Precopulatory behaviour of male rats: developmental aspects and dependence on female's solicitation

Sexual communication between sex partners can involve just one sensory modality or a combination, depending upon such factors as species, habitat, and context. Ethological aspects of sexual communication has been widely documented in rodents. In rats, sexual communication between male and female varies according to the production of signals by a female that signal receptivity, proceptivity, and attractivity. However, in the laboratory experiment, such approach is often neglected. In the present study, two types of stimulus female--Lordotic and Darting--were used with the aim to examine developmental changes in precopulatory behaviour of males. Besides the dependence of the male's precopulatory repertoire on the strength of proceptive stimuli emitted by the female was studied. Male rats ranging from 30 to 175 days of age were observed under the dyadic interaction. It was found: (a) Precopulatory behaviour of the 30-day-old males was not clear-cut, the males devoted more time to social investigation of adult (Darting) female. (b) All the 40-day-old males exhibited precopulatory behaviour in the range of the repertoire displayed by adult animals. (c) Precopulatory activity of juvenile (45-day-old) as well as of adult (90-day-old) males exposed to Lordotic female was significantly lower as compared with that exhibited by males toward Darting female. (d) Copulatory readiness of males increased with the age, in fact, all animals aged from 75-135 day were able to pass from the precopulatory into the copulatory phase of sexual interaction. (e) Although the 175-day-old males exhibited pronounced precopulatory activity, they did not initiate copulations. The implications of each of these findings are discussed from the point of view of both the developmental aspects and the stimulus-response relationships. To sum up, the development of normal flow of sexual behaviour of male rats proceeds simultaneously with the development of physiological and morphological parameters. The appearance of precopulatory behaviour is less dependent on the internal (hormonal) readiness than copulatory behaviour. The connection of both phases, i.e. precopulatory and copulatory, is terminated at about Day 75, and is the key moment of sexual interaction from the point of view of reproductive success. In fact, a successful course of sexual interaction is codetermined by the intensity of behavioural stimuli and/or by the completeness of proceptive patterns provided by the female partner. It is clear that the reproductive process cannot be completed without some degree of communication. The deterioration of sexual interaction found in males aged 175 day seems to be the consequence of their absolute heterosexual abstinence.(ABSTRACT TRUNCATED AT 400 WORDS)