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Summary Animal Behavior
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This is a summary of the textbook Animal Behavior, integrated with some lecture notes. It covers all main aspects explained in the book and in the lectures of the course
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ANIMAL BEHAVIOURCHAPTER 1 - INTRODUCTION TO ANIMAL BEHAVIOUR
Natural selection and evolution of behaviour
Behaviour an internally coordinated response of whole living organisms to external and/or internal
stimuli. It is important to understand the behaviour of animals to better design the environment where to
keep them in captivity. NB: individuals of the same species can behave differently (e.g. can build their nest
in a different way).
Charles Darwin book “On the origin of species” introduces the theory of evolution by natural selection,
that had big impact on the development of behavioural science.
Evolution of a species exists if three conditions are met:
1. Variation: members of a population differ in a certain characteristic.
2. Differential reproductive success: some individuals with a particular characteristic reproduce more
successfully.
3. Heredity: parents are able to pass on that particular characteristic to their offspring.
If these conditions are met, the population evolves and each individual will have that characteristic (trait)
associated with successful reproduction. How successful an individual is at transmitting its traits to the next
generation is called fitness. The traits associated with successful survival and reproduction are called
adaptations.
Example evolution: Galapagos finches (birds) have changed the shape of their beaks through time to adapt
to a certain diet depending on where they lived.
Evolution has to do with genes: the alleles that cause traits linked to successful reproduction will become
more common over time, while those associated with reproductive failure will disappear. Three important
points:
1. Only genes replicate themselves, organisms do not. Organisms are only vehicles in which genes
travel.
2. Evolution is NOT natural selection. Evolution = change in gene frequency in a population. Natural
selection = one of the causes of evolution.
3. The individuals that reproduce more cause a population to evolve (process called descent with
modification).
Modes of natural selection:
- Directional selection: the ones with the high values of
the trait (darker color in this case) have higher fitness
(reproduce successfully and evolve).
- Disruptive selection: the ones with the highest and
lowest value of the trait have higher fitness.
- Stabilizing selection: the ones with intermediate value of
the trait have higher fitness.
- Sexual selection: it is about competition between
individuals.
- Selection on behaviour
,Heritability H2 it is the proportion of phenotypic variation in a population that is caused by genetic
influences. NB: also behaviours can be inherited by offspring from the parents. For example, mother birds
that show more exploratory behaviour in the environment have offspring that also show high exploratory
behaviour.
To establish why a certain behaviour has evolved, behavioural biologists propose hypotheses. If only one of
these hypotheses gives an explanation about the behaviour, the other hypotheses are called alternative
hypotheses. If multiple hypotheses can apply to the behaviour, we call them non-mutually exclusive
hypotheses. The hypotheses are used to make predictions about the behaviour being studied.
Principle of parsimony simpler explanations are more likely to be correct than complex ones.
When biologists set a hypothesis and a prediction related to a potentially adaptive behaviour, they consider
the costs and benefits of that behaviour for the animal:
- Fitness costs: the negative effects of a trait on the number of surviving offspring produced by an
individual.
- Fitness benefits: the positive effects of a trait on reproductive success.
To understand how and why an animal behaves, we have to explore and integrate both the proximate and
ultimate causes of the behaviour, called levels of analysis:
- Proximate causes: they focus on understanding the immediate causes of behaviour
o Mechanism: how neuronal-hormonal mechanisms that develop in an animal during its life
control what an animal can do behaviourally
o Development (ontogeny): how genetic-developmental mechanisms influence the assembly
of an animal and its internal components.
- Ultimate causes: they focus on the role of evolution in influencing behaviour
o Evolutionary history (phylogeny): the evolutionary history of a behavioural trait from
ancestral species.
o Adaptive function: the adaptive value of a behavioural trait as affected by the process of
evolution by natural selection.
These four causes of behaviour represent the Tinbergen’s four questions:
1. Mechanism: What causes the behaviour to be performed? Which stimuli elicit or what physiological
mechanisms cause the behaviour?
2. Development: How has the behaviour developed during the lifetime of the individual? In what way
has it been influenced by experience and learning?
3. Evolution: How did the behaviour evolve? How has natural selection modified the behaviour over
evolutionary time?
4. Adaptive function: Why is the animal performing the behaviour? In which way does the behaviour
increase the animal’s fitness (i.e. its survival and reproduction)?
Approaches to studying behaviour
Observational approach: most basic; the animal is observed behaving in nature or in the lab to find a
relationship between its traits and the characteristics of its social/ecological environment, or to its
internal/developmental state.
Experimental approach: the characteristics of an animal or its environment are manipulated to find a
relationship between traits more directly.
,Comparative approach: many different species are compared to find general patterns of why a certain
behaviour evolved. This approach gives info about the evolutionary history of adaptive traits, by identifying
the characteristics that ancestral species had and how those traits gave rise to the ones we see in modern
species. This approach also informs us if there were evolutionary constraints (limitations) on the
appearance of the trait.
Example examination of a behaviour: mobbing in gulls
Mobbing = le specie di gabbiani che fanno il nido a terra (ground-nesting gulls) assalgono un potenziale
predatore che potrebbe avvicinarsi ai nidi.
Predator distraction hypothesis = mobbing potential predators distracts them from depredating nests.
Consider the costs and benefits of this behaviour for gulls: costs gulls spend time and energy by
attacking predators, and might be injured; benefits increased offspring survival because nests are not
attacked (il beneficio è più grande del costo, quindi hanno questo comportamento). They do mobbing
because the benefit is higher than the cost.
One of the predictions that results from the hypothesis, is the idea that gulls force predators to put more
effort in finding a prey than normal.
Observational approach: by observing a gull colony, it resulted that predators cannot look around to find a
prey while they are being mobbed, because they are distracted.
Experimental approach: 10 chicken eggs were placed on a line running from outside to inside the gull
colony. Eggs outside the colony were more likely to be found and eaten by predators because gulls did not
start mobbing to protect them; they only protect eggs inside the colony.
Comparative approach: different gull species are compared ground-nesting species perform mobbing
because their nests are at high risk; non ground-nesting species do not perform it because their nests are at
low risk (e.g. it is hard for a predator to find a nest on a cliff). Probably, the ancestor of gulls was a ground-
nesting species, and this trait remained in most modern gull species because they all descend from the
same ancestor.
Divergent evolution: some gull species might share the same ancestor, but have different
behaviour (e.g. una fa il nido per terra e fa il mobbing, l’altra lo fa in cima alla scogliera e non fa il mobbing)
because they are exposed to different selection pressures (and evolved differently).
Convergent evolution: some gull species have different ancestors, but have the same mobbing
behaviour because they are exposed to similar selection pressure (e.g. they make nests on the ground).
CHAPTER 3 – DEVELOPMENTAL AND GENETIC BASES OF BEHAVIOUR
Behaviour requires genes and the environment
Interactive theory of development it says that the development of a behavioural trait depends both on
the genetic information and the environmental stimuli. The interaction between genes and environmental
stimuli leads to the production of a behaviour and its evolution = behaviour is both genetic and
environmental.
Example on this theory worker bees change their roles during their life. In the first stages of life,
they clean the comb cells, then become nurses that feed larvae, then they distribute food to other worker
,bees and in the last stage of life they search for pollen. The bee changes its behaviour because there are
changes in the interactions between its genes and in its environment. It was demonstrated that in these
different types of bees also different genes are activated, and the activation of certain genes (and change of
role) depends on the needs of the brood (se c’è bisogno di più nurses, le api che puliscono l’arnia cambiano
e diventano nurses).
Another example in bees is that larvae that are destined to become queens are fed with royal jelly
for a longer period. A protein contained in it causes the larvae to become queens because it changes the
activity of certain genes, and consequently the behaviour of the bee. This is caused by epigenetic
modification (e.g. histone modification and DNA methylation), that are changes in the structure of DNA but
not in its sequence. The change in the environment is the high amount of royal jelly ingested by larvae, that
interacts with genes that consequently change their activity, so the bee adjusts its behaviour.
Behavioural differences caused by environmental differences according to the “armpit effect
hypothesis”, if individuals learn their own smell, they can use this information to understand if another
individual of the same species is a relative or not. For example, squirrels that are grown together (even if
they are not siblings) tend to show less aggression towards each other; they show more aggression towards
squirrels that were grown somewhere else because they have a different smell (even if they are siblings).
Behavioural differences caused by genetic differences an example is the diet of the garter snake:
populations of this species that live in the inland of North America eat fish and frogs, while those living in
the coastal areas of California eat banana slugs. It was demonstrated that these differences are genetic
because new born snakes coming from both areas were put in separate cages without their mother and
siblings, so they could not be influenced by their behaviour. The results were that the two different
populations still ate their favourite food.
Learning and cognition
Imprinting a learning process that occurs in the early stages of life of certain social species (e.g. birds),
for example chicks recognize the first thing they see as their mother. This is also influenced by genes and
environment.
Birds have other specialized learning abilities, such as remembering where they have hidden food. This
ability to store spatial information in their hippocampus is related to the ability of their brain to change in
response to sensory stimuli associated with hiding food.
Conclusion: learned behaviours depend on environmental stimuli and on genes.
“Sex differences learning hypothesis” it says that if males and females of the same species get a
different benefit from a certain learned behaviour, it means that there will be a difference in learning skills .
For example, some birds hide seeds for a long time to eat it when there is a lack of food. However, males
are able to better remember where they have hidden the seeds compared to females, because females
usually stay in the nest to care for eggs while males usually look for food. Consequently, males have a
better long-term memory.
Operant conditioning it is when animals learn to associate a voluntary action with the consequences
that follow that action. For example, a rat is put in a box with a bar on its wall. When the bar is pressed,
food comes in the box. At first, the rat presses it accidentally but then learns that it receives food, so it
starts to press the bar voluntarily. Another example is that when rats find a new food, they taste a little
piece and then see if it causes illness or pain; if they do, they will avoid that food.
,Evolutionary development of behaviour
Evolutionary developmental biology is a field of research that compares the developmental processes of
different organisms to deduce the relationships between them and how these developmental processes
have evolved.
Early life developmental conditions
The environmental conditions (e.g. stress, lack of food) in the early life of an individual will influence its
behaviour later in their life.
Developmental homeostasis the ability of many animals to develop more or less normally despite living
in a deficient environment or having defective genes.
Example: a young monkey is separated from its mother soon after birth and placed in a cage with
an artificial surrogate mother. The monkey gained weight normally and developed a normal physical
appearance. However, the monkey soon started to bite itself and was terrified when met another monkey
because of the lack of social interaction. Here comes the “social experience hypothesis” young animals
need social experience to develop normal social behaviour.
“Developmental constraint hypothesis” individuals born in a low-quality environment (e.g. lack of food)
have a reduced fitness later in their life (they do not reproduce successfully).
“Predictive adaptive response hypothesis” individuals tend to adjust their phenotype and behaviour
during development to overcome constraints that occur in their early life, so there is less possibility that
they will have problems later.
Conclusion: depending on the species and the environment in which it lives, early life conditions can have a
negative, positive or no effect on the development of behaviour and fitness.
Developmental switch there are many species in which more than one phenotype is possible, because
of environmental differences. These different phenotypes arise through the process of phenotypic or
developmental plasticity. An example is polyphenism when multiple phenotypes arise from the same
genotype, e.g. bees have the same genotype but each bee type (worker, queen, male etc.) have a different
phenotype.
The different phenotypes arise in response to environmental stimuli, that can be the amount or
type of food available, social interactions (e.g. certain spiders develop faster in the presence of females) or
the presence of certain predators (in this case, a more “powerful” phenotype can arise in areas where
there are more predators).
Behavioural polymorphism in this case, the formation of different phenotypes in the same species is not
influenced by environmental conditions (like in developmental switch), but by genes. These different
phenotypes arise because of the formation of a supergene a region of DNA containing many linked
genes that influence a behavioural phenotype. An example is the existence of 3 types of males in ruff: the
“independent” type, territorial with an
ornamental plumage; the “satellite” type, not
territorial and with a light plumage; the
“feader” type, not territorial and with a
female plumage but bigger testes. The last
two types have two different supergenes that
evolved independently.
,CHAPTER 2 – SONG LEARNING IN BIRDS
Calls both sexes can do them, they are not learned and have a simple structure.
Songs only males can do them, they have a complex structure and are usually learned. They are used to
attract females, to defend territory and for social coordination.
Acoustic signals in general are used to communicate over large distances.
Development of song learning (proximate cause)
How did the behaviour of song learning develop during the life of an individual?
Birds species might have a distinctive song. It was found that different populations of the same species
might sing different versions of the same song, as if they were dialects, depending on the area where they
live. This was found in the white-crowned sparrow: males sing a certain song during the mating season, but
this song differs slightly depending on the area where sparrows live. There are three non-mutually
exclusive, proximate hypotheses that might explain the development of song dialects:
- Genetic differences hypothesis differences in song result from genetic differences between
populations. However, scientists found little genetic differences between populations of white-
crowned sparrows so this is not a good explanation for the existence of dialects.
- Acoustic stimulus hypothesis differences in song result from differences in a bird’s acoustic
environment. Young males living in area A learn to the dialect that adult males of area A sing, while
young males from area B learn that sang by adults of area B, because they are what they listen to.
This hypothesis could be true, because when chicks of sparrows were hatched and raised isolated
in the lab, they were not able to sing the dialect from where they came from, because they never
listened to it. However, they were able to do it if they listened to the recordings of the dialect.
- Social interaction hypothesis differences in song result from social interactions between a
young male and its tutor. To test this, young sparrows were placed in cages where they could see
and hear a strawberry finch (another species), and hear an adult sparrow. The young sparrows
learned the song of the strawberry finch, even if it is another species, because they could see it;
they did not learn the song of the adult sparrow because they could not see it. This demonstrates
that also direct social interactions are important in song learning in birds.
NB: the studies on these hypotheses helped understand how dialects can be learned, but not how they
develop at first.
Mechanisms of song learning (proximate cause)
How do birds sing? High frequency sounds beak is open widely. Low frequency sounds beak is open
narrowly, so it can produce sequences of notes very fast. NB: birds with a big beak cannot really produce
songs like birds with pointed beaks.
What is the physiological mechanism that makes birds sing? To understand these mechanisms, we have to
study them at brain level (e.g. where is the memory of the dialect stored in the brain?).
When a young bird hears a sound, it activates sensory signals that are transmitted to the brain. These
signals probably alter the expression of certain genes, which in turn alters the biochemistry of brain cells
where the signal arrived, so also the behavior and learning process of the bird changes.
There are specific parts of the brains on sparrows and other songbirds that are involved in production and
learning of sounds. One of these parts is the high vocal centre nucleus (HVC), that is connected to other
, parts such as the arcopallium (RA). The RA is linked to the syrinx, that in birds is the structure that
produces songs. Another part of the brain is the lateral magnocellular nucleus of the anterior nidopallium
(LMAN), which is essential in memorizing/learning songs.
Evolution of song learning (ultimate cause)
How this behaviour evolved and when in the past did ancestral birds start learning their species-specific
songs and developing dialects?
Only 3 members of the 23 avian orders are able to learn songs: parrots, hummingbirds and songbirds. The
question is: did their ability to learn songs evolve independently or not? There are 2 possible answers:
- The ability to learn songs originated 3 different times (one for each group)
- It originated in the ancestor of all the 23 groups but was lost in 20 of them.
If we use the principle of parsimony (the simplest explanation is the most probable), the first answer is the
most probable.
Adaptive value of song learning (ultimate cause)
Why vocal learning has evolved? There are different hypotheses:
- Environmental adaptation hypothesis vocal learning evolved because it promotes acoustic
adaptation of vocal signals to the local habitat = gli uccelli imparano un certo dialetto/song tipico
della loro area per comunicare meglio.
- Recognition hypothesis vocal learning evolved because it allows vocal signals to become more
recognizable, and promotes identification of neighbours = they learn to better communicate with
others, both “friends” and rivals.
- Information-sharing hypothesis vocal learning evolved to allow expansion of the vocal
repertoire in systems where living with relatives favours sharing of information = il “vocabolario”
dei bird può diventare più ampio se sono in grado di imparare suoni, così possono comunicare
meglio con I relatives.
- Sexual selection hypothesis vocal learning evolved because it enables to increase the complexity
of the vocal repertoire of a bird, that is used in male-male competition, or is favoured by female
preferences.
- Geographic matching hypotheses vocal learning evolved to promote geographic variation in
vocal signals, which in turn allows assortative mating according to the area of origin and promotes
local adaptation = se un maschio impara il dialetto di una certa area, le femmine sono in grado di
capire che viene da quell’area e che quindi ha certi geni/caratteristiche. Di conseguenza la femmina
sceglie il maschio “locale” così anche la loro offspring sarà adattato a quell’area.
Ecology of acoustic communication
Based on these characteristics, the sound heard by the receiver can be different by that produced by the
sender:
1. Sound transmission characteristics. The sound can be transmitted over a dense (e.g. forest),
medium or open (e.g. field) environment. If you are in a dense forest, you will hear a different
sound from that produced by a bird 100m distant because it is absorbed by the leaves. For this
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