The impact of personality, morphotype and shore height on temperature-mediated behavioural responses in the beadlet anemone Actinia equina

Sea anemones (Actinia equina) show consistent individual differences in boldness and thoroughness but lack a behavioural syndrome

Behavioural syndromes are suites of behaviours that corelate between-individuals but the same behaviours may also show within-individual correlations owing to state dependency or trade-offs. Therefore, overall phenotypic behavioural correlations must be separated into their between- and within-individual components. We investigate how startle response duration (an index of boldness) and time taken to reject an inert item (an index of investigation thoroughness) covary in beadlet sea anemones, Actinia equina. Anemones took longer to reject a more complex item compared to a simpler one, validating this measure of investigation thoroughness. We then quantified between- and within-individual correlations using a Bayesian analysis and an alternative frequentist analysis, which returned the same results. Startle responses decreased with anemone size while thoroughness decreased across repeated observations, indicative of simple learning. For each behaviour, repeatability was significant but relatively low and there was no behavioural syndrome. Rather, the two behaviours showed a negative within-individual correlation in most individuals. Thus, boldness and thoroughness are unlikely to be under correlative selection, and they may instead be expressed independently, in line with the general pattern that cross-contextual behavioural syndromes are comparatively rare. It now appears that this pattern may extend broadly across animal diversity.

Differential metabolic responses in bold and shy sea anemones during a simulated heatwave

As climate change-induced heatwaves become more common, phenotypic plasticity at multiple levels is a key mitigation strategy by which organisms can optimise selective outcomes. In ectotherms, changes to both metabolism and behaviour can help alleviate thermal stress. Nonetheless, no study in any ectotherm has yet empirically investigated how changing temperatures affect among-individual differences in the associations between these traits. Using the beadlet anemone (Actinia equina), an intertidal species from a thermally heterogeneous environment, we investigated how individual metabolic rates, linked to morphotypic differences in A. equina, and boldness were related across changing temperatures. A crossed-over design and a temporal control were used to test the same individuals at a non-stressful temperature, 13°C, and under a simulated heatwave at 21°C. At each temperature, short-term repeated measurements of routine metabolic rate (RMR) and a single measurement of a repeatable boldness-related behaviour, immersion response time (IRT), were made. Individual differences, but not morphotypic differences, were highly predictive of metabolic plasticity, and the plasticity of RMR was associated with IRT. At 13°C, shy animals had the highest metabolic rates, while at 21°C, this relationship was reversed. Individuals that were bold at 13°C also exhibited the highest metabolic rates at 21°C. Additional metabolic challenges during heatwaves could be detrimental to fitness in bold individuals. Equally, lower metabolic rates at non-stressful temperatures could be necessary for optimal survival as heatwaves become more common. These results provide novel insight into the relationship between metabolic and behavioural plasticity, and its adaptive implications in a changing climate.

Phylogenetic meta-analysis reveals system-specific behavioural type-behavioural predictability correlations

The biological significance of behavioural predictability (environment-independent within-individual behavioural variation) became accepted recently as an important part of an individual's behavioural strategy besides behavioural type (individual mean behaviour). However, we do not know how behavioural type and predictability evolve. Here, we tested different evolutionary scenarios: (i) the two traits evolve independently (lack of correlations) and (ii) the two traits' evolution is constrained (abundant correlations) due to either (ii/a) proximate constraints (direction of correlations is similar) or (ii/b) local adaptations (direction of correlations is variable). We applied a set of phylogenetic meta-analyses based on 93 effect sizes across 44 vertebrate and invertebrate species, focusing on activity and risk-taking. The general correlation between behavioural type and predictability did not differ from zero. Effect sizes for correlations showed considerable heterogeneity, with both negative and positive correlations occurring. The overall absolute (unsigned) effect size was high (Zr = 0.58), and significantly exceeded the null expectation based on randomized data. Our results support the adaptive scenario: correlations between behavioural type and predictability are abundant in nature, but their direction is variable. We suggest that the evolution of these behavioural components might be constrained in a system-specific way.

A fast pace-of-life is traded off against a high thermal performance

The integration of life-history, behavioural and physiological traits into a ‘pace-of-life syndrome’ is a powerful concept in understanding trait variation in nature. Yet, mechanisms maintaining variation in ‘pace-of-life’ are not well understood. We tested whether decreased thermal performance is an energetic cost of a faster pace-of-life. We characterized the pace-of-life of larvae of the damselfly Ischnura elegans from high-latitude and low-latitude regions when reared at 20°C or 24°C in a common-garden experiment, and estimated thermal performance curves for a set of behavioural, physiological and performance traits. Our results confirm a faster pace-of-life (i.e. faster growth and metabolic rate, more active and bold behaviour) in the low-latitude and in warm-reared larvae, and reveal increased maximum performance, R_max, but not thermal optimum T_opt, in low-latitude larvae. Besides a clear pace-of-life syndrome integration at the individual level, larvae also aligned along a ‘cold–hot’ axis. Importantly, a faster pace-of-life correlated negatively with a high thermal performance (i.e. higher T_opt for swimming speed, metabolic rate, activity and boldness), which was consistent across latitudes and rearing temperatures. This trade-off, potentially driven by the energetically costly maintenance of a fast pace-of-life, may be an alternative mechanism contributing to the maintenance of variation in pace-of-life within populations.

The regulatory role of GABAA receptor in Actinia equina nervous system and the possible effect of global ocean acidification

Global warming and connected acidification of the world ocean attract a substantial amount of research efforts, in particular in a context of their impact on behaviour and metabolism of marine organisms, such as Cnidaria. Nevertheless, mechanisms underlying Cnidarians’ neural signalling and behaviour and their (possible) alterations due to the world ocean acidification remain poorly understood. Here we researched for the first time modulation of GABA_A receptors (GABA_ARs) in Actinia equina (Cnidaria: Anthozoa) by pH fluctuations within a range predicted by the world ocean acidification scenarios for the next 80–100 years and by selective pharmacological activation. We found that in line with earlier studies on vertebrates, both changes of pH and activation of GABA_ARs with a selective allosteric agonist (diazepam) modulate electrical charge transfer through GABA_AR and the whole-cell excitability. On top of that, diazepam modifies the animal behavioural reaction on startle response. However, despite behavioural reactions displayed by living animals are controlled by GABA_ARs, changes of pH do not alter them significantly. Possible mechanisms underlying the species resistance to acidification impact are discussed.