Social Behaviour

Learning outcomes

To know definitions of and reasons for altruism and kin selection, social behaviour in insects and the complexities of primate behaviour.

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Detailed learning outcomes Many animals live in social groups and have behaviours that are adapted to group living,

such as social hierarchy or cooperative hunting and defence.

(i) Altruism and kin selection An altruistic behaviour harms the donor individual but benefits the recipient. Reciprocal

altruism, where the roles later reverse, often occurs in social animals. The prisoners’ dilemma is a simple model.

In cases where individuals are related (kin) there may be no requirement for the roles to reverse. Instead, the behaviour benefits the donor in terms of a potential increased survival of shared genes.

(ii) Social insects In the societies of insects such as bees, wasps, ants and termites, only some individuals

contribute reproductively. Most members of the colony are workers, who cooperate to raise relatives.

(iii) Primate behaviour The long period of parental care in primates gives an opportunity to learn complex social

behaviours. To reduce unnecessary conflict, social primates use ritualistic display and appeasement

behaviours. Grooming, facial expression, body posture and sexual presentation are all important in different species.

In some monkeys and apes, alliances form between individuals. These are often used to increase social status within the group.

The complexity of social structure is related to ecological niche and taxonomic group.

Some animals exhibit altruism.Behaviour that reduces an individual's fitness while increasing the fitness of another individual.

Some altruistic acts can be explained in terms of kin selection (altruistic behaviour towards relatives).An animal can increase the survival of genes like its own by helping relatives.

Altruism and kin selection

In reciprocal altruism, a favour may be repaid later by the beneficiary or another member of the social system.

Altruism and kin selection

This explains altruistic acts by non-relatives, eg vampire bats sharing blood.

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Naked mole rats also exhibit altruism/kin selection.

The reproducing female (queen) mates with one to three males (kings).

The rest of the colony consists of non-reproductive females and males, who care for and protect the queen, kings and new offspring.

Explaining cooperation as an evolved adaptationHow can natural selection favour a habit

of cooperation? The advantages of cooperative over

solitary action (cf. Dunbar,1988):1. predator defence

2. resource defence

3. foraging/hunting efficiency

4. infant care.

Kin selection Individuals reduce their net lifetime production of

offspring in order to help their relatives reproduce.

Kin selection can lead to the extreme altruism of the workers of some social insects.

Even though the workers are sterile, they help their siblings to survive and reproduce, passing on by proxy the genes responsible for their altruistic behaviour.

Hamilton’s law A preliminary explanation: Hamilton’s law

of inclusive fitness : rB > Cr = biological relatedness of giver and receiverB = benefit to receiver (survival)C = cost to give (1)

The net benefit minus the cost must be greater than zero.

Hamilton’s law

Coefficients of relatedness table

Relationship Coefficient (r)

Parent–offspring 0.5

Siblings 0.5

Half-siblings 0.25

Uncle/aunt–niece/nephew

0.25

Grandparent–grandchild

0.25

Cousins 0.125

Hamilton’s law

How does this explain the evolution of altruism? A sister gives up her life for three of her siblings

(r = 0.5):

benefit = 0.5 × 3 = 1.5 cost = 1.0

(benefit – cost) = 1.5 – 1.0 = 0.5

Thus the sacrifice is a benefit that outweighs costs and the gene for altruism could evolve in a population.

Hamilton’s law

Social insects such as termites, wasps and bees are sisters.

Bees die once they have stung in defence of a colony – this benefits all and fits with Hamilton’s law.

In behavioural ecology a signal is a form of communication that causes a change in behaviour in another animal.

Social behaviour depends on signalling: sounds scents displays touches.

Complex social organisation hinges on complex signaling

Signalling in bees

Honeybees perform dances that seem to communicate the direction and distance of nectar to other members of the colony.

The round dance indicates that food is nearby, in an unspecified direction.

The waggle dance probably indicates both distance and direction of food.

Other examples of sociable insects:

termites ants.

Agonistic behaviour The logic of fighting is decidedly suspect in

most cases. One animal is going to win and the other will

lose. The loser has gained nothing, and may well

have sustained disastrous injury. Relatively minor injury is likely to have fatal

consequences by preventing capture of prey or allowing a predator to catch an individual with, for example, a slight muscle strain.

Even the winner may be damaged, and must balance the risk of injury with the potential gain in food, territory or mating success.

Threat displays allow animals to assess the likelihood of winning or losing before actually taking the risk of battle.

Agonistic behaviour is social behaviour consisting of threats and combat that settles disputes between individuals in a population.

Rituals involving agonistic behaviour often resolve confrontations between competitors.

Agonistic behaviour can directly affect an individual's evolutionary fitness.

The victor often gains first or exclusive access to mates, food, etc.

Threat displays usually involve displaying either strength or weaponry to the full.

This is usually enough for the smaller or weaker to realise that further conflict would be pointless.

Retreat is a very important feature of conflicts. In artificial situations where retreat is not a

possibility, it is very common for threat displays to lead to vicious and often fatal fighting.

Overcrowded domestic animals are a ready example, where battery hens have to have their beaks removed and intensively reared pigs have their canine teeth pulled out at birth to avoid injuries.

Appeasement

In natural situations where retreat is not a possibility (young birds are often the targets of redirected aggression and escape is not really an option), behaviours which can reduce the aggressive motivation without retreat may be of greater value.

Appeasement gestures fall into two groups:

• One type inhibits attack by arousing a conflicting tendency in the attacker, eg postures reminiscent of sexual activity and behaviours normally associated with young animals

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• The second type relies on demonstrating the exact opposite of threat behaviour, eg bared teeth, face to face, hackles raised all constitute threat in most dog-like species, whilst wide open mouth, head and hackles down, and a sideways-on position are appeasing gestures.

Many animals live in social groups maintained by agonistic behaviours.

Dominance hierarchy is the ranking of individuals based on social interactions.

Dominance hierarchies are maintained by agonistic behaviour

Chickens establish a ‘pecking order’

Resources are often partitioned based on the dominance hierarchy.

Dominance hierarchies and reconciliation behaviour in chimpanzees

Dr Jane Goodall is one of the world's best-known biologists.

She has studied the behaviour of chimpanzees in their natural habitat, in East Africa, since the early 1960s.

© The Jane Goodall Institute/Hugo Van Lawick

Dr Goodall’s research indicates that dominance hierarchies and reconciliation behaviours are integral parts of the lives of many primates, for example a chimpanzee that has threatened another member of its group may use a hand gesture to invite reconciliation.

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Acknowledgements

Thanks to R. Purdie at Sanquhar Academy for use of some materials.