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Aquatic organisms have to deal with different hydrodynamic regimes, depending on their size and speed during locomotion. The pea crab swims by beating the third and fourth pereiopod on opposite sides as pairs. Using particle tracking velocimetry and high-speed video recording, we quantify the kinematics and vortices in the wake of the pea crab. Where the proximal parts of the pereiopods beat in antiphase, their distal parts show an overlapping beat period. By using four instead of two limbs for propulsion, an uninterrupted forward movement is established, reducing the influence of the acceleration reaction. Before body speed is maximal, force generation of the pereiopods seems most active when passing an orthogonal position with the body. [ABSTRACT FROM AUTHOR]

Noise trauma involves a plethora of mechanisms including reactive oxygen species, apoptosis, tissue damage, and inflammation. Recently, circadian mechanisms were also found to contribute to the vulnerability to noise trauma in mice, with greater damage occurring during their active phase (nighttime), when compared to similar noise exposures during their inactive phase (daytime). These effects seem to be regulated by mechanisms involving Bdnf responses to noise trauma and circulating levels of corticosterone (CORT). However, recent studies using different noise paradigms show contradicting results and it remains unclear how universal these findings are. Here we show that these findings differ even between substrains of mice and are restricted to a narrow window of noise intensity. We found that CBA/Sca mice exposed to 103 dB SPL display differential day/night noise sensitivity as measured by auditory brainstem responses (ABRs), but not at 100 (where full recovery is observed in day or night exposed mice) or 105 dB SPL (where permanent damage is found in both groups). In contrast, neither CBA/CaJ or CBA/JRj displayed such differences in day/night noise sensitivity, whatever noise intensity used. These effects appeared to be independent from outer hair cell function, as distortion product otoacoustic emissions appeared equally affected by day or night noise exposure, in all strains and in all noise conditions. Minor differences in ribbon counts or synaptic pairing were found in CBA/Sca mice, which were inconsistent with ABR wave 1 amplitude changes. Interestingly, CORT levels peaked in CBA/Sca mice at the onset of darkness at zeitgeber time 12 reaching levels of 43.8 ng/ml, while in the CBA/CaJ and the CBA/JRj, levels were 11.9 and 15.6 ng/ml respectively and peaking 4 h earlier (zeitgeber time 8). These findings were consistent with higher period of daily rhythm in CBA/Sca mice when measured in complete darkness using running wheels (23.7 h), than in CBA/CaJ (23.45 h) or CBA/JRj (23.13 h). In conclusion, our study suggests that the differential vulnerability to noise trauma between inactive and active phase is not universal and is as sensitive as substrain differences that might be governed by the circadian amplitude of the circulating CORT profiles., (Copyright © 2021. Published by Elsevier B.V.)