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Data from: The impact of temperature on the reproductive development, body condition, and mortality of fall migrating monarch butterflies in the laboratory

Rich, Michael1; Kesselring, Jasmine H.1; Garcia, Amy1; Wallin, Danielle1; Fedorka, Kenneth1

Published Jul 30, 2025 on Dryad. https://doi.org/10.5061/dryad.sf7m0cgg5

Data files

Jul 30, 2025 version files 287.95 KB

Abstract

Overwintering populations of the monarch butterfly, Danaus plexippus, have been in decline for the past 30 years. Several hypotheses for the decline have been proposed including summer and winter habitat loss and migration mortality due to non-senescing milkweeds and the parasite Ophryocystis elektroscirrha (OE). How climate change will affect migration physiology, however, has been understudied. This is surprising because warmer temperatures will likely destabilize reproductive diapause, a physiological strategy central to migration and overwintering success. Here, we exposed wild-caught migrating monarchs to different field-realistic migratory temperatures under laboratory conditions for 30 days, followed by different overwintering temperatures until death. During the migratory phase, warmer temperatures reduced male body condition, increased male mortality, increased mating frequency, and caused females to prematurely abandon diapause and invest in oocytes in the absence of milkweed. Monarchs who experienced warm migratory conditions prior to overwintering also exhibited greater overwintering reproductive investment and mortality. Overall, reproductive investment and OE burden were the best predictors of death. These data suggest that warm migratory temperature significantly alters monarch physiology and fitness and provide a mechanism by which climate change can facilitate migratory failure, winter-breeding, and overwintering mortality, all of which decrease overwintering population size.