Weak and inconsistent associations between melanic darkness and fitness related traits in an insect

The idea that the fitness value of body colouration may be affected by biochemically mediated trade-offs has received much research attention. For example, melanisation is believed to interact with other fitness-related traits via competition for substrates, costs associated with the synthesis of melanin, or pleiotropic effects of the involved genes. However, genetic correlations between colouration and fitness-related traits remain poorly understood. Here we present a quantitative genetic study of a colouration trait correlated to melanin-based cuticular darkness (‘darkness’, hereafter) in a geometrid moth, Ematurga atomaria, which has considerable variation in larval appearance. We focus on correlations between larval darkness and fitness-related growth performance traits. Both a half-sib analysis and an ‘animal model’ approach revealed moderately high heritabilities of larval darkness and indices of growth performance. Heritability estimates of darkness derived from the animal model...