L14 Flashcards
1
Q
Brood parasitism
A
- Individuals attempt to exploit parental care provided by others
- Same and different species
Co-evolutionary arms race
- Same and different species
2
Q
Intraspecific brood parasites - Starling
A
- 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
3
Q
Intraspecific brood parasites - Burying beetles
A
- 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
4
Q
Intraspecific brood parasites - Cliff swallows
A
- 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
5
Q
Intraspecific brood parasites - Masked weaver
A
- 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
6
Q
American coot, how many pairs are parasited? How many hosts reject at least one parasitic egg
A
- 41% pairs parasitised
- 43% of hosts reject at least one parasitic egg
7
Q
How are parasitic eggs recognised in coots?
A
- 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
8
Q
How are parasitic eggs recognised in coots? Results
A
- Female more likely to accept eggs less different from its own
- Much higher rejection when more different from own
9
Q
Interspecific brood parasites Cuckoo catfish
A
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
10
Q
How many bird species are obligate interspecific brood parasites?
A
100
11
Q
Co- evolutionary arms race between cuckoo and host
A
- Arms races occur in virus and defence, predator and prey
- Brood parasites also are examples of co-evolutionary arms race
12
Q
Natural history of cuckoos and hosts
A
- 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
13
Q
Egg laying behaviour:
A
- 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
14
Q
Cuckoo egg variation
A
- 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:
15
Q
Why do cuckoo eggs hatch quicker than the hosts actual eggs?
A
- 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
16
Q
Effect of cuckoo on reed warblers (host)
A
- Makes them very unfit
- Strong selection pressure to reject parasitism
17
Q
Have cuckoos evolved in response to hosts experiment?
A
- Placed model eggs in reed warbler nests
- Are weird behaviours adaptations to get round defences warbler has evolved?
18
Q
Why wait until host starts laying?
A
- Before host lays: 100% rejected
- After host lays: 0% rejected
- Strong selection pressure to wait
19
Q
Why lay in the afternoon?
A
- Morning: 50% rejected
- Afternoon: 0% rejected
- Possibly because birds are more vigilant in morning, or spend more time round the nest in the morning
20
Q
Why lay so quickly?
A
- Model egg + stuffed cuckoo beside nest for 5 minutes: 45% rejected
- Model egg only: 0% rejected
21
Q
Why lay a small egg?
A
- Low egg mass to body mass
- Estimated size 10g = 40% rejected
- Usual egg 3.4g = 0% rejected
22
Q
Why lay a mimetic egg?
A
Reed warbler wont reject reed warbler egg but will varyingly reject other species
23
Q
Conclusion of Have cuckoos evolved in response to hosts Experiment
A
All cuckoo features are adaptive laying behaviours to counter defences by reed warbler
- Cuckoos have evolved in response to host defences
24
Q
What about counter adaptations by the host? Experiment 1
A
- Placed model eggs in 13 suitable hosts (nests accessible to humans and cuckoos)
- Variable rejection rates across host species
25
What about counter adaptations by the host? Experiment 1b
- 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
26
Sympatry vs allopatry experiments
- 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
27
Great spotted cuckoo and magpie
- Ancient sympatry, recent sympatry and allopatry
- Non- mimetic eggs are rejected most in ancient sympatry, then recent sympatry, then allopatry
- Same experiment to ^3
28
Selection for adaptation and counter adaptation is rapid evolution - observational evidence for co-evolution
- 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
29
Has there been an evolutionary arms race in egg adaptation
- 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
30
Have parasites been tracking and copying host eggs?
- 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
31
Why do mimicry and defences vary?
- Dominant idea is a snapshot of a continuing evolutionary arms race
- Don’t see whole process
32
Sequence of events:
A
B
C
D
E
33
A. before parasitism
no rejection eg unsuitable hosts / hosts in allopatry
34
B. parasitism
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
35
C evolution of mimicry by parasite
- Parasite has to counter evolve to overcome host defences
36
D ultimately host can win
- Defences are so good they can no longer be parasitised
- If no parasitism occurred host defences may weaken, so no rejection
37
Experimental evidence for host winning
- Egg rejection behaviour suggests previous exploitation as why else would they reject?
- Gradual reduction in defences
38
Selection against rejection behaviour
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
39
Summary of lecture
- 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
