Opposing health effects of hybridization for conservation

Ines Klemme,Pekka Hyvärinen,Lotta‐Riina Sundberg,Roghaieh Ashrafi,Jorma Piironen,Anssi Karvonen,Lysanne Hendrikx,Ville Räihä

doi:10.1111/csp2.379

Abstract

AbstractThe continuing decline of many natural plant and animal populations emphasizes the importance of conservation strategies. Hybridization as a management tool has proven successful in introducing gene flow to small, inbred populations, but can be also associated with health risks. For example, hybridization can change susceptibility to infection in either direction due to heterosis (hybrid vigor) and outbreeding depression, but such health effects have rarely been considered in the genetic management of populations. Here, we investigated the effects of experimental outcrossing between the critically endangered Saimaa landlocked salmon (Salmo salar m. sebago) and the genetically more diverse Atlantic salmon (S. salar) on infection susceptibility. We exposed the parent populations and their hybrids to two parasites that commonly infect these species, the bacterium Flavobacterium columnare and the macroparasitic fluke Diplostomum pseudospathaceum. We found that landlocked salmon had lower survival during the bacterial epidemic, but higher resistance against the fluke, compared with Atlantic salmon. Hybrids showed intermediate survival and resistance, suggesting that hybridization decreased susceptibility to one parasite, but concurrently increased it to another. Our results emphasize the importance of considering health effects of different types of infections when employing hybridization for conservation.

Highlights

The ongoing habitat loss and associated population declines generate a growing need for conservation actions that restore and maintain viable populations
While nongenetic health risks associated with wildlife translocations have been acknowledged and taken into account (Aiello et al, 2014; Frankham, 2015; Hess, 1996; McCallum & Dobson, 2002), empirical studies addressing explicitly the effects of genome mixing on infection susceptibility are scarce
We studied this question in the endangered Saimaa landlocked salmon whose genetic diversity decreased critically as a consequence of habitat destruction and associated population decline

Summary

| INTRODUCTION

The ongoing habitat loss and associated population declines generate a growing need for conservation actions that restore and maintain viable populations. Introducing immigrants could expose both translocated and resident individuals to new diseases (Hess, 1996; Kock, Woodford, & Rossiter, 2010; McCallum & Dobson, 2002), elevate stress levels and thereby increase susceptibility to infection (Dickens, Delehanty, & Michael Romero, 2010; Hing et al, 2017), or increase disease transmission rates due to enlarged populations (Aiello et al, 2014) In addition to these nongenetic effects, hybridization itself could have substantial impact on disease susceptibility. We asked whether hybridization of LS with AS increases survival following exposure to Flavobacterium and decreases parasite load following exposure to the eye fluke, relative to LS Such experimentally assessed health effects of multiple parasite infections could be used in conservation decision-making regarding assisted gene-flow to endangered populations

| MATERIAL AND METHODS

| RESULTS

Findings

| DISCUSSION