Behavioral repeatability and personality in pit-building antlion larvae under differing environmental contexts

Operant conditioning in antlion larvae and its impairment following exposure to elevated temperatures

Although ambush predators were previously considered limited in their cognitive abilities compared to their widely foraging relatives, there is accumulating evidence it does not hold true. Pit-building antlions are already known to associate vibrations in the sand with the arrival of prey. We used a T-maze and successfully trained antlions to turn right or left against their initial turning bias, leading to a suitable substrate for digging traps. We present here the first evidence for operant conditioning and T-maze solving in antlions. Furthermore, we show that exposure of second instar larvae to an elevated temperature led to impaired retention of what was learned in a T-maze when tested after moulting into the third instar, compared to larvae raised under a more benign temperature. We suggest that climate change, involving an increase in mean temperatures as well as rare events (e.g., heatwaves) might negatively affect the retention of operant conditioning in antlions, alongside known, more frequently studied effects, such as changes in body size and distribution.

Digging the optimum pit: antlions, spirals and spontaneous stratification

Most animal traps are constructed from self-secreted silk, so antlions are rare among trap builders because they use only materials found in the environment. We show how antlions exploit the properties of the substrate to produce very effective structures in the minimum amount of time. Our modelling demonstrates how antlions: (i) exploit self-stratification in granular media differentially to expose deleterious large grains at the bottom of the construction trench where they can be ejected preferentially, and (ii) minimize completion time by spiral rather than central digging. Both phenomena are confirmed by our experiments. Spiral digging saves time because it enables the antlion to eject material initially from the periphery of the pit where it is less likely to topple back into the centre. As a result, antlions can produce their pits—lined almost exclusively with small slippery grains to maximize powerful avalanches and hence prey capture—much more quickly than if they simply dig at the pit's centre. Our demonstration, for the first time to our knowledge, of an animal using self-stratification in granular media exemplifies the sophistication of extended phenotypes even if they are only formed from material found in the animal's environment.

Phenotype of a leaf beetle larva depends on host plant quality and previous test experience

Phenotypic expressions of insects are strongly dependent on various external and internal factors, like diet or density and age or sex. However, environmental effects on the behavioural phenotype and repeatability are rather unexplored for holometabolous insects in their larval stage. We examined the effects of the food environment (young versus old cabbage leaves) and previous test experience on growth and behaviour of Phaedon cochleariae larvae. A more nutritious diet, i.e., young leaves, had beneficial consequences on larval growth. Contrary to findings on adults, the behaviour of larvae was neither consistent over time nor across contexts, thus larvae did not show personality. Furthermore, larval behaviour was shaped independent of the diet, pointing to a stage-dependent receptivity towards diet conditions in this species. Besides, larval activity was significantly influenced by former test experience, with naïve larvae being more active than previously tested larvae. In general, in insects memories in an olfactory or sexual behaviour context can lead to behavioural responses later in life. Mechanisms of memory-learning should be further explored in different contexts in insects. Overall, the present study reveals that growth-related traits are diet-dependent and that the activity of a holometabolous larva is shaped in dependence of its previous test experience.

Foraging syndromes and trait variation in antlions along a climatic gradient

Behavioral syndromes arise when individual behavior is correlated over time and/or across environmental contexts, often resulting in inter-population behavioral differences. Three main hypotheses have been suggested to explain the evolution of behavioral syndromes. The constraint hypothesis suggests that behaviors originate from a shared mechanism with a strong genetic or physiological basis. In contrast, according to the adaptive hypothesis, behavioral syndromes depend on specific selective pressures in each environment, and thus should evolve when specific behavioral combinations are advantageous. Finally, behavioral syndromes can also arise owing to neutral stochastic processes. We tested here for variation in the foraging syndromes of pit-building antlions originating from different populations along a climatic gradient. Although inter-population variation existed in some traits, foraging syndromes were similar across populations, supporting the constraint hypothesis. These findings suggest that stabilizing selection, acting on the foraging behavior of antlions during their larval phase, outweighs local selection pressures, resulting in "constraint syndromes." We also explored behavioral repeatability of foraging-related traits within and among habitats (natural, novel and disturbed habitats), and detected different levels of repeatability: pit diameter was more repeatable than response time to prey, followed by prey exploitation efficiency. Behavioral repeatability of the same trait differed according to context, suggesting that repeatability is a trait in itself and should not be considered identical even when studying the same behavioral trait.