Sociosexual interaction among intact male and female rats in a seminatural environment

Wild rats employ a rather extensive area for their daily activities and share elaborate burrows with tunnels and chambers. When a female enters into estrus, she will copulate with multiple males during the entire period of estrus. In the typical laboratory setting, rat sexual behavior is studied in pairs of opposite sex individuals. This setting is not appropriate for an ecologically valid determination of some basic behavioral processes such as the mechanisms of mate selection and the potential behavioral factors underlying male fertility. The purpose of the present study is to explore the usefulness of a seminatural environment housing a group of rats for answering this kind of questions. One part of the environment consisted of a series of tunnels and small chambers similar to a natural rat burrow. This part was lit by infrared lamps and connected to a large open area illuminated on a 12:12 hr light/dark schedule. Water and food were available in the open area, although the animals were allowed to transport food into the burrow. Each group consisted of four intact, cycling females and 3 intact males. The subjects lived in this environment for a period of 8 days. The females were then observed for pregnancy and delivery and a piece of ear was taken from each pup for future determination of paternity. The entire 8 day period was recorded on video. Here we report the results from 2 daily observation periods of 30 min, one during the open area’s dark phase and the other from the light phase. Total duration and/or frequency of a vast series of behaviors were collected from each observation. The results show that activities mainly took place in the burrows. In fact, the subjects spent only about 10% of the observation time in the open area. Exploratory behaviors such as walking peaked within 48 hrs of the introduction of the subjects into the system. Sniffing other rats and allogrooming showed an irregular pattern throughout the entire observation period. During the period of estrus both males and females expressed individual preferences for certain potential mating partners, particularly with regard to male pursuit and female proceptivity. However, these behaviors showed no evident association with the amount of copulatory interactions. It has also been impossible to detect behavioral determinants of male fertility, but these analyses are still incomplete. The seminatural environment appears most adequate for obtaining a considerable amount of information not available in other procedures.