Reptilian reproductive modes: the oviparity-viviparity continuum

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The total period of embryonic development in an oviparous reptile may be divided into two phases: a period when eggs are retained in utero and a subsequent period of development after oviposition. I use the term Pre-laying Fraction (PLF) to indicate the proportion of the total developmental period for which the eggs are retained in utero; PLF may be defined either under field conditions or from laboratory incubation at constant temperature. I assessed PLF in four ways: (1) regular sampling of field populations; (2) measurement of gestation and incubation periods at constant temperature in the laboratory; (3) comparison of embryonic developmental periods in oviparous and viviparous forms; and (4) determination of the stage of embryonic development at oviposition. A combination of published records and original data reveals a wide range of PLF's, and hence an apparent continuum of egg-retention strategies between "pure" oviparity and viviparity. Turtles, crocodilians and a few squamates which oviposit soon after ovulation are at one end of this continuum. Viviparous squamates are at the other extreme. Surprisingly, most oviparous squamates are midway between these two endpoints, retaining eggs in utero for about half of the total period of embryonic development.

Original languageEnglish
Pages (from-to)1-8
Number of pages8
Issue number1
Publication statusPublished - Mar 1983
Externally publishedYes


  • Oviparity
  • Viviparity
  • Reptile
  • Evolution
  • Egg
  • Embryo


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