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

Male courtship displays and bright coloration are usually assumedto provide information to females about some aspect of themale's value as a mate. However, in some species, courtshipmay serve another function—namely, indicating the currentpredation risk at the mating site and assuring the female thatit is safe to mate there at this time. We developed this safetyassurance hypothesis (SAH) and tested its predictions in thebluehead 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 whiteflank patches court less intensely than less bright males.We show that such males are probably more visible to predatorsand thus need not court so intensely to provide the same degreeof safety assurance to a female. When model lizardfish predatorsare presented at spawning sites, males habituate to them quickly,but newly arriving females who see the predator are expectedto demand more assurance of site safety. Accordingly, and consistentwith the SAH, males court females more intensely (longer averagecourtship bout length) under such circumstances, but maleswith bright flank patches do not increase their courtship asmuch as duller males do. Despite this relatively low intensityof courtship, the spawning rate of bright males does not declinerelative 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 repeatedlyover the course of their life, are expected to be more concernedwith their own risk of mortality during each spawning boutthan with the quality of a particular male. It is in such speciesthat we expect the SAH to be most applicable.