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Extreme animal movements are usually associated with a single, high-performance behavior. However, the remarkably rapid mandible strikes of the trap-jaw ant, Odontomachus bauri, can yield multiple functional outcomes. Here we investigate the biomechanics of mandible strikes in O. bauri and find that the extreme mandible movements serve two distinct functions: predation and propulsion. During predatory strikes, O. bauri mandibles close at speeds ranging from 35 to 64 m·s⁻¹ within an average duration of 0.13 ms, far surpassing the speeds of other documented ballistic predatory appendages in the animal kingdom. The high speeds of the mandibles assist in capturing prey, while the extreme accelerations result in instantaneous mandible strike forces that can exceed 300 times the ant's body weight. Consequently, an O. bauri mandible strike directed against the substrate produces sufficient propulsive power to launch the ant into the air. Changing head orientation and strike surfaces allow O. bauri to use the trap-jaw mechanism to capture prey, eject intruders, or jump to safety. This use of a single, simple mechanical system to generate a suite of profoundly different behavioral functions offers insights into the morphological origins of novelties in feeding and locomotion.

Abstract The function of anti-predator signalling is a complex, and often-overlooked, area of animal communication. The goal of this study was to examine the behavioural function of an antipredator acoustic signal in the ocean. We observed the acoustic and defensive behaviours of California spiny lobsters (Palinuridae: Panulirus interruptus) to a model predator, model conspecific and blank pole, both in the tank and in the field. We found that P. interruptus make a 'rasp' sound once physically contacted by an aggressor, rather than during the approach. The model predator and conspecific elicited no discernable changes in defensive behaviour, but the responses by the lobsters to aggressors in the tank versus field were distinct. Our results indicate that the spiny lobster's rasp is used as a startle or aposematic signal, which may be coupled with visual aposematism of their spines. Alternatively, the rasp may function as a vibratory escape mechanism or as an acoustic analogue to eye-spots. This study offers insights into the role of acoustic signalling in the marine environment and demonstrates a central role for sound production in spiny lobster ecology.

Ballistospore discharge is a feature of 30 000 species of mushrooms, basidiomycete yeasts and pathogenic rusts and smuts. The biomechanics of discharge may involve an abrupt change in the center of mass associated with the coalescence of Buller's drop and the spore. However this process occurs so rapidly that the launch of the ballistospore has never been visualized. Here we report ultra high-speed video recordings of the earliest events of spore dispersal using the yeast Itersonilia perplexans and the distantly related jelly fungus Auricularia auricula. Images taken at camera speeds of up to 100 000 frames/s demonstrate that ballistospore discharge does involve the coalescence of Buller's drop and the spore. Recordings of I. perplexans demonstrate that although coalescence may result from the directed collapse of Buller's drop onto the spore, it also may involve the movement of the spore toward the drop. The release of surface tension at coalescence provides the energy and directional momentum to propel the drop and spore away from the fungus. Analyses show that ballistospores launch into the air at initial accelerations in excess of 10 000 g. There is no known analog of this micromechanical process in animals, plants or bacteria, but the recent development of a surface tension motor may mimic the fungal biology described here.

Evolutionary theory suggests that individuals should express costly traits at a magnitude that optimizes the cost-benefit ratio for the trait-bearer. Trait expression varies across a species because costs and benefits vary among individuals. For example, if large individuals pay lower costs than small individuals, then larger individuals should reach optimal cost-benefit ratios at a greater magnitude of trait expression. Using the remarkable cavitation-shooting weapons found in the big claws of male and female alpheid snapping shrimp, we test whether size- and sex-dependent expenditures explain the scaling of weapon size relative to body size and why males have larger proportional weapon size than females. We found that males and females from three snapping shrimp species (Alpheus heterochaelis, Alpheus angulosus, and Alpheus estuariensis) exhibit resource allocation tradeoffs between weapon and abdomen mass. For male A. heterochaelis, the species for which we had the greatest sample size and statistical power, the smallest individuals showed the steepest tradeoff. Our extensive dataset in A. heterochaelis also included data about pairing, breeding season, and egg clutch size. Therefore, we could test for reproductive tradeoffs and benefits in this species. Female A. heterochaelis exhibited additional tradeoffs between weapon size and egg count, average egg volume, and total egg mass volume. For average egg volume, the smallest females exhibited the steepest tradeoff relative to weapon size. Furthermore, for both sexes, large weapons were positively correlated with the relative size of their pair mate; however, for males only, large weapons were positively correlated with being paired in the first place. In conclusion, we establish that size-dependent tradeoffs underlie reliable scaling relationships of costly traits. Furthermore, we show that males and females differ in weapon investment, suggesting that weapons are especially beneficial to males and especially burdensome to females.Competing Interest StatementThe authors have declared no competing interest.

The interface of proximate and evolutionary perspectives can provide fundamental insights into acoustic signals and their evolutionary diversification. This chapter focuses on three facets of acoustic mechanisms—biomechanics, size and performance—each of which bears upon patterns of signal evolution. Our discussion of biomechanics focuses on the mechanics of sound production across the katydids. We show that the integration of biomechanics and phylogeny‐based analyses is yielding new and unexpected explanations for the generation of extremely high frequency signals, the transition from tonal to broadband signaling, and the relationships between signal features and mating strategies. Our discussion of acoustics and body size, focuses in on the evolution of acoustic frequencies. We propose that many of the most informative relationships between size and acoustic frequency occur at the level of the sound producing apparatus itself, rather than at the level of the whole body. Finally, we discuss performance in signaling mechanisms, focusing especially on acoustic tradeoffs experienced by singing birds. By pushing bird signal features to the limit, even the most fundamental features of song, such as frequency bandwidth and trill rate, can shape signal expression at both developmental and evolutionary timescales. Exploring these factors in acoustic signal evolution helps delimit the range of signaling structures possible, and thus complements more traditional analyses of signal evolution that focus on costs and reliability.