Effects of parental photoperiod and elevation on egg diapause, mortality, and synchronous hatching of Mormon crickets Anabrus simplex

Some katydid species remain in the egg stage for multiple years in prolonged diapause. Because the egg has yet to develop a nervous system, the parental generation is believed to play a large role in determining the duration of egg diapause through adult photoperiod and selection of the egg laying environment. However, little evidence exists that compares the relative influences of parental photoperiod and the egg environment on diapause. I investigated the relative effects of parental photoperiod and egg environment on diapause by burying two sets of Mormon cricket Anabrus simplex eggs, one from long-day parents and the other from short-day parents, at seven sites on an elevational gradient (1200-2800 m). As predicted, the effect of parental photoperiod on the diapause duration of the offspring was more pronounced at lower elevations than at high elevation sites. Contrary to results from a laboratory experiment, offspring of short-day parents developed faster. The field experiment confirmed that for Mormon crickets, parental photoperiod is a soft cue for prolonged diapause, especially when compared with the effects of the environment on egg diapause. Median hatching time ranged from two to eight years, depending on the elevation and microhabitat. Soil temperature was a critical factor in determining the persistence of Mormon cricket eggs in egg banks. Moreover, mortality was greater for the short-day photoperiod, particularly at higher elevations where the eggs were in the soil longer. At high elevation sites, the season for embryonic development is short and embryonic growth can only occur when the soil heats up during the day. Hence, multi-year diapause and slow embryonic development is a natural consequence of temperatures at high elevation. Mountains and canyons provide a patchy thermal environment where multiple generations of eggs are likely to be banked in the soil by which favorable environmental conditions can lead to developmental synchronization, hatching, and outbreaks.