Breeding season temporal and spatial trends in continental-scale migration of the monarch butterfly

Authors: FISHER, KELSEY - Connecticut Agricultural Experiment Station; FILANDRO, ALINA - Quinnipaic University; BRADBURY, STEVEN - Iowa State University; WANAMAKER, ALAN - Iowa State University; Coates, Brad

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/19/2024
Publication Date: 10/4/2024
Citation: Fisher, K.E., Filandro, A., Bradbury, S.P., Wanamaker, A., Coates, B.S. 2024. Breeding season temporal and spatial trends in continental-scale migration of the monarch butterfly. Environmental Entomology. https://doi.org/10.1093/ee/nvae076.
DOI: https://doi.org/10.1093/ee/nvae076

Interpretive Summary: The monarch butterfly is a sentinel pollinator that undergoes a seasonal migration from Mexico to northern regions located east of the Rocky Mountains. Seasonal dispersal patterns influence annual monarch distribution and demographics across major crop producing regions of the United States. These factors also impact the spread of genes that help in adaptation to environmental change and/or insect producer pest control practices. To study migration rates of the monarch butterfly, ARS researchers and university collaborators combined stable isotope, morphological, and genetic analyses of monarch butterflies from several locations across North America. These analyses predicted the number of migrating butterflies and distances they traveled. In addition, the research team identified significant genetic differences between monarchs collected at different times across a season. This indicates that mating among monarchs in proximity with each other can result in genetic variation. However, there are no detectable differences among monarchs at overwintering sites. The outcomes of this study are important for understanding the maintenance of genetic diversity in a beneficial insect and will be useful for conservation efforts to manage endangered monarch butterfly populations. This work will be of interest to university and industry researchers, conservation groups, and regulatory agencies.

Technical Abstract: The monarch butterfly (Danaus plexippus) is a vagile species that undertakes an annual, multi-generational migration across North. The abundance at both eastern and western overwintering sites in Central Mexico and California indicates population decline. Success of continental-scale conservation programs for a migratory species depends on providing, maintaining, and protecting habitats at appropriate temporal and spatial scales, yet remains relatively undetermined for this species. Dynamics of monarch continental scale migration and gene flow was obtained in the current study by combined stable isotope, morphological, and genetic analyses. These analyses were applied to temporal monarch samples collected from May through September during 2016 to 2021 at locations in Iowa, USA and spatial collections from Pennsylvania, Delaware, Iowa, Ohio, Nevada, Idaho, Hawaii, three Australian locations during July and August 2016, and Texas in April 2021. Evidence of seasonal multi-generational migration was obtained among deuterium stable isotope analyses of spatial collections, which was corroborated by decreased wing hue (a morphological marker for non-migratory individuals). Limited sequence variation was detected across the entire mitochondrial genome impacted subsequent capability to detect significant population genetic variation in our North American samples. However, two novel substitutions were identified and predicted to be fixed among Australia samples, contributing to intercontinental differentiation from counterparts in North America. Our assessment of temporal and spatial population dynamics across the North American monarch breeding range provide insight into continental-scale dispersal and previously undetected mitochondrial DNA variation among globally distributed populations.