Eastern monarch larval performance may not be affected by shifts in phenological synchrony with milkweed

1. Interacting species are experiencing disruptions in the relative timing of their key life history events due to climate change. These shifts can sometimes be detrimental to the fitness of the consumer in trophic interactions but not always.

2. The potential consequences of phenological asynchrony for the monarch butterfly (Danaus plexippus) and its host plant (Asclepias spp.) have not been well studied. Given that plants generally undergo seasonal declines in quality, if climate change delays the timing of the larval stage relative to the availability of younger milkweed plants, monarch performance could be negatively affected.

3. Here we explore the potential consequences for the eastern monarch population due to probable asynchrony with milkweed. We used field surveys around Ottawa, Canada to determine monarch oviposition preference on common milkweed (Asclepias syriaca) plants and the seasonal availability of these plants. To determine the potential fitness consequences when females oviposit on non-preferred plants, we conducted a field experiment to assess the effect of milkweed size on monarch larval performance (e.g., development time, final size).

4. Preferred oviposition plants (earlier stages of development, better condition) were consistently available in large proportion over the summer season. We also found that declines in leaf quality (more latex, thicker leaves) with plant size did not translate into decreases in larval performance.

5. Our results suggest that even if asynchrony of the monarch-milkweed interaction occurs due to climate change, the larval stage of the eastern monarch may not face negative consequences. Future studies should determine how the relative timing of the interaction will change in the region.

Methods
Field surveys and field experiments (mowing)