SEXUAL BEHAVIOR: A DISCUSSION

Merrell's main criticism in the preceding note refers to the use of the "male choice" method. He claims that studies by Streisinger (1948) showed that males exhibit almost no sexual preference, and that such preferences should be ascribed to the females. He uses the isolation estimate method and the female and male mating ratios to demonstrate that in many instances there is no evidence of courtship tendencies as claimed by the x method used in our paper. Merrell's criticism is based on the definite assumption that the female choice method might have provided a more sensitive test of the degree of isolation. The differences observed in homogamic versus heterogamic tendencies, he says, may be due to the fact that the inbred females moved about less than the outbred females. However, we believe that the incipient sexual isolation shown in our results is due to other aspects of female behavior. We said in our paper that female discrimination has to be recognized as the main factor in determining sexual preference, although the male contribution to discrimination is also evident. In our view, both sexes determine the "choice" involved in discriminating courtship, but we do not have the evidence to establish the relative importance of the two let alone to indicate complete lack of the importance of the male. The data presented by Streisinger (1948) refer to the behavior of males in copulations and not in courtship, and toward etherized females rather than normal females. The females, not having any threshold barrier, were equally neutral to the attacks of the males, who simply mounted and copulated with them. It is, however, in the preparatory phases of courtship that the importance of female behavior enters. The first elements of courtship, such as orientations and tappings, may be indiscriminatory in some cases, while the latter steps in courtship exhibit an extensive priority in "choice" on the part of the male, even if copulations do not necessarily follow the indicated trend of courtship (Hoenigsberg and Koref Santibanez, 1959b and 1960b). The inbred females have to be non-etherized in order to make evident threshold responses toward both males, thereby stimulating and promoting preferential behavior in one of them. Data on lickings, standings, circlings, wing vibrations, courtship time, etc., not presented in the relatively short paper which appeared in EVOLUTION have been published elsewhere (Hoenigsberg and Koref Santibanez, 1959a, b; Hoenigsberg, Koref Santibanez and Sironi, 1959). They presented considerable further information on female and male behavior and the importance played by some elements of courtship. From our experience we can say that 1) not all elements of courtship elicit response of the same intensity, (this fact must be of great significance in the lowering of the female threshold), and 2) that courtship time of females should be an indication of their critical ability to maintain the threshold. Furthermore, while studying intraspecific courtship discriminations in D. aequinoctiales and D. prosaltans, we found that only some Colombian and Brazilian males exhibited preferences in courtship time, tappings, lickings and standings of the females, while the other tropical American strains from Costa Rica. Cuba, and Colombia did not. The evolutionary significance of discriminatory behavior found in those two species is discussed by us elsewhere (Hoenigsberg and Koref Santibanez, 1960b). Obviously the problem of incipient sexual isolation is not solved by merely deciding which sex is the discriminating partner in courtship, since probably both display preferences, but calls for a detailed analysis of courtship patterns. The behavior which we discussed in our paper involves sensory discrimination in general rather than male preference only. The name "male choice" was used in the absence of a better term, only to describe the method designed by Dobzhansky and Mayr (1944).