Maladaptive migration behaviour in hybrids links to predator-mediated ecological selection.

Varpu Pärssinen,Ben B Chapman,Per Anders Nilsson,Jakob Brodersen,Kaj Hulthén,Henrik Baktoft,Christer Brönmark,Lars‐Anders Hansson,Christian Skov,Laura Prugh

doi:10.1111/1365-2656.13308

Abstract

Different migratory species have evolved distinct migratory characteristics that improve fitness in their particular ecological niches. However, when such species hybridize, migratory traits from parental species can combine maladaptively and cause hybrids to fall between parental fitness peaks, with potential consequences for hybrid viability and species integrity.Here, we take advantage of a natural cross‐breeding incident to study migratory behaviour in naturally occurring hybrids as well as in their parental species and explore links between migratory traits and predation risk.To achieve this, we used electronic tags and passive telemetry to record detailed individual migration patterns (timing and number of migratory trips) in two common freshwater fish species, roach Rutilus rutilus, common bream Abramis brama as well as their hybrids. Next, we scanned for tags regurgitated by a key avian predator (great cormorant Phalacrocorax carbo) at nearby roosting sites, allowing us to directly link migratory behaviour to predation risk in the wild.We found that hybrid individuals showed a higher number of short, multi‐trip movements between lake and stream habitats as compared to both parental species. The mean date of first lake departure differed between bream and roach by more than 10 days, while hybrids departed in two distinct peaks that overlapped with the parental species' averages. Moreover, the probability of cormorant predation increased with multi‐trip movement frequency across species and was higher for hybrids.Our data provide novel insights into hybrid viability, with links to predator‐mediated ecological selection. Increased exposure to predators via maladaptive migratory behaviour reduces hybrid survival and can thereby reinforce species integrity.

Highlights

Each year, millions of animals migrate to pursue spatiotemporal variation in suitable environmental conditions and seek shelter from natural enemies, such as parasites and predators (Chapman et al, 2014; Dingle, 2014)
The mean date of first lake departure differed between bream and roach by more than 10 days, while hybrids departed in two distinct peaks that overlapped with the parental species' averages
Members of the Cyprinidae have the highest frequency of hybridization among all groups of freshwater fishes (Scribner, Page, & Bartron, 2000) and constitute an exceptional empirical substrate to test for hybrid inviability as a result of divergent migratory traits

Summary

| INTRODUCTION

Millions of animals migrate to pursue spatiotemporal variation in suitable environmental conditions and seek shelter from natural enemies, such as parasites and predators (Chapman et al, 2014; Dingle, 2014). Different salmonid species have evolved their own suites of intraspecific migratory phenotypes, and their expression depends on traits such as body size and growth rate of the individual (Dodson, Aubin-Horth, Thériault, & Páez, 2013). The roach Rutilus rutilus and the common bream Abramis brama are common freshwater fishes that migrate from shallow lakes into connected streams during the winter season (Skov, Brodersen, Nilsson, Hansson, & Brönmark, 2008). Their migratory dynamics are shaped by temperature-driven changes in the trade-off between predation risk and growth potential (Brönmark, Skov, Brodersen, Nilsson, & Hansson, 2008). We predicted that hybrids would express a divergent migratory behaviour relative to their parent species and that this would incur a fitness cost through increased susceptibility to predation

| MATERIALS AND METHODS

Findings

| DISCUSSION