The Problems of Appeasement and of Sexual Roles in the Courtship Behavior of the Blackchin Mouthbreeder, Tilapia Melanotheron (Pisces: Cichlidae)

[1. This investigation addressed itself to two interrelated problems: (a) The appeasement hypothesis of courtship. This hypothesis predicted that as the size of the mate became relatively larger, the smaller fish would court more. It was amply borne out. (b) Sexual roles in courtship. ARONSON (1949) pointed out that in the blackchin mouthbreeder (Tilapia melanotheron) both sexes perform the same action patterns. The ♂♂ and ♀♀ differed, however, in that the ♀♀ courted more than the ♂ Our results show that which sex courts most depends on which sex of the pair is the smaller. ARONSON may have studied pairs in which the ♂♂ were mostly larger than the ♀♀. We found many small differences between the sexes, however. Regression lines of behavior as a function of relative size differed significantly between sexes in a number of ways. But the differences were nonetheless small and of degree, not of kind. Similarly, differences emerged in correlation matrices of behavior within and between sexes. And an analysis of the effect of size on correlation coefficients within pairs uncovered only occasional small differences that where statistically significant. We doubt that any of these differences between sexes are biologically very meaningful. 2. Of the 150 pairings that were attempted, 110 were successful. The proportion of successful pairings was significantly greater when the ♂ was smaller than the ♀, as compared to ♂ larger than ♀ . 3. The significant correlations between behavior and absolute weight, when examined by subgroups of relative weight, are few and follow no clear pattern. However, there is a suggestion of positive correlations between absolute size and courtship, particularly among the ♂ ♂ . Small ♂ ♂ quivered and nodded less than did the large; they also tended to forage and yawn more. 4. The discussion deals with the problem of how one decides what is courtship behavior., 1. This investigation addressed itself to two interrelated problems: (a) The appeasement hypothesis of courtship. This hypothesis predicted that as the size of the mate became relatively larger, the smaller fish would court more. It was amply borne out. (b) Sexual roles in courtship. ARONSON (1949) pointed out that in the blackchin mouthbreeder (Tilapia melanotheron) both sexes perform the same action patterns. The ♂♂ and ♀♀ differed, however, in that the ♀♀ courted more than the ♂ Our results show that which sex courts most depends on which sex of the pair is the smaller. ARONSON may have studied pairs in which the ♂♂ were mostly larger than the ♀♀. We found many small differences between the sexes, however. Regression lines of behavior as a function of relative size differed significantly between sexes in a number of ways. But the differences were nonetheless small and of degree, not of kind. Similarly, differences emerged in correlation matrices of behavior within and between sexes. And an analysis of the effect of size on correlation coefficients within pairs uncovered only occasional small differences that where statistically significant. We doubt that any of these differences between sexes are biologically very meaningful. 2. Of the 150 pairings that were attempted, 110 were successful. The proportion of successful pairings was significantly greater when the ♂ was smaller than the ♀, as compared to ♂ larger than ♀ . 3. The significant correlations between behavior and absolute weight, when examined by subgroups of relative weight, are few and follow no clear pattern. However, there is a suggestion of positive correlations between absolute size and courtship, particularly among the ♂ ♂ . Small ♂ ♂ quivered and nodded less than did the large; they also tended to forage and yawn more. 4. The discussion deals with the problem of how one decides what is courtship behavior.]