Environmental mismatch results in emergence of cooperative behavior in a passerine bird
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A major problem in the evolution of maternal effects is explaining the origin and persistence of maternally induced phenotypes that lower offspring fitness. Recent work focuses on the relative importance of maternal and offspring selective environments and the mismatch between them. However, an alternative approach is to directly study the origin and performance of offspring phenotypes resulting from mismatch. Here, we capitalize on a detailed understanding of the ecological contexts that provide both the cue and the functional context for expression of maternally induced offspring phenotypes to investigate the consequences of environmental mismatch. In western bluebirds, adaptive integration of offspring dispersal and aggression is induced by maternal competition over nest cavities. When nest cavities are locally abundant, mothers produce nonaggressive offspring that remain in their natal population, and when nest cavities are scarce, mothers produce aggressive dispersers. However, a few offspring neither disperse nor breed locally, instead helping at their parent’s nest, and as a result these offspring have unusually low fitness. Here, we investigate whether females produce helpers to increase their own fitness, or whether helpers result from a mismatch between the cues mothers experience during offspring production and the breeding environment that helpers later encounter. We found that producing helpers does not enhance maternal fitness. Instead, we show that helpers, which were the least aggressive of all returning sons in the population, were most common when population density increased from the time sons were produced to the time of their reproductive maturity, suggesting that the helper phenotype emerges when cues of resource competition during offspring development do not match the actual level of competition that offspring experience. Thus, environmental mismatch might explain the puzzling persistence of maternally induced phenotypes that decrease offspring fitness.
KeywordsPredictive adaptive response Maternally induced phenotype Competition Aggression
We thank Alex Badyaev, Erin Morrison, Dawn Higginson, Kelly Hallinger, Anne Storey, Kathryn Chenard, Georgy Semenov, and Chris Seliga for comments that greatly improved the manuscript. We thank Stepfanie Aguillon, Nerissa Hall, Megan Jacobson and numerous field and lab assistants for invaluable help with data collection and processing. Support for this project was provided by NSF DGE-1143953 to ALP and NSF DEB-918095 and DEB-1350107 to RAD).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
This study was carried out in accordance with the recommendations and guidelines approved by University Institutional and Animal Care and Use Committees, as well as complied with all state and federal permitting guidelines for using bluebirds in this study.
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