A genetic assessment of the human‐facilitated colonization history of black swans in Australia and New Zealand

Patrick‐Jean Guay,Michael A Weston,Valeria Montano,Mary Cowling,Raoul A Mulder,Randall W Robinson,Wouter F.D Van Dongen

doi:10.1111/eva.12535

Patrick‐Jean Guay, Michael A Weston + Show 5 more

Open Access

https://doi.org/10.1111/eva.12535

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Abstract

AbstractMovement of species beyond their indigenous distribution can fundamentally alter the conservation status of the populations involved. If introductions are human‐facilitated, introduced species could be considered pests. Characterizing the colonization history of introduced species can therefore be critical to formulating the objectives and nature of wildlife management strategies. The black swan (Cygnus atratus) is native to Australia but is considered a reintroduced species in New Zealand, where the endemic population was reported extinct during the 19th century. After the reintroduction of a small number of individuals from Australia, the New Zealand population expanded unexpectedly rapidly, which was attributed to simultaneous waves of migration from Australia. An alternative, but hitherto unformalized, hypothesis is that local extant populations remained and admixed with introduced individuals. To contribute to our understanding of the reintroduction history of the species, we investigated dispersal patterns and demographic histories of seven populations from Australia and New Zealand, using population genetic inferences from a microsatellite dataset. Our results on genetic structure, dispersal rates, and demographic histories provide mixed evidence on the origin of New Zealand black swans. The hypothesis that reintroduced individuals mixed with remaining local individuals and that the subsequent dramatic population expansion may have been due to genetic rescue of the inbred indigenous population cannot be discarded and needs further investigation.

Highlights

The introduction of a species to a new environment can result in a complex series of ecological consequences
We show that alternative hypotheses could explain the observed genetic patterns, questioning the current notion of New Zealand black swans being an introduced species
Genetic summary statistics for samples and loci were calculated with R package adegenet (Jombart, 2008) and R package hierfstat (Goudet, 2005)

Summary

Introduction

The introduction of a species to a new environment can result in a complex series of ecological consequences. Non-native species can outcompete or prey upon indigenous species, alter ecological processes, and lead to species extinctions (Lowry et al, 2013; Sakai et al, 2001). Humans can benefit immensely from the exploitation of introduced species (e.g., crops; Sax et al, 2007), while introduced species in the wild may benefit native species by, for example, controlling other pests (e.g., Glen & Dickman, 2005; Kerr, 2012) or providing critical habitat or food resources (e.g., van Dongen et al, 2012; Toone & Hanscom, 2003). Documenting the introduction history of species beyond their traditional distribution is critical to understanding their ecological impacts on novel environments, helps predict problematic introductions, and potentially guides proposals to translocate species in the face of climate change. Uncertainty regarding provenance may even lead to controversies about whether a species is native or introduced, a designation that radically alters the management goals (e.g., extermination versus conservation) and attention afforded to species (Grosser et al, 2016)

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