Iowa Monarch Conservation Consortium (IMCC) project alumni, Dr. Kelsey Fisher, and team leader Dr. Steve Bradbury have recently published a paper analyzing the genetic diversity of North American monarch populations and tools for distinguishing migrating monarchs from their non-migrating counterparts.
Using a combination of stable isotope measurements, morphological comparisons, and genetic analysis Fisher was able to highlight useful techniques that scientists can use to identify migratory monarchs within local populations.
The paper noted how hydrogen stable isotopes (δ2H) vary predictably across latitudinal scales and can be used to determine the general birthplace of monarchs. By comparing the δ2H signature of an adult monarch to its current location, Fisher was able to determine if individual monarchs were migrants and the general area of where they migrated from.
Her research found that the birthplace of adult monarchs found in Iowa gradually shifts north throughout the year with 10-15% of spring and summer monarchs originating from locations south of the state and 6% of midsummer adult monarchs being born in northern locations. The noted differences in birthplace indicated that a percentage of adults throughout the year were migratory individuals.
Another clue Fisher found to identify migrant monarchs came from the hue, or color, of their wings. Fisher’s research showed that spring remigrant monarchs in Texas (those migrating north from Mexico) had a darker hue to their wings compared to monarchs found in Iowa or the eastern United States during the summer. Fisher determined that these findings help support the idea that monarchs found in Texas during the early spring are migrants from the overwinter grounds and are from a different generation compared to late-season adults.
Finally, Fisher’s research looked into the global genetic analysis of the monarch populations, comparing those found in the United States to Australia. This comparison led to the discovery of previously undetected differences between the Australian and United States populations. Specifically, two unique genetic differences were identified in the Australian populations suggesting that there is increasing genetic variation between these two continental populations.
When asked about her experience with this research, Fisher shared that “This project was really rewarding because it was the result of collections from collaborators all over the world and my own collections over 6 years. It was exciting to find trends in movement patterns based on stable isotope, genetic, and morphological features. The main goal of this project was to help fill in research gaps in literature, so it was exciting to see that our results align with previous findings. The methods that I learned doing this work during my postdoc at ISU are fueling the beginning of my career as I start to work with other insects, including bumblebees and spotted lanternflies.”
Overall, Fisher’s research gave evidence of seasonal multi-generational migration and can help scientists better track the migration path of the monarchs throughout the year, highlight key reproductive areas across different seasons, and distinguish between migrant monarchs and local individuals. This information can help scientists better understand the genetic stability of the monarch population and better conserve important migration habitats.
Full article:
K.E. Fisher, Filandro, A., Bradbury, S.P., Wanamaker, A., and Coates, B. “Breeding season temporal and spatial trends in continental-scale migration of the monarch butterfly”, Environmental Entomology, 2024.