Brood Parasitism and Cooperative Breeding

Brood Parasitism and Cooperative Breeding

Definitions

• Extra-Pair Copulating (EPC):

  • Mating behavior where males engage with females outside their monogamous pair without contributing to parental care.

• Brood Parasitism:

  • A reproductive strategy where one species (parasite) lays eggs in the nest of another species (host) to avoid parental care, referred to as “ultimate cheating.”

Key Characteristics of Brood Parasitism

• Costs for Parasite:

  • Potential rejection of parasite's eggs by the host.

• Benefits for Parasite:

  • Elimination of parental care responsibilities.

Examples of Brood Parasitic Species

• Parasite Species:

  • Cuckoos, Cowbirds (over 100 species total, 1% of all bird species).

• Host Species:

  • Wrens, Reed warblers, Flycatchers (950 different species, about 10% of all bird species).

Mechanisms of Brood Parasitism

• Cuckoos can lay up to 40 eggs per season.

• Cuckoes have an innate ability to identify host nests based on color and size of the eggs.

• Arms Race:

  • Parasites evolve to exploit host parental care while hosts develop mechanisms to defend against parasitism.

Cuckoo Behavior

• Cuckoos do not build nests and lay only one egg per host nest.

• Eggs are laid strategically based on the number of eggs already in the host nest.

• Cuckoo chicks hatch first due to earlier laying and are biologically equipped to eject host eggs to monopolize parental care.

  • Innate Behavior: Cuckoo chicks eject foreign eggs using a specialized growth notched on their back.

  • They exhibit a sign stimulus of red color in their beaks which signals parents to feed them.

Host Response to Brood Parasitism

• Hosts like Wrens typically lay 3-10 eggs per season and exhibit parental behavior towards cuckoo chicks due to innate responses.

• The costs for the host can include loss of reproductive success if they raise a cuckoo chick instead of their own.

Evolutionary Implications

• Cuckoos adapt their egg color to match that of their hosts through natural selection to reduce rejection rates.

• Hosts also evolve changes in their egg coloration and patterns to reject foreign eggs.

  • Mimetic eggs (similar to host's) have less than 30% rejection rates; non-mimetic eggs have 100% rejection rates.

Additional Strategies of Hosts

• Superb Fairy Wren:

  • Adult wrens have a vocal “password” that chics must produce to receive care, discouraging cuckoo chick survival due to their inability to mimic the password.

Operational Strategies of Cuckoo and Coots

• Conspecific Brood Parasitism:

  • Involves a female laying eggs in the nest of another female of the same species, often leading to reduced survival of own spawn.

  • A large proportion (~80%) of female American Coots will lay eggs in neighboring nests, often failing to differentiate their own from foreign eggs, which may result in broader nest failures.

Cooperative Breeding

• Definition:

  • Unrelated individuals work together to breed and care for the young. An example includes the Greater Ani.

  • Pairs cooperate across seasons, usually involving 2 to 3 pairs that build and share nests without knowing which offspring are theirs.

  • In this case, the risk of predation is mitigated by collective breeding efforts.

• Princeton Study:

  • Over 11 years, a study on greater Anis found significant instances of eggs present that did not belong to the parenting pairs.

Summary

Overall, brood parasitism reveals intricate evolutionary adaptations and behavioral mechanics that highlight the tension between host species and their parasitic counterparts, showcasing nature’s survival strategies.