Appraising the Genetic Makeup of an Allochthonous Southern Pike Population: An Opportunity to Predict the Evolution of Introgressive Hybridization in Isolated Populations?

SIMPLE SUMMARY: The southern pike is a freshwater top-predator fish that is endemic to rivers and lakes across Northern and Central Italy and is threatened by population decline and hybridisation with the northern pike. In this study, we focused on a southern pike population that has been recently introduced in an artificial lake, outside the species’ native range, and used genetic data to achieve a two-fold goal: (1) to investigate genetic diversity and (2) assess whether this population entirely consists of pure southern pike or is affected by hybridisation with the northern pike. The following conclusions were drawn from the results: (1) the genetic diversity of the introduced population is as large as that observed in wild populations, and (2) the presence of hybrid individuals is likely, which might be the descendants of old crosses between southern and northern pike. Several introduction events, a large number of founders, and hybridisation itself may explain the high genetic diversity that has been found in the introduced population. The present study may help further understand the genetic drivers of the successful establishment of introduced populations in new habitats. Moreover, the southern pike population from the Alto Flumendosa Lake may also be used as a test case to study how hybridisation evolves in isolated populations. ABSTRACT: Biological invasions are a major threat to the conservation of biodiversity, as invasive species affect native biota through competition, predation, pathogen introduction, habitat alteration, and hybridisation. The present study focuses on a southern pike population, Esox cisalpinus (Teleostei: Esocidae), that has been introduced outside the species’ native range. Using microsatellite markers, this study’s objective was to gather baseline genetic information and assess the presence of hybrids between this species and E. lucius in the introduced population. The resulting estimates of genetic diversity and effective population size are comparable to those observed in the species’ native range. Although different methods yield contrasting and uncertain evidence regarding introgressive hybridization, the presence of late-generation hybrids cannot be completely ruled out. Large numbers of breeders as well as multiple introductions of genetically divergent cohorts and introgressive hybridisation may explain the high genetic diversity of this recently introduced southern pike population. The present study issues a warning that the conservation of southern pike’ introgressive hybridisation between northern and southern pike might be underestimated. The genetic information gathered herein may unravel the origin, number of introduction events, and evolutionary trajectory of the introduced population. This information may help us understand the evolution of introgressive hybridisation in the southern pike’s native areas.