to control fish, fish exposed to a simulated predator environment tended to be less aggressive, more exploratory, and more neophobic; and fish raised in both complex and variable social environments tended to be less neophobic. Exposure to a simulated predator environment tended to lower expression of dopamine receptor DRD4A, a complex environment increased expression of dopamine receptor DRD1B, while a variable social environment tended to increase serotonin receptor 5-HTR2B and serotonin transporter SLC6A4A expression. Despite both behavior and gene expression varying with early environment, there was no evidence that gene expression mediated the relationship between early environment and behavior. Our results confirm that environmental conditions early in life can affect phenotypic variation. However, the mechanistic pathway of the monoaminergic systems translating early environmental variation into observed behavioral responses was not detected.

The existence of animal personality is now well-documented, although the causes and consequences of this phenomenon are still largely unclear. Parasite infection can have pervasive effects on hosts, including altering host behaviour, and may thus contribute to differences in host personality. We investigated the relationship between the three-spined stickleback and its common parasite Glugea anomala, with focus on differences in host personality. Naturally infected and uninfected individuals were assayed for the five personality traits activity, exploration, boldness, sociability, and aggression. If infected fish behaved differently from uninfected, to benefit this parasite with horizontal transmission, we predicted behaviour increasing interactions with other sticklebacks to increase. Infection status explained differences in host personality. Specifically, Glugea-infected individuals were more social than uninfected fish. This confirms a link between parasite infection and host behaviour, and a relationship which may improve the horizontal transmission of Glugea. However, future studies need to establish the consequences of this for the parasite, and the causality of the parasite-host personality relationship. Significance statement Parasite infection that alters host behaviour could be a possible avenue of research into the causes of animal personality. We studied the link between infection and personality using the three-spined stickleback and its parasite Glugea anomala. We predicted that infected individuals would be more prone to interact with other sticklebacks, since this would improve transmission of this parasite. The personality of uninfected and naturally infected fish was measured and we observed that Glugea-infected sticklebacks were more social. Our results confirm a link between parasitism and variation in host personality.

Several studies have shown that individuals with higher metabolic rates (MRs) feed at higher rates and are more willing to forage in the presence of predators. This increases the acquisition of resources, which in turn, may help to sustain a higher MR. Elevated predation danger may be expected to result in reduced MRs, either as a means of allowing for reduced feeding and risk-taking, or as a consequence of adaptively reducing intake rates via reduced feeding and/or risk-taking. We tested this prediction in free-living great tits (Parus major) using a playback experiment to manipulate perceived predation danger. There was evidence that changes in body mass and BMR differed as a function of treatment. In predator treatment plots, great tits tended to reduce their body mass, a commonly observed response in birds to increased predation danger. In contrast, birds from control treatment plots showed no overall changes in body mass. There was also evidence that great tits from control treatment plots increased their basal metabolic rate (BMR) over the course of the experiment, presumably due to decreasing ambient temperatures over the study period. However, there was no evidence for changes in BMR for birds from predator treatment plots. Although the directions of these results are consistent with the predicted directions of effects, the effects sizes and confidence intervals yield inconclusive support for the hypothesis that great tits would adaptively suppress BMR in response to increased perceived predation risk. The effect size observed in the present study was small (~1%) and would not be expected to result in substantive reductions in feeding rate and/or risk-taking. Whether or not ecological conditions that generate greater energetic stress (e.g. lower food availability, lower ambient temperatures) could produce an effect that produces biologically meaningful reductions in feeding activity and/or risk-taking remains an open question.

Predation induces strong selection on phenotypic traits, affecting prey via consumptive and nonconsumptive effects. Communication is important for territorial behavior, but can increase susceptibility to predators. Therefore, predation risk should influence prey communication patterns, territoriality, and fitness. We evaluated how this trade-off is resolved via 2 manipulations of perceived predation risk using audio playback in wild great tits (Parus major). In the first experiment, we examined the immediate response of individuals to playback; the second experiment, replicated across 2 years, examined both immediate and carry-over effects (over days) of playback broadcast for a 5-month period (March-July) in 12 nest box populations. Birds exposed to predator sounds showed decreased singing and increased alarming compared to controls, both immediately and on days without play back exposure (carry-over effects). Perceived predation risk did not affect how birds responded to simulated territory intrusions. In combination, these studies' findings imply that individuals perceive predator vocalizations as "risky" up to days after exposure to predator cues, and adjust their behavior to minimize this risk. However, the lack of effects on territorial aggression implies that individuals are able to weigh the costs of predation against the benefits of each type of vocal behavior. Acknowledging that context changes the relative costs and benefits of antipredator behavior has important consequences for understanding predator-prey dynamics.

Predators can affect prey both directly (consumptive effects) and indirectly (nonconsumptive effects), with a growing body of literature showing the latter may have pronounced effects. Prey populations are comprised of individuals that differ in perception of and willingness to take risk; therefore, studying how different types of individuals respond to predation risk is necessary to fully understand prey dynamics. Playbacks were used to experimentally manipulate perceived predation risk in nest-box populations of wild great tits (Parus major) to examine the nonconsumptive effects of avian predators on prey behavior and morphology, and to explore individual differences in prey response. Individuals responded to our treatment, and responses differed depending on both treatment and pre-manipulation behavioral type. Birds in areas exposed to predator playback tended to decrease in body mass more than birds exposed to nonthreatening (control) playback. Differences between treatment groups were mainly driven by initially fast exploring birds: In the control treatment, fast explorers increased in mass, whereas the initially fast exploring birds in the predation treatment decreased in mass. Furthermore, birds exposed to predator playback decreased exploratory tendency compared with controls. These findings demonstrate that predation risk alters great tit behavior (exploration) and morphology (body mass) and that plasticity in response to risk relates to an individual's willingness to take risks. Our findings suggest that individuals differ in susceptibility to predation risk, causing adaptive individual differences in responsiveness to changes in predation risk. Acknowledging individuality in responses to perceived predation risk has important consequences for understanding prey dynamics.