Differential investment in pre- and post-mating male sexual traits in response to prolonged exposure to ambient UVB radiation in a fish

Changes in wax composition but not amount enhance cuticular transpiration

This study focuses on the role of the qualitative leaf wax composition in modulating the cuticular water loss using a Populus × canescens cer6 mutant line, which accumulates C34-C46 wax ester dimers and is reduced in wax monomers >C24. The two literature-based hypotheses to be tested were the importance of the amount of wax esters and the weighted mean carbon chain length in restricting cuticular water loss. The main results were acquired by chemical analysis of cuticular wax and gravimetric cuticular transpiration measurements. Besides additional physiological measurements, the leaf surface properties were characterised by scanning electron microscopy and spectrophotometric light reflectance quantification. Mutation of the CER6 gene resulted in striking changes in qualitative wax composition but not quantitative wax amount. Based on the strong accumulation of dimeric wax esters, the relative proportion of esters increased to >90%, and the weighted mean carbon chain length increased by >6 carbon atoms. These qualitative alterations were found to increase the cuticular transpiration of leaves by twofold. Our results do not support the hypotheses that enhanced amounts of wax esters or increased weighted mean carbon chain lengths of waxes lead to reduced cuticular transpiration.

Does the egg capsule protect against chronic UV-B radiation? A study based on encapsulated and decapsulated embryos of cuttlefish Sepia officinalis

Although the egg capsule plays a crucial role in the embryonic development of cephalopods, its ability to protect embryos from Ultraviolet (UV) radiation is unknown. Our study evaluated the photoprotection mechanisms of S. officinalis to UV-B radiation and estimated the ability of the black capsule to act as a physical shield against it. Embryos with and without capsule and juveniles were exposed to four experimental UVB conditions for 55 days. The effects of different UVB doses were evaluated in terms of morphological abnormalities and differences in gene expression between each group. We observed that the development might be severely impaired in embryos exposed to UVB without capsule protection, and these effects were time- and UVB-dose-dependent. In addition, we found variations in gene expression levels (light-sensitive, stress response and DNA repair) in different tissues as a function of UVB doses. We suggest a relationship between morphological abnormalities and the limit of molecular regulation. These results suggest that the quantitative differences in expression are essential for defining the survivability of the embryo face to UVB. Thus, we demonstrated that the egg capsule could ensure successful embryonic development of the cuttlefish S. officinalis even at high doses of UVB.

Influence of lighting environment on social preferences in sticklebacks from two different photic habitats. I. mate preferences of wild-caught females

Ultraviolet (UV) A signals (320-400 nm) are important in mate choice in numerous species. The sensitivity for UV signals is not only assumed to be costly, but also expected to be a function of the prevailing ecological conditions. Generally, those signals are favored by selection that efficiently reach the receiver. A decisive factor for color signaling is the lighting environment, especially in aquatic habitats, as the visibility of signals, and thus costs and benefits, are instantaneously influenced by it. Although ecological aspects of color signal evolution are relatively well-studied, there is little data on specific effects of environmental UV-light conditions on signaling at these shorter wavelengths. We studied wild-caught gravid female 3-spined sticklebacks Gasterosteus aculeatus of 2 photic habitat types (tea-stained and clear-water lakes), possessing great variation in their UV transmission. In 2 treatments, tea-stained and clear-water, preferences for males viewed under UV-present (UV+) and UV-absent (UV-) conditions were tested. A preference for males under UV+ conditions was found for females from both habitat types, thus stressing the significance of UV signals in stickleback's mate choice decisions. However, females from both habitat types showed the most pronounced preferences for males under UV+ conditions under clear-water test conditions. Moreover, reflectance measurements revealed that the carotenoid-based orange-red breeding coloration in wild-caught males of both habitat types differed significantly in color intensity (higher in clear-water males) and hue (more red shifted in clear-water males) while no significant differences in UV coloration were found. The differential reflection patterns in longer wavelengths suggest that sticklebacks of both habitat types have adapted to the respective water conditions. Adaptations of UV signals in a sexual context to ambient light conditions in both behavior and coloration seem less evident.

Body coloration as a dynamic signal during intrasexual communication in a cichlid fish

Background

Intrasexual competition over access to resources can lead to aggression between individuals. Because overt aggression, i.e. fights, can be costly for contestants, the communication of aggressive motivation prior to engagement in a physical fight is often mediated by conventional signals. Animals of various taxa, including fishes, display visual signals such as body coloration that can dynamically be adjusted depending on the individual’s motivation. Male individuals of the West African cichlid Pelvicachromis taeniatus express a yellow body coloration displayed during courtship but also in an intrasexual competition context.

Results

Within-individual variation in male yellow body coloration, as quantified with standardized digital photography and representation in a CIELab color space, was examined in a mating context by exposing males to a female and in a competitive intrasexual context, i.e. in a dyadic contest. Additionally, spectrometric reflectance measurements were taken to obtain color representations in a physiological color space based on spectral sensitivities of our model species. Exposure to females did not significantly affect male color expression. However, analysis of body coloration revealed a change in within-individual color intensity and colored area after interaction with a male competitor. In dominant males, extension of coloration was positively correlated with restrained aggression, i.e. displays, which in turn explained dominance established between the two contestants.

Conclusion

Body coloration in male P. taeniatus is a dynamic signal that is used in concert with display behavior in communication during intrasexual competition.