Do tolerant hosts amplify the threat of invasive parasites? Darwin’s finches, mockingbirds, and nest flies.

University Of Utah, Salt Lake City UT

Investigators

Abstract

One of the greatest threats to island birds and other animals is invasive parasites that are not native. One of the best examples is the nest fly Philornis downsi, which parasitizes Darwin’s finches in the Galápagos Islands. The fly, which is native to mainland South America, feeds on blood of nestling finches, which often die as a result. P. downsi is a major cause of rapid declines in several species of finches, including the Mangrove Finch, which is in imminent risk of extinction, with fewer than 100 individuals remaining. The threat posed by the flies may be exacerbated by other species of birds that are tolerant hosts of the fly. Tolerant hosts, such as Galápagos mockingbirds, which are larger in size than finches and breed earlier in the season, survive blood loss to flies and still leave the nest successfully. Thus, tolerant hosts have the potential to amplify the threat of flies to finches if they are a source of the flies that parasitize finches. The goal of this study is to test this amplification hypothesis. As part of the broader impacts of this work, the researchers will create a smartphone app (FlyTracker) that will allow biologists, Galápagos National Park rangers, and others to track data on the abundance of flies from year to year. Documentation of the indirect effects of mockingbirds on finches, together with long term monitoring of fly abundance, will contribute in a fundamental way to conservation efforts. Dispersal of parasitic flies will be measured using a fine-scale population genetic and kinship approach based on SNPs from whole genome sequences of flies (Aim 1). Next, an experiment will test whether parasitized mockingbird nests increase the number of P. downsi in nearby finch nests (Aim 2), and whether flies decrease the reproductive success of finches (Aim 3). Mockingbird nests will be GPS located and randomly assigned to experimental or control treatments. Experimental mockingbird nests will be fumigated with permethrin, which kills flies in nests. Finch nests within 35m of each mockingbird nest will also be GPS located, and the number of flies and reproductive success of finches will be quantified. Data from the experiment will be used to expand and parameterize a published population viability model for medium ground finches (Aim 4). The new model will test the degree to which proximity to tolerant mockingbirds, as well as other environmental factors, amplifies the threat of P. downsi to Darwin's finches. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.