Monarch fall migration, overwintering mortality and the effects of defence compounds released by decomposing butterflies on the soil ecosystem.

点击翻译按钮获取中文摘要

North American populations of the monarch, an iconic insect known for its migration to and from overwintering sites in Mexico, have declined due to a number of factors including habitat loss and modern agricultural practices. Habit loss due to illegal logging has declined and conservation programmes have resulted in increased availability of milkweed, the only host plant used by the monarch. However, other aspects that could help conservation efforts have received less attention. Adult monarchs migrating to Mexico are sexually immature and need nectar sources to sustain themselves during migration, and to accumulate sufficient fat reserves to survive winter, yet we do not detailed information of fat acquisition and use during this important period. Our hypothesis is that in fall the migrating adults sustain just enough reserves for flight and maintenance by feeding daily on local nectar sources and only markedly increase fat reserves once they are very close to the overwintering site. To test this, we will monitor the fat content of monarchs at different sites along the migratory corridor in Canada, USA and Mexico with those arriving at overwintering sites. We will also monitor temporal patterns of mortality during the winter to determine the relative importance of fat reserves on survival, compared with factors such as natal origin and parasite load. This study will be run over five years as the inter-year availability of nectar resources will vary with climatic conditions. For example, due to the warm summer in 2019, at the end of August early emerging adults in Ontario started reproducing rather than emigrating. If the offspring successfully complete development, adults will emerge when very few nectar sources are available, and thus would not have the necessary resources to successfully migrate. Similarly, there are far fewer flowers available this year in Mexico due to drought, so immigrants will have less opportunity to build up the reserves required to survive the winter, which is critical as few nectar resources exist at the overwintering sites. As adverse weather conditions at any point along the migratory corridor could negatively affect resource availability the results of our research will help develop management strategies that ensure nectar sources are available along the migratory route, ensuring greater survival both while migrating and during the winter. Currently, one unanswered basic question is "how do monarchs, even though they have never been there before, locate the same overwintering sites year after year?" Many monarchs die during the winter and so we are undertaking studies to determine if the release of chemicals from decomposing individuals, which live monarchs use in defend against predators, impacts the soil ecosystem and that these changes result in the production of chemical signals that the immigrating butterflies use to locate overwintering sites.