Prolonged diapause in Mormon crickets: Embryonic responses to three measures of time

Abstract

Mormon cricket eggs can remain diapausing in soil for multiple years without forming an embryo. I investigated whether embryonic development was dependent on the number of annual cycles since the egg was laid, duration of the summer period (forcing), or duration of the winter period (chilling). Male and female Mormon crickets collected in Arizona and Wyoming were paired in the lab. For each mating pair, sibling eggs were incubated 12 weeks, eggs with fully developed embryos removed, and the remaining eggs were split evenly among three treatments: a long cold period and a long warm period; a short cold period and a long warm period; and a short cold period and a short warm period, which respectively completed 2 annual cycles, 3 cycles, and 4 cycles in 60 calendar weeks. In each cycle over nine years, developed eggs and eggs that appeared inviable were counted and removed. For each mating pair, I used survival analyses to test for differences in 1) the number of annual cycles, 2) the warm period duration, and 3) the cold period duration required for the embryos to develop. For eight of 11 mating pairs, one of the three factors was not excluded as a determinant of the phenology of embryonic development. Duration of the warm period was not rejected in seven of 11 cases. Duration of the warm period required for 50 % of the eggs to develop ranged from 84 to 144 weeks. In one case from Arizona, the duration of the cold period was the only factor not rejected. Median chill time was 60 weeks, which is also more than one year. Despite this exception, I conclude that duration of the warm period is typically the factor that determines timing of embryonic development for Mormon crickets. For these two high elevation populations, median forcing or chilling exceeded one year.