Major histocompatibility complex genes partly explain early survival in house sparrows

B Lukasch,H Winkler,H Hoi,Y Moodley,F Knauer,M Strandh,H Westerdahl

doi:10.1038/s41598-017-06631-z

Abstract

Environmental factors and genetic incompatibilities between parents have been suggested as important determinants for embryonic mortality and survival. The genetic set-up of the immune system, specifically the highly polymorphic major histocompatibility complex (MHC) may also influence individual resistance to infections. MHC proteins are important for an appropriate adaptive immune response and enable T-cells to separate ‘self’ from ‘non-self’. Here we investigate the importance of MHC functional diversity for early development in birds, more specifically, if offspring survival and body mass or size depends on number of different functional MHC alleles, specific functional MHC alleles or similarity of MHC alleles in the parents. Unhatched eggs are common in clutches of many bird species. In house sparrows (Passer domesticus), embryo and nestling mortality can exceed 50%. To control for environmental factors, our study was carried out on an aviary population. We found that one specific functional MHC allele was associated with reduced nestling survival, which was additionally supported by lower body mass and a smaller tarsus when nestlings have been 6 days old. Another allele was positively associated with tarsus length at a later nestling stage (nestlings 12 days old). These results indicate that MHC alleles might influence pathogen resistance or susceptibility.

Highlights

Survival and growth rates of young nestlings are known to be directly influenced by environmental factors, such as pollutants, nutrition and microbial infections or indirectly e.g., via stressors or maternal condition[1,2,3,4,5]
In particular we investigated if survival and growth in young chicks during the nestling stage depends on the number of different functional major histocompatibility complex (MHC) alleles/individual or specific functional MHC alleles using house sparrows (Passer domesticus) as the model system
Individuals had 4.7 MHC alleles (sd: 1.5 (R1) and 1.4 (R2)) ranging from 2–8 (R1) and 1–8 (R2) alleles/individual. These could be translated into 78 amino acid (AA) MHC alleles and 59 unique functional MHC alleles (Supplementary Table 4, Supplementary Fig. 4), based on their chemical properties in the PBR41

Summary

Introduction

Survival and growth rates of young nestlings are known to be directly influenced by environmental factors, such as pollutants, nutrition and microbial infections or indirectly e.g., via stressors or maternal condition[1,2,3,4,5]. Individual variation in resistance or susceptibility to infections could depend on the genetic set-up of the immune system, where the major histocompatibility complex (MHC) plays a central role. The highly polymorphic genes at MHC loci are believed to be under some form of balancing selection maintaining the high variation, such as pathogen-driven selection[16]. In a population of house sparrows[27], found that females with a low number of alleles were most attracted to males carrying a high number of MHC class I alleles. This might reflect a mating-up preference by allele counting to obtain offspring with an optimal MHC diversity. There is variation in pathogenic selection pressure in space and time, leading to different subsets of MHC alleles across subpopulations as proposed by the ‘fluctuating selection hypothesis’[28]

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