Annotated Bibliography

How do cardenolides make up milkweed and can they be manipulated? 

 

Malcolm, S. B., & Brower, L. P. (1989). Evolutionary and ecological implications of cardenolide sequestration in the Monarch butterfly. Cellular and Molecular Life Sciences. Retrieved November 4, 2021, from https://link.springer.com/article/10.1007/BF01951814. 

 

In 1989, S.B Malcolm and L.P Brewer conducted a study revolving around the multiple species of milkweed and how monarchs react to the differing cardenolide concentration in each one. The men found that monarchs reacted the best to milkweed with intermediate levels of cardenolide rather than ones with high or low concentrations. However, the scientists did find that when the butterflies begin their migration from back from Mexico, they tend to exploit three dominant Asclepias species in the southern U.S which have a higher cardenolide concentration; This gives the monarchs a better chance of surviving predators throughout the long distance they have to travel. 

 

Ehrlich, P. R., & Raven, P. H. (1964). Butterflies and Plants: A Study in Coevolution. Evolution, 18(4), 586–608. https://doi.org/10.2307/2406212

 

Paul R. Ehrlich and Peter H. Raven, in 1964, conducted broad research on the relationship between butterflies and their food source. As they delved into the monarch butterfly, they noted that they observed a change in the chemical composition of plants based on where they were grown, the amount of sunlight they got, the nutrients in the soil, etc. They determined this because, as they grew accustomed to the ways of butterflies, they saw the monarchs being more attracted to the milkweed that was full of sap, bright green, and sturdy rather than their weaker, less nutrient-dense counterpart. 

 

Gerhardt, R. (1928). Physiological and chemical studies ... - Iowa State University. Retrieved November 4, 2021, from https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=15747&context=rtd. 

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Upon his research of milkweed, Fisk Gerhardt of Iowa State College in 1928 conducted a series of tests pertaining to the sap in the stalk of milkweed. He determined, after observing the growth of common milkweed over the span of a couple of years, that the concentration of the sap in the plant is affected simply by the seasons. In the winter the sap dried up, yet he found traces of it in the walls of the plant cells. In the spring and summer, as the plant grew again, the sap content increased. However, the chemical concentration of the sap in the winter was much different from that of the summer, which led to his discovery that the chemical contents of milkweed can be manipulated. The Join Monarch Venture verified his findings in the last 90s and Gerhardts research has now been flushed out over many years into larger projects and ventures.