A role for male bower size as an intrasexual signal in a Lake Malawi cichlid fish

Disruptive sexual selection through female mate choice has been proposed as a key mechanism driving the evolution of haplochromine cichlid fish diversity. Here we investigated if male secondary sexual traits employed by females in direct mate choice have an additional function in male competition. We conducted a field experiment on aggression among males of a lekking Lake Malawi cichlid species that build volcano-shaped spawning craters, known as bowers, in their breeding territories. Males placed on a short artificial bower received significantly more aggression from adjacent resident males than when placed on a tall artificial bower. This supports the hypothesis that bower size provides information about male competitive ability, and suggests an additional function for this extended phenotypic trait besides a role in attracting females.