L14

Question 1

Brood parasitism

Answer 1

• Individuals attempt to exploit parental care provided by others
  
  • Same and different species
    Co-evolutionary arms race

Question 2

Intraspecific brood parasites - Starling

Answer 2

• Egg on grass as a result of parasitism
  
  • Female lays egg in nest which isn’t hers and removes an egg that was already in the nest

Question 3

Intraspecific brood parasites - Burying beetles

Answer 3

• Find a carcass and lay eggs on it
  
  • Female feeds larvae emerging
  • Sometimes other beetles sneak into nest and bury eggs in carcass
  • Parent unknowingly looks after larvae of another individual
  • Quite difficult to observe as it is cryptic
  • Many adaptations therefore to facilitate parasitism

Question 4

Intraspecific brood parasites - Cliff swallows

Answer 4

• Marked eggs to identify them
  
  • Often found eggs in the wrong nest
  • Females would sometimes place eggs in other individuals nests
  • Parasitism is tricky to observe

Question 5

Intraspecific brood parasites - Masked weaver

Answer 5

• Marked eggs to identify them
  
  • Often found eggs in the wrong nest
  • Females would sometimes place eggs in other individuals nests
  • Parasitism is tricky to observe

Question 6

American coot, how many pairs are parasited? How many hosts reject at least one parasitic egg

Answer 6

• 41% pairs parasitised
  
  • 43% of hosts reject at least one parasitic egg

Question 7

How are parasitic eggs recognised in coots?

Answer 7

• Ranked colours of eggs on a scale (1-10)
  
  • Look at other eggs
  • Calculated difference between host and parasitic egg creating a colour rank difference value

Question 8

How are parasitic eggs recognised in coots? Results

Answer 8

• Female more likely to accept eggs less different from its own
  
  • Much higher rejection when more different from own

Question 9

Interspecific brood parasites Cuckoo catfish

Answer 9

Cuckoo catfish

- Parasitises cichlid fish
- Male stores eggs in mouth and looks after them
- Catfish releases eggs into mouth whilst females are laying eggs into cichlid mouth
- Cuckoo egg hatches first and eats true offspring
- Just one cuckoo catfish emerges

Question 10

How many bird species are obligate interspecific brood parasites?

Answer 10

100

Question 11

Co- evolutionary arms race between cuckoo and host

Answer 11

• Arms races occur in virus and defence, predator and prey
  • Brood parasites also are examples of co-evolutionary arms race

Question 12

Natural history of cuckoos and hosts

Answer 12

• 10 main host species in Europe
  
  • Female lays 15-20 eggs per season
  • If all eggs are successful this is many more than cuckoo could rear her own
  • Eggs can be laid and made because there is no investment in parental care

Female waits till host female lays eggs and lays her own egg in nest too

Question 13

Egg laying behaviour:

Answer 13

• Always lay eggs in afternoon (most birds lay in morning)
  
  • Small egg relative to body size
  • Egg laying is very quick
  • Remove one host egg and deposit their own
  • Females specialise on one host species and usually lays a mimetic egg

Eg pipit cuckoos parasitise pipits

- Not a separate species but they specialise in a particular host species

Question 14

Cuckoo egg variation

Answer 14

• Larger but mimetic to species
  
  • Match those of host
  • Make It harder for host to reject

When egg hatches it hatches quicker than rest of host:

Question 15

Why do cuckoo eggs hatch quicker than the hosts actual eggs?

Answer 15

• Egg is more developed
  
  • Gives advantage to kick out eggs and take over host eggs
  • Monopolise parental care
  • Mimics calling sound of mother
    Much larger in size than host

Question 16

Effect of cuckoo on reed warblers (host)

Answer 16

• Makes them very unfit
  
  • Strong selection pressure to reject parasitism

Question 17

Have cuckoos evolved in response to hosts experiment?

Answer 17

• Placed model eggs in reed warbler nests
  • Are weird behaviours adaptations to get round defences warbler has evolved?

Question 18

Why wait until host starts laying?

Answer 18

• Before host lays: 100% rejected
  
  • After host lays: 0% rejected
  • Strong selection pressure to wait

Question 19

Why lay in the afternoon?

Answer 19

• Morning: 50% rejected
  
  • Afternoon: 0% rejected
  • Possibly because birds are more vigilant in morning, or spend more time round the nest in the morning

Question 20

Why lay so quickly?

Answer 20

• Model egg + stuffed cuckoo beside nest for 5 minutes: 45% rejected
  • Model egg only: 0% rejected

Question 21

Why lay a small egg?

Answer 21

• Low egg mass to body mass
  • Estimated size 10g = 40% rejected
  • Usual egg 3.4g = 0% rejected

Question 22

Why lay a mimetic egg?

Answer 22

Reed warbler wont reject reed warbler egg but will varyingly reject other species

Question 23

Conclusion of Have cuckoos evolved in response to hosts Experiment

Answer 23

All cuckoo features are adaptive laying behaviours to counter defences by reed warbler

- Cuckoos have evolved in response to host defences

Question 24

What about counter adaptations by the host? Experiment 1

Answer 24

• Placed model eggs in 13 suitable hosts (nests accessible to humans and cuckoos)
  • Variable rejection rates across host species

Question 25

What about counter adaptations by the host? Experiment 1b

Answer 25

- Placed non-mimetic eggs in 9 unsuitable nests - Never experienced parasitism before - All 9 species showed no egg rejection behaviour - Egg rejection behaviour has evolved in only parasitised species

Question 26

Sympatry vs allopatry experiments

Answer 26

- Host defences in sympatry and none in allopatry - Rejection rate in the UK (sympatry ) was higher than in allopatry (iceland) - Presence of cuckoos selects for strong host rejection behaviour

Question 27

Great spotted cuckoo and magpie

Answer 27

- Ancient sympatry, recent sympatry and allopatry - Non- mimetic eggs are rejected most in ancient sympatry, then recent sympatry, then allopatry - Same experiment to ^3

Question 28

Selection for adaptation and counter adaptation is rapid evolution - observational evidence for co-evolution

Answer 28

- Egg collection between cuckoo finch and prinia - Prinia has more diverse egg polymorphism than any other bird - Hosts used several aspects of parasitic egg appearance to reject foreign eggs

Question 29

Has there been an evolutionary arms race in egg adaptation

Answer 29

- Both host and parasite egg changed over time - Increase in variation - Process of trackable evolutionary change Prinia egg - More diverse current eggs than historical eggs - Present eggs are more diverse in colour than historical eggs - Expanded into different colour space, selection to pressure a certain colour Cuckoo finch - Less eggs than prinia - Expansion in colour diversity

Question 30

Have parasites been tracking and copying host eggs?

Answer 30

- Same measure of difference between host and parasite egg - Historical cuckoo finch egg more similar to historical host than to current - Current day hosts show the inverse pattern - Historical cuckoo finch were more different to current day hosts when compared to current day cuckoo eggs - As time goes on host evolves defences and parasite counter adapts

Question 31

Why do mimicry and defences vary?

Answer 31

- Dominant idea is a snapshot of a continuing evolutionary arms race - Don’t see whole process

Question 32

Sequence of events:

Answer 32

A B C D E

Question 33

A. before parasitism

Answer 33

no rejection eg unsuitable hosts / hosts in allopatry

Question 34

B. parasitism

Answer 34

selection favours rejection Depends on parasitism rate Eg species dependent - Dunnock hasn’t evolve egg rejection behaviour, as there is a low parasitism rate so small selection pressure for behaviour to evolve - Low proportion of nest parasites means it takes many generations for an adaptation to be selected - If there is a high percentage of parasitism rate, because there is a high selection pressure if a mutation evolves it will be selected for and evolve quickly throughout population

Question 35

C evolution of mimicry by parasite

Answer 35

- Parasite has to counter evolve to overcome host defences

Question 36

D ultimately host can win

Answer 36

- Defences are so good they can no longer be parasitised - If no parasitism occurred host defences may weaken, so no rejection

Question 37

Experimental evidence for host winning

Answer 37

- Egg rejection behaviour suggests previous exploitation as why else would they reject? - Gradual reduction in defences

Question 38

Selection against rejection behaviour

Answer 38

Rejection may be costly - Recognition errors (eject own eggs) - Ejection cost of parasite egg is difficult (damage own eggs) Eg northern oriole - For every rejected cuckoo egg they damage one of their own egg Other defences: - Constantly defends nest instead of egg rejection - No need for egg rejection behaviour to have evolved

Question 39

Summary of lecture

Answer 39

- Brood parasites and their hosts are engaged in a co-evolutionary arms race - This interaction has been an ideal model system for experimental and observational studies of this very general phenomenon - The outcome of the arms race is variable, depending on many factors, including the frequency, or virulence, of the parasitism