Fisher’s sex ratio theory predicts that on average parents should allocate resources equally to the production of males and females. However, when the cost/benefit ratio for producing males versus females differs, the theory predicts that parents may bias production, typically through underproduction of the sex with greater variation in fitness. We tested theoretical predictions in the red-necked phalarope, a polyandrous shorebird with sex-role reversal. Since females are larger and therefore potentially more expensive to produce and may have greater variation in reproductive success, we predicted from Fisher’s hypothesis a male bias in population embryonic sex ratio, and from sex allocation theory, female biases in the clutches of females allocating more resources to reproduction. We measured eggs and chicks and sexed 535 offspring from 163 clutches laid over 6 years at two sites in Alaska. The embryonic sex ratio of 51.1 M:48.9 F did not vary from parity. Clutch sex ratio (% male) was positively correlated with clutch mean egg size, opposite to our prediction. Within clutches, however, egg size did not differ by sex. Male phalarope fitness may be more variable than previously thought, and/or differential investment in eggs may affect the within-sex fitness of males more than females. Eggs producing males were less dense than those producing females, possibly indicating they contained more yolk relative to albumen. Albumen contributes to chick structural size, while yolk supports survivorship after hatch. Sex-specific chick growth strategies may affect egg size and allocation patterns by female phalaropes and other birds.
|Number of pages||11|
|Journal||Behavioral Ecology and Sociobiology|
|State||Published - Dec 2014|
Bibliographical noteFunding Information:
Comments by two anonymous reviewers substantially improved our presentation and analyses. W.B.E.’s fieldwork was supported by Alaska Department of Fish and Game non-game program, and the National Science Foundation Office of Polar Programs grants to B.K. Sandercock. Additional funds were provided by the Northern Studies Training Program (Canada). Many thanks to E. Kwon, M. Wilson, and M. Haring for field assistance and M. Hart for laboratory analyses. D.T. and D.S. thank K. Wohl and B. Andres of the US Fish and Wildlife Service, and D. Spirtes, R. Harris, L. Selig, and L. Dalle-Molle of the US National Park Service for logistical and financial support. Additional funding came from the National Science Foundation Office of Polar Programs (OPP-9812841), the National Oceanic and Atmospheric Administration-Outer Continental Shelf Environmental Assessment Program, the University of Alaska Natural Resources Fund, United States Geological Survey-Biological Resources Division, and the Frank M. Chapman Memorial Fund. D. Matkin, P. Klein, R. Gronquist, K. Oakley, L. Johnson, J. Cole, A. Swingley, C. Acevedo, Y. Zharikov, J. Schamel, and J. T. Schamel assisted with field studies; H. Mays, R. Hanschu, and T. Roush expedited the molecular sexing. D.F.W. thanks the National Science Foundation and the University of Kentucky for indirect support of this project. W.B.E., D.S., and D.B.L. were supported by the Centre for Wildlife Ecology at Simon Fraser University.
© 2014, Springer-Verlag Berlin Heidelberg.
- Parental investment
- Red-necked phalarope
- Reproductive strategies
- Sex allocation
- Sex ratio
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics
- Animal Science and Zoology