Roundup and immune challenge have different effects on a native field cricket and its introduced competitor

Abstract

Abstract Crickets face many natural selection pressures, and humans have added to this burden by applying potentially harmful herbicides and unintentionally introducing competitors. We examine recently introduced Velafictorus micado Japanese burrowing crickets which share a microhabitat and season with native Gryllus pennsylvanicus field crickets. In this study, we assess the combined effects of Roundup (glyphosate-based herbicide) and a lipopolysaccharide (LPS) immune challenge on both crickets. In both species, an immune challenge reduced the numbers of eggs that female laid, however, this effect was much larger in G. pennsylvanicus. Conversely, Roundup caused both species to increase egg production, potentially representing a terminal investment strategy. The combined effect of immune challenge and herbicide harmed G. pennsylvanicus fecundity more than V. micado fecundity. Further, V. micado females laid significantly more eggs than G. pennsylvanicus, suggesting that introduced V. micado may have a competitive edge in fecundity over native G. pennsylvanicus. LPS and Roundup each had differing effects on male G. pennsylvanicus and V. micado calling effort. Overall, introduced male V. micado spent significantly more time calling than native G. pennsylvanicus, which could potentially interfere with G. pennsylvanicus mate-location behavior in their shared natural habitat. Despite the population-level spread of introduced V. micado, in our study, this species did not outperform native G. pennsylvanicus in tolerating immune and chemical challenge. Although V. micado appears to possess traits that make this introduced species successful in colonizing new habitats, it may be less successful in traits that would allow it to outcompete a native species.