Experiments were carried out with Mongolian gerbils (Meriones unguiculatus) to assess whether a socially mediated acquisition of diet selection exists in this species. Results showed that a gerbil was influenced in its diet choices by information extracted during a brief period of interaction with a familiar conspecific that had recently eaten a novel food. Data revealed that the acquisition of a food preference from a conspecific depends on the existence of a social bond between the interacting gerbils. Either genetic relatedness (being brother or sister raised in different litters) or familiarity (being bred in the same litter or being member of a reproductive pair) is necessary for the transfer of information. Unfamiliar and unrelated observer gerbils did not selectively choose their demonstrator's food.
The preputial glands are androgen-dependent and apparently used in pheromonal signalling in rats and mice. With light and electron microscopy (Lhl and EM) these glands from socially dominant and socially subordinated members of pairs of male laboratory 'TO' strain mice were compared with those from individually-housed counterparts. The glands of both dominant and individually hwsed animals were \\,ell-developed and actively sccreting having acini at different stages of maturation with numerous normal cytoplasmic organelles and healthy oval-shaped nuclei. The glands from subordinated animals were less developed, had fewer, smaller lipid droplets and fewer cellular organelles; the nuclei were shrunken and lobulated; and the cells often contained autophagic vacuoles, which are also found in castrated mice. The data suggest that the reduced gonadal function typical of subordinated niice compared with the other two categories exprcsses itself in preputial structure and function. The aggressiveness induced by 'isolation' cannot be attributed simply to the detrimental effects of 'social deprivation', for this behaviour is also a feature of social dominants. ACKNO\VLEDGEXIENTS The generous funding of the Iraqi Gorernment and the Consiglio Nazionale delle Ricerche (CT 81.257.04.115.3237) is gratefully acknowledged.
In recent experiments in which the social influences on feeding in Mongolian gerbils were investigated, observer gerbils acquired food preferences from conspecific demonstrators only if the demonstrators and observers were either related or familiar. Even then, the effects of demonstrator gerbils on observers' food choices lasted less than 24 h. In similar experiments with Norway rats, the familiarity/relatedness of demonstrators and observers had little effect on social learning, and the demonstrators' influence on observers' food choices lasted many days. We examined the causes of these differences and found that, after observer gerbils interacted with either unfamiliar or familiar conspecific demonstrators that had been fed using procedures typically used to feed demonstrator rats, they showed long-lasting social learning about foods, whereas observer rats interacting with conspecific demonstrators that had been fed as demonstrator gerbils normally are fed showed effects of familiarity/relatedness to demonstrators on their social learning about foods. Procedural differences, rather than species differences, seem to be responsible for reported inconsistencies in social learning about foods by rats and gerbils.
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