Summary
Although fitness costs of adaptation to herbicide are widely expected, they are not universally detected, calling into question their generality. This lack of identified costs could be due to experimental constraints such as a limited focus on measures of plant fecundity and low replication.
Here we examine the potential for a cost of herbicide resistance on seed germination, root growth, and above-ground growth using 43 naturally occurring populations of Ipomoea purpurea that vary in their resistance to RoundUp®, the most commonly used herbicide worldwide.
We show substantial costs in all three traits. Highly resistant populations had lower germination rates, slower root growth and slower above-ground growth. A visual exploration of the data indicated that the type of cost may differ and even trade off among populations.
We place our findings into a broad context using a simple model to show that the strength of the germination cost could act to slow the rate of resistance evolution in this species. Our results demonstrate that costs of adaptation may be present at stages other than the production of progeny. Additionally, the cumulative effect of costs at multiple life cycle stages can result in severe consequences to fitness when adapting to novel environments.