COS 151-5 - Migration of Eastern North American monarch butterflies via the Southeast and Atlantic: evidence from stable isotopes, thin layer chromatography, DNA, and phenotype

Abstract: Monarch butterflies, Danaus plexippus (L.), from eastern North America are well known for their incredible fall
migration to Mexico; however, not all monarchs follow this route. There is evidence of monarchs overwintering and
reproducing in Florida, arriving to insular and continental Caribbean, and roosting in the Yucatán,
Mexico. This work aims to present evidence that these monarchs are part of two current migratory routes, that
we consider as the south-eastern and the Atlantic routes, routes that were probably more prominent in the
past. Monarchs were collected for 12 months in south Florida, for 4 years in Cuba in November and once in March,
in the Yucatán and Guatemala at different times, and once in northern Venezuela. We used two independent
techniques, stable hydrogen isotope (δ2H) analyses of the wings and/or thin layer chromatography (TLC), to trace the
monarch’s natal grounds. We analyzed the DNA of monarchs collected in St. Marks in the Florida Panhandle, Cuba
and Guatemala, and compared those data against previously-analyzed DNA data from monarchs in the Americas to
characterize their genetic structure and to assess the possible movement and presence of North American monarchs
and/or their alleles outside the USA. Our results support the existence of south-eastern and Atlantic migratory
routes. TLC, isotope and DNA analyses showed the arrival of likely North American monarchs in Cuba, Yucatán,
Guatemala, Venezuela and other areas of the Americas. North American monarchs found in these areas have
different natal grounds, phenotypic traits and DNA signature than Mexican migrants. Monarchs from the southeastern
route mostly originated in the south-east USA and fed on local Asclepias spp., such as Asclepias viridis,
Asclepias humistrata, Asclepias perennis and Asclepias asperula. Butterflies from this migratory route move east,
enter the Florida Peninsula, pass to Cuba, fly to the Yucatán and then to Guatemala where they appear to overwinter
in the high mountains of Guatemala where Abies guatemalensis occurs. Monarchs that are part of the Atlantic route move east of the Appalachians, enter the Florida Peninsula, and from there pass to the insular and continental
Caribbean. The main host plants for the Atlantic monarchs are A. perennis and A. humistrata; in contrast, Mexican
monarchs mainly feed on Asclepias syriaca. Some monarchs from these two proposed migratory routes, south-eastern
and Atlantic, will stay in the places where they travelled and others will return via Florida and Mexico. We propose
a scenario for how the different migratory routes evolved.