Download Genetics and Behaviour I

Genetics and Behaviour I
Dr Mike Wride
School of Natural Sciences
Zoology Department
email: [email protected]
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
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
Alper BMJ 1995;310:272-273 (4
February)
Editorials
Biological influences on criminal
behaviour: how good is the evidence?
http://www.bmj.com/cgi/content/full/
310/6975/272
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):
41-50.
• HTR3B is associated with alcoholism with
antisocial behavior. Ducci et al., Alcohol. 2009 Feb;
43(1):73-84.
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: 851-854
•
i.e.Behavioural effect only seen in the context of the
gene-environment interaction
Genes and Behaviour
I.
Behaviour has evolved
II.
Evolution, ultimately, is a change in gene frequencies
III.
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’.
IV.
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)
Genes and Behaviour
• Three Main Topcs
• Genes and Chromosomes
• Development and Behaviour
• Behavioural Genetics
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
Mendel’s Experiments
Dominant and
recessive
phenotypes Text
“Blended” phenotype
- not dominant or
recessive
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)
Evolution - Artificial
Selection
Evolution - natural
selection
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)
But, What Does “A Gene
for Behaviour” Really Mean?
Lorenz (1965): Absolue determinism
STRUCTURAL
GENES
PROTEINS
ENZYMES
REGULATORY
No environmental influence
B
E
H
A
V
I
O
U
R
Free will?
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
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?
A “Gene” for Wind
Sensitivity in Crickets
Bentley (1975) Science 187:760
! isolate wind-insensitive
individuals
! differences
! undeveloped nerves
! no cercal-hairs
! explanations?
CERCI
Genes and Behaviour
“gene for insensitivity”
hairs
!behaviour
cercus
axon
sensory
neuron
dendrite
medial
giant
interneuron
hairs
sensory neuron
MG
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.
Genes Vs Environment?
Environmental
support
Nature Vs Nurture
Environmental
information
Acquired
behaviour
Genetic
information
Innate
behaviour
Genetic
support
But can we really put behaviour into these categories as if
there is no interaction between genetics and the environment?
Development of Behaviour
ENVIRONMENT
internal
conditions:
biochemistry
BEHAVIOUR
PATTERNS
GENES
Depends on Genes and the Environment!
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
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
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
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)
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”
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)
Definition of Innate
Behaviour
• “Behaviour that occurs without obvious
environmental influence”
Innate Behaviour 1
Konrad Lorenz (1966) Evolution and Modification of Behaviour
See also Cate (2009) Animal Behaviour 77: 785-794
Genetic Variation in a
Population Influences
Behaviour
Discontinuous
Continuous
No. of
individuals
% time spent feeding
% time spent feeding
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
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
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
Next Lecture
• Does behavioural variation have a genetic
component?
• Can we find genes involved in behaviour?
• Human behaviour and genes