Effects of host plant growth form on dropping behaviour in leaf beetles

Many leaf-eating insects drop from their host plants to escape predators. However, they must return to the leaves of the host plant after dropping, which represents a cost associated with this behaviour. In woody plants, the positioning of leaves is generally higher than that of herbaceous plants, which suggests that dropping from woody plants might be costlier for leaf-eating insects than dropping from herbaceous plants. Therefore, we predicted that dropping behaviour would be observed less frequently in insects that feed on woody plant leaves than in those that feed on herbaceous plant leaves. To test this prediction, we investigated dropping behaviour experimentally in larvae (23 species) and adults (112 species) of leaf beetles (Coleoptera: Chrysomelidae) on their host plants (86 species of 44 families) in field conditions. Larvae on woody plants exhibited dropping behaviour less frequently than those on herbaceous plants. However, this pattern was not detected in adults. Thus, host plant growth form might affect the evolution of dropping behaviour in leaf beetle larvae, but not in winged adults, perhaps owing to their higher mobility.

Dropping to escape: a review of an under-appreciated antipredator defence

Dropping is a common antipredator defence that enables rapid escape from a perceived threat. However, despite its immediate effectiveness in predator-prey encounters (and against other dangers such as a parasitoid or an aggressive conspecific), it remains an under-appreciated defence strategy in the scientific literature. Dropping has been recorded in a wide range of taxa, from primates to lizards, but has been studied most commonly in insects. Insects have been found to utilise dropping in response to both biotic and abiotic stimuli, sometimes dependent on mechanical or chemical cues. Whatever the trigger for dropping, the decision to drop by prey will present a range of inter-related costs and benefits to the individual and so there will be subtle complexities in the trade-offs surrounding this defensive behaviour. In predatory encounters, dropping by prey will also impose varying costs and benefits on the predator - or predators - involved in the system. There may be important trade-offs involved in the decision made by predators regarding whether to pursue prey or not, but the predator perspective on dropping has been less explored at present. Beyond its function as an escape tactic, dropping has also been suggested to be an important precursor to flight in insects and further study could greatly improve understanding of its evolutionary importance. Dropping in insects could also prove of significant practical importance if an improved understanding can be applied to integrated pest-management strategies. Currently the non-consumptive effects of predators on their prey are under-appreciated in biological control and it may be that the dropping behaviour of many pest species could be exploited via management practices to improve crop protection. Overall, this review aims to provide a comprehensive synthesis of the current literature on dropping and to raise awareness of this fascinating and widespread behaviour. It also seeks to offer some novel hypotheses and highlight key avenues for future research.

From tameness to wariness: chemical recognition of snake predators by lizards in a Mediterranean island

Antipredatory defenses are maintained when benefit exceeds cost. A weak predation pressure may lead insular lizards to tameness. Podarcis lilfordi exhibits a high degree of insular tameness, which may explain its extinction from the main island of Menorca when humans introduced predators. There are three species of lizards in Menorca: the native P. lilfordi, only on the surrounding islets, and two introduced lizards in the main island, Scelarcis perspicillata and Podarcis siculus. In addition, there are three species of snakes, all introduced: one non-saurophagous (Natrix maura), one potentially non-saurophagous (Rhinechis scalaris) and one saurophagous (Macroprotodon mauritanicus). We studied the reaction to snake chemical cues in five populations: (1) P. lilfordi of Colom, (2) P. lilfordi of Aire, (3) P. lilfordi of Binicodrell, (4) S. perspicillata, and (5) P. siculus, ordered by increasing level of predation pressure. The three snakes are present in the main island, while only R. scalaris is present in Colom islet, Aire and Binicodrell being snake-free islets. We aimed to assess the relationship between predation pressure and the degree of insular tameness regarding scent recognition. We hypothesized that P. lilfordi should show the highest degree of tameness, S. perspicillata should show intermediate responses, and P. siculus should show the highest wariness. Results are clear: neither P. lilfordi nor S. perspicillata recognize any of the snakes, while P. siculus recognizes the scent of M. mauritanicus and reacts to it with typical well-defined antipredatory behaviours as tail waving and slow motion. These results rise questions about the loss of chemical recognition of predators during island tameness and its related costs and benefits for lizards of insular habitats. In addition, this highlights the necessity for strong conservation measures to avoid the introduction of alien predators.

Sexual differences in behavioral thermoregulation of the lizard Scelarcis perspicillata

Temperature determines all aspects of the biology of ectotherms. Although sexual differences in thermal ecology are not the rule in lizards, some species exhibit such differences. We studied the effect of sex and reproductive condition on the thermoregulation of an introduced population of Scelarcis perspicillata during the summer in Menorca (Balearic Islands, Spain). These lizards live in the wall surfaces of a limestone quarry, where the sun is scarce because of the narrowness of the quarry walls. The population is sexually dimorphic, with larger males than females. We measured body temperature (T_b) of adult males and females in the field, and air (T_a) and substrate temperature (T_s) at the capture sites, and recorded exposure to sunlight, height of the perch, and type of substrate. We also recorded operative temperatures (T_e) as a null hypothesis of thermoregulation. Finally, we studied the thermal preferences of adult males and females in a laboratory thermal gradient. Thermal preferences were similar for pregnant and non-pregnant females, and sex did not affect the thermal preferences of lizards, even after controlling for the effect of body size. However, in the field, females achieved higher T_b than males, and occupied microhabitats with higher T_a and T_s and lower perch heights than males. Furthermore, females selected perches in full sun at a higher frequency than males. As a consequence, females achieved a higher accuracy and effectiveness of thermoregulation (0.89) than males (0.84). Thus, all else being equal, females would achieve a higher performance than males. The observed results are attributable to sexual differences in behaviour, probably in relation with the reproductive season.

Effect of refuge distance on escape behavior of side-blotched lizards (Uta stansburiana)

Side-blotched lizards ( Uta stansburiana Baird and Girard, 1852) use sagebrush desert habitat above cliffs and typically flee over and down the nearest cliff when disturbed. We tested antipredator escape tactics of lizards to a common local snake, the western yellowbelly racer ( Coluber mormon Baird and Girard, 1852). Our goal was to determine if lizards use cliffs as a refuge from snakes, which cannot climb the sheer rock face, and whether distance to refuge affects escape behavior. We located undisturbed lizards above a cliff and approached them from a random direction with a realistic rubber snake model. When the snake model approached, lizards fled nonrandomly toward the nearest cliff refuge, indicating considerable spatial awareness. Lizards fled more directly toward the cliff the farther from the cliff they were found. However, when beyond ~15 m from the cliff the escape behavior of lizards changed to one of flight in circles (nondirectional) without hiding. Performance capacity (endurance) of the lizards is much greater than 15 m, indicating that lizards have the physiological capacity to reach the cliff. We suggest that the costs of potential intraspecific interactions (i.e., escape into unfamiliar or a competitor’s territory) are greater than the immediate risks of predation by snakes.

Escape tactics of two syntopic forms of the Lacerta perspicillata complex with different colour patterns

It has been suggested that dorsal colour patterns and defence strategies could have coevolved in reptiles, the striped species being more prone to flee compared with the spotted species that rely more on crypsis. Because of the confounding effects of phylogeny and habitat, we compared closely related forms that share the same habitats and predation pressures but display different patterns. The spotted (chabanaudi) and the striped (pellegrini) forms of the Lacerta perspicillata (= Teira perspicillata ) Duméril and Bibron, 1839 complex are reproductively isolated in a locality where they live in syntopy. The responses of lizards to a direct attack by a predator, simulated by the approach of a researcher, were investigated. Both forms displayed divergent antipredatory behaviours (escaping and recovering) to optimize survival. Chabanaudi lizards showed longer approach distances and took more time to abandon shelter than pellegrini lizards when the effects of temperature and of distance fled were removed. Reappearance was related with previous flight in chabanaudi but with thermal quality of the refuge in pellegrini. Although both used similar refuges, chabanaudi selected bigger rocks that were less accessible to terrestrial predators but were more prone to bird attacks, whereas pellegrini selected fragmented rocks that faced more terrestrial predation. Our results support the hypothesis of coevolution between pattern and antipredatory behaviour.