Courtship displays and coloration as indicators of safety rather than of male quality: the safety assurance hypothesis

Male courtship displays and bright coloration are usually assumed to provide information to females about some aspect of the male's value as a mate. However, in some species, courtship may serve another function-namely, indicating the current predation risk at the mating site and assuring the female that it is safe to mate there at this time. We developed this safety assurance hypothesis (SAH) and tested its predictions in the bluehead wrasse (Thalassoma bifasciatum), a Caribbean reef fish. Females in this species come to males' territories to spawn, and males court each arriving female. Males with larger white flank patches court less intensely than less bright males. We show that such males are probably more visible to predators and thus need not court so intensely to provide the same degree of safety assurance to a female. When model lizardfish predators are presented at spawning sites, males habituate to them quickly, but newly arriving females who see the predator are expected to demand more assurance of site safety. Accordingly, and consistent with the SAH, males court females more intensely (longer average courtship bout length) under such circumstances, but males with bright flank patches do not increase their courtship as much as duller males do. Despite this relatively low intensity of courtship, the spawning rate of bright males does not. decline relative to that of duller males in the presence of a predator, suggesting that bright coloration conveys a differential benefit. Females of species like the bluehead wrasse, who spawn repeatedly over the course of their life, are expected to be more concerned with their own risk of mortality during each spawning bout than with the quality of a particular male. It is in such species that we expect the SAH to be most applicable.