Variation in parasite resistance of Arctic charr, Salvelinus alpinus, between and within sympatric morphs.

Anssi Karvonen,Skúli Skúlason,Camille A Leblanc,Samantha V Beck,Bjarni K Kristjánsson

doi:10.1002/ece3.8109

Abstract

Genetic variation in resistance against parasite infections is a predominant feature in host–parasite systems. However, mechanisms maintaining genetic polymorphism in resistance in natural host populations are generally poorly known. We explored whether differences in natural infection pressure between resource‐based morphs of Arctic charr (Salvelinus alpinus) have resulted in differentiation in resistance profiles. We experimentally exposed offspring of two morphs from Lake Þingvallavatn (Iceland), the pelagic planktivorous charr (“murta”) and the large benthivorous charr (“kuðungableikja”), to their common parasite, eye fluke Diplostomum baeri, infecting the eye humor. We found that there were no differences in resistance between the morphs, but clear differences among families within each morph. Moreover, we found suggestive evidence of resistance of offspring within families being positively correlated with the parasite load of the father, but not with that of the mother. Our results suggest that the inherited basis of parasite resistance in this system is likely to be related to variation among host individuals within each morph rather than ecological factors driving divergent resistance profiles at morph level. Overall, this may have implications for evolution of resistance through processes such as sexual selection.

Highlights

The ability of organisms to defend against parasitic infections is central in determining their fitness
There is a growing body of literature demonstrating divergent intraspecific parasitism, between morphs or ecotypes of freshwater fishes (Blais et al, 2007; Eizaguirre et al, 2011; Hablutzel et al, 2016; Karvonen, Kristjánsson, et al, 2013; Karvonen et al, 2015; Karvonen et al, 2013, 2018; Knudsen et al, 1997, 2003; Maan et al, 2008; MacColl, 2009; Natsopoulou et al, 2012; Raeymaekers et al, 2013), which on an evolutionary time scale may result in divergent evolution of resistance profiles of the populations
Work on threespine stickleback (Gasterosteus aculeatus) has shown that profiles of the major histocompatibility complex (MHC) immunogenes may readily diverge between populations exposed to different levels of parasitism (Eizaguirre et al, 2009, 2012a) and that this can take place rapidly within just few generations (Eizaguirre et al, 2012b)

Summary

| INTRODUCTION

Karvonen et al, 2005) and seasonal variation in parasite transmission (Karvonen et al, 2004; Soubeyrand et al, 2009; Taskinen et al, 1994). Arctic charr is a salmonid fish species, which has colonized a number of lakes in the Arctic and Subarctic following the last glacial period It has become one of the hallmark species of rapid adaptive radiation and speciation among freshwater fishes with several northern lake systems harboring two or more sympatric or parapatric morphs (Gíslason et al, 1999; Jónsson & Skúlason, 2000; Knudsen et al, 1997; Skúlason et al, 1999). These morphs typically show specialized morphological and ecological features including differences in habitats, feeding, life-history traits, and reproduction (Skúlason et al, 1999).

| MATERIALS AND METHODS

Findings

| DISCUSSION