Abstract
The relationship between offspring size and offspring number is crucial to life history evolution. To examine how these two life history variables are coupled and whether an altered balance between them will result in changes in maternal fitness, we manipulated clutch size of the Chinese cobra (Naja atra) by using the techniques of hormonal manipulation and follicle ablation. Females receiving exogenous follicle-stimulating hormone produced more but smaller eggs, and females undergoing follicle ablation produced fewer but larger eggs. Neither body size (body mass and snout-vent length) at hatching nor egg mass at oviposition had a role in determining hatchling survival and growth. Female hatchlings were more likely to die in early post-hatching days and grew more slowly than male hatchlings. Our data show that: (1) there is a nonlinear continuum of egg size-number trade-offs in N. atra within which there is a single inflexion where the rate at which egg size decreases with increasing clutch size, or clutch size increases with decreasing egg size, is maximized; (2) there is a fixed upper limit to egg size for a given-sized female, and the limit is not determined by her body volume; (3) egg size has no role in determining hatchling survival and growth; and (4) the extent to which females may enjoy reproductive benefits in a given reproductive episode depends on how well egg size and egg number are balanced.
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Acknowledgements
We thank Jian-Fang Gao, Hong-Liang Lu, Lai-Gao Luo, Yan-Yan Sun, Jing Yang and Ling Zhang for assistance in the laboratory, and F. Braña, R. B. Huey, R. Shine and D. W. Winkler for their insightful comments on an earlier draft of the paper. This work was carried out in compliance with the current laws of China, and was supported by grants from the Natural Science Foundation of China (NSFC30370229 and NSFC30770378) to X. J.
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Communicated by Raoul van Damme.
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Ji, X., Du, WG., Qu, YF. et al. Nonlinear continuum of egg size-number trade-offs in a snake: is egg-size variation fitness related?. Oecologia 159, 689–696 (2009). https://doi.org/10.1007/s00442-008-1252-2
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DOI: https://doi.org/10.1007/s00442-008-1252-2