Tracing Aquatic Introductions and Assessing the Genetic Changes From the Source: a Case Study Investigating the Origins of New Zealand Rainbow Trout

Determining the source and number of introductions of non-native species is often a difficult but crucial task in order to understand the genetic changes that can occur in newly established populations. Previous studies have used several different types of genetic marker, but not single nucleotide polymorphisms (SNPs). Here, we compare the ability of SNP and microsatellite markers to determine the origins of an introduced aquatic species by investigating the origins of Lake Taupo (New Zealand) rainbow trout (Oncorhynchus mykiss) translocated from California around 100 years ago. Records on the history of this introduction are varied and sometimes contradictory. Data were collected from 15 microsatellite and 93 SNP markers, using samples from the Lake Taupo population and ten sites throughout California, which included all putative populations of origin. Unsurprisingly, results revealed that the Lake Taupo population has significantly diverged from Californian populations at both microsatellite and SNP loci. The analyses showed that the Lake Taupo population was probably derived from several sources in California, and the most likely locations were McCloud River and a coastal population, but the specific sources can not be definitively identified. This finding is consistent with bottleneck simulations which suggested that the genetic patterns of a single source of introduction would still be detectable 100 years post-founding, but with multiple introductions exact source populations become more difficult to detect. These results show that even in the absence of conclusive historical records, we can utilize multiple marker types to infer the history of introduction, which can have important implications for the life history traits and persistance of introduced species.