Determinants of incubation period: do reptilian embryos hatch after a fixed total number of heart beats?

Wei Guo Du*, Rajkumar S. Radder, Bo Sun, Richard Shine

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

59 Citations (Scopus)
14 Downloads (Pure)


The eggs of birds typically hatch after a fixed (but lineage-specific) cumulative number of heart beats since the initiation of incubation. Is the same true for non-avian reptiles, despite wide intraspecific variation in incubation period generated by variable nest temperatures? Non-invasive monitoring of embryo heart beat rates in one turtle species (Pelodiscus sinensis) and two lizards (Bassiana duperreyi and Takydromus septentrionalis) show that the total number of heart beats during embryogenesis is relatively constant over a wide range of warm incubation conditions. However, incubation at low temperatures increases the total number of heart beats required to complete embryogenesis, because the embryo spends much of its time at temperatures that require maintenance functions but that do not allow embryonic growth or differentiation. Thus, cool-incubated embryos allocate additional metabolic effort to maintenance costs. Under warm conditions, total number of heart beats thus predicts incubation period in non-avian reptiles as well as in birds (the total number of heart beats are also similar); however, under the colder nest conditions often experienced by non-avian reptiles, maintenance costs add significantly to total embryonic metabolic expenditure.

Original languageEnglish
Pages (from-to)1302-1306
Number of pages5
JournalJournal of Experimental Biology
Issue number9
Publication statusPublished - May 2009
Externally publishedYes

Bibliographical note

Copyright the Author(s) 2009. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.


  • embryonic development
  • heart rate
  • metabolic rate
  • reptile
  • thermal dependence
  • thermal time


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