Abstract
Successful biological invasion requires introduction of a viable population of a nonindigenous species (NIS). Rarely have ecologists assessed changes in populations while entrained in invasion pathways. Here, we investigate how zooplankton communities resident in ballast water change during transoceanic voyages. We used next‐generation sequencing technology to sequence a nuclear small subunit ribosomal DNA fragment of zooplankton from ballast water during initial, middle, and final segments as a vessel transited between Canada and Brazil. Operational taxonomic unit (OTU) diversity decreased as voyage duration increased, indicating loss of community‐based genetic diversity and development of bottlenecks for zooplankton taxa prior to discharge of ballast water. On average, we observed 47, 26, and 24 OTUs in initial, middle, and final samples, respectively. Moreover, a comparison of genetic diversity within taxa indicated likely attenuation of OTUs in final relative to initial samples. Abundance of the most common taxa (copepods) declined in all final relative to initial samples. Some taxa (e.g., Copepoda) were represented by a high number of OTUs throughout the voyage, and thus had a high level of intraspecific genetic variation. It is not clear whether genotypes that were most successful in surviving transit in ballast water will be the most successful upon introduction to novel environments. This study highlights that population bottlenecks may be common prior to introduction of NIS to new ecosystems.
Highlights
Biological invasions are commonplace in many habitats colonized by humans
We demonstrate that genetic diversity is lost prior to an introduction event, results were taxon-specific as some species were detected for the first time toward the end of the voyage
Consistent with Wonham et al (2001), we found that zooplankton species represented by Operational taxonomic unit (OTU) and copepod abundance were reduced preintroduction and that not all taxa survive to the end of the voyage (Figs S2–S4, Table 1)
Summary
Successful invasions are contingent upon introduction of sufficient individuals to constitute a viable population, tolerance of ambient conditions, and successful integration into the existing community (Colautti et al 2006; Blackburn et al 2011). These requirements must be met across an ordered series of stages from transport, introduction, establishment, and spread (Blackburn et al 2015). Small population inocula and differences between native and introduced habitats may cause invasions to fail or trigger evolutionary changes in colonizing species (e.g., Phillips et al 2006; Moran and Alexander 2014; Blackburn et al 2015). Enhanced genetic diversity may result from high propagule pressure (i.e., number of introduced individuals),
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