Replicate evolution in avian parasite during island invasion

Increases in human movement across the globe has led to increased transmission of pathogens and introduced species. In this study, we will measure genetic changes in an accidentally introduced parasitic fly, the avian vampire fly, on the Galapagos Islands. The first adult vampire flies were caught on Santa Cruz Island in 1964. When humans began colonising the Galapagos during the 1960s, they brought many purposefully introduced species such as cattle, the smooth-billed ani to remove ticks on cattle, and pigeons for food. Both pigeon and ani are known hosts for the vampire fly on mainland Ecuador. The Galapagos National Park eradicated the pigeon on Santa Cruz Island in the 1990s, and soon thereafter, vampire fly larvae were discovered in Darwins finch nests in 1997. Vampire fly females lay eggs in bird nests, and these eggs hatch into larvae that feed on the developing chicks. The 1st instar larvae reside inside the chicks nares (beak), and the 2nd and 3rd larval stages drop to the base of the nest from where they emerge at night to feed on the blood of the developing chicks. Most chicks die in the nest, but some survive, and these birds tend to have very deformed beaks. The vampire fly is considered the biggest threat to the survival of all Galapagos land birds as it kills most birds in nests. The fly continues to spread across the Galapagos archipelago, and now occurs on 15 of 18 islands examined. This project aims to use genetic approaches to measure population size and dispersal of the fly between islands, and to identify which genes may be favourable for the fly in this rapidly evolving bird-parasite system. We will also use statistical modelling approaches to forecast where the fly is most likely to persist and evolve. Our study will generate fundamental biological insights into the speed and patterns of evolutionary change in an accidentally introduced parasite, and can provide information to develop targeted control techniques for the fly. In addition to vampire fly control, the Galapagos National Park is embarking on large-scale predator control, and aims to eradicate all introduced mammals on Floreana Island in 2023. Thereafter, across the next 10 years, the Galapagos National Park will systematically reintroduce 12 locally extinct species back on to Floreana Island. This once-in-a lifetime opportunity allows us to monitor genetic changes in the vampire fly as the bird population sizes changes in response to the ecosystem recovery on Floreana Island following predator removal. We will measure how particular genes are favoured to allow this invasive parasite to thrive across time and islands. We will also look at how gene flow changes in the fly after predator control and the return of native bird hosts. The fundamental insights generated from the project are expected to transform our understanding of evolution in host-parasite systems in general, and when humans act to recover biodiversity loss.