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Pile driving noise is an intense, repetitive, far-reaching sound that is increasing in many coastal habitats as the offshore wind energy industry expands globally. There is concern for its impacts on keystone species and vital fisheries taxa such as squids. In controlled laboratory conditions, we investigated whether exposure to pile driving noise from offshore wind farm construction altered reproductive behaviours in the short-lived semelparous species Doryteuthis pealeii. Pile driving noise had no significant effects on the occurrence rates of agonistic behaviours, mate guarding, mating, and egg laying, compared with silent control trials. The results contrast starkly with behavioural response rates of the same squid species during feeding and shoaling. The data suggest that squid reproductive behaviours may be resilient to this increasingly pervasive environmental stressor, and that behavioural context guides responses to windfarm noise for this invertebrate taxon. While some non-reproductive behaviours can clearly be disturbed, the results show that species with limited opportunity to reproduce can tolerate intense stressors to secure reproductive success.

 

Colourful displays are used by diverse taxa to warn predators of dangerous defences (aposematism). Aposematic coloration is especially widespread among amphibians, which are often protected by harmful toxins. Pacific newts (Taricha) are considered a model of aposematism because when threatened, they arch the head and tail upwards to expose a vivid orange ventrum against a dark dorsum. Given that newts are defended by tetrodotoxin (TTX), a lethal neurotoxin, this signal is assumed to warn predators that an attack would be risky. However, colours have not been quantified in Taricha, and it remains unknown whether coloration provides qualitatively honest (signalling toxic defence) or quantitatively honest (signalling toxin level) warnings. We used two colour quantification methods (spectrometry and hyperspectral imaging) to measure chromatic (hue) and achromatic (brightness) qualities of ventral and dorsal coloration in two newt species (Taricha granulosa and Taricha sierrae). We assessed qualitative honesty using visual models of potential predators (snakes, birds and mammals). Next, we evaluated quantitative honesty by measuring TTX in newts and examining the potential correlation between defence level (amount of TTX) and colorimetrics. We found support for qualitative but not quantitative honesty. Selective pressures and evolutionary constraints might impede the evolution of honest quantitative signalling in this system.

 

The behavior of permeable, elastic particles sliding along a repulsive wall is examined computationally. It is found that particles will stick or slip depending on the interplay of elastohydrodynamic and repulsive forces, and the flow in the porous particle. Particles slip when either the elastohydrodynamic lift or repulsive forces are large and create a supporting lubricating film of fluid. However, for lower values of elastohydrodynamic lift or repulsive forces, the flow within the porous particle reduces the pressure in the thin film, resulting in the particles making contact and sticking to the surface. The criteria for the slip-stick transition is presented, which can be used to design systems to promote or suppress slip for such suspensions. 

We explore the rheology during a startup flow of well-characterized polyelectrolyte microgel suspensions, which form soft glasses above the jamming concentration. We present and discuss results measured using different mechanical histories focusing on the variations of the static yield stress and yield strain. The behavior of the shear stress growth function is affected by long-lived residual stresses and strains that imprint a slowly decaying mechanical memory inside the materials. The startup flow response is not reversible upon flow reversal and the amplitude of the static yield stress increases with the time elapsed after rejuvenation. We propose an experimental protocol that minimizes the directional memory and we analyze the effect of aging. The static yield strain γ p and the reduced static yield stress σ p / σ y , where σ y is the dynamic yield stress measured from steady flow measurements, are in good agreement with our previous simulations [Khabaz et al., “Transient dynamics of soft particle glasses in startup shear flow. Part I: Microstructure and time scales,” J. Rheol. 65, 241 (2021)]. Our results demonstrate the need to consider memory and aging effects in transient measurements on soft particle glasses. 

Permeable particles are closer to the wall than impermeable particles and stick below a critical particle velocity.

 

The thermodynamics of the shear-induced phase transition of soft particle glasses is presented. Jammed suspensions of soft particles transform into a layered phase in a strong shear flow from a stable glassy phase at lower shear rates. The thermodynamics of the two phases can be computed based on the elastic energy and excess entropy of the system. At a critical shear rate, the elastic energy, the excess entropy, the free energy, the temperature, and the shear stress undergo discontinuous jumps at the phase transitions from the glassy to the layered phase. An effective temperature is defined from the derivative of the elastic energy and the excess entropy. The Helmholtz free energy is constructed using the elastic energy, excess entropy, and derived temperature. At a fixed shear rate, there is no equilibrium between the states. However, at a fixed temperature, the glassy and layered states may coexist, as indicated by the equality of their Helmholtz free energies. While this first-order phase transition is possible, it cannot be observed in simple shear because the stress is the same in both phases at the same temperature. Thus, shear banding cannot be observed in this system. Finally, an equation of state, which relates the shear stress to the excess entropy, is presented. This equation of state shows that all dynamical properties (e.g., shear-induced diffusivity and first and second normal stresses) of these jammed non-Brownian suspensions can be determined solely by measuring the shear stress.

 

The ability to exert self-control varies within and across taxa. Some species can exert self-control for several seconds whereas others, such as large-brained vertebrates, can tolerate delays of up to several minutes. Advanced self-control has been linked to better performance in cognitive tasks and has been hypothesized to evolve in response to specific socio-ecological pressures. These pressures are difficult to uncouple because previously studied species face similar socio-ecological challenges. Here, we investigate self-control and learning performance in cuttlefish, an invertebrate that is thought to have evolved under partially different pressures to previously studied vertebrates. To test self-control, cuttlefish were presented with a delay maintenance task, which measures an individual's ability to forgo immediate gratification and sustain a delay for a better but delayed reward. Cuttlefish maintained delay durations for up to 50–130 s. To test learning performance, we used a reversal-learning task, whereby cuttlefish were required to learn to associate the reward with one of two stimuli and then subsequently learn to associate the reward with the alternative stimulus. Cuttlefish that delayed gratification for longer had better learning performance. Our results demonstrate that cuttlefish can tolerate delays to obtain food of higher quality comparable to that of some large-brained vertebrates.