Exploring the embryonic development of upper beak in Octopus vulgaris Cuvier, 1797: New findings and implications for age estimation

The beak of cephalopods (in particular octopods, where statoliths are not suitable) is a useful tool for age estimation and the aging method provides essential information on cephalopod growth and life cycles. These parameters are valuable in the assessment of population dynamics and stock management. The embryonic development of cephalopod beaks is poorly known. The presence of pre-hatching increments on the reading areas (rostrum and lateral walls) is unclear and there are no data on temperature influence. In this study, egg clusters of Octopus vulgaris were reared at 16, 19, 21, 23, and 26 °C. The extracted upper jaws were observed in order to validate the age of first daily increment formation, assessing the accuracy of age inferred from the two reading areas. Jaw dimensions were also measured in order to explore the development at different temperature conditions. The growth rate was calculated for beaks of rearing condition 21 °C, and the overall dimensions were compared among all incubation temperatures. Three ad hoc developmental stages are proposed for the upper beak of O. vulgaris embryos. Increments on lateral walls appear during the second phase, whereas the first increment on the rostrum is visible only at hatching. Consequently, only the accuracy of age inferred from the rostrum surface is confirmed for the early stages. The growth rate of the rostrum region accounted for a drop in growth during the third phase. Conversely, the growth rate increased until hatching in lateral walls, suggesting that the heterogeneity of the growth rate could be due to the different role played by the beak areas. Temperature influenced beaks in terms of overall size, as embryos reared at a warm temperature (23 °C) were smaller than the others. These results confirm that the incubation environment could alter hatchling characteristics thus affecting the recruitment conditions.Postprint1,58

Generation of bright isolated attosecond soft X-ray pulses driven by multicycle midinfrared lasers

High harmonic generation driven by femtosecond lasers makes it possible to capture the fastest dynamics in molecules and materials. However, to date the shortest subfemtosecond (attosecond, 10-18 s) pulses have been produced only in the extreme UV region of the spectrum below 100 eV, which limits the range of materials and molecular systems that can be explored. Here we experimentally demonstrate a remarkable convergence of physics: when midinfrared lasers are used to drive high harmonic generation, the conditions for optimal bright, soft X-ray generation naturally coincide with the generation of isolated attosecond pulses. The temporal window over which phase matching occurs shrinks rapidly with increasing driving laser wavelength, to the extent that bright isolated attosecond pulses are the norm for 2-μm driving lasers. Harnessing this realization, we experimentally demonstrate the generation of isolated soft X-ray attosecond pulses at photon energies up to 180 eV for the first time, to our knowledge, with a transform limit of 35 attoseconds (as), and a predicted linear chirp of 300 as. Most surprisingly, advanced theory shows that in contrast with as pulse generation in the extreme UV, long-duration, 10-cycle, driving laser pulses are required to generate isolated soft X-ray bursts efficiently, to mitigate group velocity walk-off between the laser and the X-ray fields that otherwise limit the conversion efficiency. Our work demonstrates a clear and straightforward approach for robustly generating bright isolated attosecond pulses of electromagnetic radiation throughout the soft X-ray region of the spectrum