Sociosexual Interactions in Rats: Are They Relevant for Understanding Human Sexual Behavior?
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INT.J.PSYCHOL.RES. 2016; 9 (Special Issue): 76-95 Sociosexual Interactions in Rats: Are They Relevant for Understanding Human Sexual Behavior? Interacción Sociosexual en ratas: ¿son relevantes para comprender el comportamiento Sexual humano? R e v i e w a a Xi Chu * and Anders Ågmo a Department of Psychology, University of Tromsø, Norway. ARTICLE INFO ABSTRACT Article history: When a prolonged observation of groups of rats in a seminatural Received: 18-03-2016 environment is used as testing procedure, different behavioral patterns are shown Revised: 23-05-2016 compared with what observed in a pair housed in a small cage. Males and females Accepted: 26-05-2016 copulate simultaneously, they show a promiscuously and random copulatory pattern. Females remain completely receptive from the first lordosis displayed in the Key words: period of behavioral estrus until the last. There is no reduction in paracopulatory representative design, behaviors and no increase in rejections towards the end of estrus. Female seminatural paracopulatory behavior and receptivity change in a most abrupt way at both environment, sexual initiation and termination of behavioral estrus. It appears that, in the seminatural behavior, social environment, males copulate in bouts, and males do not pursue the females unless behavior, rat. they are fully receptive. Non-sexual, social behavior including affiliative and nonaffiliative interaction among rats is rather unrelated to sexual activities in both sex. RESUMEN Cuando una observación prolongada de grupos de ratas en ambientes seminaturales es usada como procedimiento de evaluación, diferentes patrones conductuales se muestran en comparación con lo que se observa con una pareja en una jaula pequeña. Machos y hembras copulan simultáneamente, muestran promiscuidad y un patrón aleatorio de copulación. Las hembras permanecen Palabras clave: diseño completamente receptivas desde su primera lordosis desplegada en el periodo de representativo, comportamiento de celo hasta el último. No hay una reducción de comportamientos ambiente seminatural, para-copulatorios y no hay incremento en el rechazo hacia el final del celo. Las conducta sexual, conductas para-copulatorias en hembras y la receptividad cambian de la manera conducta social y rata. más abrupta tanto al iniciarse como al terminarse la conducta de celo. Al parecer, en un ambiente seminatural, los machos copulan en peleas y no persiguen a las hembras a menos que ellas estén totalmente receptivas. Conductas sociales no sexuales, incluidas las interacciones afiliativas y no afiliativas entre ratas, no están relacionadas con actividades sexuales en ambos sexos. *Corresponding author: Xi Chu, Department of Psychology, University of Tromsø, Huginbakken 32, 9037 Tromsø, Norway. Fax: +47 77 64 52 91. Tlf: +47 77 64 92 13. Email address: [email protected] * ISSN printed 2011-2084 ISSN electronic 2011-2079 DOI: 10.21500/20112084.2339 C or re 76 sp on di ng R E V I E W INTERNATIONAL JOURNAL OF PSYCHOLOGICAL RESEARCH Sociosexual Interactions in Rats 1. INTRODUCTION observed. Basing notions of function, or of adaptive value, on data from an entirely artificial context is In most laboratory studies of animal behavior, extremely risky. we do not want to limit our conclusions to the specific A representative design is particularly individuals observed. Rather we wish to generalize our important when behavior is at the forefront. In studies findings to the population from which our experimental of the neurobiological mechanisms controlling a subjects were drawn. Likewise, we would often like to behavior pattern, for example the lordosis posture in the generalize our results to situations different from the female rodent or the display of paracopulatory specific procedure employed in the laboratory. These behavior, the specific procedure is probably basic notions apply to all fields of behavioral inquiry, but inconsequential. Silencing of the estrogen receptor α in we will focus on the field of rodent sexual behavior. the ventromedial nucleus of the hypothalamus will Thus, if we happened to study the structure of strongly reduce these behaviors both in a standard copulatory behavior in ten opposite-sex pairs of rats, we copulation test (Spiteri et al., 2010) and in a seminatural would like to believe that the structure determined in our environment (Snoeren et al., 2015), just to mention an pairs would apply also to other pairs of rats. We assume example. that this is the case as long as we have a random The concept of representative design is sample of rats. equivalent to what frequently is called external validity. A different question is whether the structure of Sometimes the term ecological validity is used instead. copulatory behavior in our pairs, observed for a short This, however, is most unfortunate since ecological time in a standard observation cage, would be similar if validity within the Brunswikian framework refers to the we instead observed them for a long time in a large, predictive reliability of a stimulus, and not to the complex environment. This we cannot know until we generalizability of data from a specific experimental have performed such observations. We could also ask procedure (Brunswik & Kamiya, 1953). Regardless of ourselves whether the structure of copulatory this, we will begin with an overview of some of the non- interactions observed in opposite-sex pairs would be representative designs used in studies of sociosexual similar to that observed when several males had the behaviors in rats. Then we will outline some opportunity to copulate with the same female, or when observations on the sociosexual behavior in a several females copulated with the same male, or when seminatural environment, incorporating the basic several males and several females copulated with elements of rats’ natural habitat. We will also highlight whomever they wished. Again, we would need to several of the differences between our data and some perform all these observations in order to determine if notions derived from studies in non-representative behavioral structures indeed are generalizable from procedures. one context to another. Many years ago, it was suggested that in order 2. RATS’ NATURAL HABITAT: PHYSICAL AND to generalize research findings to all possible contexts SOCIAL ASPECTS we need to employ a representative design (Brunswik, 1955). In parallel to the need of a representative sample Rats are as cosmopolitan as humans. Their of individuals from the population we wish to generalize habitat range from the skyscrapers on Manhattan to the to, a representative design means a random sample of garbage dumps in Calcutta, and from the research all the possible contexts we wish to generalize to. This stations in the Antarctic to the tropical rain forests of the is certainly quite impractical, particularly when applied Amazon. It is, consequently, impossible to make a to animal behavior, and when we wish to generalize to specific description of rats’ natural, physical habitat. It contexts outside the laboratory, for example to could probably be maintained that any setup includes conditions in the wild. Nevertheless, the Brunswikian some of the physical elements of rats’ natural habitat, spirit has been applied to studies of animal behavior and that there is none that can include them all. (Petrinovich, 1979; Petrinovich & Patterson, 1980). An There seems to be far less variability in the approximation to a representative design in animal social aspects of rats’ natural habitat. Wild rats live in behavior studies can be achieved by including as many groups, and occupy a rather extensive area for their elements as possible of the animals’ natural habitat in daily activities and share elaborate burrows with the laboratory setting. This would at least make it tunnels and chambers (Calhoun, 1962a). A typical possible to accurately describe complex behavior organization of a group of rats consists of several patterns and formulate hypotheses concerning the females, a small number of males, and offspring functional importance of the behavioral structures (McClintock, 1987). Studies involving wild rats are Chu and Ågmo (2016) int.j.psychol.res. 9 (Special Issue) PP. 76 - 95 77 R E S E A R C H INTERNATIONAL JOURNAL OF PSYCHOLOGICAL RESEARCH Sociosexual Interactions in Rats usually conducted in a field with a native rat pen. Their 3. EXAMPLES OF PROCEDURES COMMONLY sociosexual interaction has been described earlier by USED IN THE LABORATORY Calhoun (1962a). Approximately one day prior to a wild female rat enters behavioral estrus, she drags her 3.1 Standard copulation cage anogenital region over the soil around trees, bushes, The shape and size of the enclosure used for and at both sides of a burrow to mark her scent. Shortly studying sexual behavior is varied, but it is generally after, male rats notice the female scent and they mark rather small, e.g. a rectangular steel cage with a their own scent as well. The female rat wanders beyond dimension of 40 × 60 cm was used by Ågmo (1997), the limits of her normal home range and actively search and another cage of 50 × 80 cm was used by males. No copulatory behavior is observed before she Madlafousek & Hliňák (1977). This setup is commonly is fully receptive, but she copulates with multiple males used for studying social and sexual interactions during the entire period of estrus. As a consequence, between pairs of opposite sex individuals (Figure 1), many of the males involving in this group sex and it is suitable to test for behaviors in both sexually successfully copulate with the estrous female naïve and experienced animals. (Robitaille & Bouvet, 1976). In fact, multiple paternity appears to be common in wild rat populations (Miller, Russell, MacInnes, Abdelkrim, and Fewster, 2010). Figure 1. Photograph of a standard copulation cage. Compared with wild rats’ living conditions, receptive females than in that of a single female. The observing the behavioral patterns of a pair of rats in this copulatory acts of the males were distributed among kind of cage cannot be considered to be an externally multiple females but not all females received valid procedure.