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Effects of Nighttime Warming on the Reproduction of Lizards
Clarke, D.N. and Zani, P.A. 2012. Effects of night-time warming on temperate ectotherm reproduction: potential fitness benefits of climate change for side-blotched lizards. The Journal of Experimental Biology 215: 1117-1127.

Whereas most previous studies of the effects of global warming on biological systems have boosted temperatures by the same amount during all hours of the day and night, the authors note that observed real-world temperature increases have typically been "asymmetrically distributed over diurnal time frames, with daily minima increasing at a faster rate than daily maxima," citing the work of Karl et al. (1991, 1993), Easterling et al. (1997, 2000) and DeGaetano and Allen (2002). Therefore, they decided to conduct their study of the potential impact of global warming on the common side-blotched lizard (Uta stansburiana) - which they collected about 20 km south of Burns, Oregon (USA) at the northern edge of the Great Basin Desert - employing the latter more realistic imposed mode of asymmetric nighttime-only warming.

What was done
Working at their field laboratory, Clarke and Zani simulated observed trends in the asymmetric alteration of the local diurnal temperature range by increasing the nighttime temperatures in the incubators into which they transferred the female lizards (from their daytime cages) during their ovarian cycle; and they treated the eggs the female lizards produced in a similar manner during their incubation period, while carefully documenting the differences they detected throughout the entire reproductive process between the female parent and progeny lizards of the thusly-warmed and control treatments.

What was learned
The two U.S. researchers discovered that higher night-time temperatures during the female lizards' ovarian cycles "increased the probability of reproductive success and decreased the duration of the reproductive cycle," both of which findings were positive developments, while they found that the higher temperatures had neither positive nor negative effects on "embryo stage or size at oviposition, clutch size, egg mass or relative clutch mass." Back in the positive effects column, however, they report that "higher incubation temperatures increased hatchling size and decreased incubation period," noting that "subsequent hatchlings were more likely to survive winter if they hatched earlier."

What it means
In the words of Clarke and Zani, "as our findings confirm that climate warming is likely to increase the rate of development as well as advance reproductive phenology, we predict that warmer nights during the breeding season will increase reproductive output as well as subsequent survival in many temperate ectotherms, both of which should have positive fitness effects." And based on these findings, they conclude that "these effects are primarily beneficial for this population of northern lizards," and they predict that "future changes will continue to benefit the reproduction, growth and survival of individuals at this site."

DeGaetano, A.T. and Allen, R.J. 2002. Trends in twentieth-century temperature extremes across the United States. Journal of Climate 15: 3188-3205.

Easterling, D.R., Horton, B., Jones, P.D., Peterson, T.C., Karl, T.R., Parker, D.E., Salinger, M.J., Razuvayev, V., Plummer, N., Jamason, P. and Folland, C.K. 1997. Maximum and minimum temperature trends for the globe. Science 277: 364-367.

Easterling, D.R., Karl, T.R., Gallo, K.P., Robinson, D.A., Trenberth, K.E. and Dai, A. 2000. Observed climate variability and change of relevance to the biosphere. Journal of Geophysical Research 105: 20,101-20,114.

Karl, T.R., Kukla, G., Razuvayev, V.N., Changery, M.J., Quayle, R.G., Helm Jr., R.R., Easterling, D.R. and Fu, C.B. 1991. Global warming: evidence for asymmetric diurnal temperature change. Geophysical Research Letters 18: 2253-2256.

Karl, T.R., Jones, P.D., Knight, R.W., Kukla, G., Plummer, N., Razuvayev, V., Gallo, K.P., Lindseay, J., Charlson, P.J. and Peterson, T.D. 1993. Asymmetric trends of daily maximum and minimum temperature. Bulletin of the American Meteorology Society 74: 1007-1023.

Reviewed 8 August 2012