Behavioral Ecology and Sociobiology

, Volume 60, Issue 4, pp 563–571

Extra-pair paternity, offspring mortality and offspring sex ratio in the socially monogamous coal tit (Parus ater)

  • Verena Dietrich-Bischoff
  • Tim Schmoll
  • Wolfgang Winkel
  • Sven Krackow
  • Thomas Lubjuhn
Original Article

DOI: 10.1007/s00265-006-0201-5

Cite this article as:
Dietrich-Bischoff, V., Schmoll, T., Winkel, W. et al. Behav Ecol Sociobiol (2006) 60: 563. doi:10.1007/s00265-006-0201-5

Abstract

Females of many socially monogamous bird species commonly engage in extra-pair copulations. Assuming that extra-pair males are more attractive than the females’ social partners and that attractiveness has a heritable component, sex allocation theory predicts facultative overproduction of sons among extra-pair offspring (EPO) as sons benefit more than daughters from inheriting their father’s attractiveness traits. Here, we present a large-scale, three-year study on sex ratio variation in a passerine bird, the coal tit (Parus ater). Molecular sexing in combination with paternity analysis revealed no evidence for a male-bias in EPO sex ratios compared to their within-pair maternal half-siblings. Our main conclusion, therefore, is that facultative sex allocation to EPO is absent in the coal tit, in accordance with findings in several other species. Either there is no net selection for a deviation from random sex ratio variation (e.g. because extra-pair mating may serve goals different from striving for ‘attractiveness genes’) or evolutionary constraints preclude the evolution of precise maternal sex ratio adjustment. It is interesting to note that, however, we found broods without EPO as well as broods without mortality to be relatively female-biased compared to broods with EPO and mortality, respectively. We were unable to identify any environmental or parental variable to co-vary with brood sex ratios. There was no significant repeatability of sex ratios in consecutive broods of individual females that would hint at some idiosyncratic maternal sex ratio adjustment. Further research is needed to resolve the biological significance of the correlation between brood sex ratios and extra-pair paternity and mortality incidence, respectively.

Keywords

Coal tit Parus ater Extra-pair paternity Sex allocation Brood sex ratio Offspring mortality Molecular sexing 

Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  • Verena Dietrich-Bischoff
    • 1
  • Tim Schmoll
    • 2
  • Wolfgang Winkel
    • 3
  • Sven Krackow
    • 4
  • Thomas Lubjuhn
    • 2
  1. 1.Zoological Institute, TU BraunschweigBraunschweigGermany
  2. 2.Institute for Evolutionary Biology and EcologyUniversity of BonnBonnGermany
  3. 3.Institute of Avian Research “Vogelwarte Helgoland”, Working Group Population EcologyCremlingenGermany
  4. 4.Institute for BiologyHumboldt-University of BerlinBerlinGermany

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