Lecture 14: Brood parasitism Flashcards
brood parasitism 2 types:
- INTRAspecific parasites
- INTERspecific parasites
Intraspecific parasites
- Lay eggs in clutches of conspecifics (same spp)
- Moorhen
- Wood duck
- Cliff swallow
Interspecific parasites:
- lay eggs in clutches of one or more host species (diff. species)
- -> 100 (1%) bird spp. are obligate brood parasites
- cichlid & cuckoo catfish (cichlid M brood catfish young in mouth)
- Waxbill & pin-tailed whydah (pt lays egg in waxbill nest)
brood parasitism evolutionary term:
Co-evolutionary ‘arms race’
–> parasites and their hosts
Cuckoo and hosts: In europe general egg laying and number of hosts
- cuckoo has 10 main host species in Europe
- females lays 10-20 eggs per season
Cuckoo and hosts: Egg laying behaviour;
cuckoo lays;
1) after host starts laying
2) 2-5pm (uncommon)
3) quickly (10 secs)
4) small egg
5) mimetic egg
cuckoos egg weight in comparison to other birds
expected to be around 10g, much less 3.4g!!
-so can lay in smaller birds nest
cuckoos and mimetic eggs: how do they choose;
they don’t, female cuckoos socialise on one host and usually lay mimetic eggs
- -pipit cuckoos
- -wagtail cuckoos
- -redstart cuckoos
- –> each kind known as ‘gens’
successful parasitism results in ___ reproductive success for host
0 reproductive success for host
–> parasites egg hatches 24hour before others and chucks them out
evidence for co-evolution: Study by
Nick Davies & Mike Brooke
–> model eggs in reed warbler nests (communist UK host around 5% parasitism by cuckoos)
evidence for co-evolution: why wait until host starts laying?
-placed model egg in nest before and after start of lying
- Before host lays; 100% rejected
after = 0% rejected
evidence for co-evolution: why lay in afternoon ?
-placed egg in am and pm
– morning 50% rejected
afternoon 0% rejected
evidence for co-evolution: why lay so quickly?
placed stuff cuckoo by net for 5 mins before model egg
- -model& stuffed cuckoo = 45% rejected
- -model egg only 0% rejected
evidence for co-evolution: why lay such a small egg?
placed larger model eggs
-large = 40% rejected
usual model = 0% rejected
evidence for co-evolution: why lay mimetic egg
- model egg of the different gens
- -pied wagtail type: 81% rejected
- -redstart type: 70% rejected
- -meadow pipit type: 44% rejected
- -reed warbler type: 0% rejected
evidence for co-evolution: Conclusion HAVE CUCKOOS EVOLVED
YES; evolved in response to host defences
evidence for co-evolution: have hosts evolved in response to cuckoos
certain species have learnt to reject eggs, but still a lot of variation.
evidence for co-evolution: host adaption, sympatry and allopatry
those in sympatry show higher rejection, they’ve learnt! (UK& iceland –> hosts but no cuckoos)
why do mimicry and defences vary? 2 answers
- Snapshot
- acceptance/rejection in evolutionary equilibrium
- -> both probably correct, and depends on mechanism of defence
why do mimicry and defences vary? SNAPSHOT
-we only see a ‘snapshot’ of a continuing arms race,
Snapshot: sequence of events::
i) before parasitism -no rejection
ii) parasitism - selection favours rejection depends on parasitism rate
iii) evolution of mimicry by parasite (specialisation results in gens)
iv) host defences ‘win’
- -no parasitism, host defences weaken, no rejection
brown-headed cowbird and their hosts
- ‘generalist’
- exploits 216 hosts
- no mimicry
- > 50% of some hosts parasitised
strong selection –>
rapid evolution of rejection
Acceptance/rejection in evolutionary equilibrium
- rejection is costly & may not always be the best option (chuck out wrong egg)
- Acceptance = function of imprinting e.g. cuckoos & great reed warbler (Lotem 1993)
- -host learns (imprints on) own eggs and rejects different eggs, imprint son first clutch that may include cuckoo egg
