Multigenerational exposure to glyphosate has only modest effects on life-history traits, stress tolerance and...

Glyphosate is the most used herbicide worldwide, and it can be toxic to off-target species, such as insects. Although GLY-based herbicides (GBHs) can influence insect microbiomes, little is known about its cascading effects on fitness-related traits, such as life history or stress tolerance, especially in the context of long-term, multigenerational exposure. Thus, we exposed the variable field cricket, Gryllus lineaticeps, to GBH within and across generations to examine the potential role of GBH in developmental plasticity and evolution. Specifically, we measured its effects on life-history traits (e.g. developmental duration, adult body size and mass, and a life-history trade-off between investment into reproduction and flight), stress (heat and desiccation) tolerance and the gut microbiome. One generation of exposure to GBH reduced desiccation tolerance, which was also lower in flight-capable individuals. However, after 11 generations of exposure to GBH, this cost of GBH disappeared, and GBH exposure instead increased adult body size and mass in flight-incapable individuals. Flight capacity had a stronger effect on the gut bacterial community than GBH exposure, where flight-capable individuals contained more than twice as many Family Oscillospiraceae and fewer than half as many Family Erysipelotrichaceae. The effects of both flight capacity and GBH on the microbiome were only evident in generation 1. Together, our results indicate that GBH exposure may have quite modest long-term effects on stress tolerance and the gut microbiome. However, GBH may facilitate the evolution of flightlessness given its potential benefits to flight-incapable individuals, which exhibit greater reproductive potential and tolerance to climate stressors compared with flight-capable individuals.