Invasive species are one of the greatest threats to biodiversity, with endemic species on islands being at particular risk. Management programs can help to minimize these impacts, but such programs are most successful when they are well-informed. In the Galápagos Islands, Ecuador, a recently introduced avian parasitic fly, Philornis downsi, has had strong negative effects on the survival of multiple endemic bird species, including several species of Darwin’s finches. The fly now populates most of the major islands within the Archipelago and the need to better understand the population structure and connectivity patterns of this invasive fly has become increasingly apparent as various management efforts are being considered. Here, we use genomic and phylogenetic approaches to estimate population structure and connectivity for P. downsi collected from five islands within the Galápagos Islands and several sites in mainland Ecuador, which is the presumptive origin of the invasive population. Genomic data showed very little genetic differentiation between island populations of P. downsi relative to the mainland. Phylogenetic analyses, which used more conservative genetic markers than the genomics approach, showed that island and mainland populations of flies were highly related. Our study provides some of the first results using genetic data to quantify differentiation among mainland and island populations of P. downsi. In addition, our study found very little genetic differentiation between island populations of flies, suggesting that there may be considerable gene flow among islands; however, further sampling is needed to determine the extent to which this could be occurring. As management techniques aimed at controlling the impact of this parasite on endemic bird populations are being considered, our study provides important insights into the history of P. downsi’s invasion to the Galápagos Islands and current population connectivity patterns.
Bibliographical noteFunding Information:
We thank Gabriel Brito, Sarah Knutie, David Anchundia, Francesca Cunninghame, Birgit Fessl, Paola Lahuatte, Courtney Pike and Ismael Ramirez for collecting and processing the flies. Thanks to Genevieve Kozak and Christy Wails for their assistance with data analyses. Permission to conduct this study was granted by the Galápagos National Park Directorate (Project PC-35-19, PC-07-18 and PC-08-17: Control of the Invasive Parasite, P. downsi and its Impact on Biodiversity) and the Ecuadorian Ministry of the Environment (MAE-DNB-CM-2016-0043). This work was funded by a Grant from the Galápagos Conservancy (Award Number 1-68-308), International Community Foundation (with a Grant awarded by The Leona M. and Harry B. Helmsley Charitable Trust) (Award Number 20140045), Lindblad Expeditions-National Geographic (Award Number 1-01-106) and National Geographic Research and Exploration Grant (Award Number 9847-16). This is contribution number 2348 of the Charles Darwin Foundation for the Galápagos Islands.
- Darwin’s finches