Egg size and laying order in relation to offspring sex in the extreme sexually size dimorphic brown songlark, Cinclorhamphus cruralis
- Michael J. L. MagrathAffiliated withDepartment of Zoology, University of MelbourneDepartment of Animal Ecology, Centre for Ecology and Evolutionary Studies, University of Groningen Email author
- , Lyanne BrouwerAffiliated withDepartment of Animal Ecology, Centre for Ecology and Evolutionary Studies, University of Groningen
- , Jan KomdeurAffiliated withDepartment of Animal Ecology, Centre for Ecology and Evolutionary Studies, University of Groningen
Rent the article at a discountRent now
* Final gross prices may vary according to local VAT.Get Access
In some bird species, mothers can advantage the offspring of one sex either by elevating them in the laying order to promote earlier hatching or by allocating greater resources to eggs of the preferred sex. In size dimorphic species, the predictions as to which sex should benefit most from such pre-laying adjustments are ambiguous. The smaller sex would benefit from an initial size advantage to help compensate for the faster growth rate of the larger sex. However, an early advantage to offspring of the larger sex might have a greater effect on their lifetime reproductive success than an equivalent advantage to offspring of the smaller sex. We investigated these hypotheses in the polygynous brown songlark, Cinclorhamphus cruralis, which is one of the most sexually size dimorphic birds known. We conducted within-clutch comparisons and found that females hatched from larger eggs and were initially heavier (but not structurally larger) than their brothers. This may afford females an early competitive advantage, as egg volume remained correlated with chick mass until at least 5 days of age. Similarly, we found that hatch order was still positively associated with nestling mass and size when the brood was 10 days of age, but there was no clear relationship between offspring sex and hatching order. During this study, food was plentiful and there were few obvious cases of nestling starvation. When food is limited, we suggest that the greater nutrient reserves of female hatchlings could not only help compensate for their slower growth, but could also give them a survival advantage over their brothers early in the nestling period. Consequently, egg size dimorphism may be an adaptation that facilitates an early shift in brood sex-ratio towards cheaper daughters in conditions of low food availability.
KeywordsEgg size Laying order Hatching order Sex ratio Sexual size dimorphism.
- Egg size and laying order in relation to offspring sex in the extreme sexually size dimorphic brown songlark, Cinclorhamphus cruralis
Behavioral Ecology and Sociobiology
Volume 54, Issue 3 , pp 240-248
- Cover Date
- Print ISSN
- Online ISSN
- Additional Links
- Egg size
- Laying order
- Hatching order
- Sex ratio
- Sexual size dimorphism.
- Industry Sectors
- Author Affiliations
- 1. Department of Zoology, University of Melbourne, 3010, Melbourne, Victoria, Australia
- 2. Department of Animal Ecology, Centre for Ecology and Evolutionary Studies, University of Groningen, PO Box 14, 9750 AA, Haren, The Netherlands