Sexual selection remains a controversial subject despite nearly 150 years of inquiry. The forces that determine how animals choose their mates and those that drive the evolution of elaborate animal courtship displays are incompletely understood. Red breeding coloration in the threespine stickleback Gasterosteus aculeatus is one of the most intensively studied secondary sexual characters. There is evidence that the red breeding signal in males co-evolved with a female preference as an indicator of male quality. However, other evidence suggests it originated as a by-product of a preexisting, family-wide sensory bias for red-colored prey items. We tested color preferences in the brook stickleback Culaea inconstans, a representative of the stickleback ancestral condition which lacks red breeding colors, using aquarium-based paired comparison tests with novel prey items (red, orange, yellow, green, blue, and purple beads).
Results/Conclusions
Frequencies of initial bites by individuals were three to five times higher, and frequencies of total bites by groups of brook stickleback over time were three to eight times higher for red beads than yellow, green, blue, or purple. No preference for red over orange prey could be distinguished. Average numbers of bites in repeated predation attempts (in which a fish repeatedly bit a bead without turning away) were also significantly higher for red than any other color except orange. These results are further evidence for a family-wide sensory bias for the color red in the sticklebacks and a preexisting bias origin for the red breeding colors of the threespine stickleback.