Monarch butterflies are found throughout North America during the summer months, but migrate in the fall to a small cluster of colonies in the mountains of central Mexico to overwinter. The migration southward follows three major pathways: 1) through the Great Plains 2) across the Great Lakes and down the Ohio & Mississippi River valleys and 3) along the Atlantic and Gulf Coasts. Our project asks, "do monarchs following different migration paths end up at different overwintering colonies?"
There is also a non-migratory population in South Florida that is active and breeds throughout the year. One hypothesis is that this population receives a continual influx of southward migrants that "get lost", and follow the Florida peninsula instead of heading west along the Gulf Coast. Because the weather in the Miami area is warm throughout the winter (as many North American humans can attest!), these monarchs fall out of reproductive diapause when they reach South Florida, and they stop migrating. To explore this hypothesis, we will also be comparing the monarchs we collected from South Florida with those collected from the main migratory population.
Our project is unique in that we're combining two kinds of analyses that provide data on different time scales. Genetic data reflect patterns that have persisted across many generations, whereas stable isotope data identify movement patterns in the current generation. We are using genetic markers that have been useful for identifying patterns of genetic variation in monarchs and in other butterflies. Stable isotopes are different forms of an element that are not radioactive, but that vary in weight. The ratio of "heavy" to "light" isotopes of carbon and hydrogen in the wings of adult monarchs will tell us roughly where a monarch was a caterpillar, because the stable isotope ratio is established when the caterpillar is eating milkweed and doesn’t change after metamorphosis. While both genetic and stable isotope data have been used to investigate questions about monarch butterflies, no other project has merged these two types into an integrated analysis. By combining these two vastly divergent types of data, we are able to investigate patterns that would be undetectable using either type of data alone.
Monarch butterflies are some of the most distinctive animals found in North America, and are icons of the conservation ethos. Although much is known about the monarch life cycle, there are still major questions surrounding their unique annual migration. In addition to being a natural wonder (from Canada to central Mexico, individual butterflies travel more than 2,000 miles!), the migration may be key to maintaining the species’ population structure. Butterflies migrating from eastern, central, and western Canada and the United States appear to take different routes to overwintering colonies in Mexico, and thus might spend the winter in different places within the colonies. Alternatively, the butterflies may mix randomly in Mexico, regardless of where they were born. Or, males may mix, but females might not (or vice versa)! Depending on the associations between summering areas, migratory routes, and overwintering colonies, the monarch population found in eastern North America may be broken into sub-groups correlated with summering areas, or the population may be fairly well-mixed. Although monarchs themselves are not endangered, their magnificent migration is facing a variety threats both along the migration routes and in the overwintering colonies themselves: herbicides, reduction of nectar sources, logging, and loss of milkweeds. Since different regions face different threats, identifying how monarchs with different geographic origins interact is key to understanding the potential impact of these diverse threats.
We have 347 monarch butterflies that we collected from Pt. Pelee, Houston, Miami and five overwintering colonies in Mexico. Raising our $3,000 minimum will allow us to analyze 25 butterflies from each of the 5 overwintering colonies, which will give us preliminary answers about the linkages between migration paths and overwintering colonies. Analyzing stable isotopes for a single butterfly costs approximately $25, so each $25 above the minimum allows us to increase the number of butterflies we can include in the project. Ideally, we would like to analyze all 347 monarchs, since this would identify the origins of butterflies along the migration routes, as well as in the overwintering colonies and in the non-migratory population in Miami. The funds we received from traditional sources have already been used to perform the genetic analyses of these butterflies, so support from PetriDish contributors is vital to accomplishing this project.
Connections between summering areas & overwintering colonies sit somewhere along a continuum from completely random to tightly linked, and this project will identify where along this continuum these connections lie. Our results will also provide preliminary data to support development of a new research program focused on the genetic underpinnings of the monarch migration in the Wayne Lab at the University of Florida.
Carol L. Chaffee: I am a Ph.D. candidate in the Department of Biology at the University of Florida. I am broadly interested in how movement affects the distribution of genetic variation. My dissertation is focused on examining how the unique monarch butterfly migration in eastern North America affects the structure of this population, using a combination of genetic and stable isotope analyses. The current project represents a vital part of my dissertation work, and I'm excited to give PetriDish supporters a chance to be a part of it! I plan to defend my dissertation and graduate in the spring of 2013. Once I have my Ph.D., I'm looking forward to integrating my research into teaching and outreach activities, and I hope to find a faculty position at an institution focused on undergraduate research.
Marta L. Wayne, Ph.D.: I am a Professor in the Department of Biology at the University of Florida. I am an evolutionary geneticist, who uses population genetics, quantitative genetics, and genomics to address questions about how genetic variation is maintained in natural populations. The maintenance of genetic variation is interesting to me because even though genetic variation is continually created by mutation, it is also continually removed by natural selection. Current research projects focus on questions such as why monarch butterflies migrate (given that many butterflies that summer in Canada manage to overwinter, rather than migrate south), why viruses harm their hosts, and why males and females in flies (and other animals) look different, even though they share the vast majority of their genes.
Our project website has lots more pictures, a more detailed description of the project, and a blog that allows you to follow our progress.
We're now working on preparing a manuscript to publish our genetic results for the South Florida population! Analysis of the genetic results shows that this population is genetically distinct from the main migratory population, but is still tied to the main population through migrants that periodically fly down the Florida peninsula instead of migrating south to Mexico for the winter. Analyses to quantify how often this occurs are in progress.
The next step is going to be getting all the monarch wings prepared for stable isotope anaysis: washing them in a methanol:chloroform solution to remove all the surface debris & fats, then packaging up tiny amounts (about 1 microgram) into small aluminum foil cups.
Thanks for helping to support our project -- we wouldn't be able to do the stable isotope analysis without your help!
Thanks so much for the support everyone! 1/6 of the way there, and we haven't yet been live for a week!