Abstract
Introduced species have become an increasingly common component of biological communities around the world. A central goal in invasion biology is therefore to identify the demographic and evolutionary factors that underlie successful introductions. Here we use whole genome sequences, collected from populations in the native and introduced range of the African fig fly, Zaprionus indianus, to quantify genetic relationships among them, identify potential sources of the introductions, and test for selection at different spatial scales. We find that geographically widespread populations in the western hemisphere are genetically more similar to each other than to lineages sampled across Africa, and that these populations share a mixture of alleles derived from differentiated African lineages. Using patterns of allele‐sharing and demographic modelling we show that Z. indinaus have undergone a single expansion across the western hemisphere with admixture between African lineages predating this expansion. We also find support for selection that is shared across populations in the western hemisphere, and in some cases, with a subset of African populations. This suggests either that parallel selection has acted across a large part of Z. indianus's introduced range; or, more parsimoniously, that Z. indianus has experienced selection early on during (or prior‐to) its expansion into the western hemisphere. We suggest that the range expansion of Z. indianus has been facilitated by admixture and selection, and that management of this invasion could focus on minimizing future admixture by controlling the movement of individuals within this region rather than between the western and eastern hemisphere.
Highlights
Species that have recently expanded their range and established in historically non-native regions are a nearly ubiquitous feature of contemporary biological communities (Levine, 2008; Simberloff, 2013; Simberloff et al, 2013)
We find that geographically widespread populations in the western hemisphere are genetically more similar to each other than to lineages sampled across Africa, and that these populations share a mixture of alleles derived from differentiated African lineages
Together with the signature of admixture carried by the introduced populations, these results indicate that the expansion of Z. indianus populations into the western Hemisphere may have been facilitated by both admixture and selection that occurred early on during this range expansion
Summary
Species that have recently expanded their range and established in historically non-native regions (i.e., introduced, invasive, or non-native species) are a nearly ubiquitous feature of contemporary biological communities (Levine, 2008; Simberloff, 2013; Simberloff et al, 2013). Introduced species can have diverse, and frequently negative, impacts on biological communities in their introduced. Studies of introduced species have identified a number of demographic or evolutionary processes that may contribute to successful introductions (Allendorf & Lundquist, 2003; Whitney & Gabler, 2008). Multiple colonization events and hybridization (and subsequent admixture) between differentiated lineages (i.e., populations or species) have both been identified as processes that contribute to genetic diversity within introduced populations (Facon et al, 2008a). Sources of genetic variation within introduced populations have been of broad interest because genetic variation is likely to be important for populations to respond to novel biotic and abiotic selective pressures that they experience in their introduced range. Processes that increase genetic diversity within introduced populations and the fitness consequences of that genetic diversity need to be understood in order to fully appreciate adaptation (or maladaptation) in introduced species
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