The laboratory curse: variation in temperature stimulates embryonic development and shortens diapause

Authors: Srygley, Robert; Senior, Laura

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2018
Publication Date: 6/6/2018
Publication URL: http://handle.nal.usda.gov/10113/6472370
Citation: Srygley, R.B., Senior, L. 2018. The laboratory curse: variation in temperature stimulates embryonic development and shortens diapause. Environmental Entomology. 47(3):725-733. https://doi.org/10.1093/ee/nvy024.
DOI: https://doi.org/10.1093/ee/nvy024

Interpretive Summary: Laboratory and natural environments often differ greatly in their temperature and light conditions. Because Mormon crickets have been historically difficult to rear in the laboratory, we wondered if we could rear them under conditions that simulated the natural environment. Mormon crickets lay their eggs in the soil, and so we focused on temperature, which in nature varies from one day to the next in maximum and minimum and also in the proportion of the day that it is warmed by the sun (thermoperiod). In our first experiment, we tested a daily cycle that was invariant in maximum and minimum temperatures, and thermoperiod against a daily cycle that varied in all three aspects. We found that development of embryos was similar between these two environments, but eggs that developed in the more constant environment required longer to diapause even though the overwintering temperatures were the same between the two treatments. In our second experiment, we tested a daily cycle that was invariant in maximum and minimum temperatures but varied in thermoperiod against a daily cycle that varied in all three aspects. Somewhat surprisingly, development of embryos in the more constant environment was arrested at some point during our simulated summer, and those eggs that did develop in the more constant environment required longer to diapause even though the treatments appeared to be more similar than in the first experiment. We conclude that invariant cycling temperatures do not generate natural trait expression. This understanding helps develop a best practice for rearing Mormon crickets in a lab setting. Mormon crickets are best reared in cycling temperatures that emulate natural changes in temperature. They are more likely to develop and have a broader diapause window.

Technical Abstract: An ongoing biological debate is the difference in trait expression in continuous versus cycling temperature regimes, but are even daily cycling temperatures sufficient to generate natural expression of traits? We compared embryonic development and the duration of diapause for Mormon cricket eggs incubated in a daily cycling temperature constant in both amplitude and thermoperiod with those in a cycling temperature that was patterned after natural fluctuations in ambient temperature. Although the proportion of eggs developing did not differ between treatments, 128 days of vernalization was required to hatch after incubation in the constant cycling treatment relative to 42 days in the more variable cycle. We then compared these same development and diapause traits for eggs incubated in a daily cycling temperature that was constant in amplitude but varied in thermoperiod with those in the cycling temperature patterned after natural fluctuations in ambient temperature. The proportion of eggs developing in this constant cycling treatment was nearly half that in the variable treatment, and 128 days was insufficient time to break diapause following the constant cycling treatment even though the thermoperiods were now more similar. We have found that variation in the cycling temperature to mimic natural fluctuations in amplitude and period broadens the time when eggs can be warmed up for hatching and improves hatching success. Daily cycling temperatures that are constant over the season are insufficient to generate natural trait expression.