An Experimental Investigation of Local Adaptation in Common Milkweed (Asclepias syriaca)

The migratory Monarch butterfly (Danaus plexippus) population of the eastern United States has shown a marked decline in recent years. One hypothesis for that decline is a severe reduction in the abundance of Common Milkweed (Asclepias syriaca). Caterpillars of the Monarch butterfly have an exclusive feeding relationship with milkweeds and so the loss of milkweeds may limit reproduction in adult butterflies. To combat this, Common Milkweed seeds are being distributed to the public to provide food plants for Monarch caterpillars. Because Common Milkweed occurs over a wide range, however, individual populations may be adapted to local abiotic and biotic conditions, and if transplanted as seeds to another part of the range, may not grow as well. As part of a collaborative effort with several other institutions, we established a common garden experiment at Claytor Nature Study Center to test for local adaptation in Common Milkweed. We transplanted seeds harvested from local milkweed populations in Minnesota, Wyoming, Ohio, Massachusetts, and Virginia. We measured herbivore abundance, herbivore damage, and several aspects of plant growth throughout the 2018 summer. Repeated-measures ANOVA will be used to test for effects of genotype vs. environment on these variables.