A cartoon of a brown anole hatching from the egg. This cartoon was created by Francesca Luisi for Inside JEB.

A common challenge facing biologists is measuring environmental conditions in the field and appropriately replicating these conditions in a controlled experiment. What makes this particularly hard is that natural environments are always changing. For example, most lizards lay eggs in nests in the ground and then abandon them, providing no parental care during development. While eggs develop, nest temperatures are not constant; they fluctuate on a daily, weekly, and seasonal basis along with weather conditions. Think, for example, about how temperatures fluctuate every day due to the rise and fall of the sun. Most egg incubation experiments, however, fail to capture the true variation in nest temperatures when they design experimental treatments. For example, they might incubate eggs at a constant temperature or at temperatures that repeat the same daily change in temperature over and over again. Real nest temperatures, however, rise and fall by different degrees each day. Over a long incubation period (e.g. 40-60 days), eggs can experience a lot of different temperatures! This can result in lots of important effects on development because nest temperatures can influence the body size, running speed, and even learning ability of hatchling lizards.

In this study, we incubated brown anole eggs under incubation treatments that differed in how closely they match real nest temperatures. We found that natural temperature fluctuations improved hatchling lizards’ endurance and survival compared to simpler approximations (e.g. constant temperatures, repeated daily fluctuations). This paper was featured in the Journal of Experimental Biology‘s Inside JEB; therefore, Kathryn Knight has written a summary of our study for a general audience, and the cartoon above was created by Francesca Luisi to illustrate the main findings of our study.

Hall, J. M. and Warner, D. A. (2020). Ecologically relevant thermal fluctuations enhance offspring fitness: biological and methodological implications for studies of thermal developmental plasticity. J. Exp. Biol. 223, jeb231902. doi:10.1242/jeb.231902

Joshua Hall
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