Local sex ratio affects the cost of reproduction

• Published in: The Journal of animal ecology Vol. 81; no. 3; pp. 564 - 572
• Main Authors: Nicolaus, Marion, Michler, Stephanie P. M., Ubels, Richard, van der Velde, Marco, Bouwman, Karen M., Both, Christiaan, Tinbergen, Joost M.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing 01.05.2012; Blackwell Publishing Ltd; Blackwell
• Subjects: Animal and plant ecology; Animal ecology; Animal reproduction; Animal, plant and microbial ecology; Animals; Aves; Benefit cost analysis; Biological and medical sciences; Bird nesting; Breeding; Clutch size; Competition; density; disease risk; Ecology; Ecosystem; Female; Fundamental and applied biological sciences. Psychology; General aspects; Habitat; Human ecology; Hypothesis testing; intraspecific competition; Life histories; Male; Male animals; optimal clutch size; Parents; Parus major; Passeriformes - physiology; Population Dynamics; Predation; predation risk; Reproduction; Reproduction - physiology; Reproductive effort; reproductive trade‐offs; Sex Ratio; Sexual reproduction; Social environment; Survival; Vertebrates: general zoology, morphology, phylogeny, systematics, cytogenetics, geographical distribution; Social environment; Costs; Disease; Clutch size; disease risk; Density; reproductive trade-offs; Sex ratio; optimal clutch size; Vertebrata; Reproduction; Intraspecific competition; Aves; Parus major; Predation risk
• ISSN: 0021-8790; 1365-2656
• DOI: 10.1111/j.1365-2656.2011.01933.x

1. Costs and benefits of reproduction are central to life-history theory, and the outcome of reproductive trade-offs may depend greatly on the ecological conditions in which they are estimated. In this study, we propose that costs and benefits of reproduction are modulated by social effects, and consequently that selection on reproductive rates depends on the social environment. 2. We tested this hypothesis in a great tit Parus major population. Over 3 years, we altered parental reproductive effort via brood size manipulations (small, intermediate, large) and manipulated the local social environment via changes in the local fledgling density (decreased, increased) and the local sex ratio (female-biased, control, male-biased). 3. We found that male-biased treatment consistently increased the subsequent local breeding densities over the 3-year study period. We also found that parents rearing small broods in these male-biased plots had increased survival rates compared with the other experimental groups. 4. We conclude that reproductive costs are the product of an interaction between parental phenotypic quality after reproduction and the social environment: raising a small brood had long-lasting effects on some phenotypic traits of the parents and that this increased their survival chances in male-biased environment where habitat quality may have deteriorated (via increased disease/prédation risk or intraspecific competition). 5. Our results provide the first experimental evidence that local sex ratio can affect reproductive costs and thus optimal clutch size.