Zoom with Dr Moria Robinson
“Stripes, bands, and blotches – Oh My! the evolution of color and pattern in caterpillars”
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Description: Many of us fell in love with butterflies and moths for their remarkable diversity of color and pattern. Whether bright or earth-toned in color, arranged in spots or bands or irregular blotches, their appearance plays an important role: it can conceal from predators, advertise vigor for potential mates, or signal presence of distasteful or toxic compounds in their own bodies. However, while much research has focused on how and why adult butterflies and moths appear the way they do, much less attention is paid to the ‘looks’ of the immature forms. As non-reproductive larvae, moths and butterflies have a singular purpose: eat fast, get big, and metamorphose as soon as possible into an adult – without getting eaten along the way. As popular food items, caterpillars have evolved an array of strategies to avoid predators. They can be incredibly camouflaged; or they can stand out from their background, warning would-be predators away. I have been studying why this diversity of strategies has evolved. Two prominent ideas are that dietarily specialized species – those that eat only a single kind of host plant – will be more effective at sequestering toxins within their bodies, and will therefore advertise their noxiousness with warning (“aposematic”) coloration. A related hypothesis posits that species feeding on woody plants will opt for camouflage, both because woody plants tend not to produce toxins, and because there are more places to hide within an architecturally-complex shrub or tree. Other hypotheses, from the times of Darwin and Wallace, suggested that grass-feeding species should boast a stripe to help them blend in with the shape of grass blades. To test these ideas, we assembled a phylogeny (tree of life) of 1808 species of butterfly and moth in North America, for which photographs of larvae were available. We used many field guides (including from very own David Nunnallee and David James!), and categorized the colors and patterns in each species, as well as information about their diet. We were excited to find that colors and patterns can be grouped into “cryptic/camouflage” and “warning” categories, and that these colorations are related to the kind of plants caterpillars eat. We can thank the plants and the birds – the food and the predators – for the grand and beautiful parade of caterpillar appearance!
Bio: Moria Robinson is a research associate at Michigan State University, where she studies the many ways insects and plants interact. In particular, she is interested in how insects have evolved to eat the great diversity of physical, nutritive, and chemical traits found in plants, and how plants have evolved to fend off their consumers. She grew up on Vashon Island, Washington, where her interest in butterflies was encouraged by the wonderful community of WABA. She went to Middlebury College, Vermont, where she majored in biology and did a senior thesis project on host plant choice of silvery blue butterflies in suburban King County. She went on to receive her PhD from the University of California, Davis, in 2018, studying caterpillar communities in the California chaparral shrub ecosystems, and where the study she is discussing today began. When she is not stuck to her computer screen, Moria enjoys road tripping with her dog, enjoying the desert West with her partner, and photographing caterpillars on whatever plants are nearby.