Current Zoology 61 (3): 465–476, 2015 Received Jan. 5, 2014; accepted Feb. 9, 2014.  Corresponding author. E-mail: a.l.liebl@exeter.ac.uk © 2015 Current Zoology Invasion genetics: Lessons from a ubiquitous bird, the house sparrow Passer domesticus Andrea L. LIEBL 1* , Aaron W. SCHREY 2 , Samuel C. ANDREW 3 , Elizabeth L. SHELDON 3 , Simon C. GRIFFITH 3 1 University of Exeter, Cornwall Campus, Penryn, Cornwall, TR10 9EZ, UK 2 Department of Biology, Armstrong State University, Savannah, GA31419, USA 3 Department of Biological Sciences, Macquarie University, Sydney, NSW 2109, Australia Abstract Following an introduction, non-native species are exposed to environments that differ from those found in their native range; further, as these non-native species expand beyond the site of introduction, they must constantly adapt to novel environ- ments. Although introduced species are present across most ecosystems, few species have successfully established themselves on a truly global scale. One such species, the house sparrow Passer domesticus, is now one of the world’s most broadly distributed vertebrate species and has been introduced to a great part of its current range. To date, work on four continents suggests both ge- netic and phenotypic variation exists between native and introduced ranges. As such, house sparrows represent an excellent op- portunity to study adaptations to novel environments and how these adaptations are derived. The global distribution of this spe- cies and the multiple independent introductions to geographically isolated sites allow researchers to ask questions regarding ge- netic variation and adaptation on a global scale. Here, we summarize the molecular studies of invasive house sparrows from the earliest work using allozymes through more recent work on epigenetics; using these studies, we discuss patterns of dispersal of this species. We then discuss future directions in techniques (e.g. next generation sequencing) and how they will provide new in- sight into questions that are fundamental to invasion biology. Finally, we discuss how continued research on the house sparrow in light of these genetic changes and adaptations will elucidate answers of adaptation, invasion biology, range expansion, and resi- lience in vertebrate systems generally [Current Zoology 61 (3): 465–476, 2015]. Keywords House sparrow, Invasive, Passer domesticus 1 Introduction Introduced species are the second largest threat to global biodiversity. In the face of ecosystem impacts (Bakker and Wilson, 2004), economic costs (Mack et al., 2000), and the likelihood of growing commerce in- creasing the threat of new introductions (Levine and D'antonio, 2003), invasive species research has grown recently. However, in addition to invasive species mana- gement, studying invasive species in an ecological or evolutionary context will lend great insight to funda- mental questions in biology such as the general spatial structure of species interactions, allopatric speciation, and response to environmental stressors and challenges (Holt, 2003). Following an introduction, organisms cannot only endure novel environments but must also thrive in them to be successful. Additionally, as introduced species expand beyond the site of initial introduction, novel environments will likely continue to be encountered so that individuals must continuously adjust phenotypes to cope. Most introductions involve bottlenecks and foun- der effects that can reduce genetic diversity initially. Unlike many threatened species facing the same chal- lenge, introduced species are often able to overcome these reductions in genetic diversity to generate novel adaptations and adjust to novel environments; this presents a genetic paradox (Dlugosch and Parker, 2008). In novel environments, phenotypes should match new environments, thus creating phenotypic gradients con- sistent with age of population (Sol et al., 2002, Rehage and Sih, 2004, Russell et al., 2010). However, the un- derlying mechanisms of this variation in phenotypes, particularly on such short timescales, are less clear. These phenotypic changes may be due to changes in the frequency of genes across space and time, i.e. driven by natural selection, genetic drift, founder effects (Clegg et al., 2002), or spatial sorting of genes as the population expands (Shine et al., 2011). Alternatively, phenotypic variation across ranges may be determined by other fac- Downloaded from https://academic.oup.com/cz/article/61/3/465/1786647 by guest on 16 October 2022