Offspring sex ratio is related to male body size in the great tit (Parus major) |
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Authors: | Kolliker Mathias; Heeb Philipp; Werner Isabelle; Mateman A C; Lessells C M; Richner Heinz |
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Institution: | a Zoology Department, University of Bern, CH-3032
Hinterkappelen Switzerland
b Netherlands Institute of Ecology, Boterhoeksestraat 22, PO Box
40, 6666 ZG Heteren The Netherlands |
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Abstract: | Sex allocation theory predicts that the allocation of resourcesto male and
female function should depend on potential fitnessgain realized through
investment in either sex. In the greattit (Parus major), a
monogamous passerine bird, male resourceholdingpotential (RHP) and
fertilization success both depend on malebody size (e.g., tarsus length) and
plumage traits (e.g., breaststripe size). It is predicted that the proportion
of sons ina brood should increase both with male body size and plumage
traits,assuming that these traits show a fatheroffspring correlation.
Thiswas confirmed in our study: the proportion of sons in the brood
increasedsignificantly with male tarsus length and also, though not
significantly,with the size of the breast stripe. A sex ratio bias in
relationto male tarsus length was already present in the eggs because(1) the
bias was similar among broods with and without mortalitybefore the nestlings'
sex was determined, and (2) the bias remainedsignificant when the proportion
of sons in the clutch was conservativelyestimated, assuming that differential
mortality before sex determinationcaused the bias. The bias was still present
among recruits.The assumption of a fatheroffspring correlation was
confirmedfor tarsus length. Given that both RHP and fertilization successof
male great tits depend on body size, and size of father andoffspring is
correlated, the sex ratio bias may be adaptive. |
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Keywords: | body size great tits Parus major resource holding potential sex allocation sexual selection |
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