Genetic Basis of Variation in Litter Size in Scandinavian Arctic Fox (Vulpes lagopus)
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- Institutt for biologi 
The environment is in constant change, where rapid shifts is often due to human interference. To understand the mechanisms driving phenotypic change in ecologically important traits, knowledge of the genetic basis of these traits is needed. Reproductive success, including litter size, is an important life history trait. In the Scandinavian arctic fox (Vulpes lagopus), litter size is highly dependent on fluctuations in the environment, with many pups born in years with high rodent densities. If genes contribute to some of this variation, and any alleles that make Scandinavian arctic foxes enable to fully exploit years with high prey density are lost, this may reduce the ability of the arctic fox populations to increase in size, thereby reducing its long-term viability. Examining the genetic basis of and trying to identify genes that contribute to litter size may thus provide important tools for the future conservation and management of this species in Scandinavia which still struggles after a severe decline a century ago. To map the genetic architecture of litter size variation, the newly developed 702k SNP-array for fox was used for a genome partitioning and a genome-wide association study (GWAS). The genetic component was calculated both by using SNP data, and a pedigree in an animal model . Litter size seemed to be highly dependent on environment with a small genetic basis even when rodent abundance and age were accounted for, heritability = 0.05 and evolvability = 0.003. No genome-wide significant loci were detected. This, and the genome partitioning indicated that the genetic basis of variation in litter size in Scandinavian arctic fox has a polygenic inheritance pattern with a large environmental component. Thus, corroborating with earlier studies on the Scandinavian arctic fox, that environmental variation and in particular rodent phase has a large impact on litter size and the number of litters born during the breeding season. Future studies should focus on whether there is a genetic basis of phenotypic plasticity in litter size variation. This study struggled with a small sample size and illustrated some of the challenges when working with vulnerable and endangered species. Despite these challenges, this study suggests that accounting for a small genetic basis of litter size variation is not likely to be important in conservation management actions for the endangered arctic fox populations in Scandinavia.