| 1. |
- Agnvall, Beatrix
(författare)
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Early domestication? : Phenotypic alterations of Red Junglefowl selected for divergent fear of humans
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Domestication is the process through which animals adapt to conditions provided by humans. The domesticated phenotype differs from wild ancestors in a number of traits relating to physiology, morphology and behaviour. One of the most striking differences is the animals’ fear response towards humans, and reduced fear of humans is assumed to have been an early prerequisite for the success of domestication. The early alterations seen in the domesticated phenotype may be traits developed as a correlated selection response due to tameness rather than selected upon one by one.This thesis summarizes a project where Red Junglefowl were selected for divergent fear of humans during six generations. In every generation, fear response to human was assessed in a standardized test and, according to fear score, the animals were bred for either high fear of humans (H) or low fear of humans (L). The animals were, above that of the standardized selection test, behaviourally phenotyped in different tests in each generation mainly focusing on fear, exploration and social behaviour. In addition to behaviour, the animals were phenotyped for body weight, egg weight, metabolism, feed intake, plumage condition, blood plasma corticosterone and peripheral serotonin. After culling, vital organs and brains were harvested and weighed.In paper I, we demonstrated that the selection trait has a significant genetic heritability and is genetically correlated with other behavioural responses associated with fearfulness and exploration. In paper II, we concluded that animals from the L strain had better plumage condition, higher weight, laid larger eggs and also generated larger offspring. Furthermore, when tested in a social dominance test with a limited resource, they received less and performed more aggression regardless of whether the restricted source was edible or not. In paper III, we revealed that animals from the L strain had higher basal metabolic rate as chicks, gained more weight in relation to feed intake and were bolder in a Novel Object test. Furthermore, the L males had higher plasma levels of peripheral serotonin, but the corticosterone after a restraint stress test did not differ. In paper IV and V, we concluded the project by comparing brain and organ weights as well as behaviour of the parental generation (P0) with the fifth selected generation (S5). The absolute brain weight as well as the weight specific brain weight were larger in the animals selected on H than in the L-animals. The relative weight of telencephalon was significantly higher in H whereas relative weight of cerebellum was significantly lower. Heart, liver, spleen and testes were all relatively heavier in H animals than in L. Interestingly, the behaviours assessed in P0 and S5 seemed to be rather resilient to the selection with only small differences in S5.To summarize, the selection on divergent tameness in Red Junglefowl has affected several phenotypic traits associated with the domesticated phenotype. The results of this project indicate that tameness in Red Junglefowl could be an underlying factor driving trait modifications towards the domesticated phenotype.
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| 2. |
- Bélteky, Johan
(författare)
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Chicken domestication : Effects of tameness on brain gene expression and DNA methylation
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Domestication greatly increases phenotypic variation in a short time span, with selection for a single phenotype and a plethora of associated phenotypic changes as an outcome of the process. The domestication process influences the underlying genomic architecture of a species, and the success and speed of the process is likely influenced by it. The main aims of my thesis was to study how domestication affects the brain of chickens: specifically changes in morphology, gene expression, and DNA methylation. Differences in gene expression and DNA methylation between White Leghorn and Red Junglefowl chickens were mapped, and inheritance of these patterns were quantified, indicating a faithful transmission of breed-specific epigenetic markers. Selection on the behavioral trait fearfulness, generated high and low fearful lines of Red Junglefowl. Both the parental population and the fifth selected generation were used for the analyses in this thesis. One experiment studied morphological changes in the brain and other vital organs, and found that relative total brain size increased in high fearful birds, as a consequence of an increase in cerebral hemisphere size in high fearful birds and not in low fearful birds. Also, the relative heart, liver, spleen and testis size increased in high fearful birds, indicating correlated morphological changes with selection for fearfulness. Two additional experiments examined differential gene expression in the hypothalamus and the anterior cerebral hemisphere. The hypothalamus differed in expression of genes with reproductive and immunological functions, whilst the cerebral hemisphere differed in expression of genes related to social behaviors and neurological functions especially those upregulated in low fearful birds. These results indicate the occurrence of tissue- and species-specific changes in gene expression as overlap with other domestication events were nearly nonexistent. A fourth experiment sought to associate the change in fear levels and gene expression differences with DNA methylation. Chromosomal regions with differential DNA methylation between high and low fearful birds were identified, and genes in these regions had annotated functions relevant to phenotypic differences between the selection lines. This thesis is the first to study the genetic alterations of domestication using the wild ancestor of an already domesticated species to repeat the domestication process selecting against fear of humans. The findings corroborate results from previous comparisons of wild and domestic animals, and further support the theory that rigorous selection for a behavioral trait can cause a cascade of genetic and epigenetic changes facilitating the domestication of a population.
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| 3. |
- Fallahshahroudi, Amir, 1981-
(författare)
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Domestication Effects on the Stress Response in Chickens : Genetics, Physiology, and Behaviour
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Animal domestication, the process where animals become adapted to living in proximity to humans, is associated with the alteration of multiple traits, including decreased fearfulness and stress response. With an estimated population of 50 billion, the domesticated chicken is the most populous avian species in the world. Hundreds of chicken breeds have been developed for meat and egg production, hobby or research purposes. Multidirectional selection and the relaxation of natural selection in captivity have created immense phenotypic diversity amongst domesticates in a relatively short evolutionary time. The extensive phenotypic diversity, existence of the wild ancestor, and feasibility of intercrossing various breeds makes the chicken a suitable model animal for deciphering genetic determinants of complex traits such as stress response. We used chicken domestication as a model to gain insights about the mechanisms that regulate stress response in an avian species. We studied behavioural and physiological stress response in the ancestral Red Junglefowl and one of its domesticated progenies, White Leghorn. An advanced intercross between the aforementioned breeds was later used to map genetic loci underlying modification of stress response. The general pattern of the stress response in chickens was comparable with that reported in mammals, however we identified distinctive differences in the stress modulatory pathways in chickens. We showed that changes in the expression levels of several stress modulatory genes in the brain, the pituitary and the adrenal glands underlie the observed modified stress response in domesticated chickens. Using quantitative trait loci (QTL) mapping, several QTL underlying stress induced corticosterone, aldosterone and baseline dehydroepiandrosterone (DHEA) levels were detected. As a next step, we combined QTL mapping with gene expression (eQTL) mapping and narrowed two QTL down to the putative causal genes, SERPINA10 and PDE1C. Both of these genes were differentially expressed in the adrenal glands of White Leghorn and the Red Junglefowl, had overlapping eQTL with hormonal QTL, and their expression levels in the adrenal glands were correlated with plasma levels of corticosterone and al-dosterone. These two genes thus serve as strong candidates for further functional investigation concerning modification of the stress response during domestication. This dissertation increase the knowledge about genetics and physiology of the stress response in an avian species and its modification during domestication. Our findings expand the basic knowledge about the stress response in chicken, which can potentially be used to improve welfare through appropriate genetic selection.
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| 4. |
- Foyer, Pernilla
(författare)
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Early Experience, Maternal Care and Behavioural Test Design : Effects on the Temperament of Military Working Dogs
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Domestication has resulted in animals with broad variations between as well as within breeds, which allows for the selection and breeding of animals for preferred traits. This selection has affected both the genotypes and phenotypes of animals. In dogs, it has allowed for breeding for different purposes, such as companionship or the performance of specific tasks, e.g., herding, hunting, searching and protecting. Each of these types of working dogs has specific traits that are, in part, controlled by genes; however, genes are not solely responsible for the variations in the traits of an individual. The environment also plays a role, which has been studied in rodents and primates in recent decades. For instance, it has been shown that the amount of maternal care that a rat receives as a pup affects its temperament later in life; the more maternal care, i.e., licking, grooming and arched-back nursing (LG-ABN), that a rat receives, the more stress resistant, less reactive and more explorative it will be as an adult. However, the question is whether this is also true for dogs, and the investigation of how temperament in dogs is affected by environmental factors early in life is the main objective of this thesis. Three of the studies presented in this thesis focused on investigating the general parameters, particularly maternal care, that influences offspring behaviour to contribute to the understanding of temperament development in military working dogs. One of these studies concentrated on the environmental factors that influence dogs early in life, and the results indicated that some factors, such as parity, litter size and birth season, affect temperament later in life. Another study investigated how females take care of their young, and the results demonstrated that females consistently vary in their maternal style during the first three weeks postpartum and that this variation affects the temperament of the offspring. The third study focused on factors in the home environment, and the results showed that dogs approved through the evaluative temperament test were significantly associated with being hyperactive or restless and having difficulty settling down in the home environment. However, those dogs were also left home alone for more hours in a day than non-approved dogs. To be able to operate functionally, a military working dog needs to possess certain traits, or a certain temperament, and a vital characteristic is the way it responds to and copes with stress. This was investigated during an evaluative temperament test used to select dogs suitable for further training. Surprisingly, the results showed that the dogs approved for further training had significantly higher levels of salivary cortisol both before and after the test compared with the non-approved dogs. These findings may be of profound importance for understanding individual variations in behaviour and improving breeding schemes for working dogs.
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| 5. |
- Garnham, Laura, 1988-
(författare)
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Causes and Consequences of Impulsivity in Red Junglefowl
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Throughout the animal kingdom, animals vary in cognition (i.e., how they acquire, process, store, and act on environmental information). Yet, the causes and consequences of this variation are currently unclear. Inhibitory control is one such aspect of cognition that typically varies between individuals within all species investigated. Variation in inhibitory control underlies variation in impulsivity (i.e., the tendency to act without planning or considering the consequences). The causes and consequences of variation in impulsivity are, themselves, rarely explored, despite that these may have important ecological and evolutionary implications. My thesis (spanning 5 papers), therefore, aimed to fill some of these gaps by taking a holistic approach and investigating causes and consequences of variation in impulsivity (specifically, impulsive action and persistence measured in a detour task) in red junglefowl (Gallus gallus) males and females, chicks and adults. The red junglefowl was an ideal species for this investigation. Firstly, they show individual variation in impulsivity throughout their lives. They are also typically food motivated, and easily habituated to handling and new situations, which means they commonly willingly participate in behavioural and cognitive tests. Furthermore, they are precocial, which means that they can be hatched and raised without mothers, thus reducing parental effects. Finally, the large, accumulated knowledge of red junglefowl behaviour and cognition aids interpretations regarding this. As differences in experience early in life have been found to affect impulsivity, papers I and II empirically explored whether variation in two previously uninvestigated experiences in early life (exposure to enrichment, and social group size, respectively) influenced impulsivity. The dopaminergic and serotonergic systems are important signalling systems in the brain, which have been found to link to impulsivity in other species. Therefore, in paper I, I also explored if variation in impulsive action and persistence was connected to variation in dopaminergic or serotonergic gene expression. As impulsivity links to inhibitory control, in looking at the effect of group size on impulsivity, paper II explored the hypotheses that social environment affects cognition (e.g., that social environments which are assumed to be more cognitively demanding will lead to better cognitive performance, a.k.a., the social intelligence hypothesis). To uncover potential mechanisms by which group size could affect impulsivity, besides from variation in cognitive demand, paper II also investigated if behaviours that could covary with group size linked to impulsivity. As emotional arousal has been linked to impulsivity, in another species, and impulsivity is implicated in welfare issues, paper III looked into how both positive and negative affective states (which can be used to measure welfare) related to impulsivity. Prior to my thesis, whether variation in impulsivity could potentially affect animal welfare was scarcely explored. To better understand the potential consequences of impulsivity, and, thus, how selection could act on impulsivity, papers IV and V looked at potential implications of variation in impulsivity for social status (paper IV and V), foraging efficiency, and risk taking (paper V). My results showed that impulsivity could be consistent over time periods of weeks (in chicks, paper II) to months (in adults, paper V). Thus, impulsivity describes a characteristic of the individual. However, individuals could still learn to become less impulsive (paper I). Exposure to enrichment in early life could affect how impulsively individuals behaved. Environmental enrichment increased impulsivity, as did cognitive enrichment to a greater degree (paper I). Impulsive action, and persistence, correlated somewhat with brain gene expression of dopaminergic and serotonergic genes (DRD1, TPH; paper I). The social group size individuals experimentally experienced in early life did not affect their impulsivity (paper II). However, variation in impulsivity was connected to variation in activity, boldness, neophobia, and stress (paper II). Further, more impulsive individuals had less negative, more positive, affective states, but only when they were young chicks, and not as older chicks or adults (paper VI). No links were found between impulsivity and social status (paper IV and V), foraging efficiency, or risk taking (paper V). Taken together, paper I suggests that underlying explanations to observed individual variation in impulsivity could include variation in early life experiences and in dopaminergic and serotonergic gene expression, while paper II suggests that impulsivity may not be influenced by social aspects early in life. Papers II and III demonstrate that variation in impulsivity can associate with variation in behaviours and affective states (though these associations may vary over ontogeny), with the latter finding implying that variation in impulsivity could have welfare implications. Papers IV and V indicate that variation in impulsivity may have limited consequences for individuals in contexts that could affect reproduction or survival. Thus, it may not necessarily be costly to individuals if they are more impulsive than others. This, in turn, could help explain why variation in inhibitory control exists, because limited consequences of variation could result in low selection against variation. Overall, through the investigations conducted in its 5 papers, my thesis improves our understanding the potential causes and consequences of variation in impulsivity. As impulsivity is underlain by an aspect of cognition (inhibitory control), in exploring the causes and consequences of variation in impulsivity, my thesis also provides knowledge on causes and consequences of individual variation in cognition.
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| 6. |
- Hedlund, Louise, 1987-
(författare)
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Effects of commercial hatchery processing on behaviour and welfare of laying hens
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Around the world, more than 76.7 million tons of eggs are consumed every year. To meet this demand, billions of laying hen chicks are produced under highly industrial circum-stances. These chicks are hatched in commercial hatcheries for laying hens in a presumably stressful environment, which might affect their welfare and production later in life. When the eggs arrive to the hatchery, they are inserted in large cabinet incubators that can hold approximately 60 000 eggs. The incubators are calibrated for optimal hatchability which includes turning of the eggs as well as fluctuating temperature and humidity over the day. This is regulated by fans whose purpose consists of removing heat and circulating the air in the incubators. However, the drawback of these fans is that their noise levels exceed 90 dB, which is equal to the sound of a passing train. After 19 days, the eggs are moved to a hatcher for the last days of incubation, in which they are exposed to formaldehyde for disinfection purposes. The eggs hatch after 21 days of incubation but are kept in the hatcher for an additional day to maximize hatchability rate. After removal from the hatcher, the racks with chicks are tilted onto a conveyer belt and separated from the shells. The chicks are then conveyed to a sex-sorting station where the males are dis-carded, and the females are further processed to a vaccination station. Once vaccinated, the animals are automatically counted and packed in transport boxes which are loaded onto a truck and transported to rearing farms. The aim of this thesis was to investigate if and how the chickens are short- and long-term affected by this hatchery procedure, including incubation and transportation, and how this might affect their welfare. In all experiments, we have compared commercial hatchery incubated, hatched, processed, and transported White Leghorn chicks (hatchery chicks, HC) with chicks incubated and hatched in a calm environment, and gently placed in their home pens directly after hatch (control chicks, CC). In all experiments, HC and CC were from the same parental stock and kept in separate but identical pens. In paper I, we blood sampled the chicks before and after the hatchery handling to evaluate stress hormone levels (CORT) in the hatchery. The HC had significantly higher CORT levels than the CC had at a corresponding time point, which implies that the hatchery treatment is a highly stressful experience. Our results of behaviour, HPA-axis sensitivity, and feather damages showed that the commercial hatchery treatment has a long-lasting overall negative effect on the animals up to at least 20 weeks of age. In paper II, we aimed to compare chicks incubated, hatched, and sorted at the hatchery, with chicks incubated and hatched at the hatchery who were not sorted, to distinguish the stress effects of the actual conveying and handling. We could not find any major differences between the groups and concluded that the most stressful part in the commercial hatchery seems to be the incubation and hatching, potentially due to the high noise levels and formaldehyde exposure. In paper III, we investigated possible welfare implications of the hatchery procedure by using a cognitive judgement bias (CJB) test that is used to measure optimism/pessimism in animals. In general, pessimistic animals perceive the same environment as more negative than optimistic animals, hence, this has a great impact on their welfare. When testing HC and CC in a CJB test, we could see that HC were consistently more pessimistic than CC, during 1st, but also during 10th week of age. This means that the hatchery treatment has a long-lasting effect on the cognitive state of the animals, implying the animals exposed to this have a poorer welfare. In paper IV, we investigated possible effects of the hatchery treatment on production parameters. We found that HC weighed less, and laid fewer and smaller eggs than CC. HC performed more feather pecking behaviour before sexual maturity, although the feather condition after sexual maturity showed the opposite pattern. We conclude that there seems to be an effect of the hatchery treatment on traits relevant for the industry, and that this effect seems to be overall negative. In the last study, paper V, we investigated if it is possible to buffer the hatchery stress with environmental enrichment. The enriched chicks were kept in a complex environment and imprinted on, and provided with, a stuffed mother hen. We could see a supressed physiological stress reaction to restraint in enriched HC, however, the opposite pattern was shown in CC. We found no other effects of environmental enrichment, how-ever, an overall difference between the groups where HC were more pessimistic and fearful than CC, which is in line with our previous results. In conclusion, the hatchery procedure including incubation, hatching, conveying, sex sorting, vaccination, and transport seems to have an overall long-lasting negative effect on chicks, where HC are more fearful and pessimistic, have a more sensitive HPA-axis, show more feather pecking behaviour, and are negatively affected with regard to traits relevant to the industry. I think that these results are highly relevant, not only for the industry, but also for the welfare of the world’s most common farm animal.
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| 7. |
- Höglund, Andrey, 1985-
(författare)
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Quantitative genetics of gene expression and methylation in the chicken
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In quantitative genetics the relationship between genetic and phenotypic variation is investigated. The identification of these variants can bring improvements to selective breeding, allow for transgenic techniques to be applied in agricultural settings and assess the risk of polygenic diseases. To locate these variants, a linkage-‐based quantitative trait locus (QTL) approach can be applied. In this thesis, a chicken intercross population between wild and domestic birds have been used for QTL mapping of phenotypes such as comb, body and brain size, bone density and anxiety behaviour. Gene expression QTL (eQTL) mapping was also done for tissues such as comb base, medullar bone, liver and brain. By overlapping eQTL and QTL, regions were identified associated with both the gene expression levels and the phenotypes simultaneously. In this way, a number of candidate genes, underlying variation in the above-‐mentioned phenotypes, were identified. Additionally, DNA methylation QTL (mQTL) mapping was done in the brain and the methylation landscape was assessed which indicated a decrease in methylation in the domestic breed. A small number of regions were identified which affected DNA methylation levels throughout the whole genome, so-‐called trans hotspots. Finally, DNA methylation levels were correlated with eQTL to assess the degree to which gene expression is affected by methylation, and with gene expression in general to assess the relationship between the transcriptome and methylome. Taken together, these studies link the differences observed in various phenotypes between two populations of chicken to genetic variants coupled with gene expression correlations suggesting candidate genes. DNA methylation levels were influential in regulating variation in gene expression, both positively and negatively, but gene expression was also influential in regulating the methylation level. Epi-‐alleles were identified which indicated genetic variants regulating methylation levels and gene expression levels either as the causal variant or in close linkage.
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| 8. |
- Johnsson, Martin
(författare)
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Genomics of chicken domestication and feralisation
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Domestication can serve as a study system of rapid evolutionary change with wide-ranging effects on traits in animals. The chicken was domesticated from the Red Junglefowl and has diverged in behaviour, morphology and life history traits. Conversely, feralisation is a more recent process when domestic animals are again exposed and respond to an environment outside of human husbandry. Linkage-based quantitative trait locus (QTL) mapping has been used to localise genetic variants that affect domestication traits in the chicken genome. Because of the limited resolution of linkage mapping, the QTL regions associated with domestication traits are often broad and contain many genes. One approach to help sort out potential causative genes is to measure gene expression as an intermediary molecular phenotype. In this dissertation, expression quantitative trait locus (eQTL) mapping of gene expression traits is used to search for potential causative genes for domestication traits in the chicken. Expression quantitative trait loci were mapped across the whole genome in bone and hypothalamus samples, and targeted at QTL regions in the base of the comb. These studies have resulted in candidate quantitative trait genes, supported by genetic and gene expression evidence, for relative comb mass, bone allocation, egg production and fearful behaviour as measured in an open field test. Secondly, a population genomics approach was used to study the molecular basis of feralisation in a free-range feral chicken population from the Pacific island of Kauai. Mitochondrial DNA sequences and phenotypic observations establish the hybrid origin of this population as a mixture of wild and domestic chickens. Genome-wide mapping of pooled heterozygosity highlight regions that may be involved in adaptation to the feral environment. The expression QTL results bring us closer to knowledge about the molecular basis of domestication traits in the chicken, suggesting plausible candidate genes and opening up for functional studies of individual loci. The population genomic study shows that feralisation has a mostly different genomic architecture than domestication, and suggests phenotypic effects, based on overlap with domestication QTL regions, for some of the identified regions.
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| 9. |
- Karlsson, Anna-Carin, 1983-
(författare)
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Effects of domestication related genes on behaviour, physiology and gene expression in chickens
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Domestication, the process when animals adapt to captivity, tends to modify a whole array of traits towards what has been termed “the domesticated phenotype”, where the domesticated animal differs from its wild ancestor in morphology, physiology, development and behaviour. Physiological traits and behaviours are controlled by genes. One single gene can control several different traits (pleiotropy), be linked to a neighbouring gene on the chromosome, or interact with another gene that in turn controls another trait. This is the explanation why one can select for high egg production and at the same time get a change in the colour of the plumage. The aim of this thesis was to evaluate the effect of a mutation in two particular genes (PMEL17 and TSHR) related to domestication on behaviour, gene expression and other physiologial traits. The animals investigated were chickens from a cross between the ancestral Red Junglefowl (RJF) and the domesticated White Leghorn (WL) selected for high egg production traits. PMEL17 is a gene affecting plumage colour. A mutation in the gene causes a non-pigmented white plumage and has been shown to protect against feather pecking. Our studies showed that a mutation in the PMEL17 gene affects social, explorative and aggressive behaviour in chickens, but not visual ability. The thyroid stimulating hormone receptor (TSHR) plays an important role in the signal transduction of the hypothalamus-pituitary-thyroid axis that has general effects on development, behaviour and reproduction. A mutation in the TSHR gene affects incubation time, domestication related behaviours such as fear and aggression, gene expression, thyroid hormone levels and photoperiodic reproduction responses in chicken. The results from this thesis suggest that a mutation in the PMEL17 and TSHR genes have pleiotropic effects on behaviour and traits related to domestication, and it is therefore likely that both genes have been important for the domestication of the chicken.
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| 10. |
- Nätt, Daniel
(författare)
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Heritable epigenetic responses to environmental challenges : Effects on behaviour, gene expression and DNA-methylation in the chicken
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Phenotypic variation within populations is a crucial factor in evolution and is mainly thought to be driven by heritable changes in the base sequence of DNA. Among our domesticated species we find some of the most variable species on earth today. This variety of breeds has appeared during a relatively short evolutionary time, and so far genetic studies have been unable to explain but a small portion of this variation, which indicates more novel mechanisms of inheritance and phenotypic plasticity. The aim of this study was therefore to investigate some of these alternative routes in the chicken, especially focusing on transgenerational effects of environmental challenges on behaviour and gene expression in relation to domestication. In two experiments a chronically unpredictable environment induced phenotypic changes in the parents that were mirrored in the unexposed offspring raised without parental contact. This transmission was especially clear in domesticated birds. A third experiment showed that repeated stress events very early in life could change the developmental program making the birds more resistant to stress later in life. Here, the phenotypic changes were also mirrored in the unexposed offspring and associated with inheritance of gene expression. Epigenetic factors, such as DNA-methylation, could play an important role in the mechanism of these transgenerational effects. A fourth experiment showed that wild types and domesticated chickens differed substantially in their patterns of DNA-methylation, where the domesticated breed had increased amount of promoter DNA-methylation. In line with the previous experiments, this breed also showed increased transmission of methylation marks to their offspring. Conclusively, parental exposure of environmental challenges that introduce changes in behaviour, physiology and gene expression can under both chronic and temporal conditions be heritably programmed in the parent and transmitted to the unexposed offspring. Since heritable epigenetic variation between wild type and domesticated chickens is stable and numerous, it is possible that selection for favourable epigenomes could add another level to the evolutionary processes and therefore might explain some of the rapid changes in the history of the domesticated chicken.
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