Domestication in the silver fox (Vulpes fulvus Desm): Changes in physiological boundaries of the sensitive period of primary socialization

The physiological boundaries of the sensitive period of primary socialization were studied in the silver fox (Vulpes fulvus Desm). A total of 273 farm-bred foxes from 59 litters were observed from 1976 to 1978; pups were produced by vixens from two populations, one selected for domesticated behaviour and the other unselected. Results indicate that the age when the eyes are fully open, when the response to sound first appears and when exploratory behaviour is first shown in strange surroundings is 3 weeks, on average. The age when the socialization period starts appears to be 20–25 days old. The optimum period of the formation of primary social bonds appears to be 30–35 days, when maximum exploration in a novel situation is shown. The 40–45 days period appears to be the upper boundary of primary socialization in unselected foxes because pups show fear in response to novel stimuli, which prevents exploration. In pups from the population of domesticated foxes, the sensitive period of socialization is prolonged to over 60–65 days old.     

Genetics of the W locus in foxes and expression of its lethal effects.

The Georgian white mutation for coat color in foxes is inherited as a partially dominant character. It is allelic to the previously observed white-faced and platinum mutations. It was established that large litter size in Georgian white females and long daylight during pregnancy promote embryonic viability in homozygotes for this mutation. As a result, in offspring segregation patterns for coat color the proportion of homozygotes increases and that of heterozygotes decreases. It is suggested that a competitive relationship between embryos with different genotypes is established as early as at the preimplantation stage.     

Behavioral and physiological characteristics of nonagouti mutation in gray rats during selection for aggressiveness

The goal of this work was to find out to which degree the black coat color mutation nonagouti that appears in wild Norway rat in the course of breeding for the maintenance and enhancement of aggressiveness towards a human affects selected and other behavioral traits as well as stress reactivity and brain neurochemistry. Nonagouti rats displayed increased emotionality in the open-field and forced-swimming tests as compared to agouti animals, whereas there were no differences in anxiety estimated in the elevated plus-maze. Neither were there any differences in glucocorticoid reactions to a combined stressful procedure such as forced swimming. The dopamine content in the frontal cortex and striatum and noradrenaline content in the frontal cortex were increased in black rats as compared to gray rats. The result suggest that the nonagouti mutation in gray aggressive rats enhances the effects of selection for aggressiveness on some behavioral traits and brain catecholamine level.     

Kind granddaughters of angry grandmothers: The effect of domestication on vocalization in cross-bred silver foxes

The genetic basis of the effects of domestication has previously been examined in relation to morphological, physiological and behavioural traits, but not for vocalizations. According to Belyaev [Belyaev, D.K., 1979. Destabilizing selection as a factor in domestication. J. Hered. 70, 301-308], directional selection for tame behaviour toward humans resulted in domestication. This hypothesis has been confirmed experimentally on the farm-bred silver fox Vulpes vulpes population that has undergone 45 years of artificial selection for tameness and 35 years of selection for aggressiveness. These foxes, with their precisely known attitudes toward people, provide a means of examining vocal indicators of tameness and aggressiveness to establish the genetic basis for vocal production in canids. We examined vocalizations toward people in foxes selected for tameness and aggressiveness compared to those of three kinds of crosses: Hybrids (Tame × Aggressive), A-Backcrosses (Aggressive × Hybrid) and T-Backcrosses (Tame × Hybrid). We report the effects of selection for tameness on usage and structure of different vocalizations and suggest that vocal indicators for tameness and aggressiveness toward people are discrete phenotypic traits in silver foxes.     

Maternal methyl supplements affect the phenotypic variation of the <Emphasis Type="Italic">agouti</Emphasis> gene in the offspring of rats with different behavioral types

The effects of selection of agouti rats (with genotype AAHH) on the tame and aggressive behavior and dietary methyl given to females from the eighth day of pregnancy to the fifth day after the birth of the offspring on the intensity of the agouti coat color in the offspring have been studied. The morphometric parameters of hair determining the darkness of the agouti color (the total length of guard hairs, the lengths of their eumelanin end and pheomelanin band, the ratio between the lengths of the eumelanin and pheomelanin portions of the hair, the total length of the awn hairs, and the relative length of their widened “lanceolate” upper end) have been compared. It has been found that selection of agouti rats for aggressive behavior is accompanied by darkening of the coat color compared to tame rats due to an increase in the ratio of the length of the black eumelanin end of the guard hairs to the length of the yellow pheomelanin band. Methyl-containing additives to the diet of females affect the intensity of the agouti coat color in the offsprings with both types of behavior, but to different extents. Aggressive offspring is more sensitive to the mother’s methyl-containing diet: the percentage of animals that are darker than control rats is higher among aggressive animals than among tame ones due to a greater increase in the ratio between dark and light portions of hairs. The possible mechanisms of differences in the phenotypic modifications of coat color in control and experimental agouti rats with different types of behavior are discussed.     

The gradual vocal responses to human-provoked discomfort in farmed silver foxes

Vocal indicators of welfare have proven their use for many farmed and zoo animals and may be applied to farmed silver foxes as these animals display high vocal activity toward humans. Farmed silver foxes were selected mainly for fur, size, and litter sizes, but not for attitudes to people, so they are fearful of humans and have short-term welfare problems in their proximity. With a human approach test, we designed here the steady increase and decrease of fox–human distance and registered vocal responses of 25 farmed silver foxes. We analyzed the features of vocalizations produced by the foxes at different fox–human distances, assuming that changes in vocal responses reflect the degrees of human-related discomfort. For revealing the discomfort-related vocal traits in farmed silver foxes, we proposed and tested the algorithm of “joint calls,” equally applicable for analysis of all calls independently on their structure, either tonal or noisy. We discuss that the increase in proportion of time spent vocalizing and the shift of call energy toward higher frequencies may be integral vocal characteristics of short-term welfare problems in farmed silver foxes and probably in other captive mammals.     

Vocalization toward conspecifics in silver foxes (Vulpes vulpes) selected for tame or aggressive behavior toward humans

We examined the production of different vocalizations in three strains of silver fox (unselected, aggressive, and tame) attending three kinds of behavior (aggressive, affiliative, and neutral) in response to their same-strain conspecifics. This is a follow-up to previous experiments which demonstrated that in the presence of humans, tame foxes produced cackles and pants but never coughed or snorted, whilst aggressive foxes produced coughs and snorts but never cackled or panted. Thus, cackle/pant and cough/snort were indicative of the tame and aggressive fox strains respectively toward humans. Wild-type unselected foxes produced cough and snort toward humans similarly to aggressive foxes. Here, we found that vocal responses to conspecifics were similar in tame, aggressive and unselected fox strains. Both cackle/pant and cough/snort occurred in foxes of all strains. The difference in the use of cackle/pant and cough/snort among these strains toward humans and toward conspecifics suggest that silver foxes do not perceive humans as their conspecifics. We speculate that these vocalizations are produced in response to a triggering internal state, affiliative or aggressive, that is suppressed by default in these fox strains toward humans as a result of their strict selection for tame or aggressive behavior, whilst still remaining flexible toward conspecifics.