Notes
E1 Stimulus and Response
Neurobiology and behaviour
E.1.1 Define the terms stimulus, response and reflex in the context of animal behaviour
E.1.2 Explain the role of receptors, sensory neurons, relay neurons, motor neurons, synapses
and effectors in the response of
animals to stimuli.
E.1.3 Draw and label a diagram of a reflex arc for a pain withdrawal reflex.
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The central nervous system includes the brain and the spinal cord.
The spinal cord acts independently from the brain during reflex actions.
The reflex is an automatic response to specific stimuli.
The reflex response is a fast involuntary reaction which increases the chance of an animal avoiding damage and
therefore increasing chances of survival.
E.1.4 Explain how animal responses can be affected by natural selection, using two examples.
Natural selection is the mechanism of evolution and requires three things:
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Variation in the phenotypes
A genetic basis to this variation
A change in the environment
If the organism is evolving then we might expect to observe a change in the frequency of heritable characteristics.
Example 1: European Blackcap migration patterns
Example 1:Bird: Sylvia atricapilla
Common name: Blackcap
Phenotypic variation is in the direction of
migration (behaviour).
grounds in Germany to over
a)The original behaviour is that the Blackcap
migrates SOUTH from its summer breeding
winter in Spain.
(b) The new behaviour in some
migrate to in a westerly
of the Blackcap population (10%) in which they
direction to the UK.
The hypothesis is that this
an increased fitness value of
behaviour has a genetic basis and that there is
migration to the west.
Experiment:
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The researcher collected the un-hatched eggs from parent birds that had visited the UK in the previous winter.
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The un-hatched eggs are incubated away from the parents and have no contact with parent birds.
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Similarly un-hatched eggs from parent birds that over wintered in Spain the previous winter are collected,
incubated and released as before.
Results:
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Birds of UK parentage flew west.
Birds of Spanish parentage flew south.
Conclusion:
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The direction of migration is genetically determined and the population is diverging due to behaviour (not
speciation yet).
Discussion:
What is the advantage of flying west to the UK?
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Climate change will be less severe winters in the UK due to climate change
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Birds going to the UK to winter do not having to traverse the Alps in their flight path.
The UK is much closer meaning that birds returning to the breeding grounds begin pair bonding much earlier.
They will reproduce and pass on this heritable trait of ‘West flying’ to their offspring.
The ‘West flying’ behaviour will become more common.
The population has changed with two types of behaviour emerging ‘south flying’ and ‘west flying’, both are
genetically determined.
Reported that the northern wintering birds (west flying) are also producing larger clutch sizes and fledge more
young.
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Example 2: Prey preference in the Garter Snake of California
Garter Snake Image: (Thamnophis elegans)
Coastal snakes diet includes amphibians and the Banana slug
(Ariolimus californicus)
Inland snakes diet main component frog, leach and fish (slug is
absent)
Hypothesis:
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The difference in diet selection is behavioural and
genetically inherited.
Experiment:
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In an experiment pregnant snakes from the two regions have been collected. Inland and Coastal animals are
isolated from each other.
The hatchlings are offered Banana slug food over a 10 day period
Results:
Conclusion:
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Costal Garter Snake eat more Banana slugs than Inland Garter snakes
Behaviour differences are genetically based
Two populations have diverged due to a difference in behaviour (not speciation, yet).
Discussion:
This experimental conclusion was followed up with an investigation looking for the heritable aspect of the ‘slug smelling’
difference between coastal and inland Garter snakes. The difference between the coastal and inland Garter snake is
genetic, the gene allows the snake to detect the molecule that is the slugs ‘smell’. In other words the sense of smell of
the snakes is different.
The evolution of ‘slug smelling’ in coastal species is an adaptation made in the colonisation of these regions (10,000
years). Those individuals with the ‘slug smelling’ gene found more or better food than ‘non smellers’ , through better
more successful reproduction this gene become more frequent in the population.
The question which arises from this study is will the two groups become reproductively isolated from each other, in
other words speciation?