How do latitude and urban heat islands affect monarch butterfly (Danaus plexippus) larval melanisation?

Abstract

As temperatures warm in response to anthropogenic changes (climate change and urbanization), animals must respond adaptively to these changes or be displaced. Here, we use community science data (iNaturalist and BugGuide) to show that melanisation in larval monarch butterflies (Danaus plexippus (Linnaeus, 1758)); an endangered species in Canada) is correlated with latitude and temperature across a latitudinal gradient, indicating likely use in thermoregulation. We also predicted that melanisation would decrease in cities where temperatures are consistently higher than rural areas, however we found that while melanisation was lower in urban areas, it was not statistically significant. Our results demonstrate the importance of considering life stage when assessing capacity for adaptation to anthropogenic change in vulnerable animal populations, like monarch butterflies. We also show the value of using community science to sample species (particular those of most concern) distributions across the landscape.