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Behavioural Genetics

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Behavioural Genetics Behavioural Genetics Geetanjali Mishra Associate Professor Department of Zoology University of Lucknow Lucknow Behavioural genetics • Behavior, like all characteristics of animals, is shaped by a combination of genes and environment • The identification of specific genes that regulate specific behaviors has been a relatively difficult thing to achieve. • This is because behaviour is a result of activation of multiple sensory, physiological, endocrinological, neurological, muscular and many more pathways. • Which means, that there are usually multiple genes that are activated or repressed during the display of each behaviour. Hence, in most cases it is difficult to identify a single gene responsible for a particular behaviour. As more refinements come to the science of behavioral genetics, it has become apparent that for most behavioral traits this is an impossible goal. • Candidate genes (genes likely to be of importance in a particular behaviour) usually play important roles in sensory systems, channels in membranes, neurotransmitter dynamics, or muscle physiology but are rarely linked only to one behavior. • This reflects the fact that growth and development, physiology, reproduction, and behavior in a typical organism are the products of 15,000–20,000 genes. • However, studies have indicated that there are certain behaviours that are regulated by a single gene • The most fruitful aspect of behavioral genetics is the ability to place genes in their evolutionary context at many different levels. • Behavioural genetics is important in understanding whether behaviour is primarily affected by genes or can be changed and modulated by environment in which they are growing and developing. • If the effect of genetics is more then the behaviour is believed to be in the animals “nature” or instinctive/ stereotyped and if the effect of environment is more then it is considered to be shaped by “nurture” or learnt behaviour. • What is the balance between genetics (instinct or nature) and learning (nurture) in shaping behavior is the biggest question facing the study of animal behaviour and behavioural genetics • In the animal world, behavior can be envisioned as a continuum between learning and instinct. • Genetic studies of behavior require much stronger problem-solving approach than other areas of behavioral science. • This requires the choosing of the right genetic tool. • Knowledge of genetics gives students of behavior powerful windows into the evolution of behavior and the physiological regulation of behavior. The problem-solving abilities gained from behavioral genetics can be applied in the study of almost any type of behavior and form the scientific basis for understanding the nature–nurture debate. Tools of Genetics and their use in Behaviour • There are different tools involved in the study of behavioural genetics o Domestication/ Artificial Breeding/ Inbred and Outbred Lines o Phylogenetics o Quantitative and biometrical genetics o Evolutionary and Population genetics o Molecular genetics • These tools help behavioural studies through o Genetic mapping o Identifying candidate genes for behavioural regulation o Studying gene-environment interactions o Finding correlations between gene-expression and behaviour o Identifying gene regulatory mechanisms that influence behaviour o Evolution of behaviour at organismic and genomal level o Evolution of frequencies of genes responsible for behaviour in populations o Phylogeny of genes for behaviour Domestication • Humans have observed their surroundings and the plants and animals in it for years. • During their observations, they obviously observed the variation in individual behavioural traits amongst a species and also the inheritability of those traits, that is there were some behaviours which were being passed down from parents to their offspring. • Such inheritable behaviours that were desirable by humans were then selected for by breeding individuals having the same behaviour again and again through generations, leading to the selection of such behaviour. • The observations followed by such selections over the century are responsible for the domestications of animals and plants. • The huge numbers of dog breeds with different behaviours is a case in example of how behavioural traits can be selected for. Also what is necessary to keep in mind is that the processes of artificial selection can only be applied in cases of behaviour that is largely gene influenced or “nature” influenced or innate. • Behaviours that are largely influenced by environment of nurture cannot be artificially selected or domesticated. • Such artificial selection studies can be used in experimental biology to understand whether behaviour is genetic or environmental. • To determine if a behaviour is genetic or not we can select individuals displaying that behaviour and mate them. In the next generation we can choose their offspring which display the desired trait and mate them with each other. This process when done over generations creates an inbred line. If the trait is genetically influenced its display will be becoming more prominent and more widely expressed in higher number of offspring. It will also persist in different environments. • If the above behaviour is not genetically affected it will not be increasingly displayed through inbred lines. Phylogeny • Phylogeny, the history of the evolution of a species or group, especially in reference to lines of descent and relationships among broad groups of organisms. • Phylogeny gives us tools to understand the evolutionary roots of behavior, to know the time frame for the evolution of innovations, and to understand evolutionary interactions at the genetic level. • Phylogenies were traditionally developed by studying similarities in phenotypes among organisms, but current studies of phylogenies also rely on data gathered using molecular genetic techniques. • By studying the molecular structure of candidate genes or key genes we can trace the evolution of a particular behaviour in closely related species. • The above phylogenetic tree or cladogram refers to the nest building behaviour of swiftlets. All the swiftlets which are part of this cladogram belong to the same genus but are different species. The nest of swiftlets is especially interesting because it is used in a traditional South Asian delicacy, the bird nest soup. This soup is supposed to have nutritional and medicinal qualities because of the salivary glue used by the swiftlets while making it. • However, in a few swiftlet species, the nest does not use glue but primarily twigs and feathers. On the other hand some species use glue as the chief construction material. • Ethologists thus first identify the various nest building behaviours in swiftlets, and then compare relevant genes in these species. This helps identify the evolution of behaviour. In this case it shows that nest building behaviour has separately evolved three times in swiftlets and not once as would have been hypothetically expected. CLASSICAL AND MENDELIAN GENETICS • As scientific processes gained momentum, Mendel led the charge in investigations on how phenotypes were passed from generation to generation. This led to Mendel’s laws of segregation and independent assortment and afterwards, genetic dominance and epistasis. • Simple behavioral traits, such as mutations affecting coordination in fruit flies, can be studied using Mendelian approaches. • A simple study using classical genetics has demonstrated why some individuals of fire ants are monogynous (live in a nest with a single female) while others are polygynous (live in a nest with multiple unrelated females). • This behavioural variation of polygyny and monogyny in a single species has been identified and attributed to a single gene, Gp-9. This gene codes for a pheromone receptor. This receptor is capable of sensing pheromones emitted by the queen. Via perception of the pheromone workers are able to identify queens as their own or as strangers and discard the latter from the nest. • Individuals without the Gp-9 gene or a defective copy of the gene have a faulty pheromone receptor, which cannot sense pheromones emitted by the queen, and are thus not able to differentiate between their own and another queen, and thus are able to tolerate multiple queens. A single gene responsible for a shift in behaviour • Another invasive ant in California, the Argentine ant (Linepithema humile), has been highly successful, possibly because it exhibits reduced intraspecific aggression. While the native population of this ant is highly aggressive • A genetic study using microsatellite DNA markers has shown that these ants experienced a population bottleneck that reduced genetic diversity during their introduction in California. • This is consistent with the hypothesis that reduced genetic variability may impair nestmate or colony recognition, permitting the invaders to behave like one large colony. This, in turn, allows them to rise to higher densities than they do in their native habitat • Using classical genetics studies it has been demonstrated that there are certain genes in male and female Drosophila that reduces the occurrence of courtship in males and the females’ responsiveness to them. Male behavior is inhibited by genes named Nerd and fruitless and is enhanced by Voila. Female receptiveness to mating is impaired by genes such as dissatisfaction, spinster, and chaste. • To separate the effects of nature and nurture a very important method of investigation is the use of cross fostering
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