A review of escape behaviour in orthopterans

Exudate droplets incorporated on eggs by Raoiella indica Hirst female during oviposition may avoid the predation of Amblyseius largoensis (Muma)

Raoiella indica Hirst has rapidly and widely spread throughout the New World since 2004, primarily infesting coconut palms and interacting with the predator Amblyseius largoensis (Muma). Although A. largoensis feeds on R. indica at all stages of development, it cannot naturally reduce its population to levels that do not impact the host plant. Raoiella indica possesses dorsal setae that secrete exudates during all post-embryonic developmental stages, and females have a behavior that deliberately deposits droplets on the freshly laid egg, possibly as a defense strategy against predation in vulnerable stages. In this context, we analyzed whether the presence or absence of droplets in R. indica eggs affects predation using A. largoensis as a biological model. Thus, we evaluated whether some biological and behavioral characteristics of A. largoensis could be affected by the consumption of R. indica egg masses washed or unwashed with water. Also, we performed a chemical analysis of the droplets exuded by R. indica and provided a description of the oviposition behavior of R. indica. The predator showed a higher consumption rate and preference for washed eggs. The results suggest that the exudate droplets have defensive functions, which are incorporated by the female onto the egg during oviposition and subsequently during a patrolling behavior, as they lose their effect after being washed with water. Although the droplets do not prevent the predator from feeding, they reduce the number of R. indica eggs consumed without affecting the growth of A. largoensis.

Agonistic behaviors of boxer shrimps (Stenopus Species): Insights into the importance of antennae, antennules and tactile contact

Agonistic behaviors are crucial and ubiquitous among animals for the competition of limited resources. Although the study of aggression has been a popular topic, plenty of studies focused on model organisms, and typically on crayfish and lobsters for crustaceans. Variations of the agonistic behaviors and the underpinning eliciting cues of other crustaceans therefore have not been fully explored. In the present study, we targeted Stenopus, a genus of shrimp-like crustaceans that displays prominent agonistic behaviors when encountering conspecifics of the same sex owing to their monogamous social structure. Using S. hispidus (Olivier, 1811) and S. cyanoscelis (Goy, 1984) as representatives, we characterized their agonistic behaviors and fighting pattern, conducted experiments to investigate the contribution of visual, olfactory and tactile cues to inducing aggression, and examined the effects of antennal and antennular ablation on their agonistic interactions. A total of seven agonistic behaviors were documented, where antennal entwining and tactile contact is the major driver and seemingly important cue, respectively, in inducing agonistic behaviors in Stenopus. Although ablation of antennae and antennules did not inhibit fighting, behavioral changes, such as the prolonged agonistic interactions and the delayed establishment of dominance were observed, suggesting a reduction of aggressiveness. A comparison of agonistic behaviors with other crustaceans showed that certain features appeared to be unique or distinct in Stenopus, including the potential functional overlap of antennae and antennules, a higher aggressiveness of the fighting behaviors, and the exhibition of crouching behavior by submissive individuals. The present study provides a crucial background understanding for subsequent research on Stenopus and paves the way for its establishment as another crustacean model for studying aggression.

Escape behaviors in prey and the evolution of pennaceous plumage in dinosaurs

Numerous non-avian dinosaurs possessed pennaceous feathers on their forelimbs (proto-wings) and tail. Their functions remain unclear. We propose that these pennaceous feathers were used in displays to flush hiding prey through stimulation of sensory-neural escape pathways in prey, allowing the dinosaurs to pursue the flushed prey. We evaluated the escape behavior of grasshoppers to hypothetical visual flush-displays by a robotic dinosaur, and we recorded neurophysiological responses of grasshoppers' escape pathway to computer animations of the hypothetical flush-displays by dinosaurs. We show that the prey of dinosaurs would have fled more often when proto-wings were present, especially distally and with contrasting patterns, and when caudal plumage, especially of a large area, was used during the hypothetical flush-displays. The reinforcing loop between flush and pursue functions could have contributed to the evolution of larger and stiffer feathers for faster running, maneuverability, and stronger flush-displays, promoting foraging based on the flush-pursue strategy. The flush-pursue hypothesis can explain the presence and distribution of the pennaceous feathers, plumage color contrasts, as well as a number of other features observed in early pennaraptorans. This scenario highlights that sensory-neural processes underlying prey's antipredatory reactions may contribute to the origin of major evolutionary innovations in predators.

Walking kinematics in the polymorphic seed harvester ant Messor barbarus: influence of body size and load carriage

Ants are famous in the animal kingdom for their amazing load-carrying performance. Yet, the mechanisms that allow these insects to maintain their stability when carrying heavy loads have been poorly investigated. Here, we present a study of the kinematics of unloaded and loaded locomotion in the polymorphic seed-harvesting ant Messor barbarus In this species, large ants have larger heads relative to their size than small ants. Hence, their center of mass is shifted forward, and even more so when they are carrying a load in their mandibles. We tested the hypothesis that this could lead to large ants being less statically stable than small ants, thus explaining their lower load-carrying ability. We found that large ants were indeed less statically stable than small ants when walking unloaded, but they were nonetheless able to adjust their stepping pattern to partly compensate for this instability. When ants were walking loaded on the other hand, there was no evidence of different locomotor behaviors in individuals of different sizes. Loaded ants, whatever their size, move too slowly to maintain their balance through dynamic stability. Rather, they seem to do so by clinging to the ground with their hind legs during part of a stride. We show through a straightforward model that allometric relationships have a minor role in explaining the differences in load-carrying ability between large ants and small ants, and that a simple scale effect is sufficient to explain these differences.