Professor University of Colorado Boulder, Colorado, United States
Some species have large geographic ranges with distinct populations which experience variation in local habitat. One such species, Junonia coenia (Nymphalidae), sequesters the plant secondary metabolites iridoid glycosides for defense against enemies. In addition to these enemies, the common buckeye must also protect itself against pathogens and parasitoids, in which their immune system plays a critical role. Recent work suggests there is a trade-off between sequestration and immune function: individuals that sequester high amounts of iridoid glycosides have subsequently lower immune function. Understanding how differences among populations may affect this trade-off is important for understanding plant-herbivore and community interactions more broadly. Using the common buckeye as a model, I presented caterpillars from four populations (Arizona, California, North Carolina, and Florida) with an artificial immune challenge. I monitored their sequestration, growth and development, and immune challenge response.
Preliminary results show that one population, Arizona, has significantly larger pupae than the other three populations, which is an accepted measure of adult fitness. In addition, the Arizona population sequesters iridoid glycosides in different proportions than the other populations. Notably, Arizona caterpillars sequester more of the iridoid glycoside catalpol, even when fed on the same diet. These data suggest that different populations of this widespread butterfly species may differ in their sequestration abilities and thus their susceptibility to enemies. Although population did not have an effect on immune response, there may be trade-offs in immune response and sequestration at the individual level, a speculation I am eager to test in the future.
