Sex allocation in a monomorphic seabird with a single-egg clutch: test of the environment, mate quality, and female condition hypotheses |
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Authors: | BriAnne Addison Alexander S Kitaysky J Mark Hipfner |
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Institution: | (1) Center for Wildlife Ecology, Simon Fraser University, 8888 University Dr., Burnaby, British Columbia, Canada;(2) Biology Department, University of Missouri—St Louis, 1 University Blvd, St Louis, MO, USA;(3) Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK, USA;(4) Canadian Wildlife Service, Pacific and Yukon Region, RR1 5421 Robertson Rd, Delta, British Columbia, Canada |
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Abstract: | Sex allocation theory posits that mothers should preferentially invest in sons when environmental conditions are favorable
for breeding, their mates are of high quality, or they are in good body condition. We tested these three hypotheses in rhinoceros
auklets (Cerorhinca monocerata), monomorphic seabirds that lay a single-egg clutch, in 2 years that differed in environmental conditions for breeding. Results
supported the environment and mate quality hypotheses, but these effects were interactive: offspring sex was independent of
paternal traits in the poor year for breeding, while females mated to larger and more ornamented males reared more sons in
the better year. Conversely, offspring sex was unrelated to female condition, as indexed by hatching date. We propose that
good rearing conditions enable females to rear sons possessing the desirable phenotypic attributes of their mates. Results
also supported two critical assumptions of sex allocation theory: (1) dimorphism in offspring condition at independence: daughters
fledged with higher baseline levels of corticosterone than sons and (2) differential costs of rearing sons versus daughters:
mothers rearing sons when environmental conditions were poor completed parental care in poorer condition than mothers rearing
daughters in the same year and mothers rearing either sex when conditions were better. These novel results may help to explain
the disparate results of previous studies of avian sex allocation. |
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Keywords: | Body condition Reproductive investment Resource holding potential Sex ratio Trivers– Willard hypothesis Mate quality |
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