Genetics and Behaviour I. Dr Mike Wride School of Natural Sciences Zoology Department

Transcription

1 Genetics and Behaviour I Dr Mike Wride School of Natural Sciences Zoology Department wridem@tcd.ie

2 Text Books: Further Reading David McFarland (1999) Animal Behaviour 3rd Ed. Chapters 2, 3 and 4 Chris Barnard (2004) Animal Behaviour: Mechanism, Development, Function and Evolution. Chapters 2.1, 2.3 and 5 Principles of Animal Behaviour (2009). 2nd Ed. Lee Alan Dugatkin Chapter 2

3 Outline of Lectures Lecture 1: Nature Vs Nurture (Genes Vs Environment); Development of Behaviour; Innate Vs Learned Behaviours Lecture 2: Experimental approches to study behaviour: Does behavioural variation have a genetic component? Can we find genes involved in behaviour? Human behaviour and genes

4 Alper BMJ 1995;310: (4 February) Editorials Biological influences on criminal behaviour: how good is the evidence? 310/6975/272

5 Genes Influence Various Human Behaviours Including Criminality Influence of functional variant of neuronal nitric oxide synthase on impulsive behaviors in humans. Arch Gen Psychiatry. Reif et al., 2009 Jan;66(1): HTR3B is associated with alcoholism with antisocial behavior. Ducci et al., Alcohol Feb; 43(1):73-84.

6 Nature Vs Nurture Traditional approach in behavioural studies is to separate out nature and nurture in order to quantify one with respect to the other. Antisocial behaviour amongst males in an extended family - Monoamine oxidase A activity altered and correlated with the behaviour, but only amongst young men in the group who had suffered abuse as children. Caspi et al., Science (2002) 2: i.e.behavioural effect only seen in the context of the gene-environment interaction

7 Genes and Behaviour I. Behaviour has evolved II. III. IV. Evolution, ultimately, is a change in gene frequencies Thus, are there genes for behaviour? I. Where the behaviour is the phenotype. II. and where the genes for that particular behaviour are the genotype. Use of molecular genetics techniques by behavioural researchers - linkage and association studies in an attempt to find which genes might be involved in the phenotype (behaviour)

8 Genes and Behaviour Three Main Topcs Genes and Chromosomes Development and Behaviour Behavioural Genetics

9 Genes and Chromosomes Following publication of The Origin of Species by Darwin, Issue of how character traits are inherited and how variation in offspring achieved became of acute scientific interest Rediscovery of Mendel s work in 1900 reconciled genetics (rules of inheritance) with theory of evolution by natural selection and cellular physiology

10 Mendel s Experiments Dominant and recessive phenotypes Text Blended phenotype - not dominant or recessive

11 Genotype Vs Phenotype Natural Selection acts on the phenotype, but is dependent upon the genotype Behaviour of an individual is a phenotype (if we think in purely genetic terms) Genetic variation is the basis of natural selection: genetic material - the DNA Deletions/substitutions in DNA lead to genetic variation on which natural selection acts - also cellular basis of heredity (meiosis, gametes, fertilization etc)

12 Evolution - Artificial Selection

13 Evolution - natural selection

14 2 Questions Arise How can we determine or demonstrate the survival value of a particular behaviour pattern? Survival and Fitness Is there a best way for an animal to divide its time among the many activities possible (behaviours) given a certain set of circumstances? Behavioural Ecology The way in which behaviour contributes to survival and reproduction depends on ecology Krebs and Davies (1993)

15 But, What Does A Gene for Behaviour Really Mean? Lorenz (1965): Absolue determinism GENES PROTEINS STRUCTURAL ENZYMES REGULATORY B E H A V I O U R No environmental influence Free will?

16 All else being equal, if one allele at locus A makes behaviour Z more (or less) likely to occur then we have a gene for behaviour

17 A Model for Influence of Genes on Behaviour GENE! GENE! GENE! GENE! GENE! BEHAVIOUR GENE! GENE! GENE! GENE! GENE! new behaviour Is this a useful model?

18 A Gene for Wind Sensitivity in Crickets Bentley (1975) Science 187:760! isolate wind-insensitive individuals! differences! undeveloped nerves! no cercal-hairs! explanations? CERCI

19 Genes and Behaviour gene for insensitivity hairs!behaviour cercus sensory neuron axon dendrite medial giant interneuron hairs sensory neuron MG

20 Genes and Behaviour Alternative Model A cautionary note: Only in very rare cases will one gene have a privileged or unique role in causing a behaviour to occur. GENE GENE GENE GENE GENE GENE GENE GENE BEHAVIOUR The influence of genes on behaviour is complex - i.e. behaviour is regulated by multiple genes acting together - polygenic.

21 Genes Vs Environment? Environmental support Nature Vs Nurture Environmental information Genetic information Acquired behaviour Innate behaviour Genetic support But can we really put behaviour into these categories as if there is no interaction between genetics and the environment?

22 Development of Behaviour ENVIRONMENT internal conditions: biochemistry BEHAVIOUR PATTERNS GENES Depends on Genes and the Environment!

23 Genes and Behaviour Cont... Individual genes are NOT absolute instruction manuals or blueprints for performing particular behaviours (usually) The probability of a particular behaviour being performed is due to the presence of a particular form of a gene (polymorphism) and its expression in the cells/tissues of that particular organism Within a population, therefore, variation in one or more genes often underlies some of the variation in behaviour observed

24 Ontogeny: Morphogenesis Development of a fertilized egg (zygote), through all embryonic and foetal stages, including post hatch/birth maturation to adulthood Depends on genes and environment Same for development of certain behaviours

25 Development of Behaviour is an Ongoing Process Fertilized egg (zygote) P1 + G1 + E1 P2 Fertilized egg (zygote) P2 + G2 + E2 P3 As development continues affect of the environment becomes progressively more important: Epigenesis

26 Learned Vs Innate Behaviours Innate - controlled primarily by genes Learned - influenced primarily by environment at sensitive stages of development e.g. Language learning in song birds: pre-programmed - can be learned in the absence of reward and punishment (genes involved)

27 Innate Behaviour Concept of innate behaviour - controversial Early ethologists - behaviour determined by the genes (i.e. intrinsic and independent of experience) Lorenz (1939): Behaviour is heriditary, individually fixed, and thus open to evolutionary analysis Tinberg (1942): Instinctive acts are highly stereotyped coordinated movements, the neuromotor apparatus of which belongs...to the hereditary composition of the animal

28 Innate Behaviour Cont... View of Lorenz and Tinberg too rigid A naive idea of genetic determinism A rigid distinction between innate and leaned behavior is unsatisfactory because many aspects of behaviour are influenced by both genes and the environment (experiences of the individual - learned)

29 Definition of Innate Behaviour Behaviour that occurs without obvious environmental influence

30 Innate Behaviour 1 Konrad Lorenz (1966) Evolution and Modification of Behaviour See also Cate (2009) Animal Behaviour 77:

31 Genetic Variation in a Population Influences Behaviour Discontinuous Continuous No. of individuals % time spent feeding % time spent feeding

32 Problems The tendency to peck is probably innate, but the object that is pecked is modified as a result of experience i.e. due to the environment

33 Innate behaviour 2! Oh what a tangled web we weave!! How do spiders know how to weave a web immediately after hatching with no training from the parents?! Suggests an important genetic component

34 Summary of Lecture Development involves continual interaction between genes and environment. Each phase sets the stage for the next - epigenesis Environmental influences on development are most important just after birth/hatching Sensitive periods of development exist during which the animal learns important lessons Juvenile animals often have characteristic innate behaviours that are lost in adulthood Innate behaviours occur without obvious environmental influence - genetic control

35 Next Lecture Does behavioural variation have a genetic component? Can we find genes involved in behaviour? Human behaviour and genes