EFFECT OF INCUBATION TEMPERATURE ON MORPHOLOGY, GROWTH, AND SURVIVAL OF JUVENILE SCELOPORUS UNDULATUS

Abstract

Incubation temperature affects a wide range of phenotypic traits of hatchling rep- tiles. The main objective of this research was to determine if such phenotypic traits persist long enough in the field to have an effect on fitness. Eggs of Sceloporus undulatus lizards were incubated at six temperature regimes, five constant and one fluctuating, with means ranging from 23-33 C. Hatchlings were measured and their subsequent morphology, growth, and survival were monitored for 7-9 months, one to two months before individuals reached adult size. Phenotypic traits of lizards that hatched at the field site were used for comparative purposes. Morphological traits persisted for 7-9 mo. In contrast, growth rates did not differ among incubation temperature treatments after individuals were released in the field. Overall, 29 (27%) of 107 individuals that were released survived to the spring following hatching, and individuals from eggs incubated at the lowest tem- perature had higher survival than individuals from all other groups. The phenotypes of lizards incubated at intermediate temperatures tended to be most similar to those of field hatched lizards. We rejected two predictions about phenotypic responses to incubation temperature. The first pre- diction was that extreme incubation temperatures would be associated with the most deviant phe- notypes. Observed phenotypic responses to temperature were either linear or, only one extreme temperature produced a deviant phenotype. The second prediction was that hatchlings incubated at warm temperatures and that hatched early in the season would have higher survival in general and higher overwinter survival in particular than hatchlings incubated at cool temperatures and that hatched later in the season. The reverse was true; observed survival was greatest for hatchlings from the coolest incubation treatment that hatched last.