Missing history of a modern domesticate: Historical demographics and genetic diversity in farm-bred red fox populations.

The first record of captive-bred red foxes (Vulpes vulpes) dates to 1896 when a breeding enterprise emerged in the provinces of Atlantic Canada. Because its domestication happened during recent history, the red fox offers a unique opportunity to examine the genetic diversity of an emerging domesticated species in the context of documented historical and economic influences. In particular, the historical record suggests that North American and Eurasian farm-bred populations likely experienced different demographic trajectories. Here, we focus on the likely impacts of founder effects and genetic drift given historical trends in fox farming on North American and Eurasian farms. A total of 15 mitochondrial haplotypes were identified in 369 foxes from 10 farm populations that we genotyped (n = 161) or that were previously published. All haplotypes are endemic to North America. Although most haplotypes were consistent with eastern Canadian ancestry, a small number of foxes carried haplotypes typically found in Alaska and other regions of western North America. The presence of these haplotypes supports historical reports of wild foxes outside of Atlantic Canada being introduced into the breeding stock. These putative Alaskan and Western haplotypes were more frequently identified in Eurasian farms compared to North American farms, consistent with historical documentation suggesting that Eurasian economic and breeding practices were likely to maintain low-frequency haplotypes more effectively than in North America. Contextualizing inter- vs. intra-farm genetic diversity alongside the historical record is critical to understanding the origins of this emerging domesticate and the relationships between wild and farm-bred fox populations.

Defining hippocampal area CA2 in the fox (Vulpes vulpes) brain.

Since 1959, the Russian Farm-Fox study has bred foxes to be either tame or, more recently, aggressive, and scientists have used them to gain insight into the brain structures associated with these behavioral features. In mice, hippocampal area CA2 has emerged as one of the essential regulators of social aggression, and so to eventually determine whether we could identify differences in CA2 between tame and aggressive foxes, we first sought to identify CA2 in foxes (Vulpes vulpes). As no clearly defined area of CA2 has been described in species such as cats, dogs, or pigs, it was not at all clear whether CA2 could be identified in foxes. In this study, we cut sections of temporal lobes from male and female red foxes, perpendicular to the long axis of the hippocampus, and stained them with markers of CA2 pyramidal cells commonly used in tissue from rats and mice. We observed that antibodies against Purkinje cell protein 4 best stained the pyramidal cells in the area spanning the end of the mossy fibers and the beginning of the pyramidal cells lacking mossy fibers, resembling the pattern seen in rats and mice. Our findings indicate that foxes do have a "molecularly defined" CA2, and further, they suggest that other carnivores like dogs and cats might as well. With this being the case, these foxes could be useful in future studies looking at CA2 as it relates to aggression.

Genomic responses to selection for tame/aggressive behaviors in the silver fox (Vulpes vulpes).

Animal domestication efforts have led to a shared spectrum of striking behavioral and morphological changes. To recapitulate this process, silver foxes have been selectively bred for tame and aggressive behaviors for more than 50 generations at the Institute for Cytology and Genetics in Novosibirsk, Russia. To understand the genetic basis and molecular mechanisms underlying the phenotypic changes, we profiled gene expression levels and coding SNP allele frequencies in two brain tissue specimens from 12 aggressive foxes and 12 tame foxes. Expression analysis revealed 146 genes in the prefrontal cortex and 33 genes in the basal forebrain that were differentially expressed, with a 5% false discovery rate (FDR). These candidates include genes in key pathways known to be critical to neurologic processing, including the serotonin and glutamate receptor pathways. In addition, 295 of the 31,000 exonic SNPs show significant allele frequency differences between the tame and aggressive populations (1% FDR), including genes with a role in neural crest cell fate determination.

Neuropeptides as facilitators of domestication.

Animal domestication was an important stage in the human history, which coincided with or probably even promoted the advent of a turning point at which part of the humankind switched from hunting and gathering to husbandry. The leading factor in evolutionary changes at the dawn of domestication was probably selection for behavior towards humans: first natural (as the animals were habituating to a new ecological niche close to humans), then nonconscious, artificial. Selection was supposed to work on the systems that regulate behavior by reducing stress response and aggression and by inducing an emotionally positive response to humans. A possible role of the neuropeptides adrenocorticotropic hormone (ACTH), oxytocin (ОТ), arginine vasopressin (AVP), and their receptors is in the reduction in stress response and in the shaping of domestic behavior. Effects of oxytocin on the behavior of domestic animals have been actively explored in the last 10 years, with special focus on the dog. The results obtained so far suggest that this neuropeptide is substantially important for human-canine interactions, together with sex, amount of aggression experienced, and other factors. The study of AVP demonstrated its importance in aggression in domestic animals. This work lends support to the hypothesis that a substantial factor in the shaping of domestic behavior and in the reduction in stress-response might be selection for an enhanced activity of the central OT system and a reduced activity of the central AVP system, which have effects on ACTH and social behavior.

Correction to: Neuropeptides as facilitators of domestication.

The publisher regret that they failed to include the Table 1 before the publication of the original version of this article. The table is presented in this article.

Selection for tameness, a key behavioral trait of domestication, increases adult hippocampal neurogenesis in foxes.

Work on laboratory and wild rodents suggests that domestication may impact on the extent of adult hippocampal neurogenesis and its responsiveness to regulatory factors. There is, however, no model of laboratory rodents and their nondomesticated conspecifics that would allow a controlled comparison of the effect of domestication. Here, we present a controlled within-species comparison of adult hippocampal neurogenesis in farm-bred foxes (Vulpes vulpes) that differ in their genetically determined degree of tameness. Quantitative comparisons of cell proliferation (Ki67) and differentiating cells of neuronal lineage (doublecortin, DCX) in the hippocampus of foxes were performed as a proxy for neurogenesis. Higher neurogenesis was observed in tameness-selected foxes, notably in an extended subgranular zone of the middle and temporal compartments of the hippocampus. Increased neurogenesis is negatively associated with aggressive behavior. Across all animals, strong septotemporal gradients were found, with higher numbers of proliferating cells and young neurons relative to resident granule cells in the temporal than in the septal hippocampus. The opposite gradient was found for the ratio of DCX/Ki67- positive cells. When tameness-selected and unselected foxes are compared with rodents and primates, proliferation is similar, while the number of young neurons is higher. The difference may be mediated by an extended period of differentiation or higher rate of survival. On the background of this species-specific neurogenic pattern, selection of foxes for a single behavioral trait key to domestication, i.e., genetic tameness, is accompanied by global and region-specific increases in neurogenesis.

Fear, love, and the origins of canid domestication: An oxytocin hypothesis.

The process of dog domestication likely involved at least two functional stages. The initial stage occurred when subpopulations of wolves became synanthropes, benefiting from life nearby or in human environments. The second phase was characterized by the evolution of novel forms of interspecific cooperation and social relationships between humans and dogs. Here, we discuss possible roles of the oxytocin system across these functional stages of domestication. We hypothesize that in early domestication, oxytocin played important roles in attenuating fear and stress associated with human contact. In later domestication, we hypothesize that oxytocin's most critical functions were those associated with affiliative social behavior, social engagement, and cooperation with humans. We outline possible neurobiological changes associated with these processes and present a Siberian fox model of canid domestication in which these predictions can be tested. Lastly, we identify limitations of current studies on the neuroendocrinology of domestication and discuss challenges and opportunities for future research.

Aggressive behavior and stress response after oxytocin administration in male Norway rats selected for different attitudes to humans.

Oxytocin (OXT) is known to influence on social behaviors, including intermale aggression and hypothalamic-pituitary-adrenal (HPA) axis activity. However, there are no data on the effects of oxytocin on intermale aggression and HPA axis activity in rats selected for elimination and enhancement of aggressiveness towards humans. The aim of this study is to elucidate the role of oxytocin in expression of aggressive behavior and stress response in Norway rats selected for elimination (tame) and enhancement (aggressive) of an aggressive-defensive reaction to humans. Oxytocin was administered to males via nasal applications once or for 5 days (daily). Resident-intruder test showed that in aggressive males, single oxytocin administration caused an increase in the latent period of aggressive interactions and a decrease in the percentage of direct aggression time (not including the time of lateral threat postures) as compared to the control aggressive rats administered with saline. After a 5-day oxytocin administration, aggressive animals demonstrated shorter time of aggressive interactions compared to the control rats. Resident-intruder test revealed no significant changes in behavior of tame rats after single oxytocin administration, while multiple administration caused an increase in aggressive behavior in tame rats. Oxytocin applications caused an elevation of corticosterone level after restriction in aggressive males, but did not affect expression of Crh, Crh1 and Crhr2 genes in hypothalamus in either tame or aggressive rats. The data obtained indicate significant role of oxytocinergic system in the behavior formed in the process of selection by reaction to humans.

Anterior Pituitary Transcriptome Suggests Differences in ACTH Release in Tame and Aggressive Foxes.

Domesticated species exhibit a suite of behavioral, endocrinological, and morphological changes referred to as "domestication syndrome." These changes may include a reduction in reactivity of the hypothalamic-pituitary-adrenal (HPA) axis and specifically reduced adrenocorticotropic hormone release from the anterior pituitary. To investigate the biological mechanisms targeted during domestication, we investigated gene expression in the pituitaries of experimentally domesticated foxes (Vulpes vulpes). RNA was sequenced from the anterior pituitary of six foxes selectively bred for tameness ("tame foxes") and six foxes selectively bred for aggression ("aggressive foxes"). Expression, splicing, and network differences identified between the two lines indicated the importance of genes related to regulation of exocytosis, specifically mediated by cAMP, organization of pseudopodia, and cell motility. These findings provide new insights into biological mechanisms that may have been targeted when these lines of foxes were selected for behavior and suggest new directions for research into HPA axis regulation and the biological underpinnings of domestication.

Red fox genome assembly identifies genomic regions associated with tame and aggressive behaviours.

Strains of red fox (Vulpes vulpes) with markedly different behavioural phenotypes have been developed in the famous long-term selective breeding programme known as the Russian farm-fox experiment. Here we sequenced and assembled the red fox genome and re-sequenced a subset of foxes from the tame, aggressive and conventional farm-bred populations to identify genomic regions associated with the response to selection for behaviour. Analysis of the re-sequenced genomes identified 103 regions with either significantly decreased heterozygosity in one of the three populations or increased divergence between the populations. A strong positional candidate gene for tame behaviour was highlighted: SorCS1, which encodes the main trafficking protein for AMPA glutamate receptors and neurexins and suggests a role for synaptic plasticity in fox domestication. Other regions identified as likely to have been under selection in foxes include genes implicated in human neurological disorders, mouse behaviour and dog domestication. The fox represents a powerful model for the genetic analysis of affiliative and aggressive behaviours that can benefit genetic studies of behaviour in dogs and other mammals, including humans.

Author Correction: Red fox genome assembly identifies genomic regions associated with tame and aggressive behaviours.

In the version of this Article originally published, there were some errors in the affiliations: Stephen J. O'Brien's affiliations were incorrectly listed as 8,9; they should have been 7,9. Affiliation 3 was incorrectly named the Institute of Cytology and Genetics of the Russian Academy of Sciences; it should have read Institute of Cytology and Genetics of the Siberian Branch of the Russian Academy of Sciences. Affiliation 4 was incorrectly named the Institute of Molecular and Cell Biology of the Russian Academy of Sciences; it should have read Institute of Molecular and Cellular Biology of the Siberian Branch of the Russian Academy of Sciences. These have now been corrected.

Conserved methylation of the glucocorticoid receptor gene exon 1(7) promoter in rats subjected to a maternal methyl-supplemented diet.

It is well known that the early life experiences affect stress responses and other physiological and behavioral traits in adulthood. Both rat and human studies have shown that early postnatal effects are associated with methylation of the hippocampal glucocorticoid receptor gene exon 1(7) (rat) and 1-F (human) promoters. Methylation of these sites is also seen following methionine administration in adult rats. However, it remains unclear whether similar alterations in DNA methylation profiles can result from prenatal influences. To address this question, we fed pregnant rats a methyl-supplemented diet that resulted in alteration of the stress response. However, methylation analysis revealed no effect of methyl supplements on methylation patterns of the glucocorticoid receptor gene exon 1(7) promoter in offspring. These results suggest that the pre- and postnatal effects of methyl supplementation have different mechanisms.