Demographic inference provides evidence of a quaternary-driven impact on the cactus moth and sheds light on the putative role of an exotic host

Abstract

Novel host plant-insect interactions often arise from human-mediated introductions of potential hosts to areas inhabited by native insects, or invasive insects to regions with suitable hosts. These novel interactions may drive ecological and evolutionary change in native species. Here we investigate the role of the introduction of the prickly pear Opuntia ficus-indica on the demographic history of the native moth Cactoblastis cactorum. The latter became a pest in its native range after the introduction of the economically cultivated prickly pear. We evaluated potential scenarios of long-term population size changes by applying a demographic simulation framework to a large set of high-throughput sequence data. We sampled populations of the cactus moth from regions of historical incidence of prickly pear crop, in central and northwestern Argentina. To shed insight into the shared history of the exotic cactus/native moth system we integrated the historical records of the introduction of O. ficus-indica in South America into the demographic simulation. We also included a null hypothesis of stable population and/or ancient population changes. Our results reveal population size changes in both Quaternary and contemporary C. cactorum populations. Simulations pointed to a recent population expansion that coincided with the hypothesis of the introduction of the prickly pear after the arrival of Europeans in South America. The presence of the new host during the last centuries apparently prompted the expansion of C. cactorum. Overall, our results are of interest to understand the ongoing impact of introduced species and the complex ecological adjustments of native insects that occur with the introduction of new hosts.