Population genetics reveal patterns of natural colonisation of an ecologically and commercially important invasive fish

Ciar O’Toole,Peter A.H Westley,Jamie Coughlan,Karl P Phillips,Eileen Dillane,Tom F Cross,Ian A Fleming,Philip Mcginnity,Caroline Bradley,Thomas E Reed,Paulo A Prodöhl

doi:10.1139/cjfas-2020-0255

Abstract

Although historical records of introductions that trigger successful biological invasions are common, subsequent patterns of dispersal and colonisation routes are unclear. We use microsatellites to examine genetic population structuring of established invasive brown trout (Salmo trutta) populations in Newfoundland, Canada, for evidence of “natural” dispersal, human-mediated introductions, and colonisation routes. We also explored ancestry of contemporary populations relative to presumed progenitors. Results analysed using STRUCTURE, DAPC, a NJ tree and FSTcomparisons support records of historical introductions; current Newfoundland populations are largely descended from Scottish stock, with St. John’s the primary introduction site. Subsequent dispersal of these trout was facilitated principally by anadromy, largely consistent with a classic stepping-stone model, with significant isolation-by-distance. With one exception, dispersal along the north and south coasts of the Avalon peninsula appears to be natural and independent, involving stochastic processes resulting in unique outcomes for population composition. This study is a good example of dispersal patterns during a contemporary invasion underscoring the potential for non-anadromous founders to re-express anadromy, facilitating colonization of distant sites.

Highlights

The distribution of species through time and space is the result of the complex interplay between evolutionary history and everchanging ecological factors
Identifying the colonisation pathways and mechanisms involved in these changes, and the consequences for population genetic diversity, are important both for understanding present day species and population distributions, and for predicting potential future responses to anthropogenic climate change (Elton 1958; Lockwood et al 2013)
Targeted hierarchical STRUCTURE analyses restricted to samples from Newfoundland suggested a pattern of genetic structuring consistent with a geographical spread from St

Summary

Introduction

The distribution of species through time and space is the result of the complex interplay between evolutionary history and everchanging ecological factors. Identifying the colonisation pathways and mechanisms involved in these changes, and the consequences for population genetic diversity, are important both for understanding present day species and population distributions, and for predicting potential future responses to anthropogenic climate change (Elton 1958; Lockwood et al 2013). Even for the most recent major global species distribution changes, after the retreat of glaciers at the end of the Pleistocene, a significant amount of evolutionary information will have been lost. Even thousands, of generations will have passed since the events of interest and, many relevant evolutionary processes that would have been active in that time will not be detected. Whether natural or human-induced, provide useful contemporary analogues for studying the evolutionary trajectory of such events.

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