Latest Research from the Altizer Lab
This page summarizes several current and previous research projects on monarch butterfly parasites from people in the Altizer lab. Click the topic below to see a summary of the study as well as a link to the full paper.
Disease Risk for Migratory Animals
Animal migrations are expected to increase the global spread of pathogens and even make it easier for these pathogens to spread to other species. While this does happen, new research has also shown that migration allows hosts to escape from infected habitats, reduces disease levels when infected animals do not migrate successfully, and may lead to the evolution of less harmful pathogens.
Persistence of OE Spores in the Environment
This study exposed spores to either sun or shade for varying amounts of time (0-16 days) to determine if longer time spent in the environment would lead to lower infection rates in monarchs. They found that the number of spores per monarch decreased with more time spent in the environment, suggesting that some spores became inviable as a result of exposure to the environment.
It also came up with a model to determine how a monarch population would hypothetically respond to different levels of persistence of the OE parasite. Infection prevalence was determined to peak at 15% at the end of the breeding season, considering spores are able to persist in the environment for at least 80 days. However, due to the increase in monarch populations during this time, the host population was predicted to decline very little even with highly persistent spores present.
How Migration Affects the Form and Structure of Monarch Wings
Non-Migratory Behavior Increases Disease Risk
A study from our lab showed that monarchs breeding year-round in the southern U.S. face a much higher risk of parasite infection compared to migratory monarchs. Using data from 5,800 monarchs in North America collected by over 100 citizen scientists as part of Project Monarch Health, we were able to compare infection levels between migratory monarchs before migration (summer-breeding) and after migration (in Mexico), as well as non-migratory monarchs in the south (winter-breeding).
This research indicated that non-migratory monarchs were up to 5 times more likely to be infected with OE compared to migratory monarchs. In some areas with year-round exotic milkweed, 100% of monarchs were infected! This high disease risk likely occurs because winter-breeding monarchs do not have the benefits of migration, which previous research has shown can weed out sick butterflies and provide an escape from parasites.
Click here for the original paper. The study was led by Dara Satterfield, John Maerz, and Sonia Altizer and published in Proceedings of the Royal Society B.
How Migration Impacts OE Transmission
How does seasonal migration influence interactions between animals and their parasites?
We found that OE infection levels were higher at the end of the breeding season for all years compared to at the beginning. Because breeding habitats are heavily infected, migration may allow monarchs to flee areas with high levels of parasites. Among adult monarchs captured at different points along the east coast fall migratory flyway, parasite prevalence declined as monarchs progressed southward, and was also lower among monarchs sampled at two overwintering sites in Mexico than among monarchs sampled during the summer breeding period.
OE Trade-offs: Transmission Vs. Host Death
Impact of Milkweed Species on Infection Severity
Infection Severity Influences Monarch Biology
Migration Distance in Healthy vs. Infected Monarchs
Click here for the original paper. This study was performed by Sonia Altizer, Keith Hobson, Andy K Davis, Jaap de Roode, and Leonard Wassenaar and was published in PLoS ONE.
These results show how seasonal migration can help keep infection levels low in wild animal populations and suggest that sedentary behavior may lead to greater infection prevalence for North American monarchs.
Infection Hinders Monarch Flight Performance
Butterfly Use of Pollinator Gardens
A 2018 study lead by UGA graduate student Ania Majewska showed that butterfly diversity and abundance increased rapidly in human-planted butterfly garden plots near Savannah, GA. Caterpillars of four target butterfly species (monarchs, queens, gulf fritillaries and black swallowtails) were found on their respective host plants (milkweed, passionvine, and fennel). Butterfly abundance and survival did not vary with the intensity of weed maintenance. Plots with exotic plant species flowered more intensely and supported higher abundance of monarchs and gulf fritillaries. These findings indicate that human-planted gardens can be a useful resource for pollinator conservation.