A comprehensive mechanistic approach to dispersal requires the translation of the whole mobility register of the target organism into movement rules that could subsequently be used to model its displacements. According to the optimality paradigm, this procedure implies a cost–benefit analysis of mobility patterns taking into account not only movements, but also their external context and the internal state of the moving individuals. Using this framework, we detected a ‘dispersal mood’ in some individuals of the meadow brown butterfly Maniola jurtina. These adopted a direct flight strategy, which was topologically different from the previously documented foray search strategy. Those individuals that used the direct flight strategy moved straighter as soon as they left the habitat and avoided heading back to their patch of origin, which is the best inter‐patch search strategy when dispersal risks and costs are high. The direct flight strategy was conditional to sex: females used it twice as much as males. We suggest that this sex bias was due to female investment in offspring, which is maximized by male avoidance and spatial bet hedging. Inter‐patch dispersal of gravid females is crucial for the persistence of M. jurtina populations in spatially and temporally unpredictable environments.

National audience1. Antlions are opportunistic trap building predators that cannot control prey encounter. Their trap should ideally retain a great diversity of prey. However, building a single trap that captures many prey with varying characteristics can be challenging. 2. A series of five different ant species ranging from thin to large, of sizes ranging from 2.75 to 6.5 mm, and a mean weight ranging from 0.54 to 6.00 mg were offered in a random succession to antlions. The state of satiation of the antlions was controlled, and their mass and the depth of their pit were recorded. The reaction of antlion to the prey, the probability of capture as well as the time to escape were recorded. 3. The probability of an antlion reaction is an increasing function of the pit depth and a decreasing function of antlion mass. The probability of capture is highest for intermediate prey mass and is an increasing function of pit depth. The time to escape is a declining function of prey mass and an increasing function of pit depth. 4. There is an upper limit to prey mass given that large prey escape out of the pit. There is a lower limit to prey mass given the difficulty to apprehend the smallest, thin species. Consequently, there is a range of prey mass, corresponding to a medium-sized ant of 2 mg, for which the pit functions best. The physics of insect locomotion on sandy slopes was identified as the key to understanding the functioning of antlion pits

International audienceMobility varies strongly between and within species, reflecting diff erent dispersal strategies. Within species, such differences can imply suites of traits associated in syndromes. Different syndrome structures have been found within species among populations differing in the selective pressures they are exposed to. Similarly, we expect species differing in mobility to show diff erent syndrome structures in response to similar selective pressures such as landscape fragmentation. Using butterflies originating from the same fragmented landscape, we investigated the differences in mobility syndrome between four common butterflies (Pyronia tithonus , Pararge aegeria Maniola jurtina , Pieris rapae) known to differ in their mobility. We expected individuals from the less mobile species to display a resident strategy because of high dispersal cost in this fragmented landscape, and individuals from the more mobile species to display a larger range of movement strategies. Moreover, as syndromes can only be detected whenever individuals differ in their dispersal strategies, we expected mobility syndromes to be observable only in populations where dispersal polymorphism is maintained. We thus expected stronger correlations between mobility-related traits in more mobile species. Using three mobility tests in controlled conditions designed to measure different components of mobility, we showed that mobility-related traits were indeed correlated only in the most mobile species. The absence of correlation in the less mobile species may be explained by a low variation in movement strategies, dispersal being counter-selected