Maternal Natal Environment and Breeding Territory Predict the Condition and Sex Ratio of Offspring
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Females in a variety of taxa adjust offspring sex ratios to prevailing ecological conditions. However, little is known about whether conditions experienced during a female’s early ontogeny influence the sex ratio of her offspring. We tested for past and present ecological predictors of offspring sex ratios among known-age females that were produced as offspring and bred as adults in a population of house wrens. The body condition of offspring that a female produced and the proportion of her offspring that were male were negatively correlated with the size of the brood in which she herself was reared. The proportion of sons within broods was negatively correlated with maternal hatching date, and varied positively with the quality of a female’s current breeding territory as predicted. However, females producing relatively more sons than daughters were less likely to return to breed in the population the following year. Although correlative, our results suggest that the rearing environment can have enduring effects on later maternal investment and sex allocation. Moreover, the overproduction of sons relative to daughters may increase costs to a female’s residual reproductive value, constraining the extent to which sons might be produced in high-quality breeding conditions. Sex allocation in birds remains a contentious subject, largely because effects on offspring sex ratios are small. Our results suggest that offspring sex ratios are shaped by various processes and trade-offs that act throughout the female life history and ultimately reduce the extent of sex-ratio adjustment relative to classic theoretical predictions.
KeywordsHouse wren Life history Maternal effect Sex allocation Trivers–Willard Troglodytes aedon
We thank the 1999–2013 Wren Crews for field assistance and the ParkLands Foundation (Merwin Preserve) and the Sears and Butler families for the use of their properties for this work. Financial support was provided by the School of Biological Sciences, Illinois State University; National Science Foundation Grants IBN-0316580, IOS-0718140 and IOS-1118160; National Institutes of Health Grant R15HD076308-01; and student research grants from the Sigma Xi Society, the Animal Behavior Society, the American Ornithologists’ Union, the American Museum of Natural History’s Frank M. Chapman Memorial Fund, the Champaign County Audubon Society, and the Beta Lambda Chapter of the Phi Sigma Biological Sciences Honor Society.
Compliance with Ethical Standards
Conflict of Interest
The authors declare that they have no conflict of interest.
All research activities complied with current laws of the United States of America, and were performed in accordance with Illinois State University Institutional Animal Care and Use Committee permits 10-2009, 05-2010, 04-2013; U. S. Geological Survey banding permit 09211; and U. S. Fish and Wildlife Service collecting permit MB692148-0.
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