Effects of temperature on monarch caterpillar pigment variation in nature

• Published in: Insect conservation and diversity Vol. 16; no. 1; pp. 164 - 171
• Main Authors: Tseng, Michelle, Bevanda, Carolina, Bhatti, Sahibveer Singh, Black, Emily N., Chang, Elizabeth, Chiang, Jonathan, Dhaliwal, Harleen, Dimitriou, Alexandra, Gong, Sunny Y., Halbe, Eashan, Harris, Noam, Huntsman, Lydia, Lipka, Jennifer Ann, Malloff, Juniper, McHugh, Erin, Mikkelsen, Mira, Noroozbahari, Armin, Olson, Amelija, Pirouz, Daniel, Ramanathan, Kishoore, Rogers, Maryann, Singh, Suman, Skurnac, Jenna Rachel, Straus, Samantha, Sun, Yolanda, Sun, Yu Jia, Wang, Grace, Wong, Justin Kwong Ching
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.01.2023; Wiley Subscription Services, Inc
• Subjects: Biodiversity; Butterflies & moths; caterpillar; colour; Danaus plexippus; iNaturalist; monarch butterfly; pigment; Pigmentation; temperature; Temperature effects; Variation
• ISSN: 1752-458X; 1752-4598
• DOI: 10.1111/icad.12608

1. Insect colour patterns serve a wide range of ecological functions and the biotic and abiotic factors mediating colour variation in nature have been well characterised. 2. Nonetheless, the majority of studies in this field have focused on adult insects (particularly butterflies). Almost nothing is known about the factors that mediate intra‐specific colour variation in juveniles in nature, even though they are often as conspicuously coloured as their adult counterparts. 3. Here we show that temperature predicts a small but significant amount of monarch (Danaus plexippus) caterpillar pigment variation in nature. Over a 650,000‐km2 region in Canada and the USA, caterpillars found in warmer locations or lower latitudes had thinner black stripes than those found in colder locations or higher latitudes. Caterpillars have also become less black over the last five years, a result consistent with observed short‐term increases in summer temperature in this region. 4. Our study demonstrates that the relationship between temperature and monarch caterpillar pigmentation seen in laboratory settings is also apparent in nature, although with considerable variation. Our study also highlights the utility of online biodiversity repositories such as iNaturalist for characterising pattern and colour variation in nature. Insect pigmentation can have important consequences for fitness but the relative importance of temperature in mediating caterpillar pigment variation in nature is unknown. We quantified 600 iNaturalist photos of monarch caterpillars (Danaus plexippus) across a 650,000‐km2 region in Canada and the USA. Temperature had a small but significant effect on caterpillar pigmentation, with warmer temperatures associated with less pigmentation. Our study demonstrates a potentially important effect of temperature on caterpillar colouration.