MALE-MALE COMPETITION AND FEMALE MATE CHOICE THROUGH COURTSHIP DISPLAY IN THE TERRITORIAL DAMSELFISH STEGASTES NIGRICANS

Both sexes of the herbivorous damselfish Stegastes nigricans maintain individual feeding territories. These territories are distributed cont iguously, forming distinct colonies. Females visit male territories to spawn, and eggs are guarded by males until hatching. Male-male compet ition and female mate choice were studied in two colonies of different size compositions. Only larger individuals bred in both colonies. Som e males in the large colony, that were larger than the breeding males in the small colony, did not succeed in reproducing probably because o f severe attacks by the larger males while courting. However, females did not choose large size among breeding males. The most important mal e characteristic in female choice was the frequency of courtship displ ays in both colonies. Females in the large colony chose males mainly o n the basis of the frequency of displays conducted in the females' ter ritories, whereas females in the small colony chose males on the basis of the frequency of displays conducted in the males' territories. Thi s difference may be a result of the difference in colony size. The dis tances between females' and males' territories were much greater in th e large colony, and, because females cannot see courtship displays con ducted in distant male territories, males in the large colony may have had to visit female territories frequently in order to conduct courts hip near the females.