Lecture 14: Brood parasitism

Question 1

brood parasitism 2 types:

Answer 1

• INTRAspecific parasites

- INTERspecific parasites

Question 2

Intraspecific parasites

Answer 2

• Lay eggs in clutches of conspecifics (same spp)
• Moorhen
• Wood duck
• Cliff swallow

Question 3

Interspecific parasites:

Answer 3

• 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)

Question 4

brood parasitism evolutionary term:

Answer 4

Co-evolutionary ‘arms race’

–> parasites and their hosts

Question 5

Cuckoo and hosts: In europe general egg laying and number of hosts

Answer 5

• cuckoo has 10 main host species in Europe

- females lays 10-20 eggs per season

Question 6

Cuckoo and hosts: Egg laying behaviour;

Answer 6

cuckoo lays;

1) after host starts laying
2) 2-5pm (uncommon)
3) quickly (10 secs)
4) small egg
5) mimetic egg

Question 7

cuckoos egg weight in comparison to other birds

Answer 7

expected to be around 10g, much less 3.4g!!

-so can lay in smaller birds nest

Question 8

cuckoos and mimetic eggs: how do they choose;

Answer 8

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’

Question 9

successful parasitism results in ___ reproductive success for host

Answer 9

0 reproductive success for host

–> parasites egg hatches 24hour before others and chucks them out

Question 10

evidence for co-evolution: Study by

Answer 10

Nick Davies & Mike Brooke

–> model eggs in reed warbler nests (communist UK host around 5% parasitism by cuckoos)

Question 11

evidence for co-evolution: why wait until host starts laying?

Answer 11

-placed model egg in nest before and after start of lying
- Before host lays; 100% rejected
after = 0% rejected

Question 12

evidence for co-evolution: why lay in afternoon ?

Answer 12

-placed egg in am and pm
– morning 50% rejected
afternoon 0% rejected

Question 13

evidence for co-evolution: why lay so quickly?

Answer 13

placed stuff cuckoo by net for 5 mins before model egg

• -model& stuffed cuckoo = 45% rejected
• -model egg only 0% rejected

Question 14

evidence for co-evolution: why lay such a small egg?

Answer 14

placed larger model eggs
-large = 40% rejected
usual model = 0% rejected

Question 15

evidence for co-evolution: why lay mimetic egg

Answer 15

• 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

Question 16

evidence for co-evolution: Conclusion HAVE CUCKOOS EVOLVED

Answer 16

YES; evolved in response to host defences

Question 17

evidence for co-evolution: have hosts evolved in response to cuckoos

Answer 17

certain species have learnt to reject eggs, but still a lot of variation.

Question 18

evidence for co-evolution: host adaption, sympatry and allopatry

Answer 18

those in sympatry show higher rejection, they’ve learnt! (UK& iceland –> hosts but no cuckoos)

Question 19

why do mimicry and defences vary? 2 answers

Answer 19

• Snapshot
• acceptance/rejection in evolutionary equilibrium
• -> both probably correct, and depends on mechanism of defence

Question 20

why do mimicry and defences vary? SNAPSHOT

Answer 20

-we only see a ‘snapshot’ of a continuing arms race,

Question 21

Snapshot: sequence of events::

Answer 21

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

Question 22

brown-headed cowbird and their hosts

Answer 22

• ‘generalist’
• exploits 216 hosts
• no mimicry
• > 50% of some hosts parasitised

Question 23

strong selection –>

Answer 23

rapid evolution of rejection

Question 24

Acceptance/rejection in evolutionary equilibrium

Answer 24

• 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