A Laboratory Curse: Variation in Temperature Stimulates Embryonic Development and Shortens Diapause

An ongoing biological debate concerns 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 Anabrus simplex Haldeman (Orthoptera: Tettigoniidae) 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 d of vernalization was required to hatch after incubation in the constant cycling treatment relative to 42 d 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 d 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.