Constantly fluctuating in an inconsistent way: comparing the effects of sinusoidal and naturally fluctuating incubation temperatures on embryo development

Abstract

Temperature is a commonly studied environmental factor influencing embryo development in oviparous ectotherms. Though most studies use constant temperature incubation conditions, researchers are aware of the effects of fluctuating temperatures on development. Daily-repeating sinusoidal fluctuations are now commonly used in studies of developmental plasticity; however, thermal fluctuations in natural nests are highly variable from day to day. Thus, using repeated, uniform fluctuations (e.g. sine waves) may still provide an incomplete picture of how embryos develop in the wild and generate inaccurate predictions of how species will respond to future thermal conditions (e.g. climate change). We used eggs from the brown anole lizard (Anolis sagrei) to test the effects of realistic nest temperature fluctuations vs constant temperatures and sinusoidal fluctuations in the lab. We used temperature data from nests to create 4 incubation treatments: a constant mean temperature, a daily-repeating sine fluctuation, a daily-repeating asymmetrical fluctuation (i.e. mean, hourly nest temperatures), and a treatment that allowed each day’s thermal fluctuation to differ from all other days as in real nests. These 4 treatments were created for both early-season (March-April, relatively cool) and late-season (June-July, relatively warm) nest temperatures (2 by 4 factorial design; season x incubation treatment). We report results for developmental rates, physiology (VO2 and heart rate), embryo survival, as well as morphology, performance, growth, and survival of hatchlings. By comparing the effects of several commonly used experimental thermal regimes with those of natural fluctuations, our study assesses the importance of using ecologically relevant incubation conditions when studying developmental plasticity in the laboratory.