The evolution of cuckoo parasitism: a comparative analysis.

Area of Science:

• Evolutionary Biology
• Ornithology
• Animal Behavior

Background:

• Cuckoos (family Cuculidae) display remarkable diversity in breeding strategies, encompassing parental care and various forms of brood parasitism.
• Understanding the evolutionary drivers behind this diversity is crucial for comprehending avian life-history evolution.

Purpose of the Study:

• To investigate the ecological and life-history factors associated with the evolution of diverse breeding strategies in cuckoos.
• To determine the evolutionary sequence of brood parasitism and related traits like egg size.

Main Methods:

• Phylogenetic comparative methods (independent contrasts) were applied to two distinct phylogenies.
• Thirteen ecological and life-history variables were analyzed in relation to cuckoo breeding strategies.
• Pagel's method was used to establish probable evolutionary pathways.

Main Results:

• The ancestral cuckoo likely inhabited tropical forests and exhibited parental care.
• The evolution of brood parasitism correlated with shifts to open habitats, dietary changes, increased range size, migration, and decreased egg size.
• Elaborate parasitic strategies were linked to reduced egg size, dietary shifts, larger ranges, migration, shorter breeding seasons, and lower abundance.

Conclusions:

• Ecological variables such as migration and diet type appear to have preceded the evolution of brood parasitism in cuckoos.
• Brood parasitism evolved before changes in egg size, suggesting egg size is a co-evolutionary adaptation.
• The evolution of cuckoo brood parasitism is shaped by both ecological pressures and host defenses.