The selective basis for increased egg retention: early incubation temperature determines hatchling phenotype in wall lizards (Podarcis muralis)

Abstract

The thermal environment during development influences many aspects of the phenotype of hatchling reptiles. We hypothesized that temperature should differentially affect early incubation stages, in which differentiation dominates over growth, and late incubation stages, characterized by high growth rates. To test this idea, we incubated eggs of wall lizard (Podarcis muralis) under three regimes with the same mean temperature (29 °C), one constant and two variable with opposite sequences: first cold (25 °C) and then hot (32 °C), and vice versa. Hatchlings incubated at high temperature during the initial period had shorter hindlimbs and tails than those incubated under the other two temperature regimes and shorter heads than those incubated initially at low temperature. Thus, temperature experienced by embryos during the early external incubation period produced similar phenotypic responses compared to those reported in previous studies for the same constant temperature applied over the whole incubation period. Because female wall lizards select lower body temperatures during pregnancy, an increase of intrauterine retention would extend the time of exposure of developing embryos to suitable temperatures. Diminution of body temperature during pregnancy is contrary to the expected pattern under the hypothesis that egg retention has evolved to accelerate development, as proposed by the cold-climate model for evolution of viviparity in squamates, and the results of the present study support the alternative hypothesis of developmental optimization as a special case of the broader maternal manipulation view. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92, 441–447.