Graduation Year


Document Type




Degree Name

Master of Science (M.S.)

Degree Granting Department

Biology (Integrative Biology)

Major Professor

Jeremiah Sean Doody, Ph.D.

Committee Member

Alison Gainsbury, Ph.D.

Committee Member

Lisa Ganser, Ph.D.


Predation, environmentally cued hatching, reptiles, phenotypic plasticity


Early hatching is a form of environmentally cued hatching in which embryos can emerge early to improve chances of survival and is considered a means of antipredator defense. Early hatching as a response to predation has been well documented in amphibians, but its prevalence among other animal groups is unknown. Moreover, any trade-offs between early hatching and other traits, and thus survival, are not well understood. There is anecdotal evidence that lizards exhibit early hatching behavior, but quantitative evidence is limited to one study. In the present study, I tested for the presence of early hatching in six species of lizards spanning six families including: crested geckos (Correlophus ciliatus), red tegus (Salvator rufescens), brown basilisks (Basiliscus vittatus), eastern glass lizards (Ophisaurus ventralis), green iguanas (Iguana iguana), and Mediterranean geckos (Hemidactylus turcicus). Specifically, I surveyed for early hatching behavior and any potential trade-offs in body size at hatching (hatchling mass, hatchling snout to vent length (SVL) and residual yolk) or growth rates (in one species, for four weeks). Predation was simulated by rubbing a chopstick along the surface of the hatching-competent egg for two minutes, while control eggs were allowed to hatch spontaneously. Two of the six species (green iguanas and brown basilisks) did not respond to the simulated predation and hatched spontaneously, while the other four species (crested geckos, red tegus, Mediterranean geckos, and eastern glass lizards) did respond and hatched during experimental simulations. Three of those four species (crested geckos, red tegus and Mediterranean geckos) exhibited ‘explosive’ early hatching, whereby hatchlings emerged from the egg and immediately attempted to escape by running away from the perceived threat. Eastern glass lizards showed no evidence of early hatching. Though embryos pipped during predator simulation trials, they remained in their eggs for hours to days. Hatching response in this species may reflect synchronous hatching, whereby vibrations stimulate simultaneous pipping to promote hatchlings escaping the nest together. In crested geckos, earlier hatching (treatment) lizards were significantly smaller, shorter, and left a greater amount of residual yolk than spontaneously hatching (control) lizards. Growth trials with crested geckos showed that the treatment lizards were significantly shorter for the first week. However, trends suggest that the differences in length and size are distinct between treatment and controls and narrow over time eventually converging after four weeks. In red tegus, treatment lizards were significantly shorter and left a greater amount of residual yolk than control lizards. In brown basilisks, treatment lizards were significantly smaller and shorter than control lizards. While incubation periods for red tegus and green iguanas suggested early hatching, small sample sizes precluded confirmation, and the small sample size for Mediterranean geckos (N=5) also precluded analysis. The present study demonstrates early hatching in three new species and suggests its presence in two more. Collectively, my results and those of others suggest that early hatching is common in lizards, particularly in geckos, and that a smaller body size is likely a general cost of early hatching in lizards and perhaps other animals. Further research should examine how long those costs persist along with potential fitness consequences.

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Biology Commons