The first big paper from our NSF Dimensions of Biodiversity project is now out at Science Advances. To better understand the recent adoption of alfalfa as a host plant by the Melissa blue butterfly (Lycaeides melissa), we quantified arthropod assemblages and plant metabolites across a wide geographic region while controlling for climate and dispersal inferred from population genomic variation.

We found that the presence of L. melissa could be reliably predicted by direct and indirect effects of plant traits and interactions with other species. The single biggest factor was the presence versus absence of ants, which tend Lycaeides caterpillars, thereby reducing attacks by predators. Our results suggest that host use and specialization arises as a consequences of many abiotic and biotic factors rather than from simple trade-offs in developmental physiology.