Domestication—From behaviour to genes and back again☆
Section snippets
Introduction: genes and behaviour
Let's not mince matters: genes control behaviour, and this insight is one of the great achievements of ethology. Of course, every biologist is well aware that a statement like this will have to be expressed carefully to be generally true, for example, by saying that a certain part of the phenotypic variation in behaviour is attributable to variation in genotype (Alcock, 2001). However, it is quite clear that a particular behaviour expression will never be possible unless there is a particular
Domestication—a model for evolution
As already realised by Darwin, domestication offers a beautiful model for studying phenomena like this. According to Price (1997), three processes are central to domestication. Firstly, there is a relaxation of certain natural selection factors, such as predation and starvation. Secondly, there is an intensified selection of traits preferred by humans. Thirdly, there is natural selection under captivity, leading to adaptation. Side-effects of selection, such as those outlined above, constitute
The genomic strategy
Genomics generally proceeds along a specific pathway of investigations in order to identify genes involved in specific traits (Andersson, 2001), and determining its mechanisms. First, we need animals which differ on the traits we are interested in—for example growth rates, if we are interested in growth-related genes, or aggression if we are interested in genes controlling aggressive behaviour. In such animals we may use molecular methods to search for allelic differences which may help
Chickens as model species
The first part of the strategy is to find a suitable animal material and pedigree. The chicken has proved to be an excellent model animal for a number of reasons.
All poultry breeds are domesticated genotypes of the red junglefowl, Gallus gallus, which live wild in south-east Asia, and it appears that domestication commenced at least 8000 years ago (Siegel et al., 1992, Yamashita et al., 1994). Junglefowl are readily available, since they are kept in zoos throughout the world, and chickens
Behavioural differences between laying hens and red junglefowl
In order to characterise the behavioural differences between the ancestor and a selected model strain of laying hens, we compared their undisturbed behaviour in semi-natural enclosures and in different controlled behaviour test situations (Schütz and Jensen, 2001, Schütz et al., 2001). We found that mainly four aspects of behaviour differed. Firstly, layers were generally less active, showing a reduced foraging and exploratory behaviour. Secondly, they showed a less intense social behaviour,
QTL-analysis
The next step in the behaviour genomic strategy is to map the phenotypic differences to specific loci. As already mentioned, behaviour as well as the other typical components of the domestication phenotype (growth, physiology, etc.), are most likely polygenic and show a quantitative inheritance pattern. Such traits have historically been very difficult to map to specific loci, since mapping used to depend on analysing co-segregation of linked loci with Mendelian inheritance, i.e. the offspring
Coinciding QTLs for production and behaviour
We analysed for genome-wise significance and used Monte Carlo simulations to ascertaing the critical p-values for the different traits (Carlborg et al., 2003). A number of QTLs associated with growth and egg production were located. A surprising finding was that a limited number of QTLs explained a large proportion of the difference in growth rate between the junglefowl and the white leghorn—four QTLs explained 50% of the difference in adult body weight of females and 80% of that of males (
Gene localisation and animal welfare
Of course, localisation of a QTL is only the first step towards finding the actual genes and mutations causing a phenotypic effect. Using homologies between other sequenced genomes (for example mouse, rat and human) and the chicken genome, it has been possible to identify and characterise some of the genes and their causative mutations in our animals. This has enabled us to identify genes involved in plumage colouration variation in fowl. We have identified a mutation in the melanocortin
Beyond allelic variation: gene expression patterns
Traditionally, evolutionary biologists have thought in terms of Mendelian genetics, where phenotypic variation is ascribed to mutations in specific alleles, and where the inheritance patterns of these mutations hold the keys to evolution of a population. However, it has become increasingly clear that allelic variations cannot explain the vast phenotypic variation between organisms with rather similar genomes. For example, humans and chimpanzees have DNA-sequences which are on average 98.8%
Implications: breeding and animal welfare
Over the last decades, breeding for increased production has been the dominating goal for animal agriculture. It has been estimated that average production levels have increased by more than 85% since 1960, and parallel to that, many production-related diseases and disorders have increased; for example, leg problems in fattening pigs, mastitis and lameness in dairy cattle, and locomotory and circulatory problems in fast-growing broilers (Rauw et al., 1998). Hence, breeding animals with a large
Conclusions
Domestication involves a rapid and complex change of many different phenotypic changes, which act in concert in a similar manner in many different species. We have shown that, in chickens, an array of these changes are affected by few loci, and I suggest that this may indicate that domestication changes can be caused by only few genes, possibly with regulatory functions. In addition to increasing the understanding of genetic control of behaviour, this may help us understand how animals adapt to
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2023, Neuroscience and Biobehavioral ReviewsWhite Leghorn and Red Junglefowl female chicks use distal and local cues similarly, but differ in persistency behaviors, during a spatial orientation task
2022, Behavioural ProcessesCitation Excerpt :With regard to the use of distal cues, multiple studies on birds and mammals showed that inherent levels of fearfulness/anxiety can impact the way, either positively or negatively, individuals use and rely on this type of cue (Herrero et al., 2006; Lormant et al., 2020b, 2018; Packard, 2009). Since fearfulness is known to be reduced in domesticated animals compared to their wild counterparts (Campler et al., 2009; Jensen, 2006), we hypothesized that RJF would differ from WL on their use of distal cues. RJF did differ from WL in the latency to reach the target cup during tests, but this was mainly due to RJF taking a longer time during the distal test compared to the displacement test.
Reproductive and maternal behavior of livestock
2022, Genetics and the Behavior of Domestic Animals, Third EditionNo evident effect of domestication on the anti-predator behaviour of European abalone (Haliotis tuberculata): Implications for stock enhancement programs
2021, Applied Animal Behaviour ScienceCitation Excerpt :Furthermore, farm conditions and productivity targets (e.g. selection of fast-growing individuals) both result in intentional or unintentional selection. The simplified and predator-free environment of farms result in different behavioural responses from wild conspecifics, such as a decreased predator avoidance behaviours (Jensen, 2006; Jackson and Brown, 2011). As an example, Jackson and Brown (2011) showed that Salmo trutta exhibited decreased predator avoidance responses after two generations of selection (F2) compared to the F1 individuals.
Different regrouping schedules in semi group-housed rabbit does: Effects on agonistic behaviour, stress and lesions
2020, Applied Animal Behaviour ScienceChickens in motion: Effects of egg production level and pen size on the motor abilities and bone stability of laying hens (Gallus gallus forma domestica)
2020, Applied Animal Behaviour ScienceCitation Excerpt :Their domestication started approximately eight thousand years ago (West and Zhou, 1988). Domestication processes lead to multiple alterations of the genotype and phenotype, particularly given the intensive selection performed under human supervision (Price, 1999; Jensen, 2006, 2014). In addition to domestication, in recent decades, chickens have experienced strong artificial selection pressure for specific productivity traits, either for meat or egg production (Hale, 1962; Price, 1998; Schütz and Jensen, 2001).
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This paper is part of the special issue entitled International Society for Applied Ethology Special Issue—A Selection of Papers from the 38th International Congress of the ISAE, Helsinki, Finland, August 2004, Guest Edited by Victoria Sandilands and Carol Petherick.