Seasonal time constraints shape life history, physiology and behaviour independently, and decouple a behavioural syndrome in a damselfly

Abstract

The integration of traits into ‘syndromes' has been suggested as a useful framework to advance insights in trait responses to environmental stressors. Yet, how stressors shape the consistency (‘repeatability') of traits and their covariation at the individual level remains debated. We studied how seasonal time constraints shape trait repeatability and integration of life‐history, behavioural and physiological traits along a fast–slow continuum, using the ‘pace‐of‐life syndrome' as a framework. We manipulated the photoperiod during the larval development of the damselfly Ischnura elegans, generating a time‐relaxed early, a control, and a time‐constrained late group. The photoperiod treatment did not seem to affect the voltinism of the larvae. As predicted, late‐period larvae accelerated development and growth, yet this acceleration was no longer detectable for growth and metabolic rate during the final instar, possibly due to costs of the initial life‐history acceleration. This warrants caution when inferring a species' pace‐of‐life based on a specific developmental stage. The late‐period larvae were as predicted more active (only during the later stages of the final instar) and bolder than the control larvae, but not different from the early‐period larvae. Most studies on time constraints only compared late and control animals, thereby potentially wrongly concluding adaptive responses to time constraints. Activity, boldness and body mass were repeatable, while growth and metabolic rates were not. Notably, repeatabilities did not change under time constraints. There was no support for an overall trait integration in a pace‐of‐life syndrome, yet activity and boldness covaried positively as expected. Importantly, this ‘behavioural syndrome' was decoupled in the late‐period larvae, which might be adaptive to enhance energy acquisition to fuel the accelerated development rate. Our results suggest that besides the predicted plastic acceleration of life‐history, plastic changes in behavioural trait integration may also be an important but overlooked adaptive aspect of responding to time constraints.

Evolution of cold tolerance and thermal plasticity in life history, behaviour and physiology during a poleward range expansion

“…The growth rate of larvae during the first 7 days of the final instar was measured on a subset of 30 larvae per temperature-by-region (total of 240 larvae; see Appendix S2 for details). Based on data obtained when monitoring the study species until adult emergence (Tüzün et al, 2020), during this instar the largest increase in body mass occurs (~37%), and growth rates during this instar are positively correlated (r = 0.68) with adult body mass at emergence. We carried out feeding trials to quantify the food intake of the larvae when fed ad libitum at their rearing temperature.…”

Embryonic exposure to artificial light at night impairs learning abilities and their covariance with behavioural traits in teleost fish

“…If this possibility is confirmed by future studies, fitness effects of covariance disruption owing to ALAN will deserve attention in wild fish populations. The scenario might be gloomier if we postulate that this, as well as other covariations between traits, could also be altered by additional, co-occurring anthropogenic stressors [32,54,55]. Lastly, the covariance between behaviour and learning may be involved in mechanisms of invasive species success [56], suggesting the importance of studying ALAN effects in this context.…”

Responses to seasonal time constraints under global change across life stages: facilitated by warming but counteracted by invasive alien predators

“…Within the same containers, each larva was gently poked at the caudal lamellae with a thin wooden stick, triggering a larval escape response followed by freezing (inactivity). The latency of the larva to start moving following freezing was used as a proxy for boldness, with a shorter freeze period indicating bolder larvae (as done for the study species in Tüzün et al 34 . The maximum latency time was set at 5 minutes.…”

“…We hypothesise that (1) late season eggs and the associated larvae will develop faster than early season eggs and larvae, leading to a smaller size at metamorphosis, unless larval growth rate is increased 6 . To accelerate life history, we also expect late season larvae to show a higher activity and boldness 33,34 . (2) While warming is expected to increase the life history response to TC 35 , predation risk is expected to decrease the life history response to TC 36 .…”