Covariance of paternity and sex with laying order explains male bias in extra-pair offspring in a wild bird population |
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| Authors: | Oscar Vedder Michael J. L. Magrath Marco van der Velde Jan Komdeur |
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| Affiliation: | 1.Behavioural Ecology and Self-Organization, Centre for Ecological and Evolutionary Studies, University of Groningen, PO Box 11103, 9700 CC Groningen, The Netherlands;2.Institute of Avian Research, An der Vogelwarte 21, 26386 Wilhelmshaven, Germany;3.Department of Wildlife Conservation and Science, Zoos Victoria, Parkville, Victoria 3052, Australia |
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| Abstract: | It has been hypothesized that parents increase their fitness by biasing the sex ratio of extra-pair offspring (EPO) towards males. Here, we report a male bias among EPO in a wild population of blue tits (Cyanistes caeruleus). This resulted from a decline in both the proportion of males and EPO over the laying order of eggs in the clutch. However, previous studies suggest that, unlike the decline in EPO with laying order, the relationship between offspring sex ratio and laying order is not consistent between years and populations in this species. Hence, we caution against treating the decline in proportion of males with laying order, and the resulting male bias among EPO, as support for the above hypothesis. Variable patterns of offspring sex and paternity over the laying order may explain inconsistent associations between offspring sex and paternity, between and within species. |
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| Keywords: | extra-pair paternity laying sequence ovulation order polyandry sex allocation |
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