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In this module, we'll be mainly using the ... approach to animal behaviour


- equavilent to functional approach (defined by tinbergen)


Starting assumption: behaviours, like any other trait, are the product of...

natural selection - adaptations that allow organisms to survive and reproduce better than if they lacked those traits.


Social organisation of weavers:

Cassin's Malimbe is brightly coloured, generally breeds in ... ... - pair and build a nest together to raise offspring.

Grey-capped social weavers breed in ... ....

Black-headed weavers breed in ...; each male makes a nest and tries to attract a female. Nests are aggregated into large ... with dozens to hundreds of nests within a single tree. The males are much more brightly coloured than the females.

Sociable weavers build extraordinary nest structures which can weigh several tonnes and house hundreds of pairs, and can last decades. Within these communal structures, each pair makes their own ... .... Very little sexual dimorphism.

solitary territories,

small colonies (clusters of nests)

pairs, clusters

nesting chamber


How do we make sense of this diversity in weavers?

Understanding the rules and patterns observed across the species.


The first person to tackle this problem in an adaptationist way was ... ...

John Crook (1964) - early days of behavioural ecology

Asking questions such as why are some weavers solitary and others colonial, why are some dimorphic and others monomorphic?


John Crook went through all the studied weaver species and classified them according to their...

degree of sociality and the kind of pair bond that they had, in addition to their degree of dimorphism. He also recorded ecological features such as the habitat in which they lived, their diet etc.


He found some very consistent patterns that explained the degree of sociality and kind of pair bond. The percentage of species living in forests that are solitary is very ..., where as the percentage of grassland (e.g., ... ...) species that are solitary is very ....

Likewise, monogamy was far ... common in forests than grassland.

high (90%), sociable weaver, low (6%), more (100% vs 6%)

- (polygyny more common in grassland)


He observed some very consistent patterns that explained the degree of sociality and kind of pair bond. The percentage of species living in forests that are solitary is very ..., where as the percentage of grassland (e.g., ... ...) species that are solitary is very ....

Likewise, monogamy was far ... common in forests than grassland.

high (90%), sociable weaver, low (6%), more (100% vs 6%)

- (polygyny more common in grassland)


Crook was able to test the hypothesis that social structure and degree of sexual selection was a function of ... ....

- now know this is a very general pattern - long-tailed macaques live in very large groups and are primarily seed/fruit eaters, colobus monkeys live in relatively small groups that are leaf/fruit eating, golden lion tamarin monkeys primarily live in pairs (sometimes with helpers) and feed primarily on insects. Rules apply across different ... groups (... approach)

food distribution

taxonomic, comparative


Problems with comparative approach:

- phylogenetic .... Two species may share a particular behavioural trait not because they occupy similar ecological niches, but because they are closely related. This must be controlled for - tools to do so are now very powerful.



An alternative approach to the comparative one (comparing taxa) is to ask questions about ... variation - why do ... vary in morphology or behaviour. What are the causes and fitness consequences of this variation?

individual, individuals


e.g. a wading bird called a ... is a ... species. Males gather in small groups and display to visiting females, who choose a single male to mate with and then leave them to look after the offspring. Males have large ... around their heads that they use to display to females. Some males are very successful and can monopolise matings within groups. What is it about these individuals that makes them attractive compared to other males.

There are also ... males who occupy the fringes of the group trying to sneak copulations with females as they come and go.

Some males also ... ..., and do not grow a ....

ruff, lekking, plumes, satellite, mimic females, plume (again sneak copulations)


We can look at how successful different strategies are at increasing the ... of ... expressing them.

- can be used to explain seemingly counterintuitive behaviours such as infanticide and sexual cannibalism.

fitness, individuals


So comparative analysis looks at ... variation and study of individuals looks at ... variation

interspecific, intraspecific


Long-term studies of ... individuals are particularly valuable when studying intraspecific variation, and have been important in the development of evolutionary theory.

There are drawbacks
- difficult to get long-term funding (tends to only work in 3 year packages - can't ask to fund 50 yr elephant study)
- Takes a long time to get data and results, particularly for long-lived species such as red deer, elephants or humans.

marked (can follow throughout lifespan, how many offspring, survival rates of individuals following different strategies etc.),


An alternative approach is to conduct ... studies in the field or lab. Often short-term and do not require natural variation across lifetimes to determine why animals behave the way they do. Instead, certain traits are ..., and the ... of these on individual fitness are studied.

experimental, manipulated, consequences


E.g. male long-tailed widowbirds have enormous tail .... The length of these tails were manipulated to test the hypothesis that these tails were the product of ... ... (longer tailed males more attractive to females than shorter tailed males).

plumes, sexual selection


What was done to the control males?

Feathers cut off then reattached at the same length


Found that...

number of nests attracted by males varied in relation to the manipulation: longer tails = more nests.


Lab experiments have the benefit that they are often much more ... than in the field, and results are often obtained much ....

controlled, quicker (e.g. drosophila or microbes that reproduce very quickly)


The adaptationist approach:

- comparative analysis - interspecific variation

- study of individuals - intraspecific variation
- observations in field/ lab
- experimental studies in field/lab

Relies on evolutionary theory - testing predictions and hypotheses derived from evolutionary theory - sound theoretical basis allows us to propose hypotheses that we can go out and test - scientific method.


Key thinkers in development of evolutionary theory:

- Darwin (1850s-1870s)
- Fisher (1930s-1940s)
- Maynard-Smith (1960s-1990s)
- Hamilton (1960s-1990s)
- Trivers (1970s)
- Dawkins (1970s-2000s)

Bunch of ledges.


The adaptationist approach is to study behaviour and ecology of individuals and species all founded on sound evolutionary theoretical principles which allow us to test hypotheses.

Weigh up the ... and ... of a behaviour to determine its ... ..., i.e. what is the evolutionary value (...) of a particular trait - why has it evolved?

costs, benefits, adaptive significance, function


What biological unit does natural selection act upon?

Natural selection acts on ... to produce organisms that are designed to maximise their fitness

The gene or the individual
- individuals survive, reproduce and die, but the consequence is the gene frequencies in the population change through time



This means that individuals and their genes are expected to behave ....

selfishly (to maximise lifetime reproductive success)

- maximise number of copies/offspring in next generation


So genes are going to be in conflict with other alleles on the same locus, and individuals will be in conflict with other individuals to maximise LRS. Natural selections makes conflict ....



Group selection doesn't work because it is vulnerable to....

exploitation by selfish individuals.


Conflict is ... - inter- and intra-specific. It is also rife within related families. e.g. males compete with other males for females and females compete with other females; males and their female partners are in sexual conflict over investment in offspring; offspring are in conflict with their parents over how much their parents should invest in them; and offspring (siblings) are in conflict with each other over their share of the parental care.



It is expected that we see selfishless and conflict everywhere within nature. But ... is also rife in nature, within and even between species* - however, it tends to be ... in evolutionary terms.

cooperation, unstable (e.g. vulnerable to exploitation)

*e.g. fish and cleaner shrimp (cleans gill rakers and removes parasites)


The ... ... game is used to demonstrate the instability of cooperative behaviour:

A group of individuals all contribute to a public good, e.g. taxes. Everyone benefits from the public good (provision of resources and services). There may be selfish individuals in the population who do not contribute to the public good yet still gain the benefits. This creates a social dilemma, as groups of cooperators out-compete non-cooperators outside of the group, yet within the group, non-cooperators will do better than cooperators. There will always be the temptation to defect in any cooperative endeavour.

public goods


Hardin described this dilemma as the ... ... ... .... He used the analogy of livestock owners exploiting the common land. When there are shared benefits or a 'public good' that individuals contribute to, there will be a temptation to cheat, or free-load. E.g. moorhen partners may provide a lower share of the parental care if they can get away with it.

tragedy of the commons (1968)


Sociable weavers must continuously maintain their large shared nest structure, which is essentially a ... .... How is it ensured that every member of the colony contributes to this upkeep? - read van dijk et al. (2014)

common good


Adaptation is...

evolutionary change resulting from natural selection


A unit of natural selection must have the ability to survive, ... and make accurate ... of itself

reproduce, copies - general expectation that behaviour should be selfish rather than cooperative


Cooperative behaviour is defined as behaviour that benefits another ... and that has been selected for because of its beneficial effects on the ....

individual, recipient

- the selected for part is important - cows defecating is beneficial to flies etc but it hasn't been selected for because of this benefit but for other reasons


Paradox: groups composed of ... out-compete groups of ..., but ... do better than ... within groups.

cooperators, non-cooperators, non-cooperators, cooperators

- tragedy of the commons


Theoretically, ... usually replaces ..., so the tragedy results in social ....

selfishness, cooperation, collapse

- however the common existence of cooperative behaviour demonstrates that the tragedy is not inevitable and mechanisms to resolve the conflict between selfish interests and social cooperation must be widespread in nature


Who (wrongly?) proposed that "it was an evolutionary emphasis on cooperation instead of competition in the Darwinian sense that made for the success of the species, including the human", using philosophical and social arguments but providing no evolutionary mechanisms.

Peter Kropotkin - in his book "Mutual Aid: a factor in evolution" (1902)


Who coined the term "survival of the fittest" in 1864?

Herbert Spencer


Who founded the idea of eugenics and biological determinism in 1883?

Francis Galton


In the early 1900s, whose work was rediscovered and dominated work on the mechanisms of genetics and evolution?



When was this combined with Darwin's work to found neo-Darwinian modern syntheses, bringing together natural selection, Mendelian genetics and population genetics?

Ronald ... was a key architect of this.


Fisher (essentially a statistician applying this to biology. An important book was "genetical theory of natural selection" (1930))


Fisher recognised that traits favoured by natural selection are those that enhance ... fitness, and recognised that there will be "... effects in cases in which an animal favours or impedes the survival or reproduction of its relatives" though "such indirect effects will in very many cases be unimportant compared to the effects of personal reproduction"

individual, indirect


Another key figure in the development of neo-darwinism was JBS ..., who was a fan of experimental biology. He apparently quipped in a pub that he would not lay down his life for a brother, but for...

Haldane, "two brothers or eight cousins" - stated importance of relatedness in the expression of behaviour


Bill ... had read extensively on Haldane's and Fisher's ideas and was a brilliant natural historian. He noticed social behaviour everywhere in nature. He saw that the potential for an evolutionary explanation for altruism if...

Hamilton, the level of selection was considered to be the gene rather than the individual - this will only be the case "if the affected individual is a relative of the altruist, therefore having an increased chance of carrying the gene"

- this was the first verbal expression of gene-level selection


In 1964 Hamilton used his idea of gene-level selection to propose his theory of ... ....

inclusive fitness


Inclusive fitness theory:
A gene can increase transmission to the next generation by increasing the fitness of...

- the individual it is in = direct fitness
- individuals with copies of that gene = indirect fitness


inclusive fitness =

direct fitness + indirect fitness


r =

coefficient of relatedness


Fitness provided by ones own offspring only is known as...

personal fitness, or neighbour-modulated fitness


It is important to remember that inclusive fitness theory applies equally to actions whose effects on recipients are ... rather than ....

negative, positive (see table in photos - e.g. selfish or spiteful behaviour)


Cooperative behaviour can be ... beneficial or ....

mutually, altruistic

- altruism particularly interesting as decreases direct fitness of actor


In practice, inclusive fitness may be hard to measure (particularly ...; personal fitness is much easier to measure by counting the number of offspring). We have to know how many of the actor's offspring were attributable to the social interaction with another individual and how many of the recipients offspring can be attributable to the action of the actor, plus the relatedness of the offspring. Then indirect fitness can be quantified, and inclusive fitness can be derived. There are some good examples



Hamilton's rule can be used to understand whether a social trait is adaptive or not. Altruism evolves if:

rb > c

rb - c > 0

r = relatedness
b = benefit to recipient
c = cost to actor


E.g. kin selection tested in Turkeys (Krakauer, 2005):

Males form ... to court females -> ... gets all matings.
So why do subordinates help if they don't get any copulations themselves?

Relatedness among males within the coalitions is ....

The benefit to the dominant male of having subordinates (no. of offspring produced by dominant male) - (no. of offspring produced by solitary male) = ...

The cost to the subordinate (no. of offspring produced by solitary male) - (no. of offspring produced by subordinate male) = ...

coalitions, dominant, high (~0.42, nearly relatedness of brothers), 6.1, 0.9


So if rb - c > 0 = selected for, then...

(0.42 x 6.1) - 0.9 = 1.7

1.7 > 0 so cost of helping is outweighed by kin-selected benefit


Considering how long the theory has been around, remarkably few studies have actually been published that directly test this rule.

Such a shame, very meagre

It is very difficult tbf


Solutions to the difficulty of quantifying inclusive fitness e.g. using ... for fitness such as productivity of ..., not those who survive to adulthood, in a lifetime; ... of productivity e.g. single season reproductive attempt, offspring condition or mating success; survival across a ... time interval; or energy budget/food intake

proxies, offspring, snapshots, discrete


The evolution of life on earth entails a series of major transitions in complexity, e.g. the origin of chromosomes, the origin of eukaryotes, the origin of sex etc. Look more closely at origin of ... and origin of ... .... Also origin of human society/language. Each of these transitions involves ..., so social evolution theory explains each transition using the logic of inclusive fitness theory

multicellularity, social groups, cooperation


Why should single cells join to become mutually ... (origin of multicellularity)?

Hypothesis: high ... between cells played a key role in the transition to multicellularity

dependent, relatedness


There are two ways in which organisms can be multicellular: ... vs ... multicellularity.

obligate (e.g. us), facultative (e.g. slime moulds, which spend a large proportion of their lives as free-living amoebae which reproduce through mitosis. Under poor conditions they aggregate to form a slug, which eventually leads to a fruiting body)


Do obligate and facultative multicellular organisms differ in the degree of relatedness among their cells?

Inclusive fitness theory would predict a higher degree of relatedness in obligate multicellular organisms. This was tested by Fisher et al. (2015), who looked across the tree of life and found that multicellular organisms formed through clonal processes were more likely to be obligate multicellular organisms and those formed through non-clonal processes were more likely to be facultative. This fits the inclusive fitness theory prediction


Clonal groups also displayed higher ... of cells, and a higher probability of ... cells (altruism).

specialisation (suggesting higher commitment to multicellularity), sterile


So, looking at the major transition in the history of life on earth from unicellularity to multicellularity, we can see that it was facilitated by .... This was a ... transition. The relatedness has affected the degree of ..., specialisation and ... we see among the cells within multicellular organisms.

relatedness (determined by the process of group formation), cooperative, commitment, altruism


Besides kin selection, the most common evolutionary route to cooperation is probably



Mutualism describes a cooperative interaction in which...

both participants receive a more or less immediate benefit.

(reciprocity is when the benefit to the donor is delayed - risk of partner defecting before repayment)


There is little opportunity to ... in mutualistic interactions, though each partner will seek to maximise their own fitness.



Interspecific mutual interactions = ...

Intraspecific mutual interactions often referred to = ... ...

Here will refer to both as mutualism


mutual benefit


Immediate shared benefits needs no special explanation.

E.g. ... whale bubble ... -> come together and release bubbles from their blowholes to create a curtain that concentrates shoals of fish into a balling mass of food. The whales then emerge in the centre of this mass, taking huge gulps of fish = increased ... ....

humpback, netting, foraging efficiency (for all involved)


E.g. wild dogs cooperate in a mutualistic way when hunting, coordinating the way in which they chase down their prey. They have an extraordinarily successful hunting rate - around ...-...% of all hunts initiated by a wild dog are successful. Much higher than the solitary Cheetah, for example.



As lion prey increases in size, so does...

the tendency to hunt in large groups


Another mutualistic interaction in lions is ...

- female lions live in prides that vary enormously in their size. Females living in small prides will have a lot of neighbours nearby as they can't defend large territories. Females that live in large prides can defend larger territories and will have fewer close neighbours. This has important fitness consequences: increased reproductive success with fewer adult neighbours and increased wounding and mortality rate with increased number of male neighbours


Many social animals post ... to warn of predators, e.g. klipspringers, baboons and pinyon jays.

- assumed to be dangerous for sentinels (vulnerable to predators)
- used to be explained by reciprocity or kin selection. This view was turned on its head...


Bednekoff (1997) found that...

sentinels are safer than foragers, so sentinel behaviour can be explained as mutualism.


How are sentinels safer (according to Bednekoff)?

They observe predators, their identity and the direction from which they are approaching earlier than the rest of the group, so can escape more efficiently and effectively. Other individuals in the group may only have the alarm call, which is far less useful information.

Bednekoff coined the phrase "safe, selfish sentinels"


Clutton-Brock et all. (1999) supports this idea.

Meerkats feed primarily on ... dug up from the ground, spending a lot of time with their heads in the earth, unable to observe what is around them. This leaves them vulnerable to predation, especially from ... predators. To counter this risk, meerkats set sentinels, who may stand adjacent to foragers or find a higher vantage point for a better view of the surrounding terrain.

The study concluded that sentinel behaviour is an individual meerkat's optimal activity once...

invertebrates, aerial (e.g. birds of prey)

its stomach is full (meerkats fed well by researchers were more likely to become sentinels) and when no other animal is on guard.
- as advantage to being sentinel - mutualistic behaviour


Another e.g. of mutualistic sentinel behaviour is an interspecific mutualism between ... and pied .... Babblers spend a lot of time foraging for food on the ground, again leaving them vulnerable to predators, and also commonly post sentinels who make alarm calls if predators approach. Babblers also associate with drongos.

Long-term study by Ridley and Raihani (2006) found that babblers benefit from drongo alarm calls warning of predators, and drongos benefit by catching flying insects flushed by babblers on the ground.

drongos, babblers


In small babbler groups, drongos reduce the amount of time each babbler needs to spend as a sentinel. But as group size increases, the babblers become less and less responsive to drongo alarm calls, and babblers even displace drongos by chasing them away. This seems counter intuitive if the drongos provide a beneficial service to the babblers. Why is this behaviour observed?

Because drongos are not always mutualistic (often defect). At times, they try to kleptoparasitise food from the babblers by uttering false alarm calls that cause the group to flee, allowing the drongos to fly down and grab prey items that the babblers have just discovered. They particularly focus on younger babblers, who are more naive. Kleptoparasitism is more effective in smaller babbler groups as the babblers are more prepared to tolerate occasitional kleptoparasitism for the benefit provided by the sentinel drongo. As group size increases and the babblers capacity to post their own sentinels increases (+less time required to act as sentinel per capita), they no longer tolerate the kleptoparasitic behaviour and become less responsive to drongo calls and often drive them away.


Mutualistic relationships are always liable to lapse into parasitism, so this sort of uneasy mutualism is common. So how is cooperation maintained?
There are 3 solutions:

1. Facultative mutualism
2. Punishment/enforcement
3. Image-scoring/reputation


Facultative mutualism is when the 2 parties enter into the mutualistic relationship only when...

it is of benefit to both parties (e.g. babblers and drongos)


Punishment/enforcement mutualism is when...

one party is able to punish their social partner, forcing them to be cooperative (look more into).


Image-scoring/reputation mutualism is when..

it is beneficial to be seen to be cooperative - other potential partners are scoring you for your cooperative image and it is important to have a good reputation. This selects for cooperative behaviour


... and ... relationships often fall within the second and third of these categories.

Cleaner, client

(punishment/enforcement and image-scoring/reputation)


E.g.s of cleaners are:

cleaner ... (clean gills, mouth, outside of body), cleaner ..., ... (remove ticks and earwax)

wrasse, shrimp, oxpeckers


The blue-streaked cleaner wrasse eats ~... parasites (generally isopods) per day, inspecting ~2300 fish per day. Some clients visit cleaning stations every ... minutes throughout the day. Cleaners are tempted to cheat (defect) by eating mucus (for streamlining) or scales rather than the less preferred ectoparasites. How is this mutualism stabilised?

1200, 5

Punishment and reputation


How does punishment stabilise cleaner wrasse mutualism?

Clients very rarely eat cleaners (often vegetarian), so not that.

But clients are much more likely to leave or chase their cleaners as punishment for defection (blue-streaked cleaner wrasses preferred prawn over food flakes (~90% of the time) but learned to primarily feed on the flakes when fleeing or punishment (knocked by glass rod) were simulated)


How does reputation stabilise blue-striped cleaner wrasse mutualism?

Clients will often repeatedly use the same cleaning station. Clients with a choice of cleaning stations avoid cheats. 60% return to stations with a positive last interaction. Only 5% return to stations with a negative last interaction (client ignored or cleaner cheated by feeding on scales rather than ectoparasites). It is important for cleaners to have a good reputation if they want cleaners to return and provide them with food.

Additionally, clients shown a cooperative and a non-cooperative cleaner prefer to return to the cooperative cleaner (image-scoring is occuring). Cleaners are more cooperative when being image-scored as well (in a later study by Bshary and Grutter)


Another e.g. of punishment enforcing mutualistic interactions is in ... ants. They have an unusual social structure with no ... but instead a hierarchy of females with a dominant ... female, who is the only one who reproduces. There is a queue of females beneath her, waiting to assume the dominant position. Occasionally the beta female challenges the alpha in an attempt to take on her status and be able reproduce. When this happens, the alpha will try to mark the beta with a ... and, if this is successful, the challenger will be punished by other female workers. She can be pinned down for 24 hours and may lose segments of antennae or leg. Challenging has the potential to be very costly, which reduces the probability that subordinate females will challenge the alpha for a dominant status, enforcing mutualistic behaviour.

Dinoponera, queen, alpha, pheromone


Mutualistic coalitions of males may be important for securing matings with females, e.g. lions. However, males only form mutualistic coalitions with non-kin when paternity is shared relatively evenly so that there are mutual benefits among cooperating males.



(FIGS DOCUMENTARY) Sycamore figs appear never to ..., yet ... several times a year. Has no regard for season and drops leaves whenever.

flower, fruit


Figs have a mutualistic relationship with, which differ in size from the trees a billion times. Figs live centuries, ... ... live for hours. No fig tree exists without them.

fig wasps (1mm long), fig wasps


Sycamore figs found throughout tropical Africa. Thrive along .... They feed a greater variety of animals than any other tree in africa (so all rely on the fig wasp). Every few months, the tree produces up to a tonne of fruit. To reproduce, it must transfer pollen to make seeds and then disperse them.



Fig wasps are attracted by the ... of young figs. The wasps enter the figs, pollinating the flowers inside. Some of the flowers will become ..., others will become ... for the fig wasps. The tree surrounds each wasp egg with a capsule called a ..., which protects and nourishes it. The wasps inside the fig then proceed to ....

smell, seeds, nursery, gall, die (tree acts like surrogate mother until offspring hatch in 2 months time)


To feed the wasps and grow seeds, the tree must make ... with its leaves. Animals that eat these leaves are a major threat, as if too many are lost then the figs may have to be aborted. Eating the figs themselves is even worse. How does the fig tree prevent animals from eating the leaves and figs?


A sticky, foul-tasting milky latex is produced in the figs and leaves.


Some insects have evolved strategies to overcome the defences, e.g. fig longhorn beetles bite through the leaf ... to disrupt...

Fig katydids remove the leaf completely so the latex can't flow in.

veins, the flow of latex


After the wasps have entered the fig through the opening..

it is sealed up and coated with an antiseptic.


Nematodes get into the figs by using wasps like a...

... wasps use long ... to lay eggs in the fig from the outside, which kill the fig wasp and take over its gall.
... wasps can then fight steal the hole produced by this with their equally long but more flexible ....

... help the fig tree protect its figs by patrolling and killing any parasites they find. Anything too large to subdue (e.g. snake) is bitten and stung to drive it away. Their colony farms hilda nymphs on the figs and uses them to gain a supply of sweet juice from the figs that the bugs are able to extract.

trojan horse, ready to feed and then enter the next generation of fig wasps

parasitic, ovipositors, bandit, ovipositors (parasite of parasites)



After two months of producing sugar to feed the seeds and wasp, the fig tree drains the protective fluid within the figs to expose their galls. The female wasps cannot hatch yet and must wait for a mate. Male fig wasps have powerful jaws and break out of the galls. They then cut through a female's gall to let themselves in but not let her out. Males have no ... and only tiny eyes and antennae. They have very large and flexible intromittent organs. They mate with females before the females have hatched.

jaws, wings


The tree can produce up to ... figs. When the female fig wasps hatch from their galls. They are very different to the males, with large eyes, antennae and wings.



Males cut down white pollen-containing ..., the female scrapes of the pollen and packages it on her breast.



The males then burrow their way towards the edges of the fig. Their last mission is to do this and allow...

the females to escape (who then race to find another fig before nematodes devour them or predators, such as ants, munch them right up)


After the wasps leave, the figs...

ripen rapidly, becoming soft and orange and full of sugar. A feeding frenzy proceeds.


Fig trees are important food sources for so many animals as they..

fruit outside of the normal fruiting season, several times a year (as otherwise the short lived fig wasps would die out and they wouldn't be pollinated)


Living by water helps fig trees disperse their seeds, as figs...

float downstream and sprout along the strand line. Migrating catfish carry some back upstream


(MEERKAT CLIP) Meerkats search in the earth for food. Drongos produce alarm calls if they spot predators, and the meerkats escape to safety. When the predator passes the meerkats return to feed and the drongo gains their trust. The drongo then sounds another warning call, this time a false alarm, and the meerkats again flee. The drongo then feeds where the meerkats have unearthed some food. The meerkats only fall for the trick once. However, the drongo has learned to...

mimic the meerkats own sentry alarm call, and is able to trick them and get to their hard-earned food once again. The drongos are only deceitful during the hard winter months. The rest of the year they are honest and provide the meerkats with genuine protection. So overall they profit from the relationship


Reciprocity "you scratch my back...

ill scratch yours"

- Individual A helps B today
- B helps A tomorrow

- common in human societies
- e.g. rounds at the pub


This idea was introduced by ... ... in 1971

Bob Trivers


Mutualism: A+ B+

Reciprocity: A- ----> B++ then A++

One incurs cost for benefit of another, then the favour is returned so there is an overall benefit to both parties


Why is reciprocity problematic?

Because of delayed repayment - vulnerable to defection.

There is less opportunity to defect in mutualistic interactions, although each partner will seek to maximise their own fitness during these interactions


Prisoner's dilemma game (game theory):

2 players in a game with a choice of "..." or "..."

see photo on phone (matrix). I'd prob have another listen as well (L4)

cooperate, defect

Can derive from this game that the ESS will always be mutual defection, whether in a population of cooperators or one of defectors
(always defect when T > R > P > S and R > (S+T/2)

Values in table are arbitrary although their relative values do make intuitive sense


Can individuals escape this dilemma? Can reciprocity work?

No, if it is a single encounter or fixed number of encounters, defection is always the ESS

Yes, it can work with repeated, indeterminate encounters


This conclusion was reached by a game theoretician called Robert Axelrod, who, in the 1970s, played around with various versions of the prisoner's dilemma game. He gathered different strategies from colleagues in many areas and entered them into a computer tournament. The winner of the tournament (which included 62 different strategies) was a simple one called the...

tit for tat strategy


What is the tit for tat strategy?

- Individuals should cooperate on their first move, then do what their partner did.
- Can be ESS if probability of re-encounter is high
- Depends on social organisation, longevity etc.
- stable groups


Reciprocity in Vampire bats (studied by Wilkinson 1984):

Live in predominantly female roosts and fly out every night looking for animals to take a blood meal from. Most individuals are successful, but each night some are unsuccessful in finding a blood meal. When they return to the roost, the unsuccessful bats will often beg for and be fed by successful bats in the same roost, who regurgitate some blood meal.


Wilkinson worked out that there was low average ... in vampire bat roosts, but that ... were more likely to swap blood. There were 3 key facts that suggested that this was an example of reciprocity:
1. High chance of...
2. Benefit to recipient ..., cost to donor ...
3. Donation is reciprocated

relatedness, kin

future interaction (membership of roosts stable through time)
high, low (fully fed bats have around 60 hrs before starve to death - see graph on L4 slide 12)


E.g.s of reciprocity are very few and far between. This lead people to question Wilkinson's studies and whether they found good evidence for reciprocity. Various criticisms made over the years, the most persistent being that it could be that this sharing of blood was ...-....

- could be that sharing among non-kin is coercion, mistaken identity or indiscriminate altruism within kin groups (as on average members are kin)


Carter and Wilkinson (2013) carried out some more tests of the idea that vampire bats exhibit reciprocal altruism. Using many more detailed observations of roosts they asked whether blood donation depended on previous blood ..., was exchanged for ..., was related to ... with the donor, or (importantly) whether ... was a key factor.

reception, grooming, sex, relatedness


They (Carter and Wilkinson) found that...

food received was by far the best explainer of blood donation, and relatedness was the worst of the four - robust evidence for reciprocity (see screenshot on laptop)


There is also evidence for reciprocity in primates, such as baboons and vervet monkeys, which spend a lot of time ... each other and which form .... They are relatively ..., so may be able to memorise history of interactions with different individuals, so reciprocity systems would make sense. Plus humans init

grooming, alliances


Reciprocal trading of ... for ... has been studied in wild ... ....

grooming, food, vervet monkeys

- Dominants allowed subordinates access to food (increased tolerance of subordinate presence at food source) in response to recent grooming of the dominant by the focal subordinate (not shown when dom had been groomed by another subordinate to the focal one).


Pied flycatchers breed in pairs and are territorial. Each pair in the study population bred in their own nest box. Although they mostly stick to their own territory, when one pair is threatened by a predator, other pairs in neighbouring territories will sometimes...

help to mob the predator and drive it away


An experiment was carried out to investigate this apparent reciprocity. Prior to the experiment, pair B were captured and placed in a small cage at their nest box. A model owl was presented at nestbox A. In response, pair A ... the predator, and were assisted in this by the pair from nestbox C, as expected. The pair from nestbox B was then ..., and then a model owl was presented at both nestboxes B and C. It was found that...

mobbed, released

pair A assisted pair C (cooperators) in 30 out of 32 cases. In 2 cases they remained at their nest. They never assisted pair B (simulated defectors). This suggests that mobbing in pied flycatchers is reciprocated among neighbouring pairs.


A follow up experiment was carried out where a model owl was presented at nest B only...

Again, pair A refused to help due to pair B's apparent defection, but pair C did help as pair B had not defected against them.


However, looking at the primary literature, there is very little evidence for reciprocity beyond these examples. Clutton-Brock (2009) concluded that...

reciprocity is of very limited significance across the natural world

- opposed by Taborsky (2016) - suggests more reciprocity out there than many think


Why don't we see much reciprocity in nature?

One answer is that the prisoner's dilemma game is unrealistic as it views social interactions as being dyadic, meaning between two individuals. Social behaviour tends to be much more complex, often involving complex social networks with many relationships of different strengths. In reality we should expect individuals to be developing profitable relationships and terminating unproductive ones. Interactions are rarely actually dyadic.


This idea that social interactions tend to be more complex has lead to the introduction of an economic concept called ... ... ... into biology

Biological Market Theory


Biological Market Theory (Noë and Hammerstein, 1994, 1995) envisages that we can look at individuals within a population as falling within two classes:

A holding class, which holds access to a social commodity (e.g. food, capacity to groom or mob etc.) and a demanding class who seek access to the social commodity.


The relationship between these two classes is determined by trade dynamics (... and ..., ..., commodity ...)

supply, demand, advertisement, value


E.g. Macaques live in large groups. In these groups a lot of grooming occurs. The researchers looked particularly at male to female grooming. They noticed that the great majority of such groomings (89%) occured towards ... females (in ...), and, in 37% of these cases, grooming lead to .... They investigated this grooming behaviour in relation to the availability of females per male (how many females in estrus to per male). They found that grooming duration...

receptive, estrus, mating

was high when there few females available (prepared to invest more time). If there were many females available, males invested far less in grooming. Grooming duration was related to the supply of females, as predicted by biological market theory.


BMT has also been influential in introducing the idea that there are different kinds of reciprocity. So far have been talking about ... reciprocity (you scratch my back, i'll scratch yours - direct interaction between 2 parties). 2 other kinds have been proposed:


The first is known as generalised reciprocity - help anyone if you have been helped by someone. Shown to work in theory and one good supportive lab experiment

The second is indirect reciprocity - the idea that individuals should help someone who has been observed to be helpful (reputation important) - works in theory, some evidence. (think about mutualism and reputation)


Example of generalised reciprocity: Norway rats. Pre-experimentally trained, over several weeks, to pull lever and deliver food to partner in nextdoor cage. A focal rat was exposed to a series of cooperative interactions (with rats who pulled levers and delivered food to it) OR put in a social environment where there was no cooperation. In the third part of the experiment, the focal rat was put in a social interaction with a complete stranger. The prediction was that..

if the focal rat had previously been in a cooperative environment, they themselves would be more likely to cooperate and supply food to a stranger (by pulling a lever)

- control rats observed to see whether those from a cooperative environment were more likely to pull the lever when no other rat was present


They found that pulling frequency was...

on average 21% more likely after experiencing help - supporting evidence for generalised reciprocity theory


Cooperation may be enforced if defection is ...

punished (high cost of cheating)
- true of reciprocity
- threat of punishment also seems to work
(see and listen to slide 32 L4 again)


Threat of punishment: Study conducted where researchers put a different image over the drinks counter at a coffee shop every week for 10 weeks. One week there would be a pair of eyes, the next there would be a bunch of flowers. The researchers monitored the amount of money put into the honesty box each week and asked whether there was any difference between weeks with eyes (simulating someone watching and the threat of punishment) and weeks with flower. They found that...

on average, payment was 3 times greater when images of eyes were put up than when images of flowers were. Simply the threat of a punishment can indeed enforce reciprocity


Reciprocity works in theory, but current evidence suggests reciprocity is not widely important, except in humans.



One individual may be tricked or coerced into behaving altruistically towards another - what looks like altruistic cooperation is actually ...

manipulation (see photo on phone)


A classic example of manipulative behaviour is by ..., who manipulate their ... into being altruistic.

parasites, hosts

- exploit resources of hosts, can severely reduce host fitness
- parasitism is everywhere in the natural world


Brood parasitism can be ... (e.g. european starling) or ... (e.g. cuckoo, cuckoo finch), the latter of which can cause a coevolutionary ... ....

intraspecific, interspecific, arms race


Reed warbler chicks communicate their need for food to their parents in two ways: begging calls and .... Parents respond to a ... signal (we'd expect these signals to be an ... statement of the hunger of the chicks). They provide more food if a signal from more chicks (4 vs 1 vs 0) is played. The signal is a cue for how much to invest.

gaping, bigger, honest


Hosts feed a single cuckoo chick at a similar rate to ... reed warbler chicks. How do cuckoos persuade host parents to care for their young, considering the clear differences in appearance (including the gape: colour and size)?


Cuckoo chicks mimic begging calls of >4 reed warbler chicks (more notes per time). Older cuckoo chicks beg at a substanially higher rate than 4 reed warbler chicks. Cuckoo chicks are deficient in one signal: their gape, but compensate with a much higher auditory signal which dupes the host parents


The common cuckoo's strategy of increasing begging frequency to manipulate the host into providing more food works very well in very safe nests, like those relatively inaccessible nests of reed warblers. If, on the other hand, the host's nest is on the ground, calling very loudly and constantly may advertise the location of the nest to predators and be a dangerous strategy. This may lead to an alternative manipulation strategy. This is seen in another species:...

Horsefield's hawk-cuckoo
- single cuckoo chick evicts host chicks
- high rate of nest predation (begging loudly too risky)
- chicks evolved a false gape on underside of wing, which is bare of feathers, bright yellow and looks like a very large gape, manipulating the host into provisioning food at a high rate

- Cuckoos do not simply mimic reed warbler hosts, instead exploiting hosts provisioning rules and their integration of visual/auditory cues.


An e.g. of interspecific brood parasitism morphing into mutualism (very rare, often other way around due to instability of mutualism): great-spotted cuckoo and carrion crow. Researchers noticed that host chicks in host nests that had a cuckoo chick inside were more likely to fledge than were those without a cuckoo chick. They also noticed that their hands frickin reeked after handling the nests or chicks. These cuckoos benefit hosts by...

emitting a foul-smelling secretion from their cloaca that repels predators

- these cuckoos do not evict host chicks


An e.g. of the reverse, i.e. mutualism lapsing into interspecific manipulation: ... ... and ants. These caterpillars emit secretions which ants feed on, and in return ants help to defend the caterpillar from potential predators and paraitoids. In this particular relationship (Narathura japonica larvae and Pristomyrmex punctatus ants), the butterfly produces a secretion from its ... ... organ, which has the effect of reducing the locomotory activity of the ants. The lycaenid also emits a secretion from its tentacle organs either side of the dorsal nectary organ, which makes the ants more .... This means that ants that feed on the nectary organ are more likely to ... the ... (remain as locomotory activity reduced) and better protect the larvae as standing guards.

lycaenid butterfly, dorsal nectary, aggressive, attend larva

- manipulative drug that decreases dopamine in ant brains increases aggression


The fourth of the social interaction types described in hamilton's 1964 paper is ...


- behaviour which incurs a cost for the actor but also for the recipient


According to hamilton's rule, spiteful behaviour can evolve when...

rB > C (i.e. B is negative and C is positive, so relatedness must be negative)


How can r be negative?
Well r = relatedness coefficient = proportion of genes shared identically by descent, relative to the population (geometric view of relatedness).

Imagine a population where half of all genes are shared within it. A carries the actor's genes at a higher frequency than the population, so r > 0. B carries the actor's genes at a lower frequency so r < 0. C has 50% identical genes with the actors so its relatedness is 0.

see photo


A spiteful gene may spread through a population if..

it harms individuals not carrying that gene and benefits other carriers of the spiteful gene (related individuals)


Spite seems to be really rare in nature. Nevertheless, an e.g. of spite: ... ... wasp called Copidosoma floridanum.

Eggs are laid into moth larvae. Each egg divides ..., producing thousands of male and female larvae. Some females develop as ... ... that attack other larvae within the host. Females r to other females = 1, as they are clonal (multiply by mitosis). Females r to males = ... as they are haplodiploid. To satisfy the conditions for spite, this behaviour must be costly to its actor (reduce its fitness). This is the case in this situation as the female larvae are sterile (can't reproduce). The behaviour targets relatively ... individuals (males and unrelated females) and close kin benefit from the harmful behaviour, satisfying the criteria for spite following hamilton's rule.

polyembryonic parasitoid, asexually, sterile soldiers, 0.25


Why is spite apparently rare in nature?

A spiteful act towards non-kin incurs a cost for the actor and may benefit a relative, but may also benefit other individuals in the population to whom the actor is not related. In this case, the actor may incur a direct cost from this spite.

Secondly, while an individual may be able to recognise the relatively small number of close kin in a population it will generally be much harder to identify individuals with negative relatedness in the population from distant relatives - a risk that spiteful behaviour directed towards distant kin.