Title: Obligate Brood Parasitism: occurs in 90 species, has evolved 7 times
1Obligate Brood Parasitism occurs in 90 species,
has evolved 7 times
2Brood Parasites and Their Hosts
- Old World and New World Cuckoos host
passerines - Whydahs, Indigo Birds and Parasitic Weaver host
related finches - Honeyguides host other cavity-nesters in same
order (woodpeckers, barbets) - Cowbirds hosts other passerines
- Black-headed Duck host coots
3Obligate brood parasites cannot reproduce without
hosts
- Some cuckoos feed their own fledglings, no other
parental care performed by obligate brood
parasites
4Evolutionary Pathways to Obligate Brood Parasitism
- Intraspecific to facultative interspecific to
obligate interspecific brood parasitism - Intraspecific egg dumping is widespread
- Facultative interspecific parasitism is less
common, occurs cuckoos and ducks - Nest parasitism to obligate brood parasitism
- Nest parasitism occurs cowbirds, weavers
5Factors Affecting Payoff of Brood Parasitism
Option
- Specialized foods may make parasitic species poor
parents - Toxic caterpillars cuckoos
- Beeswax honeyguides
- Nest predation may favor spreading eggs among
several nests - Host behavior not a barrier, parasites exploit
strong host response to own eggs, young
6Brood parasitism is an antagonistic evolutionary
interaction between species
- Parasites benefit, hosts suffer
7Adaptations of Parasites
- Develop faster than host
- Shorter incubation, hatch before host young
- Grow faster after hatching
- Hold eggs in oviduct before laying to allow
embryo to develop - Also enables parasites to hatch first
8End result parasites outcompete host young for
food (cuckoos, cowbirds)
Weavers replace host egg with one of own, host
raises parasite plus (one less of) own young
9Cuckoo chicks flip host eggs, young out nest
- Honeyguide chicks (and a few cuckoos) stab host
young to death using hook on bill
10Additional Points
- Lack of relatedness of parasite chick to
nestmates promotes harmful behaviors - Brood parasites lay eggs in clutches
- Lay more total eggs than normal birds, success
of eggs less because host defenses sometimes work
11Defensive Adaptations of Hosts
Counter-adaptations of Parasites
- Aggressive to female parasites near nest
- Scout nests, sneak into nests, lay quickly
- Few cuckoos mimic hawks, male induces mobbing
while female sneaks into nest - Egg recognition reject parasite eggs
- Not normally present in birds, evolves in
response to parasitism
12Respond to parasite egg by removing the egg,
abandoning the nest, or covering over clutch
13Counter-adaptation is egg mimicry
14- Recognize young refuse to feed parasitic young
- Mimicry of young
15Whydahs mimic mouth markings of finch hosts, some
cuckoos mimic general appearance of hosts
16Adverse Impacts of Brood Parasites on Host
Populations
- Brown-headed Cowbirds have decimated populations
of Kirtlands Warbler, Wood Thrushes other
species in eastern US - Cowbird population explosion due to increased
food increases impact of parasite
17- Shiny Cowbirds threaten Yellow-shouldered
Blackbird populations in Puerto Rico - Host has no evolutionary history with, defenses
against, recent invader
18Normally Hosts and Parasites Coexist
- Parasites are uncommon compared to hosts, numbers
regulated by food supply - Long history of interaction with parasite leads
to host defenses that protect host - Parasites and hosts coevolve, become more tightly
linked over time - Each exerts evolutionary pressure on the other,
neither wins
19Example of Coevolution
- Finches evolve recognition of young, whydahs
evolve mimicry of finch young - Whydah species can only mimic one finch species,
causing host specialization - Each whydah has only one finch host, each finch
has only one whydah parasite
20Are cases where different races of the same
parasite species specialize on different
hosts(1) indigo bird races mimic young of
different finch houses (sympatric
speciation?)(2) Common Cuckoo races mimic eggs
of different passerine hosts
21Cowbirds illustrate that more recently evolved
parasites exhibit less coevolution
- Brown-headed Cowbird most recent species, has
200 hosts whose defenses range from none to egg
recognition - The oldest parasitic species, the Screaming
Cowbird, has only 1 host, another (non-parasitic)
cowbird
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23Coevolution of Giant Cowbirds and Chestnut-headed
Oropendolas
- Oropendolas tolerate cowbirds when parasitism
improves reproductive success - Cowbird chicks remove botfly larvae from
oropendola chicks - Oropendolas attack cowbirds, reject their eggs
when parasitism reduces reproductive success - Nest near wasps, wasps protect from botflies
- Cowbirds mimic oropendola eggs
24Black-headed Duck
- Commensalism rather than parasitism
- Neutral for coots, for duck
- Ducklings leave nest after hatching, require no
parental care - Trivial cost to coots (incubating duck eggs)
- No host defenses have evolved in coots
25Mating Systems of Brood Parasites
- Some are monogamous, defend territories that
include host nests (cuckoos, cowbirds) - Some exhibit resource defense polygyny
- Little value to male parental care
- Honeyguides defend bee nests
- Some exhibit female defense polygyny (whydahs)
- Females have no nest, travel in groups