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.
Great tits differ in patterns of age‐dependent reproduction as a component of pace‐of‐life. Slow explorers produce stable clutch sizes throughout their reproductive lives. Fast explorers by contrast show age‐related increases followed by reproductive senescence. Age‐related reproduction therefore constitutes a key component of personality‐related life‐history variation.
The adaptive evolution of timing of breeding (a component of phenology) in response to environmental change requires individual variation in phenotypic plasticity for selection to act upon. A major ...question is what processes generate this variation. Here we apply multi-year manipulations of perceived predation levels (PPL) in an avian predator-prey system, identifying phenotypic plasticity in phenology as a key component of alternative behavioral strategies with equal fitness payoffs. We show that under low-PPL, faster (versus slower) exploring birds breed late (versus early); the pattern is reversed under high-PPL, with breeding synchrony decreasing in conjunction. Timing of breeding affects reproductive success, yet behavioral types have equal fitness. The existence of alternative behavioral strategies thus explains variation in phenology and plasticity in reproductive behavior, which has implications for evolution in response to anthropogenic change.
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.
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.
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.
•We studied effects of experimentally altered rearing experiences on impulsivity.•We measured two aspects of impulsivity: impulsive action and persistence.•Cognitive enrichment affected impulsivity and rate of inhibiting impulsivity.•Brain monoaminergic gene expression linked to both aspects of impulsivity.•Thus, both environment and neurobiology contribute to variation in impulsivity.
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.
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Plain Language Summary
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.
Cross‐system resource flux is a fundamental component of ecological systems. Allochthonous material flows generate trophic linkages between adjacent food webs, thereby affecting community structure ...and stability in recipient systems. We investigated cross‐habitat trophic linkages between canopy and understorey food webs in a terrestrial, wooded, ecosystem in South Florida, USA. The focal community consisted of three species of Anolis lizards and their prey. We described interspecific differences among Anolis species in the strength and routing of these cross‐habitat flows using stable isotope analysis, stomach content analysis and habitat use data. All three Anolis species in this study consumed different prey and occupied vertically distinct arboreal habitats. Despite these differences, carbon isotope and stomach content analysis revealed strong integration with understorey and canopy food webs for all Anolis species. Modes of resource flux contributing to the observed cross‐habitat trophic linkages included prey movement and the gravity‐driven transport of detritus. Our study shows that terrestrial systems are linked by considerable bidirectional cross‐system resource flux. Our results also suggest that considering species‐specific interactions between predator and prey is necessary to fully understand the diversity of material and energy flows between spatially separated habitats.
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