Brood parasitism Flashcards
What is brood parasitism?
Individuals that exploit parental care
What are intraspecific brood parasites?
- Exploit individuals from same species
- Lay eggs in clutches on conspecifics (e.g. european starling, cliff swallows)
How have Masked weavers adapted to intraspecific brood parasites?
- They breed in large colonies - lots of opportunities to parasitise offspring
- 23-35% rate of parasitism
- Egg divergence and recognition
- Huge variation of patterns and colour of eggs within a colony, evolved as a way for parent to recognise own eggs
How has the american coot adapted to intraspecific brood parasitism ?
- 41% of pairs parasitised
- 43% of hosts reject at least one parasitic egg
- Egg colour variation between hosts
- Study showed that females were more likely to reject eggs that were different colour
what are Interspecific brood parasites?
Between species parasitism (e.g. cuckoo)
interspecific brood parasite examples
- Cuckoo catfish parasites cichlid fish brood
- Pin-tailed whydah - host common waxbill
Brood parasitism between cuckoo and their host
(Co-evolutionary arms race).
What is the natural history?
- female lays 15-20 eggs per season
- Always lay eggs in afternoon (most birds lay in morning)
- Lay small eggs very quickly
- Remove one host egg from nest and replace with own
- Females specialise on one host species and usually lay a mimetic egg
Have cuckoos evolved in repsonse to hosts? (how did the study show this?)
- Davies and Brooke
- Placed model egg in reed warbler nest
Have cuckoo behaviours evolved as co-evolution of host behaviours?
Why wait until host starts laying?
- Placed model egg in nest before and after start of laying
- 100% of eggs were rejected before host started laying
- 0% was rejected after laying
Have cuckoo behaviours evolved as co-evolution of host behaviours?
Why lay in the afternoon?
- 50% were rejected when placed in the morning
- 0% rejected in the afternoon
Not sure why, possibly due to increased bird vigilence in the monring
Have cuckoo behaviours evolved as co-evolution of host behaviours?
Why lay so quickly?
- Placed stuffed cuckoo by nest for 5 mins
- model egg and stuffed cuckcoo: 45% rejected
- Just model egg: 0% rejected
Have cuckoo behaviours evolved as co-evolution of host behaviours?
Why lay a small egg?
- Placed large model egg (expected size of cuckoo egg) in nest
- Large egg model: 40% rejected
- Usual model egg: 0% rejected
Have cuckoo behaviours evolved as co-evolution of host behaviours?
Why lay a mimetic egg?
- Placed model egg of different gens in reed warbler nests
- Varying levels of rejection for the other eggs
- lowest rejection was 44% because eggs were similar to host eggs
Why have cuckoos evolved these unusual behaviours?
- To overcome the host species defence
- Evolutionary arms race
What species has egg rejection evolved in?
- Parasitised species
- Non-parasitised species did not reject any eggs placed in their nests
How does sympatry and allopatry show experimental evidence for co-evolution within cuckoo and their host species?
- Compare hosts that live in UK or Iceland
- There are no cuckoos on Iceland
- Rejection % much lower on Iceland
- Rejection has evolved where cuckoos are present
Why did the icelandic species still show low levels of rejection?
The Iceland population may have migrated there from somwhere with cuckoo parasitism in the the distamt past and over time the response decreases
Further evidence for sympatry vs allopatry
- In spain and sweden, hosts have variable exposure to cuckoos
- Ancient sympatry (long lived parasitism): 94% rejection
- Recent Sympatry: 67% rejection
- Allopatry: 0% rejection
Prinia vs cuckoo finch
- Prinia eggs very diverse
- Prinia eggs have got more diverse over time
- Cuckoo finches eggs track the diversity
Why do mimicry and defences vary?
- What we’re looking at is only a snapshot in time of a continuing evolutionary arms face
- Cant see the adaptations in time
what are the sequence of events for host-parasite evolutionary arms race?
- Before parasitism - no rejection
- Parasitism - selection favours rejection
- Evolution of mimicry by parasite
- Host defences ‘win’
Once host defences win - no parasitism so host defences weaken and there is no rejection.. parasitism can start again
