Contact: Dr. Emily Mohl, St. Olaf College, mohl@stolaf.edu
Initiated: 2015
Project Status: Varies between subprojects. Refer to details below (‘Description’).
Description
An investigation of geographic variation in common milkweed populations and their interactions with animals. Multiple subprojects exist in varying stages of completion:
- Milkweed Phenology and Herbivory: Currently accepting new participants!
- Milkweed Adaptation – Part 1: Accepting contributions of seeds, but the first iteration of this study is complete.
- Milkweed Adaptation – Part 2: No longer accepting new participants.
Training videos, background info, datasheets, protocols, and curricular materials are available at the project website: marenweb.com.
Milkweed Phenology and Herbivory Project. There is variation in every population of milkweed in terms of its phenology, or the timing of developmental stages like emergence in the spring, flowering in the summer, and seed dispersal in the fall. Furthermore, different milkweed populations exhibit different phenologies. For example, northern populations emerge earlier than southern populations when they are all grown in the same place. How does the phenology of a plant’s development affect its interactions with pollinators and herbivores, especially monarch butterflies, whose populations have been declining? Can we use the data we gather to make predictions about the impacts of shifts in milkweed phenology as the climate changes or as a result of planting milkweed seeds in novel environments?
We have developed three different protocols to investigate milkweed interactions with pollinators and herbivores across time and space. Conduct observations in natural populations of milkweed in the spring, summer, or fall, or conduct. Visit marenweb.com and look for the Phenology page to learn more.
Milkweed Adaptation – Part 1. As climate changes, plants may either shift their ranges or adapt to avoid extinction. In either case, plant responses to climate change may impact their interactions with herbivores. Previous research (Woods et al. 2012) observed that northern milkweed populations emerge earlier, grow more slowly and are more resistant to herbivory, even though herbivore diversity and damage was greatest in the central part of the range. They hypothesized that northern plants have the lowest ability to tolerate herbivory, favoring higher resistance because herbivory has a greater impact on plant fitness. Participating schools will contribute seeds that will allow us to test this hypothesis, and others, at St. Olaf College.
Milkweed Adaptation – Part 2. As the public has become aware of declines in monarch populations, more people are planting milkweed, a critical resource for this specialist butterfly. Participating schools will plant seeds from local and non-local populations and gather data annually in spring and fall to determine whether milkweed populations are locally adapted, meaning it would be beneficial to plant locally sourced milkweed genotypes, or whether there are certain superior milkweed genotypes that perform better in all locations. Note that concerns about introducing non-local genotypes will be addressed in protocols; however, preventing pollen dispersal may be challenging.
Phenology Hypotheses/Objectives::
1. Plants that reach a developmental stage early or late experience reduced herbivory, and possibly pollination, compared to those with more average development. If this is true, then shifts in milkweed phenology could result in phenological mismatches.
2. Because higher latitudes have shorter growing seasons, the abundance and diversity of herbivores and pollinators, and the amount of herbivore damage decreases at higher latitudes.
1. Milkweed displays local adaptation such that those plants growing in their home environments outperform those growing in nonlocal environments.
2. Because higher latitudes have shorter growing seasons, the abundance and diversity of herbivores and the amount of herbivore damage decreases at higher latitudes.
Summary of Methods: Participating schools can choose to provide milkweed seeds and/or collect observational data from natural populations. Access to native Asclepias syriaca populations is strongly preferred. Protocols for measuring damage to plants, censusing herbivores and pollinators, and conducting outplant experiments to characterize the risk of herbivory have been developed. Sample Protocol and Data Sheet: Milkweed Seed Collection Protocol; Milkweed Adaptation Sample Data Sheet.
Expanded Project Info: You can access background information, datasheets, and detailed current protocols at marenweb.com.
Curriculum: We developed a curriculum that highlights principles of evolution and local adaptation, risks of genetic swamping, scientific debates about the monarch decline, phenology, and the ethics of citizen science. Access learning objectives and instructional materials for the milkweed project via ‘Teaching Materials’ at marenweb.com.
Other Project Materials: Find current information and join the community at marenweb.com.
Milkweed Project Participants [Excel worksheet updated in October 2015]
Publications will be linked here when available.