Patterns and coevolutionary consequences of repeated brood parasitism

Area of Science:

• Evolutionary Biology
• Behavioral Ecology
• Ornithology

Background:

• The lack of adaptive host responses to virulent parasites is paradoxical.
• Brood parasitism, where one species lays eggs in another's nest, presents a significant evolutionary challenge for hosts.
• Antiparasitic strategies, such as egg ejection, are crucial for host survival and reproductive success.

Purpose of the Study:

• To investigate the theoretical possibility that avian hosts' lifetime experiences with brood parasitism delay the evolution of antiparasitic egg-ejection strategies.
• To understand how repeated exposure to brood parasitism influences the development and effectiveness of host defense mechanisms.

Main Methods:

• Development and analysis of a theoretical model to assess the impact of repeated parasitism on host learning strategies.
• Empirical data collection from three populations across two host species to document lifetime experiences with brood parasitism.
• Analysis of spatial and temporal patterns of parasitism in relation to host philopatry.

Main Results:

• An analytical model indicated that repeated exposure to brood parasitism decreases the relative benefits of learning-based egg-ejection strategies, especially when parasitism is costly.
• Empirical findings supported the model, showing individual female hosts experienced repeated brown-headed cowbird (Molothrus ater) parasitism across breeding attempts.
• Spatially and temporally non-random patterns of parasitism were observed, consistent with host philopatry.

Conclusions:

• Repeated lifetime exposure to brood parasitism can paradoxically hinder the evolution of effective antiparasitic egg-ejection strategies in avian hosts.
• This phenomenon may explain counterintuitive coevolutionary dynamics observed in spatially structured host-parasite populations.
• Understanding lifetime learning and exposure is critical for comprehending host-parasite coevolution.