Association between temperament related traits and single nucleotide polymorphisms in the serotonin and oxytocin systems in Merino sheep

Abstract

Background: Animal temperament is de ned as the consistent behavioural and physiological differences that are seen between individuals in response to the same stressor. Neurotransmitter systems, like serotonin and oxytocin in the central nervous system, underlie the variation in temperament in humans. The variations like single nucleotide polymorphisms (SNPs) in the genes for tryptophan 5-hydroxylase (TPH2), the serotonin transporter (SLC6A4), the serotonin receptor (HTR2A), or the oxytocin receptor (OXTR) are associated with the behavior phenotypes in human. Thus, the objective of this study was to identify SNPs in TPH2, SLC6A4, HTR2A and OXTR and to test if those variations predict the temperament of Merino sheep. Results: Using ewes from the UWA temperament ock, that has been selected on emotional reactivity for more than 20 generations, eight SNPs (rs107856757, rs107856818, rs107856856 and rs107857156 in TPH2, rs20917091 in SLC6A4, rs17196799 and rs17193181 in HTR2A, and rs17664565 in OXTR) were found to be distributed differently between calm and nervous sheep. These eight SNPs were then genotyped in 260 sheep from a non-selected ock that has never been selected on emotion reactivity, followed by the estimation of the behavioural traits of those 260 sheep using an arena test and an isolation box test. We found that several SNPs in TPH2 (rs107856757, rs107856818, rs107856856 and rs107857156) were in strong linkage disequilibrium, and all were associated with behavioural phenotype in the non-selected sheep. Similarly, rs17196799 in HTR2A was also associated with the behavioural phenotype. Conclusions: We thus conclude that, rs107856856 and rs17196799 could be used as gene markers for the temperament of Merino sheep, with allele C of rs107856856 and allele A of rs17196799 being associated with calm temperament. Background Animal temperament is often referred to as personality or a behavioural syndrome [1]. More speci cally, animal temperament is the consistent behavioural and physiological differences that are observed between individuals in response to an eliciting event [2]. The variability in temperament is often described along dipoles such as shy to bold, sociable to aggressive, exploring to avoiding, or behavioural activity or inactivity [2]. That individual variability is thought to re ect the individual's perception of the surrounding situation. Non-human animals, in a similar way as humans, evaluate a situation based on particular characteristics of the eliciting event such as its suddenness, familiarity, pleasantness, controllability, and predictability, and how the event accords or deviates from their expectations [3]. The perception of a situation leads to an emotional state that is experienced by the individual. The emotion then elicits physiological and behavioural responses, and those responses have been used to qualify the temperament of individual animals [3, 4]. In sheep, the phenotype and the genetic heritability of temperament traits [5-7], have been assessed using behavioural tests. Tempera...

Identification of Candidate Genes and Pathways Linked to the Temperament Trait in Sheep

“…In addition, this QTL is close to the gene encoding the oxytocin receptor (OXTR) which is associated with social (Sala et al, 2013;Damián et al, 2021) and maternal behaviors (Champagne et al, 2001;Feldman et al, 2012). An study support this revealing a SNP rs17664565 in chromosome 19 maps within the gene OXTR (Ding et al, 2020).…”

“…In this same study, the EEF1A1 gene (LOC101110773) was also described as part of a set of genes of biological interest that contributes to elucidating the genetic basis of the Merino phenotype. Two SNP have been reported for temperament trait (Ding et al, 2020) in Merino sheep and the associated gene is 5hydroxytryptamina receptor 2A (HTR2A) in chromosome 10 (rs17196799, rs7193181) (Ding et al, 2020). Half of the SNP of chromosome 10 that contribute to the genetic variance of temperament were associated with molecular functions of energetic activity.…”

“…Since 1990, the University of Western Australia (UWA) has selected Merino sheep establishing lines of calm and nervous sheep (Qiu et al 2017). In these temperament flock, eigth SNP were found to be distributed differently between calm and nervous sheep (Ding et al 2020), associated with the serotonin, oxitocin and dopamine systems as well as the stress response axis according to their temperament (Qiu et al 2016;Ding et al 2020). In a recent review, Alvarenga et al (2021) repored 148 genomic regions associated with 22 behavioral traits (Poissant et al, 2013;Hazard et al, 2014;Pant et al, 2016;Qiu et al, 2016) and 15 candidate genes in sheep.…”

Behavioural and physiological responses to stressors in sheep with temperament classified by genotype or phenotype

“…The data presented above strongly suggest that SNP rs107856856 in the TPH2 gene in Merino sheep could affect the physiological response to a stressor, including changes in body temperature, cortisol, prolactin, DHEA, and BDNF, in addition to the behavioural responses that have already been studied 10 . In the present study, we aimed to test whether there were differences in the physiological responses to stress between sheep that were classified as calm or nervous in two ways, (1) genetically and (2) phenotypically on their behavioural responses to specific tests of temperament.…”

“…In cattle, many single nucleotide polymorphisms (SNPs) and candidate genes have been associated with temperament where temperament has been categorised by the behavioural responses of the animals to the approach of a human, contact with a human, handling by a human, or social isolation 2 – 7 . Similarly, in young Merino sheep, several genetic variants have been associated with the behavioural response of the animals to human contact and/or social isolation around weaning, including SNPs located in genes that encode for dopamine receptor 2, steroid 17α-hydroxylase/17,20-lyase, the serotonin receptor, and tryptophan hydroxylase-2 (TPH2) 8 – 10 . Nearly all these studies on the genetic basis of temperament have focused on the association between SNPs and behaviour.…”