, Volume 154, Issue 1, pp 65–73 | Cite as

Fitness of juvenile lizards depends on seasonal timing of hatching, not offspring body size

  • Daniel A. Warner
  • Richard Shine
Population Ecology


To understand how selection shapes life-history traits, we need information on the manner in which offspring phenotypes influence fitness. Life-history allocation models typically assume that “bigger offspring are better”, but field data paint a more complex picture: larger offspring size sometimes enhances fitness, and sometimes not. Additionally, higher survival and faster growth of larger offspring might be due to indirect maternal effects (e.g., mothers allocate hormones or nutrients differently to different-sized eggs), and not to offspring size per se. Alternative factors, such as seasonal timing of hatching, may be more important. We examined these issues using 419 eggs from captive jacky dragon lizards (Amphibolurus muricatus). The mothers were maintained under standardized conditions to minimize variance in thermal and nutritional history, and the eggs were incubated under controlled conditions to minimize variance in offspring phenotypes due to incubation temperature and moisture. We reduced the size of half the eggs (and, thus, the size of the resultant hatchlings) from each clutch by yolk extraction. The hatchlings were marked and released at a field site over a 3-month period, with regular recapture surveys to measure growth and survival under natural conditions. Growth rates and survival were strongly enhanced by early-season hatching, but were not affected by hatchling body size.


Amphibolurus muricatus Body size Jacky dragon Growth rate Offspring survival 



We thank T. Child, T. Schwartz, J. Thomas, and C. Warner for assistance in the field. DAW was supported by and International Postgraduate Research Scholarship and International Postgraduate Award. This project was supported by grants from the Australian Society of Herpetologists (to DAW) and the Australian Research Council (to RS). This project was approved by the University of Sydney Animal Care and Ethics Committee (proposal no L04/12-2004/1/4018), and the New South Wales National Parks and Wildlife Service (license no. S10658).


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Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  1. 1.School of Biological SciencesUniversity of SydneySydneyAustralia
  2. 2.Department of Ecology, Evolution, and Organismal BiologyIowa State UniversityAmesUSA

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