Morphological and Optical Modification of Melanosomes in Fish Integuments upon Oxidation

Reactive oxygen species (ROS) such as superoxide radicals O2−, hydroxyl radicals OH−, and hydrogen peroxide H2O2 may have detrimental effects on marine organisms, including their integuments and visual appearances. Although some studies have described the impact of ROS on marine ecosystems and species ecology, the influence on the optical response of the integuments of marine species and on their visual appearances remains unknown. In this article, we used histology and optical characterisation to show, for the first time, that skin melanophores (melanin-containing chromophores) of the coral reef fish, Stegastes apicalis, change their shapes and fluorescent proprieties upon oxidation with H2O2 radicals. Our observations also suggest that pheomelanosomes may occur in fish integuments, where, previously, it was thought that fish melanosomes only contain eumelanin. This investigation relied on light and electron microscopy and steady-state fluorimetry, as well as time-resolved streak imaging systems. We suggest that the changes in the morphological and spectral characteristics of melanophores can be used as a marker of physiological stress induced by environmental factors such as ROS. Moreover, S. apicalis may be used as a potential model for studying the interaction between the surrounding environment and natural organisms in biologically diverse ecosystems, such as the Great Barrier Reef in Australia

Nonlinear optical spectroscopy and two-photon excited fluorescence spectroscopy reveal the excited states of fluorophores embedded in a beetle's elytra

This is the author accepted manuscript. The final version is available via the DOI in this record.Upon illumination by ultraviolet light, many animal species emit light through fluorescence processes arising from fluorophores embedded within their biological tissues. Fluorescence studies in living organisms are however relatively scarce and so far limited to the linear regime. Multiphoton excitation fluorescence analyses as well as nonlinear optical techniques offer unique possibilities to investigate the effects of the local environment on the excited states of fluorophores. Herein, these techniques are applied for the first time to study of the naturally controlled fluorescence in insects. The case of the male Hoplia coerulea beetle is investigated because the scales covering the beetle's elytra are known to possess an internal photonic structure with embedded fluorophores, which controls both the beetle's coloration and the fluorescence emission. An intense two-photon excitation fluorescence signal is observed, the intensity of which changes upon contact with water. A third-harmonic generation signal is also detected, the intensity of which depends on the light polarization state. The analysis of these nonlinear optical and fluorescent responses unveils the multi-excited states character of the fluorophore molecules embedded in the beetle's elytra. The role of form anisotropy in the photonic structure, which causes additional tailoring of the beetle's optical responses, is demonstrated by circularly polarized light and nonlinear optical measurements.Wallonia–Brussels InternationalBelgian National Fund for Scientific Research2018 Biomimetics Travel AwardFWO FlandersHercules FoundationAction de Recherche ConcerteNanoscale Quantum OpticsFRSFNRSMinistry of Science, Republic of Serbi

Catch Me If You Can - Referee–Team Relationships and Disciplinary Cautions in Football

The central hypothesis of this study is that relationships develop systematically between referees and teams and affect referees ’ decisions. Referees ’ travel distance to respective stadiums and count of matches refereed for respective teams are used to measure long-term relationships. We find some evidence that the count of referee–team interactions affects disciplinary cautions in lower divisions of the English Football League. This is less evident in higher divisions where, however, distances between referees ’ hometowns and stadiums appear to play a role. The influence of distance further increases with the extent of referees ’ experience with the respective teams

Measuring the effect of watch-preceded and direct rating changes: a note on credit markets

This paper analyzes the importance of distinguishing between watch-preceded and direct rating changes for the credit default swap (CDS) market by examining a total of 2991 rating change announcements, 1526 watchlist placement announcements, and 430 rating affirmations following watchlist placements. The results show that watch-preceded downgrades do not lead to significant CDS market reactions, while direct downgrades are associated with a significant increase in CDS spread levels. Likewise, we document that watchlist placements for downgrade lead to increases in firms’ CDS spreads. CDS markets do not react to rating upgrades but watchlist placements for upgrade result in an immediate decrease in CDS spreads. Rating affirmations following watchlist placements for downgrade lead to slight reductions in CDS spreads, while affirmations following watchlist placements for upgrade have no effect on CDS spreads. These findings demonstrate the importance for empirical research on the interaction between credit markets and rating announcements to differentiate between watch-preceded and direct rating changes, particularly for rating downgrades