Using molecular tools to guide management of invasive alien species: assessing the genetic impact of a recently introduced island bird population

Aim: Biological invasions are a major threat to island biodiversity and are responsible for a large proportion of species declines and extinctions worldwide. The process of hybridization between invasive and native species is a major factor that contributes to the loss of endemic genetic diversity. The issue of hybridization is often overlooked in the management of introduced species because morphological evidence of hybridization may be difficult to recognize in the field. Molecular techniques, however, facilitate identification of specific hybridization events and assessment of the direction and timing of introgression. We use molecular markers to track hybridization in a population of an island endemic bird, the Aldabra fody (Foudia aldabrana), following the recent discovery of a co-occurring population of non-native Madagascar fodies (Foudia madagascariensis).

Location: Aldabra Atoll, Seychelles. 

Methods: We combine phylogenetic analyses of mitochondrial and nuclear markers to assess whether hybridization has occurred between F. madagascariensis and F. aldabrana on Aldabra. Using coalescence models and comparing different hybridization scenarios, we estimate the timing of such events and confirm the geographic origin of F. madagascariensis. 

Results: Our analyses confirm a recent hybridization event between the two species of Foudia, and we find evidence that the invasive F. madagascariensis originate from the neighbouring island of Assumption, where they were introduced in the 1970s. Main conclusions: Our results validate the threat of losing the unique genetic diversity of F. aldabrana through admixture due to recent invasion of F. madagascariensis. We show that molecular analyses can be a valuable tool in formulating strategies for the management of invasive birds.