Abstract
Recent declines in the migratory North American populations of monarchs (Danaus plexippus) have necessitated efforts to evaluate the current status of the species, including worldwide populations. While monarchs originate from North America and may be ancestrally migratory, they have expanded throughout many parts of the world over the past 200 years. Most of these newer populations no longer migrate and face a variety of threats across a wide range of habitats, but we lack a comprehensive review of locations and characteristics of these worldwide populations. We thus delineated the current range of monarchs and their status throughout the world, recording over 90 countries, islands, and island groups where monarchs occur (74 with recent documented sightings) and known features of these populations. We discuss the major differences between these populations, focusing on morphology, migration, overwintering, natural enemies, larval diet, and genetics. The differences documented here provide the species with adaptive capacity, thus better allowing the species to adapt to novel changes in its environment. We end with a discussion of current gaps in our understanding of monarchs worldwide and directions for future research.
Highlights
Monarchs (Danaus plexippus) are well-known within North America for their long distance migration to overwintering sites along the western coast and in central Mexico
We examined the literature for differences between monarchs throughout the world in morphology, larval diet, natural enemies, migration, overwintering, genetics, and population sizes and trends, to help us better understand the potential worldwide sources of adaptive capacity for the species
We know that variation occurs in monarch morphology, with butterflies having varying wing shape, color, and length throughout their range
Summary
Monarchs (Danaus plexippus) are well-known within North America for their long distance migration to overwintering sites along the western coast and in central Mexico. With the recent declines in both the eastern and western North American populations, the U.S Fish and Wildlife Service (USFWS) was petitioned to list monarchs under the Endangered Species Act (ESA) of 1973 (Center for Biological Diversity, 2014) As part of this process, the USFWS is conducting a Species Status Assessment (SSA) to evaluate the status and viability of the species. The ability of a species to adjust to novel changes in its physical and biological environment, is important to evaluate to understand the continued success and viability of the species (Nicotra et al, 2015) This mini-review summarizes the findings on monarchs throughout the world, primarily focusing on areas outside of the eastern and western North American populations
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