Response of Native Texas Milkweeds to Light

Milkweeds (Asclepias spp.) serve as the host plant for monarch butterfly larvae (Danaus plexippus Linnaeus), and adult monarchs seek out and lay their eggs almost exclusively on milkweeds. Milkweeds secrete a milky substance containing toxic cardenolides used as a defense against herbivory. However, monarch larvae have developed the ability to sequester these toxic cardenolides making the larvae unpalatable to predators and acting as a deterrent against future predation. Over time, the eastern migrating monarch population have been declining and one of the reasons may be due to a lack of milkweed within their breeding range primarily due to land use conversion. This study evaluates the photosynthetic response of seven milkweed species to different light levels using a Li-COR Infrared gas analyzer. Leaf gas exchange measurements for Asclepias asperula, A. curassavica, and A. oenotheroides showed light responses characteristic of heliophytes or sun plants. Leaf gas exchange measurements for, Asclepias incarnata, A. tuberosa, and A. viridis showed responses characteristics of intermediates plants. While, Asclepias syriaca showed responses characteristic of sciophyte or shade plant. Results of this study may improve our understanding of the light requirements for various milkweeds in Texas, allowing natural resource professionals to better manage milkweed populations potentially increasing monarch habitat along their migration route.