Pre-Copulatory and Copulatory Behaviour in Relation To Stages of the Oestrous Cycle in the Female Mongolian Gerbil

Abstract

1. Most previous studies of sexual behaviour in female rodents have concentrated on lordosis, and there have been few attempts to quantify pre-copulatory behaviour of the female. Conditions of testing commonly used in previous research into rodent sexual behaviour particularly seem to have focussed attention on copulatory behaviour of the female, leading to the neglect of female pre-copulatory behaviour. 2. The present study aimed to investigate both pre-copulatory and copulatory behaviour in the female Mongolian gerbil in relation to different stages of the oestrous cycle. 3. The experimental design of the present study was intended to provide an increased opportunity for females to display pre-copulatory behaviour. Daily observations were made of the behaviour of ten male/female pairs of Mongolian gerbils which were living together continuously over the four days of the oestrous cycle. Each female was paired with a test male on the day following the day of behavioural oestrus and the pair remained together until the end of the next day of behavioural oestrous. Experimental females and test males were all sexually experienced before use as subjects. 4. Under these conditions, females displayed a number of pre-copulatory behaviour patterns (piloerection posture, present posture, darting and foot-stomping) on the day of oestrus which did not appear on other days of the cycle. On the day of oestrus, females also showed pre-copulatory increases in rates of allogrooming initiated by the female and in rates of olfactory investigation of the male's head and anogenital regions compared to other days of the cycle. Oestrus females also approached and left the male more frequently than non-oestrous females. 5. Unlike behaviour, sequences of female pre-copulatory behaviour involving darting and the present or piloerection postures did not depend on tactile stimuli associated with male mounting. Sequences of female pre-copulatory behaviour always preceded instances of male pre-copulatory following and mounting. 6. During copulation, male sexual behaviour was organised into ejaculatory series of mounts and intromissions, separated by post-ejaculatory intervals. All males initiated a final incomplete series of mounts and intromissions which did not culminate in ejaculation. Female receptivity, as measured by the lordosis ratio, remained high until the end of mating, and declined only in the final series of mounts and intromissions following the last ejaculation. However, the display of female proceptive behaviour patterns (darting, foot-stomping, present posture and piloerection posture) declined over successive ejaculatory series. 7. Sequence analysis showed that each mount or intromission was preceded by one of seven types of behaviour sequence, the most common sequence, Type O, consisting of female darting, male follow, female present and male moult without intromission or male mount with intromission. At the beginning of mating, most Type O sequences were preceded by female behaviour patterns (approaching the male, investigating the male and foot-stomping). As mating proceeded, an increasing percentage of these sequences was preceded by male behaviour patterns (approaching the female and investigating the female's head). 8. It is concluded that, in the present study, oestrous female gerbils played an active role in the performance of sexual behaviour. Pre-copulatory activities of the female seemed to have a stimulatory effect on male sexual behaviour and probably made an important contribution to the initiation of mating. During copulation, females actively participated in the initiation of mounts and intromissions, and, in the earliest stages of mating, played an important role in the patterning of copulatory behaviour. In the later stages of mating, the male played an increasingly important role in the initiation of mounts and intromissions.