Influence of environmental complexity and space on social interactions of mice (Mus musculus and Peromyscus leucopus).

Abstract

The effects of environmental space and complexity on social behavior were examined in three forms of mice: albino laboratory mice (Mus musculus), wild house mice (M. musculus), and wild white-footed mice (Peromyscus leucopus). Pairs of males or females of each form were introduced into circular arenas of 0.5-, 1.0-, or 2.0-m diameter containing 0, 8, or 16 internal barriers, and behavioral interactions were observed. Behavioral characteristics were assessed by multivariate cluster and principal components analyses. Differences between laboratory Mus and the two wild forms reflected the better sensory capabilities and greater reactivity of the wild mice. The wild forms were reactive at greater distances, they spent more time freezing and/or grooming, and their behavior was influenced by environmental complexity. The laboratory Mus exhibited reactions only at short distances. Both Mus forms were more aggressive than Peromyscus, and Mus males were more aggressive than females. Although the amount of space available influenced all three forms, effects differed. Laboratory Mus simply encountered each other less often in larger areas, whereas the wild forms actively used the space to avoid other individuals. Male Mus were more aggressive as space decreased; female Mus and Peromyscus showed no such change. Behaviors related to orienting toward other mice and moving away from them were more frequent in more open areas. Vision appeared to be the sensory modality used, although audition may have played a role. Social behavior occurs in an environmental context that may strongly influence the interactions among organisms. The effects of amount of available space and configuration of that space may vary, depending on the sensory communication patterns and social behavior patterns of animals. As communication signals travel through space, signal intensity decreases with distance. Also, elements within the space that add complexity (Berlyne, 1960) attenuate signals. Thus, the amount of space available as well as complexity can influence how easily animals contact or avoid each other, and which sensory modalities they use. Generally, when space is reduced, aggression increases (Colvin, 1973;Erickson, 1967; Myers, Hale, Mykytowycz, & Hughes, 1971; Southwick, 1967; Ulrich, 1966; Willis, 1966), but the effects may be more subtle (Vestal & Hellack, 1977). Increased complexity or cover also may be correlated with reduced agonistic interactions (Jenkins, 1961; Melchior, 1965; Warnock, 1965; Wilson, 1971, 1972), although complexity as an independent variable has