Data from: The sexual selection paradigm: have we overlooked other mechanisms in the evolution of male ornaments?

Extravagant male ornaments expressed during reproduction are almost invariable assumed to be sexually selected and evolve through competition for mating opportunities. Yet, in species where male reproductive success depends on the defence of offspring, male ornaments could as well evolve through social competition for offspring survival. However, in contrast to female ornaments, this possibility has received little attention in males. We show that a male ornament that is traditionally assumed to be sexually selected - the red nuptial colouration of the threespine stickleback – is under stronger selection for offspring survival than for mating success. Males express most colouration during parenting, when they no longer attract females, and the colour correlates with nest retention and hatching success but not with attractiveness to females. This contradicts earlier assumptions and suggests that social selection for offspring survival rather than sexual selection for mating success is the main mechanism maintaining the ornament in the population. These results urge us to consider also other forms of social selection than sexual selection when seeking to explain the function and evolution of male ornaments expressed during reproduction. An incorrect assignment of selection pressures could hamper our understanding of the process of evolution.