Brood Parasitism Flashcards
(10 cards)
What is intraspecific brood parasitism?
Lay eggs in clutches of conspecifics
Give some examples of intraspecific brood parasitism
Masked Weaver:
- breeds in large colonies
- 23-35% rate of parasitism
- egg divergence and recognition
American coot:
- 41% pairs parasitised
- 43% of hosts reject at least one parasitic egg (reject eggs that look different from own eggs)
What is interspecific brood parasites?
Lay eggs in clutches of one or most host species
1% of bird species are obligate brood parasites
What is the natural history of cuckoos and hosts?
10 main host species in Europe
Female lays 15-20 eggs per season (can lay more than other birds as not rearing offspring)
Unusual egg-laying behaviour (she lays in a few seconds compared to normal birds who lay in a few minutes)
Females specialise on one host species and usually lay a mimetic egg e.g. pipit cuckoos (each kind known as gens)
Parasitism results in zero reproductive success for the host
Give some experimental evidence for co-evolution on the cuckoo side
Why wait until host starts laying to lay own?
- placed a model egg in nest before and after laying
- before = 100% rejection
- after = 0% rejection
Why lay in the afternoon?
- placed model egg in nest in morning and afternoon
- mornings = 50% rejected
- afternoon = 0% rejected
- may be more vigilent in the morning
Why lay so quickly?
- placed stuffed cuckoo by nest for 5 minutes
- model egg + stuffed cuckoo = 45% rejected
- just model egg = 0% rejected
Why lay a small egg?
- placed larger model egg in nest
- large egg = 40% rejected
- usual model egg = 0% rejected
If place model eggs of different gens into a reed warbler nest, most get rejected (44-81%)
So cuckoos HAVE evolved in response to host defences
Have hosts co-evolved in response to cuckoos?
Placed non-mimetic eggs in nests of hosts that are usually parasitised and ones that arent
Rejection of eggs only happened in those that are parasitised, the unsuitable hosts didnt reject any eggs
Birds that could be hosts (but have no cuckoos in the country aka allopatry) have very little rejection rate whereas birds that have sympatry or recent sympatry do
What is sympatry and allopatry?
Sympatry = living together
Allopatry = living apart
Give some observational evidence for co-evolution
Prinia birds have more diverse egg polymorphisms than any other bird
Hosts use several aspects of parasitic egg appearance to reject foreign eggs
Looked at eggs over the last 30 years and found the parasites have been tracking host eggs
Why do mimicry and defences vary?
We are looking at a snapshot of a continuing evolutionary arms race
Rejection may be costly:
- recognition errors by rejecting own eggs
- ejection costs by damaging own eggs
May have other defences:
- nest defence instead of egg rejection
What are the sequence of events for the continuing arms race of mimicry and defence?
Before parasitism - no rejection:
- possibly due to host being unsuitable or being in allopatry
Parasitism - selection favoures rejection:
- this depends on parasitsm rate
Evolution of mimicry by parasite:
- get specialisation results in gentes
Host defences ‘win’:
- no parasitism due to good defence methods
- host defences weaken due to no parastism
- eventually stop rejection
- parasitism starts again
