Stay and lay or fly away? Development in the wing polyphenic sand cricket (Gryluss firmus)

Wing polyphenisms represent a classic life history trade-off between investment in reproduction or dispersal. While the analysis of trade-offs known as life history theory (LHT) explains why this phenomenon occurs, how it occurs at evolutionary, developmental, and physiological levels remains unknown in most taxa. To determine if the LHT predictions previously empirically evaluated – namely in Hemiptera - hold across evolutionary origins of this extreme form of phenotypic plasticity, we assessed a variety of environmental cues in three genetically distinct populations of Gryllus firmus. Two of these populations had undergone decades of selection for the flighted or flightless morph respectively, and one was freshly collected from a wild population. We confirmed that tactile cues are integral to the population density signal, with the sensitive period extending into late nymphal stages. Contrary to the predictions of LHT, and previous results from hemipteran systems, we found that the production of the flightless morph increased under diet restrictions. Additionally, we tested a novel cue, parasite infection. We predicted that parasite infection would shift all sexes and populations to produce predominately flightless adults. We found an increase in production of the flightless morphs in all population by sex combinations except one. This revealed the importance of interpopulation variation in wing polyphenic development. More broadly, our results reveal both mechanistic similarities to and differences from the previously evaluated systems. This research not only highlights the importance of utilizing diverse insect taxa systems to empirically test physiological and evolutionary theory, but also genetically distinct populations.