Rachael Y Dudaniec¹, Michael G Gardner^1,2, Steve Donnellan² and Sonia Kleindorfer¹

¹School of Biological Sciences, Flinders University GPO Box 2100, Adelaide, South Australia 5001, Australia

²Centre for Evolutionary Biology and Biodiversity, University of Adelaide, South Australia 5005, Australia

BMC Ecology 2008,
8:13.

 

Abstract

Background

Understanding the dispersal and genetic structure of invasive
insects across islands is important for designing management plans that
are appropriate at spatial and temporal scales. For invasive parasites,
population dynamics are largely determined by the distribution and
density of their host species. The introduced parasitic fly, Philornis downsi,
parasitises nestlings of endemic birds on all major islands of the
Galápagos archipelago. The fly’s high mortality and fitness impacts are
of conservation concern for vulnerable and declining species of
Darwin’s finches. Using microsatellite data in Bayesian clustering and
landscape genetic analyses, we examine gene flow and dispersal in P. downsi between
three islands and across habitats (highlands, lowlands) and examine for
the presence of population bottlenecks. We also examine variation at
the mitochondrial gene CO1 across islands to establish if cryptic species were present.

Results

Both the mitochondrial and microsatellite data were consistent with
there being a single species across islands. We found low genetic
differentiation between islands and strong evidence for inter-island
gene flow, or shared recent ancestry among individuals. Landscape
genetic analysis identified two genetic clusters: one encompassing
Santa Cruz and Isabela, and one on Floreana Island. There was no
evidence of genetic differentiation between habitats and molecular
variance was mainly attributable to within individuals. The combined P. downsi population was found to have undergone a population bottleneck.

Conclusion

Philornis downsi populations have high connectivity within
and between islands, with low levels of genetic differentiation between
Floreana and the other two islands examined. The genetic bottleneck
found across islands suggests there was a small founding population or
few introduction events of P. downsi. The high dispersal capacity and wide habitat use of P. downsi highlights
the significant threat that this parasite poses to the Galápagos
avifauna. Our findings are relevant for assessing the viability of
methods to control P. downsi on Galápagos, such as the sterile insect technique.