MHC-mediated local adaptation in reciprocally translocated Chinook salmon

Abstract

Most Pacific salmonid populations have faced significant population declines over the past 30 years. In order to effectively conserve and manage these populations, knowledge of the evolutionary adaptive state of individuals and the scale of adaptation across populations is needed. The vertebrate major histocompatibility complex (MHC) represents an important adaptation to parasites, and genes encoding for the MHC are widely held to be undergoing balancing selection. However, the generality of balancing selection across populations at MHC loci is not well documented. Using Chinook salmon (Oncorhynchus tshawytscha) from two populations, we follow the survival of full-sib family replicates reared in their natal river and reciprocally transplanted to a foreign river to examine selection and local adaptation at the MHC class I and II loci. In both populations, we found evidence of a survivorship advantage associated with nucleotide diversity at the MHC class I locus. In contrast, we found evidence that MHC class II diversity was disadvantageous in one population. There was no evidence that these effects occurred in translocated families, suggesting some degree of local adaptation at the MHC loci. Thus, our results implicate balancing selection at the MHC class I but potentially differing selection across populations at the class II locus.

Viability selection creates negative heterozygosity–fitness correlations in female Black Grouse Lyrurus tetrix

“…In addition to body mass, heterozygosity also positively influenced the survival of female Black Grouse. This is similar to the findings of many other studies where genome-wide heterozygosity and heterozygosity at specific loci have been associated with increased survival in some vertebrate species [mammals (Banks et al 2010;Forcada and Hoffman 2014); fish (Evans et al 2010); birds (Worley et al 2010;Cézilly et al 2016)]. Similar to body size, the relationship between survival and heterozygosity has been mainly found in juveniles (e.g.…”

Sexual selection for genetic compatibility: the role of the major histocompatibility complex on cryptic female choice in Chinook salmon (Oncorhynchus tshawytscha)

“…It has been suggested that the MHC class II confers local adaptation in Chinook salmon (Evans et al, 2010). Our findings suggest that the low MHC class II diversity found in this and other Chinook salmon populations Evans et al, 2010) could be maintained via CFC, possibly to preserve adaptation to the parasite community at the spawning ground.…”

“…This variation could not be attributed to the MHC class I either. In contrast, MHC class II, which possibly plays a role in local adaptation (Evans et al, 2010), appears to be a significant driver of non-random gamete fusion in Chinook salmon. Since Chinook salmon are strongly adapted to their breeding ground, which is known to complicate the supplementation of endangered populations (Taylor, 1991), the MHC class II-based CFC could potentially be considered in targeted supportive breeding programs to augment and conserve endangered salmon populations.…”

“…MHC class II-assortative CFC could be associated with some of the key life history traits of salmonids: Chinook salmon return to their natal freshwater stream and populations to spawn and thus, fish are thought to exhibit local adaptation to their breeding ground (Taylor, 1991). It has been suggested that the MHC class II confers local adaptation in Chinook salmon (Evans et al, 2010). Our findings suggest that the low MHC class II diversity found in this and other Chinook salmon populations Evans et al, 2010) could be maintained via CFC, possibly to preserve adaptation to the parasite community at the spawning ground.…”

Declining diversity of egg-associated bacteria during development of naturally spawned whitefish embryos (Coregonus spp.)

“…Members of the salmonid family cover a wide range of different life-history strategies (Hutchings and Morris 1985;Crete-Lafreniere et al 2012) and ecological conditions (e.g., Maret et al 1997;Evans et al 2010Evans et al , 2012Hecht et al 2012). Symbiotic microbes may to a large degree reflect these ecological conditions.…”