Population density, mouse genotype, and endocrine function in behavior.

Abstract

In comparison with behavior in isolation, 6 strains of inbred mice, C57BL, BALB/c, DBA/2, A, C3H/2, and Rill, respond to increases in population size of 10 and 20 with heightened behavioral reactivity within the population confines and during tests on 2 different measures of exploration. Adrenal and testis reactivity shows more individuality among strains; however, in most cases within-group variance of adrenal weight is lower at higher densities. Genotype sets the limits of response for both behavioral and endocrine measures, although these appear to be regulated independently.

Social isolation in young rats: Effects of cage size on open-field behavior

“…Bell, Miller, Ordy, & Rolston (1971) distinguish between studies using a crowded-group paradigm (CG) in which different size groups are placed in a cage of constant size and those using a density-group paradigm (DG) in which cage floor space is proportional to group size. Studies using CG have found isolated mice to be more active (Essman, 1966) and to have heavier adrenals than aggregated animals (Thiessen, 1964), while those using DG have found the opposite (Bailey, 1966;Christian, 1955). Even though many such investigations are not dit·ectly comparable for reason~ mentioned earlier (Essman, 1966), it is nevertheless true that different cage sizes have often been used for isolated animals when comparing them with animals from both DG and CG groups of varying numbers.…”

Persistent genotypic differences in mouse activity under unusually varied circumstances

“…, 1965 , Vo l. 3 in some ca se s , with separate breeding histories extending over 35 yr. Experiential and experimental variations are just as great. Some investigators applied early noxious stimulation to their animals (Lindzey etal,1960(Lindzey etal, , 1963; others used alcohol fuming immediately prior to te sting (Schlesinger et al, 1962); and one altered population density by 20-fold (Thiessen, 1964). Moreover, the investigators worked on the East and West coasts and the Midwest of the United States over a period of 11 yr.…”

Behavioral changes due to overpopulation in mice

“…Another group that can be eliminated in this quest for universality are those experimen ters who artificially overpopulated their groups and did not allow natural overpopulation (Christian & Lemunyan, 1958;Thiessen, 1964).…”

“…Deevey (1960) found that overpopulation disturbed the entire pituitary-adrenal system and di verted or suppressed the hormones governing sexuality and parental care. Thiessen (1964) found that gonadotropic activity was antagonized HI and reproductive capacities failed when a population becomes over-' 'Populated. He also found that in super~saturated populations, as was Calhoun's, the intensity of thesE: effects was maximized--social CUIl flict was widespread, hormonal aberration greatest and mortality ex tensive.…”