Brood sex ratio in the Kentish plover |
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Authors: | Szekely Tamas; Cuthill Innes C; Yezerinac Stephen; Griffiths Richard; Kis Janos |
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Institution: | a Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath BA2 7AY UK
b Centre for Behavioural Biology, School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK
c Department of Biology, Reed College, 3203 SE Woodstock Blvd., Portland, OR 97202, USA
d Molecular Laboratory, DEEB, Graham Kerr Building, Glasgow University, Glasgow G12 8QQ, UK
e Behavioural Biology Research Group, Department of Ecology, Szent István University, Pf 2, H-1400, Budapest, Hungary |
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Abstract: | How and why do the mating opportunities of males and femalesdiffer in natural population of animals? Previously we showedthat females have higher mating opportunities than males inthe Kentish plover Charadrius alexandrinus. Both parents incubatethe eggs, and males provide more brood care than females; thusit is not obvious why the females find new mates sooner thanthe males. In this study we investigated whether the sex-biasedmating opportunities stem from biased offspring sex ratios.We determined the sex of newly hatched, precocial chicks usingCHD gene markers. Among fully sexed broods, 0.461 ± 0.024(SE) of chicks (454 chicks in 158 broods) were male, and thissex ratio was not significantly different from unity. The proportionof males at hatching decreased significantly over the breedingseason, which occurred consistently in all 3 years of the study.Large chicks were more likely to be males than females. Neitherparental age nor body size of male and female parents was relatedto brood sex ratio. We also sexed a number of chicks that werecaught after they left their nest (range of estimated ages 017days) and found that the proportion of males increased withbrood age. This relationship remained highly significant whencontrolling statistically for hatching date. As brood size decreaseddue to mortality after the chicks left their nest, these resultssuggest that the mortality of daughters was higher than thatof the sons shortly after hatching. Taken together, our resultsshow that the female-biased mating opportunities in the Kentishplover are not due to biased brood sex ratio at hatching but,at least in part, are due to female-biased chick mortality soonafter hatching. |
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Keywords: | Charadrius alexandrinus Kentish plover mating opportunities parental care seasonal trends sex allocation sex ratio |
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