Sex-specific effects of inbreeding on body colouration and physiological colour change in the cichlid fish Pelvicachromis taeniatus.

Background: Colour expression is highly variable in animals. In fishes, rapid colour change, i.e. physiological colour change, can be observed in multiple contexts, e.g. in camouflage or communication, and is affected by various factors, such as stress. Pelvicachromis taeniatus is a cichlid fish from West Africa with sexual dichromatism and both sexes being brightly coloured and flexible in ornament expression. In the present study, inbred and outbred P. taeniatus were photographed before and after a stress situation to investigate the stress response regarding colour expression in both sexes.

Results: The chromaticity and the colour patch size (relative coloured area at the abdomen) were determined at both timepoints and the changes were analysed. Additionally, the coefficients of variation within family groups for the chromaticity (CV_chromaticity) and colour patch size (CV_area) were calculated. Chromaticity as well as the extent of colouration increased significantly following handling stress. The change in chromaticity was not significantly different between in- and outbred individuals in females and males. Inbred males showed more intense yellow colouration than outbred males. Independent from inbreeding, the CV_chromaticity decreased following the handling stress. The change in CV_area of females and males differed between in- and outbred individuals. In females, the decrease was significantly stronger in inbred individuals and in males the decrease was stronger in the outbred group.

Conclusion: The results show that short-term stress can increase colouration, potentially advertising individual's stress tolerance. Furthermore, this study shows positive inbreeding effects on a sexually selected trait.